AT the DUKE LEMUR CENTER by Kathleen Marie Mcguire B

THE SOCIAL BEHAVIOR AND DYNAMICS OF OLD RING-TAILED LEMURS (LEMUR CATTA) AT THE DUKE LEMUR CENTER

Kathleen Marie McGuire

B.S., Georgia Institute of Technology, 2014

A thesis submitted to the faculty of the University of Colorado in partial fulfillment of the requirement for the degree of Master of Arts. Department of Anthropology 2017 ii

This thesis entitled: The Social Behavior and Dynamics of Old Ring-tailed Lemurs (Lemur catta) at the Duke Lemur Center written by Kathleen Marie McGuire has been approved for the Department of Anthropology

______Dr. Michelle L. Sauther (Committee Chair)

______Dr. Herbert H. Covert

______Dr. Joanna E. Lambert

Date

The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline.

IACUC protocol # A168-14-07

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Abstract

McGuire, Kathleen Marie (M.A. Anthropology)

The Social Behavior and Dynamics of Old Ring-tailed Lemurs (Lemur catta) at the Duke Lemur

Center

Thesis directed by Professor Michelle L. Sauther

There has been little emphasis within primatology on the social and behavioral strategies old primates might use to meet the challenges of senescence while maintaining social engagement, such as assuming a group role like navigator. Understanding how old primates maintain sociality can reveal how behavioral flexibility might have facilitated an increase in longevity within the order. Using focal sampling of old (N = 9, 10+ years) and adult (N = 6, <10 years) Lemur catta at the Duke Lemur Center, activity budgets, social interactions, and group traveling information were recorded and compared from May to August of 2016. I found that both male and female old lemurs maintained sociality in the group, with older females being more social than adults. I failed to support the second hypothesis that older individuals would have a behavioral profile distinct from adults. Finally, I found preliminary support that older females help care for a daughter’s offspring in the form of carrying. These results indicate that social manifestations of age and senescence depend on a myriad of factors such as environment, life history, and individual personalities. This research also reveals the importance of decoupling ideas of chronological age, being an old individual, with senescence because somatic decline depends on these other factors besides age.

Understanding these complex interactions is essential as we strive to define senescence and explore how age has shaped evolutionary trajectories among primates.

Dedication

This thesis is dedicated to “Mom” Syble Sweat, a primate grandmother who taught me the importance of family and the pursuit of knowledge.

Acknowledgements

First, I would like to thank my advisor Dr. Michelle Sauther for her patience and essential support during all stages of this research and thesis. I would also like to thank Dr. Herbert Covert and Dr. Joanna Lambert for their mentorship as I developed and executed this work. I am also incredibly grateful to the Duke Lemur Center staff for permitting me to conduct my research. In particular, I thank Dr. Sara Zher, Andrea Katz, Erin Shaw, and Dr. Erin Ehmke for their unwavering enthusiasm and for providing essential information about the histories of these lemurs.

I am incredibly grateful to Dr. James Millette for taking the time out to discuss aspects of my data collection, management, and analysis.

I would also like to thank my family Michael P., Michael C., and Oliver McGuire for their love and support. I appreciate the many hours of conversation with Brittany Miles and Elizabeth

McMillian about statistics, old age, and writing that helped to foster this research and thesis.

Getting the opportunity to pursue my passion for primate social behavior would not have been possible without Dr. Linda Green and Dr. Joe Mendelson and their research project at Zoo Atlanta.

Finally, thank you to Charles Hughes who endures my endless discussion of primates and their social lives, while relentlessly encouraging me to pursue this work.

Funding for this study was provided by the University of Colorado, Department of

Anthropology and the University of Colorado Boulder Graduate School. This work would have not been possible without the support of these institutions.

Table of Contents

Chapter 1: Introduction ...... 1 Senescence ...... 1 Why Studying “Old” Primates Matters ...... 4 Old Social Involvement in Nonhuman Primates ...... 7 Individual Factors and Old Primate Social Behaviors ...... 10 The Social Role of Older Primates ...... 11 Lemur catta as a Suitable Model for Primate Aging ...... 12 Studying Aging in Captivity ...... 13 Lemur catta Mortality at the Duke Lemur Center ...... 14 Infants and Juveniles (Birth to 2 years) ...... 14 Adults (2-10 years) ...... 17 Old Adults (10+ years) ...... 18 Study Aims and Hypotheses ...... 19 Chapter 2: Methods ...... 21 Study Site ...... 21 Study Animals ...... 23 Behavioral Methods ...... 23 Data and Statistical Methods ...... 26 Chapter 3: Results ...... 28 Degree of Sociality ...... 28 Proximity ...... 28 Physical Contact ...... 29 Activity Budgets ...... 31 Locomotion (Travel and Movement) ...... 31 Feeding and Foraging ...... 34 Resting ...... 34 Frequency of Behaviors ...... 40 Agonistic Point Events ...... 40 Affiliative Point Events ...... 41 Grooming ...... 42 Stink Fights ...... 43 Vocalizations ...... 44 vii

Individual Factors ...... 46 Dominance Rank ...... 46 Social Roles ...... 48 Case Studies ...... 48 Aracus ...... 48 Sprite ...... 50 Shroeder ...... 50 Lilah ...... 51 The Other Individuals ...... 52 Chapter 4: Discussion ...... 54 Discussion of Results in Terms of Study Hypotheses ...... 54 Decoupling Chronological Age and Senescence ...... 54 Individual Variation and the Disposable Soma Hypothesis ...... 55 Primate Buffers against Senescence-Associated Mortality ...... 61 Captivity Caveats ...... 64 Small Sampling Size and Limited Group Composition ...... 64 Reduction in Agonism among Individuals ...... 65 Conclusions ...... 67 Bibliography ...... 68 Appendix 1: Behavioral Definitions ...... 78 Appendix 2: Sampling Schedule ...... 85 Appendix 3: Pedigree Charts for Study Subjects ...... 86

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List of Tables

Table 1. Previous Work on Aged Primate Sociality……………………………………………...8

Table 2. Cause of Death Information for Infants and Juveniles at the Duke Lemur Center…...... 16

Table 3. Cause of Death Information for Adults at the Duke Lemur Center……………………...17

Table 4. Cause of Death Information for Old Individuals at the Duke Lemur Center…………….18

Table 5. Study Animals………………………………………………………………………..…24

Table 6. Mean Physical Contact Time Comparison between Old and Adult Females with and without Liesl and Infants…………………………………………………………………………29

Table 7. Female Individual Analysis of Physical Contact Time………………………………….30

Table 8. Mean Physical Contact Time Comparison between Old and Adult Males with and without Liesl and Infants…………………………………………………………………………………30

Table 9. Locomotion, Travel, and Movement Comparisons between Adult and Old Females…...32

Table 10. Male Individual Analysis of Locomotion and Movement Times……………………...32

Table 11. Male Individual Analysis of Travel Times…………………………………………….33

Table 12. Locomotion, Travel, and Movement Comparisons between Adult and Old Males with and without Aracus and Licinius included……………………………………………………..…33

Table 13. Female Individual Analysis of Feeding/Foraging Times……………………………...34

Table 14. Analysis of Old and Adult Female Total, Solitary, and Social Resting Times…………35

Table 15. Female Individual Analysis of Total Resting Time……………………………………35

Table 16. Female Individual Analysis of Social Resting Time………………………………….36

Table 17. Female Individual Analysis of Solitary Resting Time…………………………………37

Table 18. Female Individual Analysis of Solitary Resting Time Not In Proximity with at Least One Group Member………………………………………………………………………………37

Table 19. Analysis of Old and Adult Male Total, Solitary, and Social Resting Times………….38

Table 20. Male Individual Analysis of Social Resting Time……………………………………..38

Table 21. Male Individual Analysis of Solitary Resting Time…………………………………...39

Table 22. Analysis of Adult and Old Male and Female Total, Solitary, and Social Sleeping Times……………………………………………………………………………………………..39

Table 23. Female Agonistic Event Counts Based on Act Initiated, Received, or Unknown……...40

Table 24. Female and Male Agonistic Event Counts Based on Act Initiated, Received, or Unknown…………………………………………………………………………………………41

Table 25. Male Agonistic Event Counts Based on Act Initiated, Received, or Unknown………..41

Table 26. Female Affiliative Event Counts Based on Act Initiated, Received, or Unknown……41

Table 27. Male Affiliative Event Counts Based on Act Initiated, Received, or Unknown……….41

Table 28. Female Total Grooming Event Counts Based on Act Initiated, Received, or Unknown…………………………………………………………………………………………42

Table 29. Male Total Grooming Event Counts Based on Act Initiated, Received, or Unknown…42

Table 30. Female Grooming (Unidirectional) Event Counts Based on Act Initiated, Received, or Unknown…………………………………………………………………………………………43

Table 31. Male Grooming (Unidirectional) Event Counts Based on Act Initiated, Received, or Unknown…………………………………………………………………………………………43

Table 32. Female Mutual Grooming (Bidirectional) Event Counts Based on Act Initiated, Received, or Unknown…………………………………………………………………………...43

Table 33. Male Mutual Grooming (Bidirectional) Event Counts Based on Act Initiated, Received, or Unknown………………………………………………………………………………………43

Table 34. Female Affiliative Vocalization Event Counts Based on Act Initiated, Responding, or Unknown…………………………………………………………………………………………44

Table 35. Male Affiliative Vocalization Event Counts Based on Act Initiated, Responding, or Unknown…………………………………………………………………………………………44

Table 36. Male and Female Affiliative Vocalization Event Counts Based on Act Initiated, Responding, or Unknown………………………………………………………………………...44

Table 37. Female Alerting and Antipredator Vocalization Event Counts Based on Act Initiated, Responding, or Unknown………………………………………………………………………...45

Table 38. Male Alerting and Antipredator Vocalization Event Counts Based on Act Initiated, Responding, or Unknown………………………………………………………………………...45

Table. 39. Social Ranks of Study Individuals……………………………………………………47

Table 40. Non-Maternal Carrying Behavior of Griselda…………………………………………48

Table 41. Male Individual Analysis of Social Proximity Time………………………………….49

List of Figures

Figure 1. Infant/Juvenile Causes of Death……………………………………………………….16

Figure 2. Adult Causes of Death…………………………………………………………………17

Figure 3. Old Individual Causes of Death……………………………………………………….19

Figure 4. Map of the Duke Lemur Center’s Natural Habitat Enclosures………………………..22

Figure 5. Average Time Spent More Than Two Meters Away From Group Members…………28

Figure 6. Average Time Spent in Physical Contact with at Least One Group Member…………30

Figure 7. Average Time Spent in Physical Contact with at Least One Group Member Compared between Old Males and Females…………………………………………………………………31

Figure 8. Percent Leading During Travel Between Old and Adult Individuals…………………46

Figure 9a. & 9b. Pictures of Lilah……………………………………………………………….51

Chapter 1: Introduction

Senescence

As a species, humans are living longer. In 1955, the average life expectancy was 48, in

1995 it was 65 (WHO 1998). The World Health Organization predicts that human global life expectancy is currently around 80 years old (WHO 2015). As older individuals continue to represent more of the global population, understanding the aging process and the physical effects that age can have on the body can facilitate efforts to improve the quality of life for older individuals.

Old is a term used to describe a group individuals that have lived for a relatively long time for their species. Therefore, being old is often based on the average or maximum life expectancy of a species. The assumed state of an old individual is that they are aging or are experiencing senescence. However, organisms such as some turtle species and naked mole rats exhibit little evidence of physical aging (Finch 2009), indicating that some organisms can be old but not necessarily be senescent. For the purposes of this study, I will use old to describe individuals beyond the expected life span of wild lemurs (10-15 years). To date, very few wild ring-tailed lemurs live beyond 15, and the majority disappear between 10-15 years of age (Bennett et al.

2016).

Senescence has been broadly defined as the phenotypic change in an animal associated with advanced age (Monaghan et al. 2008). This change is typically connected with a decline in somatic function, which theoretically should result in a reduction in fitness and an increase in both extrinsic and intrinsic mortality. Extrinsic mortality is death as a result of environmental factors such as predation and disease. For example, if an individual has a severe loss in hearing, they might 2 not hear the call of a predator or the warning vocalizations of their social group and are not able to evade capture and death. Intrinsic mortality is death as a result of physical and functional degradation of an organism’s body. For example, if the cells in an individual’s heart stops working, it can result in death due to cardiovascular failure. Because of this association between senescence and higher rates of intrinsic and extrinsic mortality, the challenge becomes understanding why natural selection would favor life history patterns that produce senescent individuals.

Three hypotheses seek to explain the relationship between senescence and fitness. The first suggests that because individuals die as the result of extrinsic factors, selection declines with age relative to that individual’s reproductive value (Haldane 1941, Medawar 1952). The second hypothesis of antagonistic pleiotropy argues that particular alleles that confer benefits on survival and reproduction early in life are favored by natural selection despite negative effects later in life

(Williams 1957). The third disposable soma hypothesis suggests that there are trade-offs between reproduction and somatic maintenance that leads to a decline in function due to the accumulation of damage in favor of resource allocation towards reproduction and support of offspring

(Kirkwood 1977, 2002, Kirkwood and Holliday 1979). Some research has supported the latter two hypotheses of antagonistic pleiotropy and disposable soma (Kirkwood & Austad 2000, Wilson et al. 2008). These hypotheses have been tested on a mechanistic level with observations of free radicals, methylation patterns (Maegawa et al. 2017), and other factors affecting the life expectancies of individuals (see Monaghan et al. 2008).

Though mechanistic-based studies are important to understand how senescence occurs on a metabolic and cellular level, evolution does not occur in a vacuum but is shaped by the ecological, environmental, and demographic context in which individuals live. Therefore, studies of diverse taxa in the wild are essential when exploring these questions. Researchers have used a 3 myriad of variables to operationalize senescence at the individual, population, and species scales, which makes comparing senescence across taxa more challenging. Some researchers have defined senescence as the decline in age-specific survival and fecundity (Galliard et al. 1994, Promislow

1991). Others have measured age at death as a means of measuring senescence, which does not accurately account for sources of extrinsic mortality (Monaghan et al. 2008). One of the challenges with using life-history variables to approximate senescence is that these variables can be affected by other factors such as the environment in which animals live and, one would posit, social factors.

For example, Ricklefs and Cadena (2007) measured the relationship between fecundity and longevity in captive mammals as a proxy for senescence but offered no extensive discussion about the mechanistic means of how the captive environment tends to extend life in these populations.

To begin exploring these metrics, sources of mortality must be explored.

Other researchers have tried to create holistic metrics such as a physiological frailty index

(Antoch et al. 2017) to approximate the overall degree of physical senescence in individuals, accounting for multiple age-correlated factors such as grip strength, red blood cell count, and hemoglobin. These methods directly describe aspects of individual health and ways in which physiological changes occur. Focusing on specific phenotypical manifestations of advanced age can also provide a starting place for targeting specific genetic mechanisms for senescence. Such direct measurements of health can also reveal how the environmental and ecological context might affect senescence (Brownikowski et al. 2005). This lack of consensus regarding how researchers describe and measure senescence impairs the ability to compare across taxa. Nevertheless, the comparative method is a powerful tool to provide a means of understanding how animals differ in their patterns of senescence and what factors have affected the evolution of senescence. 4

Age-associated decline can affect the behavior of an individual and can provide insight into how these changes affect aspects of survival. Most research has looked at how age affects behavior with respect to predation and foraging (Roach and Carey 2014). For example, research with horses

(Mota et al. 2005), fish (Reznick et al. 2004) and birds (Cosantini et al. 2008) indicates that older individuals experience a reduction in athletic ability with age; this reduction can make older individuals easier to catch by predator species and lead to higher mortality (Fuller and Keith 1980,

Slobodkin 1968). With respect to foraging, studies with birds (Catry et al. 2006, Lecomte et al.

2010) indicate that some species experience a reduction in efficiency years before death.

Therefore, older individuals might become less able to extract energy from the environment, which can be determined based on behavioral observations.

Why Studying “Old” Primates Matters

The diverse taxa of the primate order generally are longer-lived for their body size compared to other mammals (Charnov and Berrigan 1993, Jones and MacLarnon 2001). Being old in the wild often is considered to be a disability that leads to rapid death (Nussey et al. 2013, Roach and Carey 2014). However, senescence is present in a variety of wild taxa; a recent review (Nussey et al. 2013) highlighted 340 studies of 175 animal species that showed signs of senescence in the wild, not only indicating that wild individuals certainly experience senescence but also that the relationship between advanced age and increased mortality is more complex. One possible means of reducing the effect of disability or senescence is to flexibly modify behavior which is characteristic of the primate order (Jones 2006). For example, impaired primates living with reduced dentition (Millette et al. 2009) and congenital limb malformations (Turner et al. 2012) learn to accommodate these physiological challenges and survive with their disabilities. Because 5 of their capacity to flexibly modify their behavior, primates might have a greater capacity to accommodate senescence compared to other taxonomic groups.

Degree of sociality has been thought to explain possible differences in senescence among taxa (Promislow 1991). The primate order is characterized by highly social species with most living in social groups (Fleagle 2013). Therefore, comparison among primates could provide a robust means of investigating how social factors might affect the evolution of senescence across a broad range of ecological and environmental contexts. Evidence suggests that patterns of senescence are less evolutionarily constrained, allowing for species to respond flexibly to forces of evolution even at the population level (Bronikowski et al. 2011). Aspects of group living seem favorable for increasing lifespans in taxa and possibly buffering against environmental challenges through anti-predator behaviors, inherited dominance, and collective knowledge (Roach and Carey

2014). The primate order has also been of particular interest in exploring the roles of older individuals in the social environment because intelligence in conjunction with sociality provides both experience and wisdom to the group at large. In exploring how primates can inform larger- scale patterns of senescence in the animal kingdom, we must first define what an old primate is and what behavioral patterns characterize this cohort of individuals.

Defining Old Primates and Their Behavioral Profile

Primatologists have been classifying individuals as old for decades but lack a consensus on a unified definition of what old actually is. The assumption of this classification is that there is some delineation between a regular adult in the social group and an old individual. The implied difference is that these older individuals are senescent, but research on primate gerontology is still very much in its infancy and lacks a consensus on what exactly old is. The few studies that have been conducted reveal this important problem associated with studying these older individuals 6

(Table 1.). Many researchers often used the third trimester of life (Corr 2000, McDonald 1988,

Taylor 2008). Others use the age at which females experience a decline in fecundity (Kato 1999).

One study (Almeling et al. 2016) even used the inability to get a peanut out of a tube as indicative of functional decline that meant a primate was old. Therefore, it is essential to explore the behavior of old primates so that a concrete and standard definition of old can be established.

To distinguish old individuals as a distinct life history cohort, we need to achieve a better understanding of what aspects of senescence are used to define this cohort as old. Use of the last trimester of life standard accounts for chronological but not physical age. This standard assumes that all individuals in the last trimester of life are experiencing senescence equally, which is not the case in different environments. For example, across a range of ages the ring-tailed lemurs at the Bezà Mahafaly Special Reserve experienced severe dental wear and loss based on utilization of the tamarin fallback food (Cuozzo and Sauther 2006). These results indicate that aspects of physiology might appear to be experiencing decline well before an old age, depending on the environment. Therefore, it becomes important to establish a clear definition of old with a more detailed perspective of physiology so that we have an understanding of what normal, both behaviorally and physiologically, looks like in this age cohort. Furthermore, establishing the old profile enables researchers to clearly determine pathological conditions that deviate from the old- age norm.

The majority of social and behavioral studies addressing questions of aging in primates are with species of macaque (Table 1). Establishing a “primate pattern,” if possible, with respect to the behavior of old individuals must incorporate other species besides macaques because primates exhibit a large range of behavioral and phenotypic plasticity. Defining an old behavioral profile based primarily on macaque research would not adequately represent patterns for the whole order, 7 and if researchers are to compare primates to other groups, a more representative sampling of primate behavioral and social gerontology much be conducted.

Old Social Involvement in Nonhuman Primates

One key way that researchers have expected primates to modify their behavior to accommodate the challenges of senescence is to reduce their degree of sociality. Informed by disengagement and activity theory from human social gerontology (Achenbaum and Bengtson

1994, Cumming and Henry 1961, Lemon et al. 1972), early studies on the social engagement of older primates predicted that these individuals would withdraw from the social group due to the physiological demands of aging. Theories of disengagement imply that social behaviors are less essential and might be reduced to allow for greater time spent on essential behaviors such as foraging and predator avoidance. The majority of studies on social gerontology have used macaque species as study subjects and have focused primarily on captive populations (Table 1.). The results of these studies have provided little support for social disengagement in older primates. Work with female Japanese and stump-tailed macaques found that older individuals spent significantly less time interacting socially compared to younger individuals (Hauser and Tyrell 1984, Nakamichi

1984, Nakamichi 1991). Kato (1999) validated these results but also found that individual differences in the social behavior of aged Japanese macaque females were dependent on factors such as individual rank and season. Other research with Japanese (McDonald 1988) and rhesus macaques (Williams 1982) found no indication of social withdrawal but rather more time spent resting. More recent work (Almeling et al. 2016) with Barbary macaques found that older individuals are more interested in their social environment compared to younger individuals.

Table 1. Previous Work on Older Primate Sociality. Adapted from Table 1.1 in Corr (2000) and updated with current literature. *Indicates experimental studies. Study # of Period/Data Definition Basis for Citation Species Subjects Sex Amount of Old Definition of “Old” Williams L. Rhesus (1982) Macaque 18 F 7 months Unknown Unknown Fitts S. Rhesus (1982) Macaque 10 F 8 hours 25+ years Unknown Nakamichi Japanese Estimation of senility in M. (1984) Macaque 14 F 4 months 20+ years Itoigawa (1982) Maximum lifespan in Hauser et al. Japanese captivity and physical (1984) Macaque 18 F 2.5 months 18+ years characteristics Maximum lifespan in Hauser et al. Stumptail captivity and physical (1984) Macaque 14 F 3 months 18+ years characteristics McDonald Japanese M. (1988) Macaque 40 F 15 months 20+ years Third trimester of life Huffman, M. (1990) Chimpanzee 9 F & M 10 months 41+ years Unknown Nakamichi Japanese M. (1991) Macaque 23 F 230 hours 20+ years Hauser et al. (1984) Lipold et al. Rhesus (1992) Macaque 12 F 3 months Unknown Unknown Picq J. Grey Mouse (1992) Lemur 12 F & M 2 months 9+ years Unknown Parks K. Rhesus (1993) Macaque 7 F 15 years Unknown Unknown Soumi et al. Rhesus 16-20 (1993) Macaque 8 F & M 15 years years Unknown Veenema et Long-tailed Prior studies in cognitive al. (1997) Macaque 35 F & M 485 hours 14+ years decline in this species Taylor L. (1996) Lemurs 34 F & M 540 hours 18+ years Last trimester of life Kato E. Japanese (1999) Macaque 16 F 383 hours 21+ Decline in fertility Baker K. (2000) Chimpanzee 34 F & M 240 hours 30+ years Unknown Corr J. Rhesus (2000) Macaque 49 F & M 627 hours 20+ years Last trimester of life Veenema et Long-tailed Prior studies in cognitive al. (2001) Macaque 55 F 485 hours 14+ years decline in this species Nakamichi Japanese Behavioral findings of this M. (2003) Macaque 85 F 261 hours 15+ years study Inability to get peanut out of Almeling et Barbary tube; offer no discussion of al. (2016)* Macaque 118 F & M N/A 19+ years this benchmark Ryu et al. Bonobos (2016) Chimpanzee 14 F & M 4 months 40+ years Distance while grooming

Physiological challenges such as a reduction in hearing, cognition, and even eyesight can possibly impair a primate’s ability to function in the social group. Yet, rather than distancing themselves from the group, many aged primates learn to accommodate these physical challenges.

As noted previously, older bonobos suffering from long-sightedness tend to groom at farther distances away from the receiving individual than younger bonobos (Ryu et al. 2016). If aged primates are behaviorally accommodating the challenges of senescence, theoretically the profile of their social behavior should be distinct from younger individuals.

Social contact time can be described as the duration an individual spends engaged in a specific behavior involving another member of the group like grooming and social resting. Other researchers (e.g. Corr 2000, Taylor 2008) have used proximity to individuals as a metric for social contact as well. Behavioral frequencies are how often an individual engages in a particular behavior. Directionality, such as initiating or receiving grooming behavior, is also measured to determine if old individuals are passively or actively maintaining sociality. For example, an individual who only receives grooming approaches from other individuals might be maintaining passive social engagement. Notably among the frequency analysis, previous work with aged female Japanese macaques suggests that old individuals might use affiliative vocalizations to maintain social relationships with unrelated individuals at lower energetic costs (Mitani 1986).

Recent work (Kulahci et al. 2015) suggests that ring-tailed lemurs utilize this strategy to groom other individuals at a distance. Therefore, aged lemurs might use vocalizations to maintain sociality at a lower energetic cost to themselves.

The Biology of Aging in Primates

Older primates must accommodate the challenges associated with physiological decline as they age, which might hinder their involvement in the group, requiring them to modify their 10 behavior to maintain social engagement. Therefore, while I do not directly measure aspects of physiology in this study, understanding the physiological context of age is also important in characterizing the old behavioral profile of these primates. One of the key debates in the physiology of aging is the frequency of reproductive senescence that is observed in human females.

Many individuals may reach an age that leads to a decline in fecundity (Kato 1999, King et al.

2005, Parga and Lessenau 2005, Wright et al. 2008,), but few exhibit complete reproductive termination (Pavelka and Fedigan 1999) with a post-reproductive lifespan.

Some studies have also found age-related decline in other physiological systems besides reproduction. Among lemurs in particular environments, age-associated tooth wear has been found

(Cuozzo and Sauther 2006, King et al. 2005), but many of these species utilize behavioral strategies to accommodate this dental wear and loss and are able to survive for many years despite these impairments (Cuozzo and Sauther 2006, Millette et al. 2009). Research with bonobos (Ryu et al.

2016) indicates that, during grooming, older individuals will have a greater distance between their fingers and their eyes, indicating that these individuals are long-sighted. Hearing loss and loss of eyesight in older hanuman langurs also has been seen (Borries 1988). Other researchers have documented a reduction in cognitive function among macaques (Corr et al. 2002, Veenema 1997,

2001). Learning how old primates navigate these biological challenges can not only provide insight into the methods of accommodating disability but also how these adjustments could have facilitated the selection for longer lifespans in the primate order. Once again, characterizing the normal behavioral profile for wild species also allows for researchers to identify pathology in an individual or a population (Singleton et al. in press).

Individual Factors and Old Primate Social Behaviors

Individual-specific factors such as sex, dominance rank, membership in a dominant matriline, and reproductive history may influence the social behavior of old primates. Early work in social gerontology expected the social behavior of old primates to look generally the same.

Notably, many of the studies investigating primate social gerontology have only focused on females of particular species. In contrast, studies that compared the social engagement of older males and females have found differences between the sexes. Older female rhesus macaques spend less time in social contact compared to younger females, while aged males spend more time compared to younger males, suggesting that there is not a species-specific strategy to accommodating the challenges of senescence but sex-based strategies might exist (Corr 2000).

Kato (1999) was one of the first researchers to find that sociality varied not only with age but also with dominance rank and season in Japanese macaque females. Nakamichi (2003) found that high- ranking old female Japanese macaques received grooming from unrelated individuals at the same frequencies as younger high-ranked females, while lower-ranked females mainly associated with kin during grooming. Studies of captive lemurs also found sex differences in the social engagement of old individuals but documented the opposite of what has been found in macaques: older males were more socially withdrawn than older females (Taylor 2008). Importantly, in this study, aged females maintained their dominance over males, indicating that female dominance in lemur species does not change with increased age. The sex differences in social engagement could be the result of both female dominance in lemur species and the fact that males do not remain in their natal groups after reaching sexual maturity. Female individuals have more experience and kin relationships to facilitate their continued sociality compared to male individuals. These findings reveal that aged social strategies seem to differ based on dominance rank and perhaps other factors.

The Social Role of Older Primates

One of the strategies old primates might utilize to maintain sociality is to assume a specific role in the social group. Research with other long-lived mammals has indicated that older females assume important roles based on their prior experiences. In killer whales, post-menopausal females will lead their social group to food resources during times of scarcity (Brent et al. 2015). Old female elephants are more sensitive to predatory threats, presumably based on their experience, and are able to protect their social groups (McComb et al. 2011). In primates, older members might fulfill specific roles in the social group like aunt, grandmother, or group navigator (Maxim 1979).

It has even been suggested that a post-reproductive lifespan in females could have evolved so a mother could care for a daughter’s offspring and increase her own reproductive success (Hawkes et al. 1997). While this “grandmother hypothesis” continues to be debated, some work with langurs have found support that older females will aid grandchildren in a facultative manner, when the cost is low and the likelihood of aggression is minimal (Borries et al. 1991). Research in wild populations of L. catta (Soma et al. 2012) and macaques (Wooddell et al. 2016) have shown that the death of an old “grandmother” in a social group leads to social instability.

Lemur catta as a Suitable Model for Primate Aging

L. catta (ring-tailed lemur) are strepsirrhine primates endemic to southwestern

Madagascar. They have relatively long life-spans in the wild (up to 15 years of age, Sauther unpublished data). They live in large (up to 30 individuals) multi-male, multi-female groups, with minor sexual dimorphism between males and females (Kappler 1990, Cuozzo unpublished data).

This study species provides an important context to explore questions of social gerontology because of the complexity and dynamic nature of their social groups (Sauther et al., 1999). L. catta’s lack of body size sexual dimorphism, like many other strepsirrhines, helps to weigh the trade-offs between reproduction and somatic maintenance between the sexes with more ease 13 because males do not seem to be allocating more resources to large increases in body size like those observed in anthropoid primates (Kappler 1990). Additionally, they exhibit true female dominance over males in both feeding and non-feeding contexts (Sauther et al. 1999). Kin-based group living can provide the asset of inherited status that can increase the survival of an individual such as matrilineal rank and dominance (Odling-Smee et al. 2003). The context of female dominance in L. catta provides a concrete means of investigating the relationship between kin- based and inherited advantages and aging. Results could also inform social behavior before the rise of catarrhine primates which can identify possible behavioral patterns that could be deeply- rooted in the primate order.

Studying Aging in Captivity

With more individuals in captivity representing the older age cohort, it is also important to characterize what the social needs of these primates are. For example, in captive chimpanzees, older individuals displayed lower levels of activity and object manipulation but still maintained social engagement with others (Baker 2000). Practices of placing older individuals into smaller social groups or even alone in captivity might be counterproductive for their wellbeing. Therefore, understanding what the social needs are of aged individuals can improve husbandry efforts to help maintain healthy populations in captivity.

Besides the direct implications of husbandry research, captive populations provide an important context in which to study the social and physiological effects of aging to further conservation efforts. These environments generally lead to a reduction in extrinsic mortality due to the access to medical care and resources as well as lower rates of predation, although this will vary depending on their housing conditions. As a result, mammals tend to live longer in captivity

(Lemaitre et al. 2013, Tidiere et al. 2016) with a large percentage of captive populations consisting 14 of old individuals. As ring-tailed lemurs in the wild are suffering reductions in population numbers in areas where good census data is available (Gould and Sauther 2016; LaFleur et al., 2016), it becomes even more essential to preserve the captive populations with the hope of potentially re- establishing wild populations and maintaining genetic diversity in the species. Therefore, understanding not only the social context of aging for these captive populations but also sources of mortality for old individuals is also crucial for successful husbandry and conservation of this species. If captivity helps to reduce the impact of extrinsic sources of mortality, the question becomes what leads to mortality in these environments?

Lemur catta Mortality at the Duke Lemur Center

To explore the question of how do old lemurs die in captivity, I utilized Duke Lemur Center

(DLC) records to find trends in mortality of ring-tailed lemurs. I classified the deaths of 126 individuals into categories based on the reported cause of death information from the records keeper (Zher 2017). I then divided these individuals into three age categories: Infant/Juvenile (0-

2 years old), Adult (2-10 years old), and Old (10+ years old). In this study, an individual was considered old based on the tendency of wild L. catta individuals to disappear between 10-15 years of age (Bennett et al. 2016). It should also be noted that ring-tailed lemurs experience a decline in fecundity after the age of ten in captivity (Parga and Lessnau 2005). Because of the smaller sample sizes, I did not conduct a formal statistical analysis, but I do report percentages based on general classification of cause of death. The “other” category includes causes of death that occur only one time in the data sample. Examples would include deaths due to infection, pneumonia, and pneumothorax.

Infants and Juveniles (Birth to 2 years)

The majority of the individuals in the data set died between birth and two years of age at the DLC (N=91). Of these deaths, 35% in this age range (Table 2) are categorized as missing from the enclosure and were not seen again (Figure 1). DLC records (Zher 2017) indicate that many of the deaths classified as missing are probably due to predation, but other sources of mortality cannot be ruled out. At Berenty Reserve, 20% of infants were reported missing within the first month and

50% within the first year with little clear cause of death (Nakamichi et al. 1996).

Of deaths in this age category 23% are due to trauma, with 3% of these trauma-related deaths resulted from injuries related to a fall and 2% based on injuries related to predation. Records also note that the other 18% of trauma-related deaths are most likely the result of falls, predation, or injury due to group conflict. Many infant deaths at the DLC have been tied to bite wounds and other injuries sustained from group conflict, with younger mothers having a significantly higher likelihood of losing infants to bite wounds (Charpentier and Drea 2013). According to DLC records (Zher et al. 2014), the youngest maternal age of conception for a ring-tailed lemur was

1.34 years; this youngest mother was one of the individuals in this study (Liesl), who is still alive.

However, 52.94% of infants, where maternal age at conception was less than two years old, died within the first year. In the wild, very few females at Berenty Reserve (Koyama et al. 2001) and no females at Bezá Mahafaly Special Reserve (Sussman 1991) give birth at two years of age.

Therefore, while infant mortality among these extremely young ring-tailed lemur females is still high, these findings also suggest that the captive environment allows for an earlier age at parturition than in the wild, perhaps due to nearly-unlimited food resources.

Table 2. Cause of Death Information for Infants and Juveniles at the Duke Lemur Center. *Deaths due to “Other” include aspiration of stomach contents, moderate focal cardiomyocyte degeneration, and heart-interventricular septal defect. Cause of Death Subset Count Percentage Missing 32 35.17% Trauma Total 21 23.07% From Fall 3 3.30% Predation 2 2.20% Euthanized Total 8 8.80% Euthanized due to Trauma 6 6.60% Unknown 10 10.99% Infection 2 2.20% Stillbirth 10 11.00% Failure to Thrive 3 3.30% Premature 2 2.20% Other* 3 33.33%

Infant/Juvenile Causes of Death 2.20% 3.30% 3.30% Missing Trauma

11.00% Euthanized 35.17% 2.20% Unknown Infection 10.99% Stillbirth Failure to Thrive 8.80% Premature 23.07% Other

Figure 1. Infant/Juvenile Causes of Death. These percentages represent cause of death information for 91 individuals from the Duke Lemur Center.

Adults (2-10 years)

Among adults (N=18) with recorded deaths at the DLC, 44.44% died due to trauma

(Figure 2) with 13% of these deaths being from injuries sustained from a fall or from predation

(22.22%). More individuals in this age category were euthanized (16.67%) compared to infants.

Table 3. Cause of Death Information for Adults at the Duke Lemur Center. *Deaths due to “Other” include pneumonia and pneumothorax. Cause of Death Subset Count Percentage Trauma Total 8 44.44% From Fall 2 11.11% Predation 4 22.22% Euthanized Total 3 16.67% Due to Infection 1 5.56% Unknown 3 16.67% Cardiac-Related Death 2 11.11% Other* 2 11.11%

Adult Causes of Death

11.11%

Trauma 11.11% Euthanized 44.44% Unknown 16.67% Cardiac-Related Death Other

16.67%

Figure 2. Adult Causes of Death. These percentages represent cause of death information for 18 individuals from the Duke Lemur Center.

Old Adults (10+ years)

The oldest male in this data set was 31, and the oldest female was 26. Among aged individuals (N=17), a little less than half (41.18%) (Table 4) had to be euthanized (Figure 3) due to a broad range of causes such as stroke, paralysis, and renal failure. Two lemurs (11.76%) died from pneumonia. Importantly, death related to predation is not as prevalent as the other age cohorts discussed. Though the sample size is small, it appears that old ring-tailed lemurs at the DLC die from causes that often are seen in modern, old humans such as stroke, pneumonia, and organ failure. In 2015, the leading causes of death in the United States of individuals above 65 years old were heart disease, cancer, chronic low respiratory disease, and cerebrovascular causes like stroke

(National Center for Health Statistics 2016). If lemurs are dying of old age in this captive setting, the question becomes how does the physiological effects of old age impact these lemurs socially and what strategies do individuals use to navigate this landscape. Perhaps, there are aspects of the ring-tailed lemur social environment that helps to accommodate these old lemurs.

Table 4. Cause of Death Information for Older Individuals at the Duke Lemur Center. *Deaths due to “Other” include unknown cause of death, infection, multifocal acute hemorrhage, and shock. Cause of Death Subset Count Percentage Euthanized Total 7 41.18% Due to Cardiac Failure 2 11.77% Due to predation 2 11.77% Pneumonia Total 2 11.76% Trauma Total 4 23.53% Other* Total 4 23.53%

Old Individual Causes of Death

23.53% Euthanized 41.18% Pneumonia Trauma Other 23.53%

11.76%

Figure 3. Old Individual Causes of Death. These percentages represent cause of death information for 17 individuals from the Duke Lemur Center.

Study Aims and Hypotheses

The primary goal of this study was to characterize the social behavior of old ring-tailed lemurs at the Duke Lemur Center. Based on reviews of the literature on primate aging, I developed the following research questions:

1. Do older individuals of both sexes maintain sociality with increased age?

2. Accounting for individual factors such as rank, reproductive history, and number of

offspring, is the social behavior, measured by time budgets and frequency of

behaviors, of aged individuals distinct from younger groups?

3. Do older individuals exhibit specific social patterns indicative of roles such as

grandmother or group navigator?

To address these questions, I tested the following hypotheses: 20

1a. Old individuals will exhibit levels of sociality, measured by time and frequency of

social behaviors, similar to those of other age groups.

1b. Old females will exhibit higher levels of sociality in the group compared to old males.

2. The social behavior of older individuals will be distinct from those of younger age groups to behaviorally accommodate the somatic challenges of old age.

i. Older individuals will spend more time resting than younger individuals.

ii. Older individuals will initiate social interactions less frequently than younger

individuals.

iii. Older individuals will vocalize for affiliative purposes more frequently than

younger individuals to maintain social relationships using less energy.

3. Old individuals will exhibit specific behavioral patterns indicative of social roles.

i. Old individuals will lead during group travel with a higher frequency than

adults. This behavioral pattern is indicative of a group-navigator social role.

ii. Old females will carry related infants at a higher frequency than other non-

maternal kin. This behavioral pattern is indicative of a grandmother or aunt

social role, depending on the kin relationship.

Chapter 2: Methods

I observed six groups of ring-tailed lemurs at the Duke Lemur Center for an 11-week period from May to August 2016 to compare the social behavior of old and adult individuals. Early on in the study, one of the groups (occupying NHE2) was removed from the sample due to illness.

Study Site

The Duke Lemur Center (DLC), formerly the Duke Primate Center, consists of nine natural habitat enclosures (NHEs) within the Duke Forest in Durham, North Carolina, United States of

America (Figure 4). Each NHE is surrounded by a 1.8-meter-high chain link fence with additional electronet fencing to prevent animal escapes. Additionally, the land 15 feet from the fence has been cleared of vegetation to discourage leaping from the trees into areas outside of the enclosure.

Subjects were only observed when they had free-ranging access to the forest enclosure. Individuals also had access to an indoor enclosure, outdoor enclosure, and an outdoor hallway that leads to the

NHE. Individuals were primarily observed in the natural habitat enclosures.

Free-ranging groups were provisioned once daily at a designated feeding site with commercial primate chow and fruits and vegetables occasionally. Food items were scattered widely at the feeding site to reduce aggressive encounters over food. The study subjects also had access to bowls of water located around the enclosure which were replenished twice daily by DLC husbandry staff. The study subjects would also supplement their diet from the variety of vegetation growing in the enclosure. They were observed to eat an array of fruits, flowers, leaves, soils, and insects in the enclosure. Other researchers (Taylor and Sussman 1985) have also observed lemurs at the DLC eating bark, fungi, and herbs in the enclosure. 22

(5.8 hectares) (5.8

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NocturnalBuilding

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Figure 4. Map of the Duke Lemur Center’s Natural Habitat Enclosures. This study was conducted with ring-tailed lemur groups living in NHEs 3,4,7,8, and 9. Map was obtained from the DLC Researcher’s Manual (Ehmke et al. 2016). 23

Study Animals

When observations began in May of 2016, the sample population consisted of six groups and a total of 19 individual lemurs. This period of time did not include the breeding season, which at the Duke Lemur Center is between November and February (Drea 2007). This population was selected based on which ring-tailed lemur individuals were free-ranging during the study period.

However, during the third week of data collection, one of the groups (from NHE2) had to be quarantined due to illness, and the group was removed from the study. Therefore, a total of 15 lemurs, nine of which were considered old (>10 years of age) and six of which were considered adults (2-9 years of age) were observed for the purposes of this study. This sample consisted of individuals from five groups ranging in size from two to six individuals (Table 5.). All individuals were identified using a combination of collars and physical features and all were born in captivity.

Each of the groups shared the NHE with groups of other lemur species, with which the ring-tailed lemurs sometimes interacted. Several of the enclosures also shared a common fence line where individuals could see adjacent groups but could not make physical contact with them due to several meters distance between fences. Furthermore, local fauna such as red foxes (Vulpes vulpes), raccoon (Procyon lotor), and black rat snakes (Panthrophis obsoletus) were occasionally seen in the NHEs.

Behavioral Methods

Focal sessions were recorded using an Acer tablet personal computer (Acer America, San

Jose, California, USA) programmed with Boris for Windows software with the pre-loaded ethogram (Appendix 1) of behaviors (Behavioral Observation Research Interactive Software,

Torino, Italy) (Friard and Gamba 2016). A Livescribe Echo Smartpen (Livescribe, Inc., Oakland,

California, USA) was also used to audio record vocal notes, including leading behaviors, 24 miscellaneous information, and to prevent loss of detail. Audio files were transcribed and used to provide more detail and context to the recorded activity budget files. I spent the first four days of the study refining my ethogram and data recording methods before beginning data collection for thesis research.

Table 5. Study Animals. Code represents the four-digit number assigned to the lemurs at the DLC at birth. Total Offspring indicates the total number of offspring that the lemur had. Surviving Offspring indicates the number of offspring that are still alive. Family trees of the study animals can be found in Appendix 3. Birth Age Total Surviving Code Sex Name Date (yrs) Category Offspring Offspring Descriptors NHE3 (Group 2) 6534 M Aristides 3/21/1993 23.13 O 0 0 chubby 6711 F Sosiphanes 4/13/1997 19.07 O 4 2 black collar 6857 F Lilah 3/28/2005 11.11 O 0 0 gimpy arm NHE4 (Group 3) black RC 6440 M Aracus 5/23/1991 24.96 O 16 14 .175 6956 F Shroeder 3/22/1992 24.13 O 2 2 very large 6957 F Liesl 7/15/2008 7.81 A 6 6 mid shave base shave; 7087 F Gretl 4/9/2012 4.07 A 0 0 no tail tip 7239 F Hedwig 3/28/2016 0.1 I 0 0 lighter color 7240 F Griselda 3/28/2016 0.1 I 0 0 darker color NHE7 (Group 4) 2 colored 6909 F Sierra Mist 5/1/2008 8.01 A 0 0 eyes 6835 M Berisades 3/28/2004 12.11 O 0 0 NHE8 (Group 5) orange RC 6528 M Licinius 3/17/1993 23.15 O 0 0 .614 6831 F Tellus 3/18/2004 12.13 O 0 0 teal RC .545 NHE9 (Group 6) 6863 F Sprite 3/17/2001 15.14 O 13 13 short tail orange RC 7084 M Jones 3/17/2012 4.13 A 0 0 .714 w/tag black RC 7086 M Stewart 3/30/2012 4.1 A 0 0 .654 7176 F LuLu 3/19/2014 2.13 A 0 0 mid shave

A total of 637 data files (318.5 hours) were generated, each representing one 30-minute focal session. In the final analysis, 560 files were analyzed, representing 280 hours of observation.

77 data files were not included in the analysis because the group was removed from the sample due to illness (NHE2) or the focal follows were incomplete in duration. Because of the inequitable ratio of old and young adult lemurs, less time was spent following each old individual (15 hours) compared to young individuals (23 hours), but the total amount of time spent observing individuals from each age group was approximately the same (Old: 139.5 hours, Adults: 140.5 hours).

At the beginning of sampling, I randomly assigned social groups to particular days using a random number generator. A day of data collection was seven to eight hours of data collection, while a half-day was three to four hours of data collection. When the NHE2 was removed from the sample, I randomly reassigned the sampling schedule due to the reduction in sample size, particularly in the young age group (Appendix 2). Due to husbandry practices at the DLC, it sometimes became necessary to switch the group I was following or cease following a particular group. If this occurred, I followed the social group randomly assigned to the next day of observation and picked up the prior group the next day they were free-ranging again. On several occurrences, I followed groups for only a half a day but did my best to make sure that groups were sampled at different times of the day. A nonrandom sampling strategy was utilized to maintain an equitable number of observations between old and adult individuals. A focal follow was terminated and removed from analysis if the individual was out of view for more than ten minutes. When possible, I avoided repeat observations of the same individual, trying to make sure that at least one observation period separated these focal follows. However, in the smaller social groups, repeat observations of the same individual were recorded if the other group members were not found. 26

For each observational period the following data were recorded: focal animal ID, observation time, behavioral state, behavioral direction, social partner ID, number of individuals within two meters of focal animal, and notes collected ad libitum. Behavioral direction indicated if a particular behavior was initiated by the focal individual or received from another member of the social group. All occurrences of agonistic behaviors were also recorded for the creation of dominance hierarchies. Dominance hierarchies were established using methods from Sauther

(1992) and Taylor (1986). During a focal observation period, if the subject engaged in a vocalization, type, and directionality (initiated vocalization or responding to another individual’s) were also recorded. Ring-tailed lemurs have different types of vocal calls (Macedonia 1993); therefore, I classified calls into three different categories: affiliative, alerting and antipredator, and agonistic vocalizations. All behaviors recorded are listed in Appendix 1, adapted based on an ethogram developed by Sauther (1992) and modified by Millette (2007).

Data and Statistical Methods

Data processing and analysis was conducted in JMP (JMP 13, SAS Institute Inc., Cary,

North Carolina, USA). Significant differences between age categories were assessed using students t-tests and Tukey-Kramer Honest Significant Difference (HSD) tests. Due to the directional nature of the hypotheses, one-tailed t-tests were used and were conducted in JMP. Both tests were used and reported to indicate the strength of the statistical results with respect to the hypotheses tested. When comparing count data, a Fisher’s exact test was used due to small sample sizes. An ANOVA was used to determine if individual identity significantly predicted the variation among times in the activity budget such as time in physical contact, travel, etc. If a particular individual was found to be a major cause of variation, a Tukey-Kramer all pairs post-hoc analysis was conducted to determine patterns in individual activity budgets. This method of comparison 27 was used because it allowed for the significance level to be held constant across all pair-wise tests.

For all statistical tests, significance was set at α≤0.05.

Chapter 3: Results Degree of Sociality

Proximity

Not accounting for sex, old individuals spent significantly more time per focal follow alone, more than two meters away from a group member (Old mean = 739.77 ± 33.25,

Adult Mean = 503.54 ± 32.82; DF = 557.85; t=-5.06; p<0.0001). When sex is accounted for, both old females (Old mean = 709.14 ± 45.47, Adult Mean = 455.35 ± 37.28; DF = 314.89; t=-4.32; p<0.0001) and males (Old mean = 778.61 ± 48.58, Adult Mean = 599.40 ± 63.36; DF = 185.59; t=-2.24; p=0.026) spent significantly more time alone than adult individuals. This relationship was still significant between female age categories when Liesl was removed from the data set (Old mean = 709.14 ± 44.24, Adult Mean = 557.25 ± 46.54; DF = 295; t=-2.37; p=0.0093) (Figure 5).

Liesl and interactions with her infants were removed from parts of the analysis because she was expected to have more physical contact with other individuals because she had nursing infants during data collection.

900 Old 800 Adult 700 600 500 400 300

200 Seconds Focal Seconds Per Follow 100 0 Female Male Sex

Figure 5. Average Time Spent More Than Two Meters Away from Group Members. This comparison reflects measures of proximity without Liesl and her infants. Error bars reflect the standard error of the mean. 29

Physical Contact

As mentioned before, proximity to group members might not be an accurate measure of sociality compared to physical contact. Not accounting for sex, adult individuals spent significantly more time in physical contact with other individuals compared to old lemurs (Old mean = 268.73 ± 26.35, Adult Mean = 340.57 ± 30.13; DF = 548.78; t=1.79; p=0.037). Among females, adults spent significantly more time in physical contact with others than old females (Old mean = 317.60 ± 36.33, Adult Mean = 410.45 ± 39.16; DF = 340.91; t=1.74; p=0.0415) (Table

6.).

Table 6. Mean Physical Contact Time Comparison between Old and Adult Females with and without Liesl and Infants. This relationship was not significant when a Tukey comparison was conducted. Adult Female Old Female Means Means D.F. t-value p-value With Liesl and Infants 410.45 ± 39.16 317.60 ± 36.33 340.91 1.74 0.0415 Without Liesl and Infants 218.02± 33.88 308.61 ± 36.32 294.9 -1.82 0.0346

However, the variation in physical contact time was strongly predicted by individual

(ANOVA, F=14.37, DF=8, p<0.0001), and the post-hoc analysis indicated that Liesl spent significantly more time in physical contact with group members compared to all of the other females in this study (Table 7). Because this high physical contact time was most likely a function of Liesl having two infants, I also conducted the physical contact analysis without these individuals

(Figure 6). When these individuals were excluded from the analysis, the inverse significant relationship was found: old females spent significantly more time in physical contact with other individuals than adult females (Old mean = 308.61 ± 36.32, Adult Mean = 218.02 ± 33.88; DF =

294.9; t=-1.82, p=0.035) (Table 6.). No significant relationship in physical contact time between old and adult males was found both including and excluding Liesl and her infants (Table 8.). 30

Table 7. Female Individual Analysis of Physical Contact Time. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Physical Contact Connecting Individual Mean Letters Liesl 980.87 A Sosiphanes 428.95 B Lilah 347.19 B Shroeder 338.13 B Lulu 291.22 B Tellus 282.68 B Sierra Mist 234.94 B Sprite 196.73 B Gretl 146.89 B

Table 8. Mean Physical Contact Time Comparison between Old and Adult Males with and without Liesl and Infants. This relationship was not significant when a Tukey comparison was conducted. Adult Male Old Male p- Means Means D.F. t-value value With Liesl and 201.56 +/- 206.74 +/- Infants 41.91 37.50 202.54 -0.092 >0.05 Without Liesl and 201.56 +/- 203.37 +/- Infants 41.91 37.61 202.82 -0.032 >0.05

400 Old 350 Adult 300

250

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150

100 Seconds Seconds Focal Per Follow 50

0 Female Male Sex

Figure 6. Average Time Spent in Physical Contact with at Least One Group Member. This comparison reflects measures of physical contact without Liesl and her infants. 31

Furthermore, when comparing physical contact time between old males and females, old females were found to spend significantly more time per focal in physical contact with other individuals, excluding Liesl and her infants, compared to old males (Old Female Mean = 308.61

± 36.32, Old Male Mean = 203.37 ± 37.61; DF = 270.49; t=-2.01; p=0.02). No significant difference in physical contact time between adult males and females was found, especially when

Liesl was removed from the analysis (Adult Female Mean = 218.02 ± 33.88, Old Male Mean =

201.56 ± 41.91; DF = 198.09; t=-0.31; p=0.38). These results indicate that old females are more social than old males when using physical contact as a measure of sociality (Figure 7.).

400

350

300

250

200

150

100

Average Average Per Time FocalFollow 50

0 Female Male Sex

Figure 7. Average Time Spent in Physical Contact with at Least One Group Member Compared between Old Males and Females. This comparison reflects measures of physical contact without Liesl and her infants.

Activity Budgets

Locomotion (Travel and Movement)

As a group, old lemurs spent significantly more time per follow in locomotion (Old

Mean = 270.43 ± 12.23, Adult Mean = 206.88 ± 11.84; DF = 557.29; t=-3.73; p=0.0001). When 32 broken down by sex, a significant difference between time spent in locomotion between old and young females does not exist (Table 9.). Individual identity was not found to significantly predict any variation in female locomotion times (ANOVA; F=1.48; D.F.=8; p=0.37), travel (ANOVA;

F=1.95; D.F.=8; p=0.07), and movement (ANOVA; F=1.21; D.F.=8; p=0.54).

Table 9. Locomotion, Travel, and Movement Comparisons between Adult and Old Females. No significant difference was found between age groups when comparisons were conducted using a Tukey-Kramer Honest Significant Difference test. Adult Female Old Female Behavior Means Means D.F. t-value p-value Locomotion 223.81 ± 12.83 230.35 ± 14.24 328.4 -0.34 0.37 Travel 20.57 ± 3.47 28.63 ± 4.30 312.16 -1.46 0.07 Movement 203.24 ± 11.59 201.72 ± 12.32 333.24 0.09 0.54

Individual identity was found to significantly explain variation in male locomotion

(ANOVA; F=8.25; D.F.=5; p<0.0001), travel (ANOVA; F=3.32; D.F.=5; p=0.0066), and movement (ANOVA; F=8.84; D.F.=5; p<0.0001). The old male Aracus had a significantly higher amount of locomotion and movement activity than most of the other males (Table 10.).

Table 10. Male Individual Analysis of Locomotion and Movement Times. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Locomotion Movement Mean Connecting Mean Connecting Individual (seconds/follow) Letters Report (seconds/follow) Letters Report Aracus 441.18 A 420.8 A Licinius 356.22 A B 297.14 A B Berisades 271.76 B C 245.92 B C Aristedes 219.8 B C 189.26 B C Jones 178.71 C 170.81 B C Stewart 167.49 C 147.82 C

Licinius was found to spend significantly more time traveling (Table 11.) than the two young males Stewart (Tukey-Kramer HSD, p=0.035) and Jones (Tukey-Kramer HSD, p=0.0016). 33

Therefore, in comparing these behaviors between age categories, I also conducted the comparison without Aracus for locomotion and movement and Licinius for travel.

Table 11. Male Individual Analysis of Travel Times. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Travel Individual Mean Connecting Letters Report Licinius 59.08 A Aristedes 30.51 A B Berisades 25.84 A B Aracus 20.38 A B Stewart 19.67 B Jones 7.89 B

A significant difference (t=-4.69, p<0.0001) between old and younger male locomotion time exists, even when Aracus is removed (t=-3.25, p=0.0007) from the data set, indicating that old males spent more time moving around in general than the two adult males. When locomotion is broken down between movement and travel, old males spend significantly more time traveling than adults (t=-2.69, p=0.0039). However, when Licinius is removed from the analysis, this relationship is no longer significant (Table 12). Old males spend significantly more time (t=-4.39, p<0.0001) moving than adults, even if Aracus is removed (t=-2.81, p=0.0027).

Table 12. Locomotion, Travel, and Movement Comparisons between Adult and Old Males with and without Aracus and Licinius included. *Indicate comparisons where the Tukey- Kramer Honest Significant Difference test was significant. Behavior Young Male Old Male D.F. t-value p-value Locomotion* 173.22 ± 24.28 321.27 ± 20.21 195.11 -4.69 <0.0001 Locomotion without Aracus* 173.22 ± 24.28 282.58 ± 23.24 184.73 -3.25 0.0007 Travel* 13.66 ± 5.08 34.06 ± 5.65 214.82 -2.69 0.0039 Travel without Licinius 13.66 ± 5.08 25.63 ± 14.78 182.7 -1.61 >0.05 Movement* 159.56 ± 22.98 287.20 ± 17.76 186.55 -4.39 <0.0001 Movement without Aracus* 159.56 ± 22.98 244.11 ± 19.37 180.16 -2.81 0.0027

Feeding and Foraging

Overall, old and adult feeding and foraging times did not differ significantly (Old

Mean = 80.01 ± 7.99, Adult Mean = 96.71 ± 9.27; DF = 547.61; t=1.36; p=0.91), and there were no sex differences for these behaviors (Old Female Mean = 72.61 ± 10.03, Adult Female Mean =

92.75 ± 10.99; DF = 341; t=1.35; p=0.91) (Old Male Mean = 89.39 ± 12.91, Adult Male Mean =

104.58 ± 17.11; DF = 183.61; t=0.71; p=0.76). The ANOVA indicated that individual identity strongly explained the variation in feeding and foraging time for females (F=2.42; DF=8; p=0.02) but not males (F=0.32; DF=5; p=0.90). The post-hoc analysis among the females (Table 13) indicated that Lulu spent significantly more time feeding and foraging per focal than Liesl (Tukey-

Kramer HSD, p=0.0048) and Sprite (Tukey-Kramer HSD, p=0.0321).

Table 13. Female Individual Analysis of Feeding/Foraging Times. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Feed/Forage Individual Mean Connecting Letters Lulu 161.72 A Gretl 81.71 A B Tellus 80.96 A B Shroeder 78.28 A B Sosiphanes 76.57 A B Sierra Mist 74.07 A B Lilah 68.8 A B Sprite 58.79 B Liesl 52.65 B

Resting

For total resting, no significant difference was found between old and adult individuals for total resting time (Old Mean = 1129.63 ± 18.87, Adult Mean = 1083.61 ± 23.65;

DF = 532.61; t=-1.52; p=0.06). Old females spend significantly more time resting than adult females (t=-3.91, DF=340.89, p<0.0001) (Table 14). Comparison of total resting time significantly 35 varied by individual (ANOVA; F=9.69; D.F.=8; p<0.0001); post-hoc analysis indicated that Sprite spent significantly more resting time than Gretyl (Tukey-Kramer HSD, p=0.0161) and Liesl

(Tukey-Kramer HSD, p<0.0001) and that Liesl spent significantly less total time resting than all of the other females (Table 15). Therefore, I conducted the comparisons between female resting age categories with and without Liesl in the analysis. When the age comparison is conducted without Liesl included, the significant difference in female resting time disappeared (Table 14).

Table 14. Analysis of Old and Adult Female Total, Solitary, and Social Resting Times.

Adult Female Old Female D.F. t-value p-value With Liesl 1005.64 ± 27.74 1151.18± 24.88 340.89 -3.91 <0.0001 Total Without Resting Liesl 1099.61± 30.14 1151.18± 24.88 278.83 -1.32 0.09 With Liesl 193.39 ± 26.4 168.52 ± 24.71 340.79 0.69 0.75 Social Without Resting Liesl 140.78 ± 30.94 168.52 ± 24.71 274.6 -0.7 0.20 With Liesl 812.25 ± 33.70 982.66 ± 33.28 338.9 -3.6 0.0002 Solitary Without Resting Liesl 958.82 ± 34.93 982.66 ± 33.28 292.12 -0.49 0.31

Table 15. Female Individual Analysis of Total Resting Time. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Total Resting Connecting Individual Mean Letters Sprite 1287.88 A Tellus 1169.95 A B Sierra Mist 1147.98 A B Sosiphanes 1137.75 A B Lulu 1122.81 A B Lilah 1088.21 A B Shroder 1064.28 A B Gretl 1028.03 B Liesl 717.63 C

A significant amount of the variation in social resting time among females was explained by individual variation (ANOVA, F=3.19, DF=8, p=0.0017) with Liesl spending significantly more time in social rest than Sprite (Tukey-Kramer HSD, p=0.017) and Gretl (Tukey-Kramer

HSD, p=0.0002) (Table 16). No significant differences in time spent in social rest were found when Liesl was both included and excluded from the comparison (Table 14). Old females spend more time in solitary rest (t=-3.6, p=0.0002), but this significant relationship disappears if Liesl is removed from the analysis. A significant amount of the variation in solitary resting time among females was explained by individual variation (ANOVA, F=13.83, DF=8, p<0.0001) with all females spending significantly more time (Tukey-Kramer HSD, p<0.05) in solitary rest than Liesl

(Table 17). Therefore, when Liesl is removed from the data analysis for solitary rest the significance between old and adult females is no longer present.

Table 16. Female Individual Analysis of Social Resting Time. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Social Resting Connecting Individual Mean Letters Liesl 354.66 A Sosiphanes 233.17 A B Lulu 225.86 A B Lilah 176.71 A B Tellus 173.15 A B Shroeder 170.49 A B Sierra Mist 154.46 A B Sprite 91.46 B Gretl 42.02 B

Old females spent significantly more time (Old Mean = 468.46 ± 38.03, Adult Mean =

291.62 ± 29.72; DF = 296.97; t=-3.69, p=0.0001) resting by themselves with no individuals within two meters of them compared to adult females, even when Liesl is removed from the analysis (Old 37

Mean = 468.46 ± 38.03, Adult Mean = 368.80 ± 36.12; DF = 286.93; t=-1.9, p=0.0292). Individual strongly predicted the variation in time spent resting not in proximity to group members (ANOVA,

F=10.30, DF=8, p<0.0001). The post-hoc analysis indicates that Sprite spent significantly more time resting alone than most of the other females while Liesl spent the least amount of time solitary resting alone (Table 18).

Table 17. Female Individual Analysis of Solitary Resting Time. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Solitary Resting Connecting Individual Mean Letters Sprite 1196.42 A Tellus 996.8 A B Sierra Mist 993.52 A B Gretl 986 A B Lilah 911.5 A B Sosiphanes 904.58 A B Lulu 896.95 B Shroeder 893.79 A B Liesl 362.97 C

Table 18. Female Individual Analysis of Solitary Resting Time Not In Proximity with at Least One Group Member. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Solitary Resting (NN=0) Connecting Individual Mean Letters Sprite 692.36 A Tellus 653.02 A B Sierra Mist 545.06 A B C Lulu 371.58 B C D Lilah 369.09 B C D Sosiphanes 328.54 C D E Shroeder 288.99 C D E Gretl 193.75 D E Liesl 53.06 E

Adult males spent significantly more time resting total than Old males (t=2.78, p=0.003)

(Table 19.). Total resting time was strongly predicted by individual (ANOVA, F=2.91, DF=5, p=0.0146), but a post-hoc analysis of total resting time indicated no significant differences among males (Table 20.). This significant difference existed for solitary resting (t=2.45, p=0.0076) but not for male social resting (Table 19.). Both social (ANOVA, F=2.80, DF=5, p=0.018) and solitary resting (ANOVA, F=2.59, DF=5, p=0.0269) times were strongly predicted by individual identity among males. Licinius spent significantly more time in social rest (Tukey-Kramer HSD, p=0.0215) than Aracus (Table 20.). Stewart spent significantly more time in solitary rest than Licinius (Table

21.). Adult males spent significantly more time resting in close proximity to at least one group member compared to old males (Old Mean= 501.18, Adult Mean= 699.49; DF=167.20; t=2.90, p=0.0021).

Table 19. Analysis of Old and Adult Male Total, Solitary, and Social Resting Times.

Adult Male Old Male DF t-value p-value Total Resting 1238.71 ± 39.78 1102.30 ± 28.85 178.85 2.78 0.003

Social Resting 123.07 ± 33.57 128.49 ± 28.40 196.91 -0.12 0.45 Solitary Resting 1115.64 ± 46.38 973.81 ± 34.70 182.62 2.45 0.0076

Table 20. Male Individual Analysis of Social Resting Time. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Social Resting Connecting Individual Mean Letters Licinius 260.17 A Jones 174.62 A B Berisades 165.22 A B Aristides 77.92 A B Stewart 69.28 A B Aracus 6.72 B 39

Table 21. Male Individual Analysis of Solitary Resting Time. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. Solitary Resting Connecting Individual Mean Letters Stewart 1151.07 A Jones 1081.69 A B Berisades 1066.42 A B Aracus 1029.52 A B Aristides 971.93 A B Licinius 829.16 B

Sleeping

No significant differences in total, social, and solitary sleeping times for both males and females were found (Table 22.).

Table 22. Analysis of Adult and Old Male and Female Total, Solitary, and Social Sleeping Times. Adult Mean Old Mean D.F. t-value p-value Total Females 92.22 ± 18.94 85.45 ± 18.63 339.1 0.26 0.60 Sleeping Males 105.77 ± 26.79 58.54 ± 20.1 182.96 1.41 0.92 Social Females 36.52 ± 12.62 28.22 ± 11.3 340.87 0.49 0.69 Sleeping Males 28.30 ± 18.69 17.35 ± 9.84 143.3 0.52 0.70 Solitary Females 55.71 ± 14.10 57.23 ± 13.47 340.3 -0.08 0.47 Sleeping Males 77.47 ± 18.52 41.19 ± 17.65 207.89 1.42 0.92

Auto-grooming

No significant differences between adult and old auto-grooming were found overall (Old

Mean = 116.62 ± 8.20, Adult Mean = 120.88 ± 7.72; DF = 555.71; t=0.38; p=0.65) or within the sexes (Old Female Mean = 116.22 ± 10.62, Adult Female Mean = 131.11 ± 9.18; DF = 322.93; t=1.06; p=0.86) (Old Male Mean = 117.12 ± 12.88, Adult Male Mean = 100.54 ± 13.94; DF =

205.46; t=-0.87; p=0.19).

Allo-grooming 40

No significant differences between female adult and old total allo-grooming time was found (Old Mean = 101.27 ± 11.00, Adult Mean = 85.18 ± 8.85; DF = 311.73; t=-1.14; p=0.13).

When grooming is broken down based on directionality (mutual vs. unidirectional), older females spent significantly more time engaged in mutual grooming (Old Mean = 70.36 ± 8.37, Adult Mean

= 37.50 ± 4.94; DF = 255.87; t=-3.38; p=0.0004). Adult females spent significantly more time engaged in unidirectional grooming behavior (Old Mean = 30.91 ± 5.50, Adult Mean = 47.67 ±

6.17; DF = 340.81; t=2.03; p=0.02). No significant differences were found between old and adult males in total allo-grooming (Old Mean = 47.59 ± 7.92, Adult Mean = 39.87 ± 8.51; DF = 206.05; t=-0.66; p=0.25), mutual grooming (Old Mean = 39.06 ± 7.07, Adult Mean = 27.66 ± 5.73; DF =

213.89; t=-1.25; p=0.11), or unidirectional grooming (Old Mean = 8.53 ± 2.34, Adult Mean =

12.21 ± 3.51; DF = 168.89; t=0.87; p=0.81).

Frequency of Behaviors

Agonistic Point Events

The number of agonistic events initiated and received did not significantly differ between adult and old females (Fisher’s Exact Test, p=0.54) (Table 23.). Females initiated agonistic acts more than males (Fisher’s Exact Test, p<0.0001) (Table 24.). The number of agonistic events initiated and received did not differ between adult and old males (Fisher’s Exact

Test, p=0.38), with males more likely to be recipients of agonistic acts (Table 25.).

Table 23. Female Agonistic Event Counts Based on Act Initiated, Received, or Unknown. Table probability using a Fisher’s Exact Test is P=0.0405 with p=0.54. Initiated Received Unknown Total Old 51 21 0 72 Young 77 39 2 118 Total 128 60 2 188

Table 24. Female and Male Agonistic Event Counts Based on Act Initiated, Received, or Unknown. Table probability using a Fisher’s Exact Test with p<0.0001. Initiated Received Total Female 94 59 153 Male 6 58 64 Total 100 117 217

Table 25. Male Agonistic Event Counts Based on Act Initiated, Received, or Unknown. Table probability using a Fisher’s Exact Test is P=0.041 with p=0.38. Initiated Received Unknown Total Old 5 34 5 44 Young 1 24 1 26 Total 6 58 6 70

Affiliative Point Events

The number of affiliative events initiated and received did not differ between adult and old individuals of both sexes (Tables 26. & 27.).

Table 26. Female Affiliative Event Counts Based on Act Initiated, Received, or Unknown. Table probability using a Fisher’s Exact Test is P=0.036 with p=0.41. Initiate Received Unknown Total Old 53 66 1 120 Young 64 65 0 129 Total 117 131 1 249

Table 27. Male Affiliative Event Counts Based on Act Initiated, Received, or Unknown. Table probability using a Fisher’s Exact Test is P=0.177 with p=0.81. Initiate Received Total Old 24 27 51 Young 11 15 26 Total 35 42 77 42

Grooming

When comparing the initiation and receiving information for grooming bouts, I found that adult females initiated significantly more grooming events (69.41%) than old females

(30.59%) (Fisher’s Exact Test; p<0.0001) (Table 28.). Among the males, I found that adult individuals received significantly more (59.1%) grooming behaviors than old males (40.91%)

(Fisher’s Exact Test; p=0.02) (Table 29.). When directionality is broken down based on grooming type, adult females still initiate significantly more unidirectional grooming bouts (77.59%) than old females (22.415%) (Fisher’s Exact Test; p<0.0001) (Table 30.). No significant difference in adult and old male directionality in grooming was found (Fisher’s Exact Test; p=0.77) (Table 31).

Looking at mutual grooming, adult females initiate significantly more mutual grooming bouts

(57.82%) than old females (42.18%) (Fisher’s Exact Test; p=0.0001) (Table 32.), whereas, old males initiate more mutual grooming bouts (62.71%) than adult males (37.29%) (Fisher’s Exact

Test; p=0.01) (Table 33.).

Table 28. Female Total Grooming Event Counts Based on Act Initiated, Received, or Unknown. The Fisher’s Exact Test one-tail probability is p<0.0001. Initiated Received Total Old 156 145 301 Adult 354 78 432 Total 510 223 733

Table 29. Male Total Grooming Event Counts Based on Act Initiated, Received, or Unknown. The Fisher’s Exact Test one-tail probability is p=0.02. Initiated Received Total Old 55 45 100 Adult 43 65 108 Total 98 110 208

Table 30. Female Grooming (Unidirectional) Event Counts Based on Act Initiated, Received, or Unknown. The Fisher’s Exact Test one-tail probability is p<0.0001. Initiated Received Total Old 67 77 144 Adult 232 41 273 Total 299 118 417

Table 31. Male Grooming (Unidirectional) Event Counts Based on Act Initiated, Received, or Unknown. The Fisher’s Exact Test one-tail probability is p=0.77. Initiated Received Total Old 18 17 35 Young 21 25 46 Total 39 42 81

Table 32. Female Mutual Grooming (Bidirectional) Event Counts Based on Act Initiated, Received, or Unknown. The Fisher’s Exact Test one-tail probability is p=0.0001. Initiated Received Total Old 89 68 157 Young 122 37 159 Total 211 105 316

Table 33. Male Mutual Grooming (Bidirectional) Event Counts Based on Act Initiated, Received, or Unknown. The Fisher’s Exact Test one-tail probability is p=0.0122. Initiated Received Total Old 37 28 65 Young 22 40 62 Total 59 68 127

Stink Fights

Stink fighting is a directed, agonistic encounter during which a male rubs carpal spurs against his sternal glands and then moves his tail in the face of the receiving individual (Jolly

1966). During the course of the entire period of data collection, I only recorded five occurrences of stink fighting. Both occurrences of stink fighting by Aracus were directed towards Randy, the male inhabiting the enclosure across the fence. Licinus’ single recorded stink fight was directed at 44

Jones across a fence, and both of Berisades’ stink fight occurrences were directed at individuals of another species sharing an enclosure with him.

Vocalizations

Old females responded to affiliative vocalizations at a significantly higher frequency (61.15%) than adult females (53.76%) (Fisher’s Exact Test; p=0.038) (Table 34). No significant difference existed between the number of initiated versus responded affiliative vocalizations for males of the different age groups (Fisher’s Exact Test; p=0.93) (Table 35). Males initiated more affiliative vocalizations whereas females tended to respond more (Fisher’s Exact

Test; p<0.0001) (Table 36).

Table 34. Female Affiliative Vocalization Event Counts Based on Act Initiated, Responding, or Unknown. The Fisher’s Exact Test one-tail probability between initiated and received events is p=0.038. Initiating Responding Unknown Total Old 108 170 5 283 Adult 160 186 0 346 Total 268 356 5 629

Table 35. Male Affiliative Vocalization Event Counts Based on Act Initiated, Responding, or Unknown. The Fisher’s Exact Test one-tail probability between initiated and received events is p=0.93. Initiating Responding Total Old 135 57 192 Adult 34 22 56 Total 169 79 248

Table 36. Male and Female Affiliative Vocalization Event Counts Based on Act Initiated, Responding, or Unknown. The Fisher’s Exact Test one-tail probability between initiated and received events is p<0.0001. Initiating Responding Unknown Total Female 268 356 5 629 Male 169 79 0 248 Total 437 435 5 877

No significant differences were found between the number of initiated and responded alerting and antipredator vocalizations (Fisher’s Exact Tests; p=0.09, p=0.94) (Tables 37 & 38) for both sexes based on age. Old individuals of both sexes participated in more alerting and antipredator vocalizations compared to adult individuals, but this difference is most likely a function of the NHE that these individuals inhabited rather than age (see discussion).

Table 37. Female Alerting and Antipredator Vocalization Event Counts Based on Act Initiated, Responding, or Unknown. The Fisher’s Exact Test one-tail probability between initiated and responding events is p=0.09. Initiating Responding Unknown Total Old 111 173 0 284 Young 5 2 1 8 Total 116 175 1 292

Table 38. Male Alerting and Antipredator Vocalization Event Counts Based on Act Initiated, Responding, or Unknown. The Fisher’s Exact Test one-tail probability between initiated and responding events is p=0.94.

Initiating Responding Unknown Total Old 29 56 1 86 Young 5 19 0 24 Total 34 75 1 110

Leading Behavior

No significant difference in group travel leading behavior was found between adult and old females. However, old males were found to lead group travel (56%) with a greater frequency (Fisher’s Exact Test, p=0.0030) than adult males (18%) (Figure 8). 46

60% 56% Old Adult 50%

40%

30% 23% 21%

20% 18% Percentage Percentage of Leading

10%

0% Female Male Sex

Figure 8. Percent Leading During Travel Between Old and Adult Individuals.

Individual Factors

Dominance Rank

All females were socially dominant to males in both feeding and non-feeding contexts, indicating that, even with older age, females are still socially dominant to males. Due to the lack of agonistic interactions during feeding, separate ranks based on feeding and non-feeding context could not be constructed (Table 39.). Females still maintained social dominance with advanced age, indicating that this dominance persists in old females consistent with findings in other lemur taxa (Taylor 2008). In two of the social groups with more than one female, the oldest females (Sosiphanes and Sprite) were socially dominant to the other female in the group. In both cases, the younger females (Lilah and Lulu) were the daughters of the dominant female, consistent with studies in wild populations (Sauther 1992; Pereira 1993; Nakamichi et al. 1997). These findings also show that old females are not being targeted by younger individuals as a means to rise in rank, consistent with research on other species of lemur at the DLC (Taylor 2008). 47

Liesl was the most dominant female of her social group, ranking above both her mother

(Shroeder) and her daughter (Gretl). Liesl was the only female in this population who had dependent infants and was still lactating during the study period. Yet, she spent less time overall

(52.65 seconds) per focal feeding than many of the other females studied, though this was not significantly different from other females. Liesl’s dominance over her mother in the social group could be a function of her infants, giving her greater access to foods to meet her needs for lactation.

Due to the composition of the social groups at the DLC, I was not able to compare how advanced age affects the social rank of males but such a question will be an important area for future inquiry.

Table. 39. Social Ranks of Study Individuals. In all instances, males were subordinate to females. Sex Name Age Category Rank NHE 3 M Aristides 23 O -- F Sosiphanes 19 O 1 F Lilah 11 O 2 NHE 4 M Aracus 24 O -- F Shroeder 24 O 3 F Liesl 7 A 1 F Gretl 4 A 2 F Hedwig 0.1 I -- F Griselda 0.1 I -- NHE 7 F Sierra Mist 8 A -- M Berisades 12 O -- NHE 8 M Licinius 23 O -- F Tellus 12 O -- NHE 9 F Sprite 15 O 1 M Jones 4 A 2 M Stewart 4 A 1 F LuLu 2 A 2

Social Roles

Infant Care

One of the primary ways that I measured infant care was the amount of time that particular individuals carried the infants Hedwig and Griselda. Over the course of my study, only two other individuals Shroeder, their grandmother, and Aracus, their father, were observed to carry an infant besides Liesl (Table 40). Furthermore, both of these individuals carried only Griselda specifically and not her sister Hedwig or both infants at the same time.

Table 40. Non-Maternal Carrying Behavior of Griselda. Mean Time Individual Relationship (seconds) N Aracus Father 9.809 1 Shroeder Grandmother 57.298 11 Gretl Sister 0 0

Case Studies

Grouping the data from subjects based on certain characteristics (age, sex, etc.) was an important way to address my hypotheses. However, rather than constructing a concrete behavioral profile for old ring-tailed lemurs, I found that the effects of aging must be understood at the individual level. While I was able to explore a few individual factors that seem to affect behavioral patterns in old lemurs like sex and dominance rank, these factors did not seem to adequately capture the range of individual variation that I observed. The following case studies provide more depth to the primary finding that senescence affects individuals differentially based on characteristics of the animal like personality, life history, and even disability.

Aracus

Aracus is a 24-year old male living in the only social group I sampled with infant individuals. He was the father of the infants, Hedwig and Griselda, and was the only male in the 49 social group. Of all of the males in my sample, Aracus spent the most time per focal follow

(average: 441.18 seconds) in locomotor behaviors (traveling and moving), which was significantly different (Table 10.) from four of the five other males. When locomotion is broken down based on duration, Aracus spent the most time moving (average: 420.80 seconds) which was significantly different than four of the other five males (Table 10.). With respect to travel, Aracus was among the middle males in time spent traveling (Table 11.). Among the males, he spent the second least amount of time in proximity to group members, but this relationship is not significantly different from any of the other males (Table 41.). Aracus seemed to actively avoid members of his social group at times, which might explain his inclination to move around the enclosure by himself.

Table 41. Male Individual Analysis of Social Proximity Time. Social proximity was considered to be within two meters or less of at least one group member. The connecting letters reports reflect the results of comparisons for all pairs using the Tukey-Kramer Honest Significant Difference test. This post-hoc analysis was conducted after the ANOVA for physical contact time among the males was strongly predicted (F=2.85, DF=5, p=0.0164) by individual.

Social Proximity Connecting Individual Mean Letters Jones 1294.47 A Aristedes 1000.83 A B Berisades 989.33 A B Stewart 984.94 A B Aracus 965.34 A B Licinius 837.51 B

Aracus also spent the least amount of time in social rest (average: 6.72 seconds), but this time was only significantly different (Table 20.) from Licinius. When observing Aracus, he would commonly investigate parts of the enclosure that were nearby for other ring-tailed lemurs that were across the fence. He also is among the top two of individuals in number of times approaching or scent marking the researcher or their chair (N=16 times). Aracus has been in numerous research studies during his time at the DLC and is known to be incredibly cooperative 50

(Zher 2016). Therefore, his inclination to greater movement could be in part related to his prior experiences with humans in captivity.

Sprite

Sprite is a 15-year old female living in a social group with her daughter (Lulu), her son (Jones), and her grandson (Stewart). Sprite spent the most amount of time among the females solitarily resting (1196.42 seconds on average/follow) and was significantly different from Liesl and Lulu (Table 17.). Sprite also spent the second least amount of time in social rest (91.46 seconds/focal) after Gretl, but this relationship was only significantly different from Liesl (Table

16). Sprite spent the least amount of time each focal (185.5 seconds) in locomotion, but this relationship was not significantly different from the other females in the sample. When observing

Sprite, she would often select a tree in which to rest while her group members would explore the forest and feed.

Shroeder

Shroeder is a 24-year old female living in a social group with her daughter (Liesl), unrelated male (Aracus), and three granddaughters (Gretl, Griselda, and Hedwig). Her daughter

Liesl is the highest-ranked female of the social group. According to DLC records, the last time

Shroeder was pregnant with an infant she “stole” Liesl’s newborn infant and cared for it until DLC staff realized that she was still pregnant (Zher 2016). After her own infant was born, Liesl’s infant was seen trying to nurse from Shroeder and would even ride on her back. During the study period,

Shroeder was observed carrying her daughter’s infant Griselda (Table 40), but never her other granddaughter Hedwig. She spent the most time carrying Griselda compared to the non-maternal members of the social group. 51

Lilah

Lilah is an 11 year old female living in NHE3 with her mother Sosiphanes and an unrelated male Aristedes. Sosiphanes was found to be dominant over her daughter. In September

2007, at two years of age, Lilah broke her left humerus, requiring her to have surgery (Zehr 2017).

Researchers think that she obtained nerve damage either post-surgery or from the injury itself which required several months (until March 2008) with a splint and physical therapy. By May of

2008, sensation had returned to her arm, and she was able to move the digits of her left hand, but she seldom used her arm after this time. Researchers at the DLC suspect that the joints became stiff during her recovery. Therefore, at this point in her life, she began not putting weight on this arm, holding it out to her left when she moved. She has been able to use the arm for support (Figure

9.).

a. b.

Figure 9a. & 9b. Pictures of Lilah. This image of Lilah depicts her resting with her left forelimb positioned out to the left of her body. She holds her arm in a similar manner when walking or running. b) This image is a close-up side view of how Lilah uses her arm for occasional stability when at rest. Note that she does not place significant weight on it.

In April of 2012, during the application of flea and tick medication, she broke her left ulna and radius, which were in a splint until the end of May 2012. DLC records note that this additional 52 injury did not seem to cause any additional lack of mobility in her left arm than was already there

(Zher 2017). Therefore, Lilah had spent approximately nine years living with the challenges of her injured left arm before the data in this study were collected. Individual-based analysis of activity budgets indicate that this impaired older lemur does not spend her time differently than other females in this study. It should be noted, that she spent the most time of all of the females (mean:

299.91 seconds/follow) in locomotion, but this was not found to be significantly different to any of the other females. Lilah’s impairment does not seem to result in drastic modifications to her activity budget compared to other females.

The Other Individuals

While I have emphasized particular findings for the four individuals above, I wanted to highlight characteristics of the other individuals in this study to be mindful of in the interpretation of my results. Aristides is a 23-year-old male living with the two non-related females

Sosiphanes and Lilah in NHE3. It should also be noted, that when Aristides was younger, he was castrated during two separate mating seasons by members of his social group. Sosiphanes is also a member of NHE3 and is the 19-year-old mother of Lilah.

Liesl is a seven year old female living with her three daughters, mother, and non-related male Aracus in NHE4. Liesl during the duration of this study was still lactating and allowing the infants Hedwig and Griselda to nurse from her. Towards the end of the data collecting period, she tended to carry one of her daughters, Hedwig. Gretl is Liesl’s four-year-old daughter who had no occurrences of infant carrying in the social group. It should also be noted that during data collection, a family of foxes was living in NHE4, which affected the frequency of antipredator vocalizations observed in this study. 53

Sierra Mist is an eight-year-old female living in NHE7 with Berisades, a 12-year-old male.

Several years before this data was collected Berisades escaped the NHE enclosure in which he was living and was eventually found at an elementary school before he was returned to the DLC. The period of data collection was the first time Berisades was allowed to free-range since escaping from his enclosure.

Tellus is a 12-year-old female living with 23-year old Licinius in NHE 8. It should be noted that during the sampling period, several raccoons were living in NHE8 which affected the antipredator vocalization rate of these individuals.

Jones is a four-year-old male living in NHE9 with Sprite, two-year old Lulu, and Stewart whom is the same age as Jones. Jones, Stewart, and Lulu frequently spent their mornings exploring the enclosure while Sprite often selected a tree and rested separately from the group.

Chapter 4: Discussion

Discussion of Results in Terms of Study Hypotheses

Decoupling Chronological Age and Senescence

In this study, I used the age in which ring-tailed lemurs often disappear in wild environments as a means of operationalizing old in this population. I expected to observe a clear difference in the social and behavioral profile of these old individuals compared to adults, but the data do not support this hypothesis. Age did not explain any of the variation in locomotion, feeding, and resting between old and adult individuals. My failure to support this hypothesis indicates that age-related benchmarks do not adequately distinguish senescent individuals from other cohorts within this captive population.

The struggle of primatologists and bio-gerontologists to operationalize old in conjunction with my own findings reveals that age-related approximations of senescence inadequately describe aging individuals. Patterns of senescence are not only individual-dependent, but different mammalian systems and tissues seem to experience rates of senescence at different times

(Hayward et al. 2015). Though we observe a general trend of physiological decline associated with advanced age, different factors can reduce or hasten this decline. This suggests that strictly age- dependent means of defining senescence like the standard used in this study should also include metrics that focus on individual, somatic variation like the physiological frailty index (Antoch et al. 2017). It is also critical that age-related descriptor of old be decoupled with ideas of aging and senescence. My work has shown that senescence is strongly dependent on ecological, demographic, and life history factors in addition to expected association with chronological age.

One significant reason why the old cohort cannot be clearly distinguished from adults is that individuals exhibit a vast range of behavioral variability even within the small population of 55 this study. Much of the significant variation that I observed disappeared with the removal of one individual from the analysis. For example, Liesl spent the least amount of total time resting than the other females (Table 15); when she was removed from the analysis, the significant differences in female resting time disappeared (Table 14). Liesl’s status as a lactating female with two infants resulted in significant differences in her behavior compared to the other females in this study. Such individual variation in status affects the construction of a categorical behavioral profile based on chronological age because different individuals can experience life history milestones like first reproduction at different ages in their life.

Individual Variation and the Disposable Soma Hypothesis

Differences in life history patterns are particularly key in captive settings like the Duke

Lemur Center where curators must manage which individuals are going to be reproducing and which ones are not. For example, only five of the 15 individuals in this study have ever produced offspring (Table 5): Sosiphanes, Aracus, Shroeder, Liesl, and Sprite. Liesl was just over a year old when she gave birth to her first infant whereas her mother Shroeder was 15 (Zehr et al. 2014).

Such artificially-imposed differences in reproduction provide an important means of observing senescence under the disposable soma theory of aging.

The disposable soma hypothesis predicts that individuals that start breeding at a later age should experience lower levels of senescence because a delay in reproduction allows for resources to be allocated towards somatic maintenance and survival (Kirkwood and Rose 1991). Based on this hypothesis, the lack of behavioral and social differences between the old and adult individuals in this study may be explained by only one third of the population having produced offspring.

Because most of the individuals have not had to allocate resources towards reproduction, the majority of these resources, which are more abundant in captive settings, can be directed towards 56 somatic maintenance. If these individuals are allocating resources towards maintenance, I expect them to be exhibiting fewer signs of senescence than individuals who have been reproductive, particularly those who were reproducing earlier in life.

Female costs for reproduction are viewed to be higher not only in mammals but also in primates due to the costs of gestation and lactation (Russell and Lummaa 2009). Among haplorrhine primates, males tend to allocate energy towards the growth of larger body size to enable male-male competition for females (Leigh 1992). However, ring-tailed lemurs do not exhibit sexual dimorphism in body size (Kappeler 1990). Therefore, we should not expect ring- tailed lemur males to invest more energy in the growth of a larger body size, but rather allocate resources to other means of competition such as physical agility. Notably, at the Duke Lemur

Center, because breeding pairs are established and placed in the environment to give them the best possible chance of producing offspring, males have reduced pressure to invest in traits essential for competition. This reduction in male-male competition is further supported by the minimal frequency of stink-fighting (five total occurrences) observed during this study. Because of the size monomorphism and reduced competition in captivity, I expect that females in this environment would be allocating more energy directly to reproductive efforts than males. For the females that have been reproductive, under the disposable soma theory, we should expect higher rates of senescence, especially in females that are reproductive earlier in life.

The differential allocation of resources can help to explain some of the individual variation in behavior if I compare the two reproductive old females in this study, Sprite and Shroeder. As mentioned previously, Sprite spent a significant amount of time resting away from her social group compared to other old females in this study. Though she was not the oldest female (12 years old),

Sprite had not only had the most total offspring but also the most surviving offspring (N=13) 57 among the three reproductive females (Table 5). She gave birth to her first infant at age four (Zher et al. 2014). Shroeder, by contrast, was very active in her social group to the point of helping to carry her infant granddaughter Griselda. She was also the oldest female (age 24 years) but only had two offspring, both of which were still alive at the time of this study (Table 5). She gave birth to her first infant, Liesl, at 12 years of age (Zher et al. 2014). Behaviorally, Sprite seems to be exhibiting a lower level of activity than Shroeder despite the fact that she is 12 years younger than her. The differences in fecundity between these two females could explain why behaviorally Sprite seems less-active than Shroeder. This comparison further supports my assertion that chronologically-based means of describing aging does not adequately represent patterns of senescence.

If older individuals such as Sprite experience a decline in metabolic rate, they might spend more time resting to accommodate this challenge and reduce energy expenditure. For example, impaired Japanese macaques will spend more time resting as a possible means of accommodating the extra energy expenditure associated with moving with their injury (Turner et al. 2012). The only other individual in this study who had high levels of fecundity was Aracus, but he did not seem to experience a reduction in activity level compared to other males. This contrast further reveals how differential reproductive investment between the sexes could affect patterns of senescence. My findings indicate that there are differences in behavior among old individuals, suggesting that advanced age variably affects physiology. If senescence affects individuals differently, we might expect to see a range of strategies that animals use to accommodate the challenges of physiological decline.

This comparison highlights the importance of individual-based research in wild populations where humans do not artificially select which animals are reproducing and 58 contributing to the gene pool. Though only a few individuals in this study produced offspring, recent curation efforts at the Duke Lemur Center seem to have produced a more genetically-diverse population of captive ring-tailed lemurs (Grogan et al. 2017). Research with captive mammal populations, with ring-tailed lemurs included in the analysis, indicates that early in life reproduction and fecundity does not lead to a reduction in longevity (Ricklefs and Cadena 2007).

However, longevity does not indicate the degree of senescence and quality of life for individual animals, especially since they all have access to medical care. Future research should look at sources of mortality among individuals based on their degree of fecundity in both captive and wild populations. Such work could reveal not only how reproductive effort affects somatic aging but also would provide specific mechanisms to target for future cellular and genetic aging research.

These efforts could also help to improve the quality of life for captive individuals to support efforts to maintain and expand the genetic diversity of the captive gene pool of the species.

In failing to support my hypothesis that I would observe an age-specific behavioral profile indicative of senescence, I found that the cohort-based approach is ineffective in furthering our understanding of aging. I have already discussed above how age and fecundity can help explain differences among individuals with respect to behavioral patterns associated with aging.

Dominance rank can also lead to considerable variation among individuals when observing behavioral indicators of senescence. Females were found to initiate more agonistic events than males which is consistent for this species due to female dominance. These results along with my findings on rank (Table 39) indicate that not only do older females maintain social dominance over males, but they also indicate that younger females are not targeting older females as a means of rising in rank. These findings are consistent with those in other lemur species at the DLC (Taylor

2008). Future work in a larger wild population can help to discern if this is a species-specific 59 pattern or if perhaps it is a function of the captive environment. Older and low-ranking female baboons have been found to experience higher rates of injury than those younger and higher-ranked

(Archie et al. 2014). All of the old females in my sample population except for Shroeder and Lilah, who was below her mother in rank, were the dominant female in their social group. Therefore, it is difficult to determine if this lack of targeted aggression by old females is a result of their higher dominance rank or their age. Targeting of handicapped or senile female ring-tailed lemurs has been documented in a wild population (Takahata et al. 2014), indicating that the conditions of my study might have helped to buffer older individuals from targeted aggression.

The presence of kin in the social group can also differentially impact the behavior of individuals. Older females were found to spend more time in physical contact with other individuals compared to older males (Figure 7), providing support for my hypothesis that females would exhibit higher degrees of sociality compared to males. This is consistent with findings in other lemur species (Taylor 2008) and could be the result of female dominance or greater presence of kin in the social group. Greater physical contact among older females could be a function of the group compositions of my sample; all females in groups larger than a pair were living with kin

(Appendix 3). Related females are more likely to maintain close proximity and grooming relationships both in the wild (Nakamichi and Koyama 1997) and in captivity (Taylor 1986), while unrelated individuals generally spend more time alone. The presence of kin in the social group might help to increase the survival of old individuals by providing more social partners, particularly for grooming. Conversely, older individuals with less kin support might be at a disadvantage that might make them more susceptible to extrinsic sources of mortality. For example, grooming plays an essential role not only in solidifying social bonds but also in removing parasites that could lead to infection and even death. 60

Senescence and disability are often viewed as equivalent states with respect to fitness: that the old and disabled will not survive due to impairment. However, Lilah’s case study reveals that, in the captive setting of the Duke Lemur Center, her injury does not seem to impair her activity compared to other females. Millette et al. (2009) found that dentally impaired ring-tailed lemurs spent more time feeding and foraging in the early afternoon rather than resting like other members of their social group. Foraging while others are resting reduces the competition over food objects and could be a way to compensate for their impairment. In this study food stealing occurred only three times in Lilah’s social group during the observation period, but two of those three times

Sosiphanes stole food from Lilah. Lilah’s injury might impede her ability to obtain and hold onto food in a group-feeding context. If Lilah were in a larger social group where there might be more competition to obtain and keep food, she might have to utilize an alternative strategy to meet energetic and nutritional needs, such as foraging while others are resting.

Furthermore, Sosiphanes’ presence in Lilah’s social group could be an important social resource for her. Notably, disabled Japanese macaque females were found to have less social affiliates than unimpaired individuals (Turner et al. 2014). These authors indicate that presence of kin in a group helps to increase the number of social partners a disabled individual has. Therefore, having a related female in Lilah’s group might have significantly bolstered her level of sociality compared to her being in a group with an unrelated female. Overall, the smaller social group size in this provisioned environment along with maternal presence in the group might provide a buffer for Lilah. This case study reveals how individual-dependent factors like disability and social group composition interact to affect behavior and sociality. This capacity to modify behavior and benefit from the social environment are two possible key factors that have helped primates to accommodate the challenges of aging that have led to longer lifespans in the primate order. 61

Primate Buffers against Senescence-Associated Mortality

Based on my findings, the ability to be behaviorally flexible and the benefit of social groups could help buffer some individuals from both extrinsic and intrinsic sources of mortality. As an order, primates have a great capacity for behavioral flexibility that allows for many species to occupy a diverse variety of environments and niches. Part of this plasticity is being able to accommodate challenges through modification in the amount of time spent on an activity or how the activity is done often to reduce the amount of energy expended. Sprite’s reduction in activity level in this study could be a behavioral modification to accommodate the physiological challenges associated with senescence. Furthermore, older females were found to respond to affiliative vocalizations at a significantly higher frequency than adult females. No significant difference was found between male age groups, but males tended to initiate affiliative vocalizations while females responded with a higher frequency. These results suggest that older females might be using vocalizations as a means of grooming close social group members from a distance. Ring-tailed lemurs are more likely to respond to a frequently-groomed partner’s affiliative vocalizations than an individual that they rarely groom (Kulahci et al. 2015); this groom-at-a-distance strategy of maintaining close ties within a social group could be a way for older individuals to maintain social ties while expending less energy. A similar pattern has been observed in older Japanese macaque females as a means of maintaining social relationships with non-kin social partners with reduced energetic cost (Mitani 1986). Behavioral flexibility may be an essential tool to accommodate the challenges associated with senescence. Learning to accommodate these challenges would have led to gradual increases in longevity and could explain the trend towards longer lifespans in the primate order. 62

I found support for the hypothesis that older ring-tailed lemurs would maintain engagement in the social group. Old individuals might have a higher motivation to be social because it helps to buffer these individuals against extrinsic sources of mortality, like predation and parasitism, that group living helps to prevent. Evidence in Barbary macaques (Almeling et al. 2018) suggests that older primates might have a higher motivation to be social than younger individuals in the social group. No significant differences in initiated and received affiliative events between the age groups existed. Therefore, I failed to support the hypothesis that old individuals would initiate more social interactions than adult individuals. These results suggest that not only are old individuals still socially engaged in the group, but that they are also actively pursuing affiliative interactions rather than passively receiving the social advances of other members. This active pursuit of social behaviors also supports the idea that old individuals are still motivated to engage in social behavior.

Therefore, higher degrees of sociality in older ring-tailed lemurs of a wild population could provide a selective advantage against extrinsic mortality.

Social groups also can provide inherited advantages such as higher rank or association with a dominant matriline (Roach and Carey 2014). For example, had Sprite been living in a wild social group, though she might experience a decline in activity level as a result of the reproduction- maintenance trade off, her higher fecundity might help to buffer her against this challenge because she might have more support from her female offspring. Future work should examine both the costs and benefits sociality might confer to older individuals. For example, the highly-agonistic social environment observed with ring-tailed lemurs might be more stressful for lower-ranked females (Cavelli et al. 2003), which could lead to faster physiological decline in certain systems.

Social groups also allow for individuals with varying levels of experience live together.

Older individuals have been thought to contribute their experience and wisdom to collectively 63 support the whole social group by fulfilling a specific role in the group (Roach and Carey 2014).

With respect to my third research question, I found very preliminary indications that ring-tailed lemur old individuals might fill the role of grandmother in the social group. Shroeder carried her granddaughter Griselda both on average more times but also more frequently than other non- maternal kin in this study (Table 40). These findings indicate that older individuals have the potential to take on an allomaternal role in this species. Similar patterns have been found in chimpanzees (Hayaki 1988) and hanuman langurs (Borries 1988). Future work exploring this question should take into account the potential energetic cost that allmothering might have on an individual.

During the mating season, Shroeder was given a contraception injection, but she was not on birth control during the rest of the year. Her prior behavior indicates that she might be particularly interested in infants when she does not have her own. Allomothering is common in both captive (Taylor 1986, Periera and Izard 1989) and wild ring-tailed lemurs (Gould 1992).

Instances of facultative grandmothering in hanuman langurs suggest that these individuals seem to only help out their grandchildren when there is minimal cost to themselves, especially since these old individuals showed signs of visual and hearing impairment (Borries 1988). Therefore, grandmaternal carrying might have been observed in the captive setting of the DLC because of the energetic buffers this environment can provide since food is nearly-unlimited. Furthermore, the presence of a grandmother in the social group of a wild populations seems to provide stability to the social group, with more females being evicted and higher levels of aggression occurring right after her death (Soma and Koyama 2012). Similar observations have been documented in rhesus macaques (Wooddell 2016) suggesting that older individuals can also play an essential role in reducing stress levels by helping to stabilize the social group. Such social roles might not only 64 help the fitness of individuals but also the group as a whole. While aspects of the social group might differentially help older individuals more, the group can benefit from the experience and wisdom of having old individuals actively engaged in the group. Having value to the whole group could reduce the socially-negative effects of senescence-associated impairment. For example, individuals might not target an older female if she helps guide them to food resources during times of scarcity. Furthermore, the interactions between senescence and sociality are heavily environment-dependent. It is thus important to note how the captive environment has shaped my findings.

Captivity Caveats

Small Sampling Size and Limited Group Composition

In finding a location for my study, locating a captive population with an adequate sample size proved to be a challenge. As noted above, the sizes of the social groups of my sample population are considerably smaller than those seen in the wild. These smaller groups limited the degree to which I could measure how aging might affect factors such as social rank, number of offspring, and social network size. For example, I had no means of determining how older age might affect male-male interactions and social rank because I had no social groups that contained more than one old male or a combination of old and adult males. Had old males been allowed to interact with other males, their measures of sociality could have been similar to old females, as affiliative social interactions among males in the same social group are high during the non-mating season (Gould 1999). Observing more male-male interactions would also helped to describe how males might differentially allocate resources in favor of competition for mating opportunities.

Understanding male competition is essential for understanding how reproduction-maintenance trade-offs can affect patterns of senescence in this sexually monomorphic species. 65

Older males were found to spend significantly more time in total locomotion and moving.

Older males were also found to lead more instances of group traveling than younger males.

However, I was not able to conclude that these higher rates of locomotion and leading during travel were a function of these older males’ age. In wild populations (Gould 1999, Nakamichi and

Koyama 1997), males in the social group frequently seek to drive out solitary or migrating males from a particular group’s territory. Part of this male-male agonism are stink fights which are observed fairly frequently in the wild. As noted before, I observed only five total instances of stink fighting between males during the course of my entire study. Therefore, the higher rates of travel seem to be more a function of the captive environment rather than age: males were moving around more to look for other ring-tailed lemur males.

Other research (Corr 2000) on primate social gerontology was able to characterize rhesus macaque social networks, finding that aged female networks were smaller, while old males had larger networks compared to those younger. A network-based approach helps to quantify and characterize which individuals from all the options an animal chooses to affiliate with. The smaller social groups of my sample provide very limiting social options. Therefore, I was not able to apply such an approach to this sample population to small social groups.

Reduction in Agonism among Individuals

A practice when feeding the lemurs at the DLC was to spread out the food throughout a designated feeding site. This was done to reduce female agonism during feeding so that each individual in a social group could have equitable access to the provisioned foods. This practice severely impaired my ability to establish dominance ranks for the individuals in this study in the context of feeding. Furthermore, a significant amount of the agonism among individuals in wild populations are in the context of feeding. For example, only 14% of the agonism observed at the 66

Bezà Mahafaly Special Reserve could be categorized as non-feeding (Sauther 1993). Therefore, this reduced-agonistic state of the DLC might not adequately represent species-specific patterns with respect to age.

Additionally, all of the social groups in my study consisted of females from the same matriline per group, with either maternal or grandmaternal relationships between older individuals and those younger. Therefore, the composition of these groups might help to remove the agonistic pressure during feeding that can often occur between multiple matrilines. Tension among matrilines can even be fatal at the DLC (Charpentier and Drea 2013) and in wild populations

(Kittler and Dietzel 2016). This single matrilineal group composition might enable the old females to maintain their high rank with less challenges than if there were more than one matriline present.

Conclusions

Old ring-tailed lemurs at the Duke Lemur Center still maintained their engagement in the social group. Old females appeared to be more socially engaged than adults. These results indicate that in this captive setting, age-associated physiological change does not appear to impair an individual’s ability to remain engaged in the social group. I also found that, as a whole, the old behavioral profile of both male and female individuals was not distinct from adults. These results suggest that older individuals do not have to significantly modify their behavior to accommodate age-related physiological challenges, at least in a captive setting. Most of the differences that I observed between the age categories, such as those with male locomotion and number of antipredator vocalizations, were most likely a function of the captive environment. I found preliminary support that old females can help care for their daughter’s offspring (grandmothering) in the form of carrying an infant on her back.

This work reveals how aspects of captivity can affect the study of behavioral and social manifestations of senescence which further reveals the importance of testing these questions in the wild. My study provides concrete evidence that research with senescence should decouple old age and senescence as the same phenomenon, in that one can occur without the other. Furthermore, work with senescence should focus on inter-individual variation rather than differences between the old and adult cohorts. Important individual factors like sex, rank, kin relationships, and disability can affect patterns of senescence. This research reveals how behavioral flexibility and sociality can help buffer aging primates against somatic decline with possible implications for the increase in longevity across the primate lineage.

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Appendix 1: Behavioral Definitions

Definitions are based upon an ethogram for ring-tailed lemurs developed and utilized by Sauther

(1992) and further refined by Millette (2007) with the addition of Stink Fight (s) and Displace (d) as separate behaviors. I also included infant-related behaviors: Riding(r) and Nursing(n).

Event/Point Behaviors

Agonistic

Bite (b) – The mouth is used to forcefully and agonistically grasp a social partner with the dental apparatus. Biting behavior is directional, and may be initiated by the animal against a social partner or may be received from a social partner. Behavior has been combined into the category of “Agonism” for purpose of analysis.

Cuff (c) – Animal makes contact with the palm of the hand or wrist against the head or face of a social partner. Cuffing behavior is directional, and may be initiated by the animal towards a social partner or may be received from a social partner. Behavior has been combined into the category of “Agonism” for purpose of analysis.

Chase (h) – Animal locomotes towards and pursues a social partner who withdraws and departs away from the animal directing the chase. The directing animal peruses the social partner following withdraw for at least one meter. Chasing is a directional behavior and may be initiated by the focal animal towards a social partner or may be received from a social partner. Behavior has been combined into the category of “Agonism” for purpose of analysis.

Displace (d) – Animal moves towards another animal and causes that animal to vacate its location. This is a directional behavior, and may be initiated by the focal animal towards a social 79 partner or may be received from a social partner. Behavior has been combined into the category of “Agonism” for purpose of analysis.

Fight (f) – Agonistic encounter between the focal animal and a social partner involving biting, grappling, chasing and physical contact. Fight is a directional behavior. Initiated is scored if focal animal unidirectionally commences Fight towards a social partner. Received is scored if a social partner unidirectionally commences FI towards the focal animal. Behavior has been combined into the category of “Agonism” for purpose of analysis.

Food Steal (f) – Animal displaces an animal engaged in feeding and then consumes that animal’s food item. Food steal may also involve taking a food item from an animal through use of agonistic behaviors such as fighting, cuffing or biting. Food steal is a directional behavior.

Initiated is scored if focal animal takes a social partners food. Received is scored if a social partner takes the focal animal’s food item. Behavior has been combined into the category of

“Agonism” for purpose of analysis.

Jump Fight (j) – Agnostic encounter in which one individual attacks another through jumping. Behavior has been combined into the category of “Agonism” for purpose of analysis.

THIS BEHAVIOR WAS NOT OBSERVED.

Nip (n) -- Animal uses the anterior dentition to quickly and lightly grasp a social partner with the anterior portion of the dental apparatus. Nipping behavior is directional, and may be initiated by the animal towards a social partner or may be received from a social partner.

Behavior has been combined into the category of “Agonism” for purpose of analysis.

Slap (s) – Animal makes contact with the palm of the hand against a social partner. This behavior is directional, and may be initiated by the animal towards a social partner or may be 80 received from a social partner. Behavior has been combined into the category of “Agonism” for purpose of analysis.

Stink Fight (s) – An agonistic encounter in which an animal rubs the carpal spurs against the sternal glands, “charges” the tail with the carpal spurs, and subsequently directs the tail towards the face of a social partner. Direction of the tail towards a social partner is also accompanied by movement of ears to a posterior position in which they lie flat against the head.

Directing stink fight is limited to male individuals, although males may attempt to SF with females. SF is a directional behavior. Initiated is scored if focal animal unidirectionally commences SF towards a social partner. Received is scored if a social partner unidirectionally commences stink fight against the focal animal. Mutual is scored if both animals initiate SF simultaneously. Behavior has been combined into the category of “Agonism” for purpose of analysis.

Affiliative

Approach (a) – Focal animal locomotes within one meter of a social partner, or a social partner locomotes within one meter of the focal animal. AP is a directional behavior. Initiated is scored if the focal animal locomotes to within one meter of a social partner. Received is scored if a social partner locomotes to within one meter of the focal animal.” Behavior has been combined into the category of “Affiliative” for purpose of analysis.

Nose Poke (n) – Focal animal and a social partner briefly touch noses. Nose poking is most frequently seen as two animals approach and “greet.” NO is a mutual social behavior.

Other (Socially Neutral) 81

Scent Mark (s)-- Focal animal marks a target object (most frequently a small branch or tree) utilizing scent glands in the anal/genital region, carpal spurs and the sternal glands,.

Behavior has been combined into the category of “Other” for purpose of analysis.

Defecate (D) – Focal animal excretes feces through the anus.

Stand (S) – Individual maintains a vertical posture in which the posterior limbs are used to support the entire weight of the body and the anterior limbs are not in contact with the ground or other substrate. Standing may be accompanied by visual monitoring.

Urinate (U) – Focal animal excretes urine through the urethral opening.

State Behaviors

Affiliative

Nearest Neighbor (N)— Establishes the number of social group members are within 2 meters of the focal individual. Can be 0-6 individuals.

Social Groom (g) – Individual is observed pass the toothcomb or anterior portion of the muzzle (in cases of toothcomb loss) through the fur. Grooming is most frequently observed to feature a rhythmic anterior-posterior movement of the head during which the toothcomb is used to remove ectoparasites. Grooming behavior is frequently marked by licking in addition to passing the toothcomb through the fur. Grooming is a directional behavior. Social grooming may consist of initiated grooming in which the focal animal is subject to grooming by conspecific partner, received grooming where the focal animal grooms a conspecific partner, and mutual grooming in which the focal directs grooming towards a social partner while simultaneously receiving grooming.

Social Rest (R) -- Focal animal is not engaged in any other defined behavior and is in physical contact with at least one other individual. Resting behavior features a lack of any 82 locomotor activity. If an observed behavior cannot be categorized but includes physical contact with another individual, social rest is assigned.

Social Sleep (S) – Focal animal is motionless with eyes closed and is in physical contact with at least one other individual. Sleep may be scored with the eyes slightly open (e.g. the pupil is obscured) as individuals frequently only partially close their eyes. If eyes open while attempting to determine closure status or the eyes are obscured rest is scored.

Infant-Related States

Riding (r)—One or more infants cling to the ventral or dorsal surface of focal individual while the focal individual is moving. If individual is not moving, then infant(s) and focal are in social rest.

Nursing (n)—One or more infants seen to be making oral contact with focal individual’s nipple. If mouth to nipple contact is not visible, then social rest is used.

Other

Drink (d) -- Focal animal ingests water through the mouth. Water may be ingested either by licking a water source or by using the hand to “cup” water from a source. Drink may be scored for either ingestion of water from a concentrated source such as a bucket of water or a puddle, or by licking items as dew-wet leaves or damp concrete. Behavior has been combined into the category of “Other” for purpose of analysis.

Feed/Forage (f) – Focal animal searches for, selects, manipulates, processes, and ingests food items. Behavior commences with processing a food item or mastication. Feed/forage behavior is broken once the focal animal has been observed to cease mastication. Behavior has been combined into the category of “Other” for purpose of analysis. 83

Mate (m) – Focal animal engages in copulatory behavior with a conspecific social partner and most frequently includes intromission of the penis into the vulva. Intrasexual mounting behaviors are also included within MA. THIS BEHAVIOR WAS NOT OBSERVED.

Movement (m) – Individual locomotes across a distance not less than one meter but no greater than 10 meters. Movement includes all forms of locomotion (e.g. walking, leaping, climbing, running and, galloping), but does not include minor repositioning or postural changes while engaged in other behaviors.

Out of View (O) – Individual is not visible to the observer.

Play (p) – Individual engages in behaviors which may include mock fighting, non- agonistic chasing, light wrestling, jumping, and high-velocity movement or travel. Play may be a social behavior or a solitary behavior. Social play is typically accompanied by a “play face,” marked by a wide gape of the mouth without bearing of teeth. Behavior has been combined into the category of “Other” for purpose of analysis.

Solitary groom (g) -- Individual is observed pass the toothcomb or anterior portion of the muzzle (in cases of toothcomb loss) through their own fur. Grooming is most frequently observed to feature a rhythmic anterior-posterior movement of the head during which the toothcomb is used to remove ectoparasites. Grooming behavior is frequently marked by licking in addition to passing the toothcomb through the fur.

Solitary Rest (R) -- Focal animal is not engaged in any other defined behavior. Resting behavior features a lack of any locomotor activity. If an observed behavior cannot be categorized, RE is assigned.

Solitary Sleep (S) – Focal animal is motionless with eyes closed and making no physical contact with other individuals. Sleep may be scored with the eyes slightly open (e.g. the pupil is 84 obscured) as individuals frequently only partially close their eyes. If eyes open while attempting to determine closure status or the eyes are obscured rest is scored.

Sun (S) -- Focal animal exposes the ventral surface towards the sun in a stereotyped vertical sitting position where the arms are placed laterally to the torso and legs. Sunning animals often close the eyes or turn the head away from the sun. In such cases of closed eyes, sleep is not scored. Sun may be scored if one arm is not placed laterally to the torso or inside legs, if as to maintain balance or prevent a fall. Sun occurs most frequently during cold periods.

Travel (T) – Individual locomotes for a distance greater than 10 meters. Movement includes all forms of locomotion (e.g. walking, leaping, climbing, running and, galloping).

Individual may pause for a short period (no more than 2-3 seconds) during a travel bout, as to engage in activities such as locating the next point of movement or viable substrate, prepare to leap, or wait for another individual to clear from the line of movement. Traveling behavior was designated individual (I) traveling if focal individual and/or some of the group was moving or group (G) traveling if all individuals were involved in the behavior. Behavior is considered a subset of the locomotion behaviors.

Watch Observer (W) – Individual visually monitors and/or visually tracks the observer.

Visual monitoring must be clearly directed towards the observer. Short “glances” directed towards the observer or monitoring in which the animal monitors several visual targets in rapid succession are not included within this behavioral category.

Appendix 2: Sampling Schedule

Sampling Date of Sampling Date of Day Sample Group # Day Sample Group # 1 23-May No Sampling: July 4th 2 24-May No Sampling: July 4th 3 25-May 31 6-Jul NHE7 4 26-May 32 7-Jul NHE3 W. 1 5 27-May NHE3 W. 7 33 8-Jul NHE9 No Sampling: Memorial Day 34 11-Jul NHE4 6 31-May NHE4 35 12-Jul NHE3 7 1-Jun NHE4/NHE* 36 13-Jul NHE4 8 2-Jun NHE4 37 14-Jul NHE4 W. 2 9 3-Jun NHE2 W. 8 38 15-Jul NHE3 10 6-Jun NHE2/NHE3 39 18-Jul NHE9 NHE9/NHE 11 7-Jun NHE3 40 19-Jul 7 12 8-Jun NHE8 41 20-Jul NHE7 13 9-Jun NHE4 42 21-Jul NHE9 W. 3 14 10-Jun NHE2 W. 9 43 22-Jul NHE3 15 13-Jun NHE9 44 25-Jul NHE9 16 14-Jun NHE7 45 26-Jul NHE4 17 15-Jun NHE8 46 27-Jul NHE8 18 16-Jun NHE9 W. 47 28-Jul NHE9 W. 4 19 17-Jun NHE4 10 48 29-Jul NHE9 20 20-Jun NHE4 49 1-Aug NHE10 21 21-Jun NHE4 50 2-Aug NHE7 NHE7/NHE 22 22-Jun NHE3 51 3-Aug 8 23 23-Jun NHE4 W. 52 4-Aug NHE4 W. 5 24 24-Jun NHE9 11 53 5-Aug NHE8 25 27-Jun NHE9 26 28-Jun NHE7/NHE9 NHE7/NHE9/NHE 27 29-Jun 4 28 30-Jun NHE4/NHE9 th W. 6 No Sampling: July 4

Appendix 3: Pedigree Charts for Study Subjects Pedigrees were generated thanks to open-source data from the DLC. Squares indicate males and circles indicate females. Individuals that were included in this study are in green.