Endocrine Correlates of Social and Reproductive Behaviours in a Group
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ENDOCRINE CORRELATES OF SOCIAL AND REPRODUCTIVE BEHAVIOURS IN A GROUP-LIVING AUSTRALIAN PASSERINE, THE WHITE-BROWED BABBLER A thesis submitted in partial fulfillment of the requirements for the award of the degree DOCTOR OF PHILOSOPHY from UNIVERSITY OF WOLLONGONG by Suzanne Oppenheimer B.A., M.A. Department of Biological Sciences 2005 i ABSTRACT To investigate the evolutionary rationale for the seemingly altruistic behaviours commonly seen in cooperatively breeding Australian passerines, I examined alloparental behaviour in the White-browed Babbler Pomatostomus superciliosus (WBBA). Toward this end, I analysed behavioural, hormonal, and genetic factors in both free-living and captive WBBAs. Studies of free-living birds examined social and reproductive behaviours and hormonal correlates to reproduction. With captive birds, I performed both observations and manipulative experiments focusing on intragroup social structure, social behaviours, and the endocrine correlates to such structure and behaviours. The WBBA was selected as a study species as they live in sedentary, year-round social groups that engage in cooperative breeding. Field work was conducted in Back Yamma State Forest, in the central west region of New South Wales, Australia. In this population of WBBAs, groups included many close genetic relatives, and neighboring groups also shared several related individuals. There were multiple breeding pairs within most groups, and reproductive behaviours between breeding pairs were similar to those of many biparentally breeding songbirds. However, nest defense and post- fledgling care were undertaken by large cooperative groups. In free-living WBBAs, plasma levels of testosterone (T), estradiol (E2), progesterone (P), prolactin (Prl), and corticosterone (B) were measured, and laparotomies were performed to ascertain gonadal condition. Endocrine profiles in WBBAs were similar to those reported for a number of passerines and likely reflected physiological changes necessary for breeding, such as spermatogenesis and ovulation. Males’ T profiles resembled those of some polygynous passerines, in that plasma T iii levels rose after the completion of the female partners’ clutch. This may reflect the possibility for extra-pair copulations in WBBA groups with multiple breeding females. There was some indication that WBBAs’ endocrine system may have been fine-tuned to support alloparental behaviour. In adult males that chaperoned fledglings and juveniles, elevated plasma Prl titres may have facilitated alloparental care. Furthermore, elevated plasma P levels in some adult females may have been related to non-breeding behaviour and perhaps also to care of post-fledging young. Unlike many temperate zone species, many WBBAs maintained recrudesced gonads for much of the year, reflecting their extended (if not perpetual) breeding season. Studies on captive WBBAs were conducted in aviaries at the University of Wollongong. Extensive observations were undertaken to investigate intragroup social structure and associated allofeeding behaviour. Despite an absence of aggression, intragroup social structure appeared stratified and was maintained by ritualised behaviours and vocalisations. In particular, allofeeding behaviour appeared to act as an important social signal within groups, indicating high social standing of the feeder and low social status of the receiver. Plasma levels of B and Prl were measured and compared to social factors, but I found no hormonal correlates to WBBA social status or behaviour in groups with stable social structures. To further examine the relationship between the endocrine system and social behaviours and structure, manipulative experiments were carried out on captive WBBAs. Removal of group members from socially stable groups elicited no overt aggression, and exchange of members between groups elicited little aggressive behaviour; however, both experiments resulted in significant social restructuring. Nevertheless, I found no significant hormonal correlates (T, E2, and B were measured) to social instability caused by these perturbations. Another social behaviour, roost nest iv building, was correlated with elevated plasma T and E2 levels, in some months of the year but not others. Field and captive studies of the WBBA supported hypotheses suggesting that (1) alloparental behaviours evolved via kin selection mechanisms and (2) alloparental behaviours are important signals of quality used to help select mates and/or attract collaborators. In WBBAs alloparental behaviours seem to be either directed toward kin or co-opted as a means of advertising social status. v TABLE OF CONTENTS Page Part 1: Literature Review Chapter I. Aspects of Sociality and the Relationship between Hormones and Behaviour ………………………………………………………………….......... 1 Part 2: Field Studies of Free-living White-browed Babblers Chapter II. Natural History and Morphometrics of White-browed Babblers in Back Yamma State Forest Introduction ………………………………………………………………... 32 Material and Methods …………………………….……………………… 34 Results ……………………………….………………………….…………. 46 Discussion …………………………………………………………………. 68 Conclusions………………………………………………………………… 81 Chapter III. Gonadal and Hormonal Phenologies in Free-living White-browed Babblers Introduction ……………………………………………………………….. 82 Material and Methods ………………………………….………….……… 88 Results ……………………………………….………………….…………. 97 Discussion …………………………………………………………….…… 115 Conclusions………………………………………………………………… 133 vi Part 3: Behavioural and Endocrine Studies of Captive White-browed Babblers Chapter IV. White-browed Babbler Group Organisation and Social Behaviour Introduction ……………………………………….…………………….. 137 Material and Methods ………………………………….…….…………… 140 Results ……………………………………….…………………………….. 147 Discussion ……………………………………….……………………..….. 165 Conclusions ………………………………………………………………... 176 Chapter V. Physiological Correlates of Social Behaviour During Periods of Social Stability Introduction ………………………………………….…………………..… 177 Material and Methods ………………………………….…………..…….... 182 Results ……………………………………………………….……….……. 187 Discussion …………………………………………………………….....… 204 Conclusions ……………………………………………………….………. 211 Chapter VI. Physiological Correlates of Social Behaviour During Periods of Social Instability Introduction ……………………………………………………………….. 213 Material and Methods ……………………………….………………..…... 216 Results ……………………………….………………………….……...…. 223 Discussion …………………………………………………………….....… 246 Conclusions ……………………………………………………………….. 256 vii Chapter VII. Physiological Correlates of Social Behaviour During Periods of Intense Social Interactions Associated with Roost Nest Building Introduction ……………………………….…………………………….…. 257 Material and Methods ……………………………….…..……………..….. 261 Results …………………………….………………………...….…………. 264 Discussion …………………………………………………….………....… 270 Conclusions ……………………………………………….………………. 275 Chapter VIII. General Conclusions ……………………..……………………… 276 Literature Cited ………………………………………………………………… 285 viii List of Tables Table Page 2-1 Mean number of bands scored per WBBA using three different DNA 49 probes (Jeffreys’ 33.15 and 33.6 and Per). 2-2 Comparison of bandsharing coefficients between WBBAs in the same 53 social group (“Intragroup”) to those birds from different social groups (“Intergroup”). 2-3 Morphometric measurements of male and female WBBAs, presented 62 as mean and standard error for each measure. 2-4 Morphological variables used in discriminant function analyses to 63 identify gender of WBBAs, and the percent of birds correctly classified for gender using combinations of these variables. 2-5 Mean bandsharing coefficients between unrelated and related 71 individuals in six avian species. 3-1 Number of WBBAs assessed for hormone levels and gonad condition 89 in each month. 3-2 Number of WBBAs assessed for hormone levels and gonad condition 89 in each breeding stage. 3-3 Number of females caught each month with a brood patch and without a 106 brood patch. 4-1 Dates of captivity and gender composition of groups of WBBAs held in 141 the aviary at Wollongong NSW. 4-2 Definitions of behavioural idioms used to identify common behaviours 144 exhibited by captive WBBAs during feeding competition observations. 4-3 Mean and Standard Errors of Behaviour Quotients for Behavioural 149 Classes generated by cluster analyses. 4-4 Criteria for assigning Standard Behavioural Classes. 151 4-5 Numbers of WBBAs per group that were categorised into each Access 152 and Allofeeding Class. 4-6 Interrelationship between Access and Allofeeding Classes in groups of 153 WBBAs. 4-7 Number of male and female WBBAs in each Access and Allofeeding 154 Class. ix 4-8 Variation in body size and mass among Access and Allofeeding Classes. 155 4-9 Number of males and females classified as raspy callers or beggars. 158 4-10 Number of WBBAs that gave begging calls, raspy calls, and duets in 158 each Access and Allofeeding Class. 4-11 Number of allofeeding events in 10 groups of WBBAs. 160 5-1 Comparison of eight measures of the capture stress response between 188 free-living and captive WBBAs. 5-2 Comparisons between 3 measures of body condition and 8 measures of 190 the capture stress response in WBBAs. 5-3 Inter-Assemblage variation in B secretion during the serial capture stress 191 protocol. 5-4 Comparisons of Prl titres between genders, Access Classes, and 201 Allofeeding Classes. 6-1 Table 23. Schedule of blood sampling, treatment, and hormones 217 evaluated in the Removal Experiment. 6-2 Identity, gender, and Access Class of WBBAs used in the Exchange 219 Experiment. 6-3 Schedule of blood