ABSTRACT FEMALE RESPONSES TO MALE CHEMICAL CUES IN PARDOSA MILVINA WOLF SPIDERS by Michael T. Stanley Females often use male signals and cues to locate potential mates and assess their quality. These male signals can be transmitted across one or multiple signaling modalities. In the wolf spider Pardosa milvina, males use a visual courtship display to attract female attention and encourage sexual receptivity. However, whether or not other signaling modalities influence female mate choice in this species is poorly understood. I hypothesized that male chemical cues may play a role in female mate choice in addition to visual cues. I tested females for their ability to detect and assess males based on their chemical cues, both isolated and when combined with a visual signal. Females did not change their activity in the presence of isolated male chemical cues. When presented with males either surrounded by or lacking their chemical cues, I found that while male courtship played a major role in female detection and attraction, females tended to spend less time near males when their chemical cues were present. This research suggests that while male courtship displays are necessary and sufficient for mate attraction, chemical signals may play a limited role by helping females more quickly assess a male’s visual display. FEMALE RESPONSES TO MALE CHEMICAL CUES IN PARDOSA MILVINA WOLF SPIDERS A Thesis Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Master of Science by Michael T. Stanley Miami University Oxford, Ohio 2018 Advisor: Ann L. Rypstra Reader: Brian Keane Reader: Nancy G. Solomon Reader: Ann L. Rypstra ©2018 Michael T. Stanley This Thesis titled FEMALE RESPONSES TO MALE CHEMICAL CUES IN PARDOSA MILVINA WOLF SPIDERS by Michael T. Stanley has been approved for publication by The College of Arts and Science and Department of Biology ____________________________________________________ Ann L. Rypstra ______________________________________________________ Brian Keane _______________________________________________________ Nancy G. Solomon Table of Contents List of Tables…………………….iv List of Figures……………………v Dedication………………………..vi Acknowledgements………………vii Introduction………………………1 Methods…………………………..5 Results……………………………10 Discussion………………………..11 References………………………..16 Tables & Figures…………………22 iii List of Tables Table 1………………….24 Table 2………………….25 Table 3………………….26 Table 4………………….27 Table 5………………….28 Appendix 1……………..34 Appendix 2……………..36 Appendix 3……………..43 iv List of Figures Figure 1……………….22 Figure 2……………….23 Figure 3……………….29 Figure 4……………….30 Figure 5……………….31 Figure 6……………….32 Figure 7……………….33 v Dedication I would like to dedicate this thesis to my wife Gabby, who stuck by my side through thick and thin, always encouraged me to never give up, and continually inspires me to be a better person. I would also like to dedicate this to my parents (and former Miami alumni) Mary and Jim, as without their unconditional love and support I never would have gotten to where I am today. vi Acknowledgements I would first like to thank my advisor, Dr. Ann Rypstra, not only for providing excellent scientific insight when helping me with my experiments, but also for always being there to support and guide me through the crazy process that is graduate school. Thanks also to my excellent committee members Dr. Nancy Solomon and Dr. Brian Keane for sticking with me through a somewhat unorthodox scientific journey. I would also like to acknowledge Miami University for supporting my studies and providing funding for these experiments. Finally, I would like to thank all the members of the Rypstra lab, graduate and undergraduate alike, for ensuring that the Miami spider lab was always an interesting place to be. vii Introduction Being able to find and choose a mate is crucial in organisms that reproduce sexually. In order to accomplish this task, many organisms rely on a variety of signals that must be received and interpreted against other stimuli in the environment (Guilford and Dawkins 1991). These signals can be visual, olfactory, tactile, auditory, or any combination of the above. This diverse range of signals allows them to be used in a wide variety of ways, such as to locate potential mates (Ryan 1991), to indicate that an organism is a conspecific (Byrne and Keogh 2007), to inform of mating status (Roberts and Uetz 2005), and to indicate to the opposite sex that a potential mate is of high quality (Knapp and Kovach 1991). Understanding the types of signals an organism uses in order to locate and choose a mate will therefore allow for a better understanding of what types of information an organism processes and pays attention to before engaging in reproduction. In many species, signals sent by males are the primary way in which females choose a mate. These signals can be passive ornaments (Zahavi 1975, Husak and Swallow 2011) or active courtship displays (Girard et al. 2015, Zambre and Thaker 2017). Females then use these signals in order to judge male attractiveness and quality before committing to reproduction. This puts selective pressure on males to develop signals that will not only catch the female’s attention, but also allow them to indicate that they are of high enough quality that they will be worth the energy that females are about to invest in mating and reproduction (Zahavi 1975, Hamilton and Zuk 1982, Hill 2015). For example, in the scorpionfly Panorpa vulgaris (Mecoptera: Panorpidae), the number of nuptial salivary gifts a male can provide to a female accurately reflects his nutritional status (Engels and Sauer 2006). Additionally, in the eastern kingbird Tyrannus tyrannus (Passeriformes: Tyrannidae), early singing males and males with a high song rate also had long flight feathers, indicative of superior body condition (Murphy et al. 2008). By communicating their quality to females through the use of signals, males can increase their chances of successfully attracting a mate. In many cases, females do not rely exclusively on single display modalities when evaluating males. Rather, males can signal their quality to females through the use of multiple signaling modalities (Partan and Marler 1999, Candolin 2003, Higham and Hebets 2013). By employing more than one mode of communication, males can more accurately inform females 1 about their quality and increase their probability of detection by females (Candolin 2003, Hebets and Papaj 2005). For example, in the squirrel treefrog Hyla squirella (Anura: Hylidae), Taylor et al. (2007) found that while vocalizations by males were sufficient for female attraction, females also used visual cues to discriminate between males with similar call qualities, preferring males with a higher quality visual cue (larger lateral stripe). Males can also benefit from multimodal displays by producing an enhanced response in female receivers compared to separate unimodal signals (Partan and Marler 2005). In the fruit fly Drosophila melanogaster (Diptera: Drosophilidae), males that produced a combined acoustic and chemical display had greater mating success (61%) than males which were limited to only acoustic (37%) or only chemical (10%) signals (Rybak et al. 2002). The ability of multimodal signals to help males signal their quality to females and enhance female responses highlights the potential for signaling in multiple modalities to be beneficial for organisms that rely on signaling for mate attraction. Multimodal signals have actually been extensively studied in the context of arachnid sexual signaling. While many male web spiders rely on the plucking and tapping of female webs to initiate courtship and mating (Segoli et al. 2008, Wignall and Herberstein 2013), groups that are cursorial such as wolf spiders (Lycosidae) primarily rely on visual courtship displays in order to attract and secure a mate (Rovner 1968, Koomans et al. 1974). Many species, especially those in the genus Schizocosa, augment their visual leg waving displays with vibratory cues (Uetz and Roberts 2002, Hebets 2008). This multimodal display helps males communicate in a structurally complex environment with a variety of substrates, as males have been found to shift between primarily visual or seismic signals based on the surrounding substrate (Gordon and Uetz 2011). Females of multiple species detect multimodal cues faster than visual or seismic cues alone, suggesting that these multimodal displays enhance the detection of males (Uetz et al. 2009). Females can also use both modalities present in these displays to assess the condition of males. Males in better condition have significantly larger foreleg tufts (Uetz et al. 2002) and are able to produce louder and shorter seismic signals (Gibson and Uetz 2008, 2012), both of which are preferred by females. Visual and vibratory signals therefore appear to be important components of wolf spider courtship. However, this does not mean that these are the only signaling modalities which may play a role in female mate choice. 2 Spiders use chemical signals in many situations, such as microhabitat selection and trail following (Tietjen and Rovner 1980), foraging (Persons and Uetz 1996, Persons and Rypstra 2000), and predator detection (Barnes et al. 2002). However, while female-based chemical signals are used by males of many spider species in order to locate the opposite sex (Gaskett 2007, Foelix 2011), the extent to which females detect and assess males based on their chemical cues has received significantly less attention (Ross and Smith 1979, Ayyagari and Tietjen 1987, Huber 2005). There are many ways that females could benefit from using chemical information from males in addition to a more conspicuous visual display (Gomez-Diaz and Benton 2013). Chemical signals may allow a female to find a male in a visually complex environment. In the American lobster Homarus americanus (Decapoda: Nephropidae), for example, females were able to discriminate between occupied and unoccupied shelters from two meters away by following male chemical cues (Bushmann and Atema 1997). Male chemical signals could also be used by females to determine if a potential mate is worth her attention.