Signal Complexity in Schizocosa Ethospecies
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Good Vibrations: Signal Complexity in Schizocosa ethospecies A thesis submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of Master of Science in the Department of Biological Sciences of the College of Arts and Sciences by Madeline Lallo B.S. University of Cincinnati March 2019 Committee Chair: George W. Uetz, Ph.D. Cincinnati, OH Abstract Communication signals have evolved to convey information from a sender to a receiver through different sensory modalities. These signals may vary in their complexity to ensure successful transmission through the environment and enable receiver discrimination. Sibling wolf spider species, Schizocosa ocreata and S. rovneri, have recently diverged and are reproductively isolated by their behavior during courtship. Males of both species court females using multicomponent vibratory signals that vary in their complexity. The vibratory signal of male S. ocreata represents a complex pattern of stridulation and percussion components, compared to that of S. rovneri, which produces a regular pattern of brief pulses of nearly simultaneous (combined) stridulation and percussion components. I examined the role of signal complexity in species recognition and mate preference using vibratory playback via piezoelectric disc benders of separate individual components (percussion and stridulation) from each male signal. Female S. ocreata and S. rovneri were exposed to either conspecific or heterospecific signals within four treatment groups: complete signal, percussion only, stridulation only, or white noise. The number of female receptivity displays varied significantly among treatment groups for both S. ocreata and S. rovneri females, however there was no difference in female receptivity to individual components (stridulation and percussion) compared to complete signals. There were significant differences in the number of female receptivity displays for both S. ocreata and S. rovneri when presented with playback of complete conspecific vs. heterospecific vibration signals as females were more receptive to conspecific signals. Each focal species responded differently to treatment groups, with S. rovneri displaying significantly more receptivity displays compared to S. ocreata. I determined that individual signaling components are redundant and when combined in a complete signal they elicit an equivalent response in terms of number of female receptivity ii displays. My results show that females of these two ethospecies recognize isolated vibratory signaling components of conspecifics and heterospecifics. iii iv Acknowledgments First and foremost, I want to thank my advisor, Dr. George Uetz, for all the advice, opportunities, and support over the six years I have known him. I will never forget the day I walked into his office, career binder in hand, trying to impress him. He “molded my brain” into the scientist I am today, and I will never be able to repay him. Thank you, George. And special thanks to Kitty Uetz for all her support and baked brie. Thank you to my committee members, Dr. Nate Morehouse and Dr. Elke Buschbeck, for all their feedback and comments they gave me over the years. And to the Cincinnati Nature Center and Great Parks of Hamilton County for letting me collect spiders at their parks. Thank you to the friends I have made over the years – Dr. Brent Stoffer, Dr. Alex Sweger, Dr. Rachel Gilbert, Tim Meyer, Trinity Walls, and most importantly, Emily Pickett, for all the support and pushing I needed to accomplish this feat. Time with you all has been an unforgettable journey. Special thanks to Olivia Bauer-Nilsen for being there my last year as a lonely graduate student. To my grandfathers, Jim Lallo and John Cernica, who both passed away during my first year in the program. They were the strongest and smartest men I knew. Thank you so much, you’ve given me something to strive for. Last, but certainly not least, I would like to thank family. None of this was possible without them, and for that, I am forever grateful. Thank you to my siblings – Nicholas, Anthony, and Vivian, for the late nights of soccer and beer when I needed it the most. My parents gave me immense love and support throughout my graduate school career, so thank you Mom and Dad. Words cannot express how thankful I am to have you both in my life. v Table of Contents Abstract ……………………………………………………………………………..……..…….. ii Acknowledgments …………………………………………………………………....………….. v List of Tables and Figures ………………………………………………….……………...….. vii Introduction ……………………………………………………………………...……...….…… 8 Study Species and Research Problem …………………………………...…..…….….… 10 Goals and Objectives …………………………………...……………………..……...… 11 Methods …………………………………...………………………………………..………...… 15 Collection and Rearing ………………………………..………………...…..………..… 15 Exemplars …………………………………...……………………………....………...… 15 Calibration and Playback …………………………………...………………………..… 16 Experimental Trials …………………………………...……………………..………..… 17 Data Analysis …………………………………...…………………………...………….. 18 Results …………………………………………………………………...……...…..…….….… 21 Seasonal Differences …………………………………...…..……………………..….… 21 Generalized Linear Models …………………………………...…..…………...….…..… 21 Latency to Move …………………………………...……………………………….…… 22 Latency to Receptivity …………………………………...…..………………………..… 23 Discussion …………………………………...…………………………………….…………..... 38 Conclusion …………………………………………………………………...…..………..…… 43 References …………………………………………………………………...…..………..…… 45 vi List of Tables and Figures Figure 1: Phylogeny of the ocreata clade of the genus Schizocosa. Figure 2: Vibratory signals of male S. ocreata and S. rovneri. Figure 3: Laser Doppler vibrometer. Figure 4: Experimental trial set up. Table 1: Generalized linear model results. Figure 5: Female receptivity responses to the presence/absence of signaling components. Figure 6. Female receptivity to presence/absence of stridulation and percussion separated by species. Figure 7: Female receptivity to conspecifics and heterospecifics. Figure 8: Number of receptivity displays by focal species. Table 2: Parametric survival analysis of latency to move. Figure 9: Latency to move by focal species. Figure 10: Latency to move to presence/absence of percussion signals. Figure 11: Latency to move to conspecific/heterospecific stridulation signals. Figure 12: Latency to move to all conspecific and heterospecific treatments. Table 3: Parametric survival analysis of female latency to receptivity. Figure 13. Latency to receptivity to presence/absence of stridulation. Figure 14: Latency to receptivity to presence/absence of percussion Figure 15: Latency to receptivity of all treatments. vii Introduction Communication is ubiquitous in the animal kingdom, and signals have evolved to convey information from a sender to a receiver. Some communication signals are more varied or complex, which may ensure there is successful transmission through the environment and allow for receiver discrimination. Signals are used to grab the attention of receivers, which comes with some risk if the receivers are unintended (such as potential predators, competition, other species) but will potentially lead to some reward with intended receivers, such as mates. Communication signals may relay species information to assist in recognition of conspecifics, which in turn helps ensure behavioral reproductive isolation between closely related species. Pre-mating isolation, (e.g., behavioral isolation between two species prior to copulation and fertilization), enhances fitness, as it prevents potential interspecies hybrids, which are likely sterile and do not contribute to future generations. Examples of this behavioral reproductive isolation can be found in models such as tree frogs (Gerhardt 1974), Heliconius butterflies (Southcott & Kronsforst 2018) and wolf spiders (Stratton & Uetz 1981). Behavioral pre-mating reproductive isolation is predominantly driven by female recognition of species- specific male signals, likely arising from or reinforced by mate choice. Some animals use a combination of different sensory modes to ensure successful transmission of information. When two or more of these modalities are used simultaneously, it is defined as multimodal communication (Partan & Marler 1999). The use of multimodal communication is prevalent across many animal taxa, ranging from vertebrates – such as primates (Ghazanfar et al. 2005; Leavens et al. 2010), fish (Maruska et al 2012) - to invertebrate taxa such as spiders (Uetz 2000; Uetz & Roberts 2002; Hebets 2008; Uetz et al. 2009), and crayfish (Acquistapace et al. 2002; Crook et al. 2004). There are several different hypotheses 8 explaining the use of multimodal vs. unimodal communication: 1) the multiple messages hypothesis (Møller & Pomiankowski 1993) which states that separate modes are used to send different information about the subject (bright colored plumage for parasite load, acoustic calls for quality/size, etc.); 2) the redundant signals hypothesis (Møller & Pomiankowski 1993) which proposes that these signals are all sending the same information, with regard to mate quality, to the receiver about the signaler; and 3) the species recognition hypothesis, which states that species recognition is more effective when a combination of different traits/modalities are used (Pfennig 1998). Invertebrate animals, and spiders in particular, are more frequently becoming recognized models in which to study communication, despite earlier bias toward vertebrate animals (Witt & Rovner 1982, 2014; Uetz 2000;