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Sexual Conflict and Secondary Sexual Traits in West Australian Riffle Bugs (Insecta: Hemiptera: Veliidae)

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Sexual Conflict and Secondary Sexual Traits in West Australian Riffle Bugs (Insecta: Hemiptera: Veliidae) Sexual conflict and secondary sexual traits in West Australian Riffle Bugs (Insecta: Hemiptera: Veliidae). An overview of the relationship between morphology and behaviour Paige Maroni (BSc) 32202683 This thesis is presented for the degree of Bachelor of Science Honours (Biological Science) School of Veterinary and Life Sciences Murdoch University 2017 Supervisors: Dr. Kate Bryant Dr. Nikolai Tatarnic With support from: I declare that this thesis is my own account of my research and contains as its main content work which has not previously been submitted for a degree at any tertiary education institution. Paige J. Maroni Abstract How and why an animal chooses its mate is characteristic of morphological and behavioural adaptations developed to maximize reproductive success. This thesis compares patterns of sexual dimorphism (through micro-CT analyses) in three Veliidae species (Microvelia oceanica, Nesidovelia peramoena and N. herberti) and aims to explain these in the context of sexual conflict. Sexually antagonistic morphological and behavioural traits were also of interest and were documented through examinations of male-female reproductive interactions of N. peramoena via video recordings and micro-CT scan outputs of interlocked pairs, frozen in copula. Interlocked pairs were captured through a new technique for snap freezing surface dwelling insects, which was developed within this thesis. In all three species, females were found to be generally larger than males and macropters larger overall than apters, as is often the case with insects. All specimens examined were documented to express some form of a secondary sexual trait which are likely to be coevolving in an evolutionary arms race. In females, these resistance traits variously included connexival convergence, genital concealment and setal tufts. Females of N. peramoena showed strong pre-mating resistance behaviours evidenced by either fleeing or vigorously struggling during 96% of all observed intersexual interactions. In both Nesidovelia species, males expressed persistence traits such as a ventral abdominal process on segment 8 and ventral abdominal segment 7 medial concavity. Through this study, these traits are now known to act as a pregenital clamp grasping to the females on the underside of her proctiger during the pre-mating struggle, as well as during copulation. Interestingly, while macropterous males retain their secondary sexual traits, macropterous females were found to lack their putative resistance traits, suggesting either an energetic iii or mechanical trade-off in development. This study is one of the first to provide evidence that sexual conflict is the likely driving force behind the behaviours and sexual dimorphism in the Veliidae. The array of different secondary sexual traits makes those in the Gerridae (the current model group for sexual conflict and sexually antagonistic character studies) seem tame in comparison. Within these riffle bug species, unique coevolved male-female grasping and anti-grasping structures provide strong evidence for sexual antagonism in veliid mating that have not previously been documented in any surface dwelling insects. iv Acknowledgments To the following people I would like to express my sincere appreciation for your help in making this project possible. To Dr. Kate Bryant, I wish to sincerely thank you Kate. Without your encouragement, support and feedback, none of this year would have been possible! To me, you are the perfect teacher and mentor and I have valued learning so much from you this year. I also wish to thank you for all of your time and understanding when things didn’t go to plan! I will always look back on my honours year and smile and that is hugely because of you! To Dr. Nikolai Tatarnic, Words cannot express how many thanks I have for you Nik! Thank you for introducing me to the crazy world that is bugs sex lives! Thank you for all of your time, your wisdom and insight into the processes that go on between male and female insects. Thank you also for all your help in every other aspect of this project from experimental design to field collection techniques…without you I would be lost! I look up to you and admire your drive and passion for science so thank you very much for all you have taught me over the past few years! To Dr. Jeremy Shaw, Thank you for all of your instruction, advice and help for using the Micro CT Xradia. Without your technical support none of the amazing images that have been produced through the software under your care within the CMCA facility would have been possible and the v results produced throughout this project would not have been anywhere as incredible as I believe they are. Thank you very much Jeremy. To Jacqueline Dyer & the Honours Chairs, Thank you Jacqueline, and all other honours personnel who supported my application to conduct an honours year and more recently, aided me through the times when my health stood in the way of finishing the honours year on time. I cannot understate how thankful I am for all your support. To Dr. Michael Calver, Thank you very much for allowing me to kick start this amazing project in 2015 and it is because of you that I was able to utilize the micro-CT and image my specimens throughout this thesis so I truly am extremely thankful. Thank you also for your time and great feedback throughout this honours year. To Dr. Bruno Buzatto, Thank you for your great advice and time throughout this honours year. I am deeply thankful for your comments in regards to the betterment of my literature review. To my Family and Friends, A big thank you to my amazing support network! Mum, thank you for your huge amounts of support and my veliid colonies thank you for all the flies you caught for their meals! To my Dad and two sisters, Tessa and Meg, thank you for helping me through this very stressful year! All your advice and encouragement is so appreciated! Lastly, thank you to the two greatest, Claire and Danica for keeping me sane and laughing through the stressful times! vi Table of Contents Declaration of independence ii Abstract iii Acknowledgements V Table of Contents vii List of Tables x List of Figures xii List of Abbreviations xvii List of Appendices xviii 1.0 Chapter One - Introduction 1 1.1 General introduction 1 1.2 Sexual selection and sexual conflict in nature 2 1.3 The economy of mating in Insecta and resistance traits 5 1.4 Adaptations of persistence, resistance and harassment in Insecta 8 1.4.1 Male harassment 8 1.4.2 Secondary sexual morphologies 10 1.4.3 Grasping traits 11 1.4.4 Antigrasping traits and other resistance traits 14 1.4.5 Convenience polyandry 17 1.5 Sexually antagonistic coevolution 17 1.6 Water striders as a model taxon 21 1.7 This study 25 1.7.1 Project significance and overview 25 1.7.2 Study species 29 1.7.2.1 Veliidae, fam. Microvelia, gen. Nesidovelia, gen. 29 1.7.2.2 Species overview 30 1.7.3 Life cycle 31 1.8 Study approaches and objectives 32 vii 2.0 Chapter Two - Morphology 37 2.1 Introduction 37 2.2 Collection and maintenance of study species 37 2.2.1 Field locations 37 2.2.2 Laboratory colony 39 2.3 Comparative morphology 40 2.3.1 Micro-CT scanning 40 2.3.2 Digital image preparation 41 2.3.3 Putative secondary sexual traits 42 2.3.4 Size and shape 43 2.4 Reproductive behaviour and functional biology 46 2.4.1 Mating trials 46 2.4.2 Freezing engaged pairs 48 2.4.3 Videoed mating trials 50 2.4.4 Quantitative and qualitative measures 50 3.0 Chapter Three – Results 52 3.1 Comparative morphology and putative secondary sexual traits 52 3.1.1 Comparative morphology 52 3.1.1.1 Microvelia oceanica 52 3.1.1.2 Nesidovelia peramoena 56 3.1.1.3 Nesidovelia peramoena 59 3.1.2 Size and shape 63 3.1.2.1 Microvelia oceanica 67 3.1.2.2 Nesidovelia peramoena 68 3.1.2.3 Nesidovelia herberti 68 3.1.2.4 Abdominal segment 7 69 3.1.2.5 Female egg carrying capacity 69 3.2 Reproductive behaviour and functional biology 73 3.3 Micro-CT imaging of antagonistic structures 77 viii 4.0 Chapter Four – Discussion 81 4.1 Introduction 81 4.2 Putative secondary sexual traits 81 4.3 Size and shape 87 4.4 Female polymorphism 91 4.5 Reproductive behaviour and functional biology 93 4.6 Refinement of freezing methodology 97 4.7 Limitations and future works 98 5.0 Chapter Five – Conclusions 100 References 102 Appendices 119 Appendix 1 119 Appendix 2 122 Appendix 3 124 Appendix 4 126 Appendix 5 128 Appendix 6 133 ix List of Tables Table 1 Review of 12 published papers highlighting the scope of knowledge 28 presented on Australian Veliidae. This systematic review was performed in the late months of 2016 to the early months of 2017 and databases such as: Web of Science, Scopus, and JSTOR, were searched for relevant literature. Table 2 Distributions of the four species groups of Nesidovelia, as defined by 30 Andersen and Weir (2003). Table 3 Collecting details for the three study species (Nesidovelia peramoena, 39 N. herberti and Microvelia oceanica). Table 4. Localities and number of individuals of each morph of the three study 44 species. Numbers in parentheses are the total numbers of adult animals collected for this study. Numeric values prior to the parentheses are total number of individuals scanned, measured or examined. Table 5 Quantitative and qualitative measurements taken from all micro-CT 46 scanned specimens. All measures were taken from micro-CT volumes using Drishti.
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