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Kristina Meredith Barclay

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Kristina Meredith Barclay Exploring the Past, Present, and Future of Predator-Prey Interactions Between Crabs and Their Gastropod Prey by Kristina Meredith Barclay A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Earth and Atmospheric Sciences University of Alberta © Kristina Meredith Barclay, 2020 Abstract Interactions between predators and prey play an important role in structuring their communities and shaping evolution. However, human-induced climate change has the potential to influence both predators and prey and disrupt their interactions. The fossil record provides an enormous resource to investigate how both past and current climate change has affected organisms, their interactions, and ecosystems. In particular, scars left on prey by failed predatory attacks provide an excellent record, and often the only evidence, of predator-prey interactions in both modern and fossil ecosystems. However, as these injuries, known as repair scars, are records of failed rather than successful attacks (with successful attacks destroying the prey), it can be difficult to interpret whether repair scars signal overall attack rates, or the success/failure rate of the predator. Furthermore, the presence of repair scars can be affected by the structural integrity of the prey’s defenses, such as a gastropod shell, as well as prey selection by the predator. Here, shell-crushing crabs and their gastropod prey were used as a model system for exploring potential relationships between prey defenses, prey selection, and repair scars in the past, present, and possible future. Specifically, the goals were: 1) to use modern experiments to understand how prey defenses are affected by ocean acidification, a major by-product of carbon dioxide emissions, 2) to test patterns of prey selection by crabs, and 3) to then examine how patterns of repair scars in gastropods manifest through both space and time. Along the west coast of North America, crabs such as Cancer productus and their gastropod prey are key members of rocky intertidal communities. Exploration of the potential mechanisms by which human activity might disrupt these predator-prey interactions could provide insights to help protect these critical species and their relationships. In Chapter 2, I tested how gastropod shells are affected by both ocean acidification and predation cues in the ii gastropods Tegula funebralis and Nucella ostrina. After exposure to decreased seawater pH and/or predation cues for six months, both shell growth and strength in T. funebralis was drastically reduced. However only shell strength, and not growth of N. ostrina was impacted by low pH treatments, and not as severely as T. funebralis. Examination of shell composition and microstructure of both species in Chapter 3 used microCT scans, XRD analysis, and SEM imaging, indicated that the loss of shell strength was from dissolution of the outermost shell layer in both species, with the microstructural arrangement of T. funebralis shells likely causing more severe dissolution than observed in N. ostrina. Patterns of crab (C. productus) prey selection between three species of the gastropod Nucella were examined in Chapter 4 to understand how crabs attack and select prey. The experiment revealed that crabs are most likely to attack the first gastropod they detect, with a preference for the largest species most likely driven by their inability to always recognize smaller prey. I then explored patterns of repair scars in T. funebralis both geographically along the modern west coast of Canada and the U.S. (Chapter 5), as well as temporally between the Late Pleistocene and modern of southern California (Chapter 6). By measuring the size at which repair scars occur, I demonstrate that it is possible to distinguish between repair frequency and predator success, allowing more accurate comparisons of predation between samples. Crab predation in the modern also showed strong regional, but not latitudinal, variation along the west coast, with the lowest number of attacks in southern California. Furthermore, comparisons of modern and fossil repair scars in southern California indicated that there are fewer crab attacks today, suggesting that crab populations may already be affected by human activity. By studying how prey defenses, prey selection, and repair scar systems manifest, we can explore how predator-prey relationships have changed both in the past and present, and how they may continue to change due to our current climate crisis. iii Preface Chapter 2 of this thesis has been published as: Barclay, K. M., B. Gaylord, B. M. Jellison, P. Shukla, E. Sanford, & L. R. Leighton. 2019. Variation in the effects of ocean acidification on shell growth and strength in two intertidal gastropods. Marine Ecology Progress Series, 626:109 – 121. DOI: 10.3354/meps13056. I was responsible for all data collection, analyses, and composition of the manuscript and associated tables and figures. B. Gaylord, E. Sanford, B. M. Jellison, and L. R. Leighton assisted with the study design. P. Shukla instructed and assisted with data collection. E. Sanford, B. M. Jellison, and L.R. Leighton assisted with analyses. All authors assisted in compiling the manuscript. L.R. Leighton was the supervisory author. Chapter 4 of this thesis has been previously reviewed as: Barclay, K. M., C. R. Sinclair, & L. R. Leighton. Factors influencing crab preference between three similar gastropod species. I was responsible for all data collection, analyses, and composition of the manuscript. C. R. Sinclair and L. R. Leighton assisted with data collection and study design. All authors assisted in compiling the manuscript. L. R. Leighton was the supervisory author. The manuscript has been resubmitted to the Journal of Experimental Marine Biology and Ecology as a new submission, with all reviewer concerns addressed and included. iv Dedication For my sister, Danielle. Your courage, perseverance, and unyielding strength in the face of terrible hardships inspires me daily. I am a better, stronger person and scientist because of you. In loving memory of my grandmother, Marion Barclay. A fellow writer and kindred spirit who would have been the first person to read this work from cover to cover. v Acknowledgments Funding for this research was provided by a Vanier Canada Graduate Scholarship (Barclay), Michael Smith Foreign Study Supplement (Barclay), and Discovery Grant (Leighton) from the Natural Sciences and Engineering Research Council of Canada, a President’s Doctoral Prize of Distinction from the University of Alberta (Barclay), a Unitas Malacologica Student Research Award (Barclay), a Natural History Museum of Los Angeles County Student Collections Grant (Barclay), and a Paleontological Society Richard Osgood Award (Sinclair). I would like to thank my supervisor, Dr. Lindsey Leighton, for his support, encouragement, and advice. It has been a pleasure to work for him over the past several years, and I would not have decided to pursue this degree, or become the scientist I am today, without his support, patience, guidance, and thorough feedback. I feel lucky to have had such a caring and involved supervisor. I am also eternally grateful for his trust and flexibility in letting me pursue this degree long-distance, which allowed me to spend more time at home with my family. I hope that I have made him proud, even if I continue to split infinitives. I would also like to thank the members of my supervisory committee, Drs. Brian Gaylord, and John-Paul Zonneveld for their support, advice, and feedback. I am so grateful to Dr. Gaylord and his students for welcoming me into their lab, and providing me resources, support, and guidance. Dr. Gaylord’s kindness, guidance, and understanding during a troubling family crisis made a very strong impression in deciding the kind of mentor I’d like to be. There are also many mentors, peers, and fellow students who have provided me support, discussion, and assistance, both in the lab, field, and in their friendship. I thank Dr. Chris Schneider, Dr. Carrie Tyler, Dr. Eric Sanford, Dr. Tessa Hill, Darrin Molinaro, Steven Mendonca, Caroline Sinclair, Matthew Pruden, Rylan Dievert, Aaron Dyer, Denny Maranga, vi Claudia Selles, Austin Pugh, Dr. Brittany Jellison, Priya Shukla, Dr. Gabe Ng, Kristen Elsmore, Aaron Ninokawa, and Dr. Sam Bashevkin. I am also incredibly indebted to the amazing students and staff of Bodega Marine Laboratories who welcomed me into their community, shared their knowledge, and supported me through a stressful time and long experiment. They contributed enormously to my growth as a scientist, and I learned much from being in their company. Finally, I owe the majority of my success to my family and friends. I will forever be grateful to my husband, Chris Beckett, for his infinite patience and support, especially while I lived out of a suitcase and moved to Edmonton, and then California, during the first years of our marriage. His kindness and caring have held me together when my world was falling apart. I am also thankful to my parents, Glenn and Shirley, for their continued support and encouragement throughout my education, and for always providing me the opportunity to pursue my passions, as well as a shoulder to lean on. My sister, Danielle, is the single most resilient human I have ever met, and I am thankful just to call her my sibling and to learn from her example how to make a difference in the world. I also thank my in-laws, Ken and Sherril, my extended family, and wonderful circle of friends for their interest, encouragement, and support through the years. As a biologist, I am constantly falling in love with the animals I meet. The strength of connections we can derive from our animal friends is one of my favourite things about my field of study. I must therefore acknowledge two animal friends who have helped me complete my studies while working from home. I credit my cat, Widget, for helping me stay focused when studying for my candidacy exam.
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