Coevolution of Rhagoletis hosts and their parasitic wasps

iii ACKNOWLEDGEMENTS I am deeply indebted to my advisor, Andrew Forbes, whose encouragement and support over the years has been invaluable. I wish to thank my committee, for their guidance, support and feedback. A special thanks goes to my lab-mates Amanda Nelson, Alaine Hippee, Kristina Ottens and Eric Tvedte for driving me crazy while keeping me sane over the past five years. Thank you to Eileen, Misty and the rest of the Biology Department administrative staff for making life so much easier for all of us. The same can be said for the Graduate College and the OGI staff. Thank you for all of your years of support – I don't know what I would have done without it. The biggest thank you goes to my parents. I would be lost without your continuous love and support. Thank you for driving me to zoo camp and letting me travel all around the world. Thank you for letting me make mistakes and helping me learn from them. And thank you for listening to my practice talks and telling me I did a great job, even if you didn't understand a word. Finally, to my science friends and my best friends – I couldn't have done this without you: ABSTRACT Phytophagous (plant-feeding) insects are extremely species-rich and typically display tight host associations (meeting and mating on or near their host plant) with one or a small number of hosts. This specialized lifestyle can promote diversification through assortative mating, ultimately leading to genetically differentiated host races (host associated differentiation; HAD). It has been shown that HAD can cascade up to the parasitic wasps (parasitoids) that utilize the phytophagous insects as hosts. Cascading HAD occurs when there is genetic differentiation among parasitoids as a result of differential host plant use by their host insects. Thus, host switching can promote parasitoid diversification as well. Here, I present three studies designed to help understand aspects of parasitoid shifts to novel hosts and environments. All of the studies in this dissertation utilize the Rhagoletis complex of flies and their associated parasitoids. Specifically, I address i) the role of subtle trait variation and environmental context in predicting successful parasitoid host shifts; ii) whether parasitoid host discrimination (a trait that can influence host shifts) is an innate or learned behavior; and iii) whether contemporary patterns of host shifts among parasitoids are echoed by historical host shifts in cophylogenetic analyses …