Portland State University PDXScholar Dissertations and Theses Dissertations and Theses Fall 11-24-2015 The Impeccable Timing of the Apple Maggot Fly, Rhagoletis pomonella (Dipetera: Tephritidae), and its Implications for Ecological Speciation Monte Arthur Mattsson Portland State University Follow this and additional works at: https://pdxscholar.library.pdx.edu/open_access_etds Part of the Biology Commons, and the Ecology and Evolutionary Biology Commons Let us know how access to this document benefits ou.y Recommended Citation Mattsson, Monte Arthur, "The Impeccable Timing of the Apple Maggot Fly, Rhagoletis pomonella (Dipetera: Tephritidae), and its Implications for Ecological Speciation" (2015). Dissertations and Theses. Paper 2627. https://doi.org/10.15760/etd.2623 This Thesis is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. The Impeccable Timing of the Apple Maggot Fly, Rhagoletis pomonella (Diptera: Tephritidae), and its Implications for Ecological Speciation by Monte Arthur Mattsson A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Biology Thesis Committee: Luis A. Ruedas, Chair Deborah I. Lutterschmidt Jason E. Podrabsky Wee L. Yee Portland State University 2015 © 2015 Monte Arthur Mattsson Abstract Speciation is the process by which life diversifies into discrete forms, and understanding its underlying mechanisms remains a primary focus for biologists. Increasingly, empirical studies are helping explain the role of ecology in generating biodiversity. Adaptive radiations are often propelled by selective fitness tradeoffs experienced by individuals that invade new habitats, resulting in reproductive isolation from ancestral conspecifics and potentially cladogenesis. Host specialist insects are among the most speciose organisms known and serve as highly useful models for studying adaptive radiations. We are just beginning to understand the pace and degree with which these insects diversify. The apple maggot, Rhagoletis pomonella, is a well- studied insect whose eastern and southern populations are models for ecological speciation. Recently (40–65 ya), the fly has invaded the Pacific Northwestern United States through human-transported apples infested with larvae. There, populations of R. pomonella have rapidly colonized two novel hawthorn hosts whose fruiting times bracket apple’s (early-season native Crataegus douglasii and introduced C. monogyna, which fruits late in the season). The recent introduction might initiate host shifts, providing opportunities to examine the pace and mechanistic means with which host races (an evolutionary stage preceding speciation) become established. Here, I demonstrate that host-associated populations at a site in southwest Washington are partially allochronically isolated from one another, and life cycles temporally match with natal host fruit ripening times in sympatry. If spatially widespread, these temporal barriers could result in reproductive isolation and possibly cladogenesis. Implications of these findings reach i beyond academic import, as R. pomonella is expanding not only its host range, but its geographic range is encroaching upon central Washington, the site of a multi-billion dollar per year apple-growing industry. ii For my parents, Jim & Laura Mattsson, whose charisma to explore the world and listen to music was the greatest heirloom. iii Acknowledgements I thank: My wife and kids for their loving support, labor, curiosity, and hilarity; Luis Ruedas for telling me when I was blowing it, as well as killing it; My committee: Jason Podrabsky, Deborah Lutterschmidt, and Wee Yee, who have supported and steered me when I occasionally went off-roading; Jeff Feder and Glen Hood for their pointed insights, suggestions, and influence; Robert Richardson for his unwavering support and encouragement; Forbes-Lea Endowed Fund for Student Research and the Theodore Roosevelt Memorial Grant from the American Museum of Natural History. Ernest Hemingway and John Steinbeck for their refreshing approaches to writing. iv Table of Contents Abstract ............................................................................................................................... i Dedication ..........................................................................................................................iii Acknowledgements ............................................................................................................iv List of Tables ....................................................................................................................vii List of Figures ..................................................................................................................viii Chapter 1: Introduction..........................................................................................................................1 Chapter 2: Rapid and Repeatable Shifts in Life History Timing of Rhagoletis pomonella (Diptera: Tephritidae) Following Colonization of Novel Host Plants in the Pacific Northwestern United States Abstract..................................................................................................................17 Introduction............................................................................................................19 Materials and Methods...........................................................................................24 Results....................................................................................................................31 Discussion..............................................................................................................36 Tables.....................................................................................................................42 Figures....................................................................................................................46 Chapter 3: Effects of Pre-winter Conditions on Mortality Rates and Diapause Phenologies of Host- associated Populations of Rhagoletis pomonella (Diptera: Tephritidae) in Southwest Washington State Abstract..................................................................................................................52 Introduction............................................................................................................54 v Materials and Methods...........................................................................................62 Results....................................................................................................................67 Discussion..............................................................................................................72 Tables.....................................................................................................................78 Figures....................................................................................................................81 Chapter 4: Life History Adaptations Traverse Trophic Levels Abstract..................................................................................................................91 Introduction............................................................................................................93 Materials and Methods...........................................................................................97 Results..................................................................................................................100 Discussion............................................................................................................103 Tables...................................................................................................................105 Figures..................................................................................................................109 Chapter 5: Summary, Conclusions, and Future Directions...............................................................114 Table....................................................................................................................121 Bibliography....................................................................................................................122 Appendix: Supplementary data for Chapter 2................................................................ 141 Table A.1 Specific dates of fruit data collection.................................................141 Table A.2 Data describing mean dates of eclosion for individual replicates.......142 Table A.3 Soil temperature data..........................................................................143 Fig. A.1 Fruit firmness and diameter, showing interquartile ranges and standard errors, respectively..........................................................................144 vi List of Tables Table 2.1 Larval infestation times of alternative hosts in 2013 42 Table 2.2 Statistical tests of alternative host fruit ripening times 43 Table 2.3 Pairwise post hoc tests of host-associated eclosion times 44 Table 2.4 Estimates of reproductive isolation among host-associated populations 45 Table 3.1 Numbers of R. pomonella pupae reared from host fruits during times of peak activity 78 Table 3.2 Estimates of prewinter intervals experienced by alternative host populations