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Coevolution and Cospeciation in a Bark-Beetle Fungal Symbiosis University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2015 Coevolution and cospeciation in a bark-beetle fungal symbiosis Ryan Russell Bracewell Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Bracewell, Ryan Russell, "Coevolution and cospeciation in a bark-beetle fungal symbiosis" (2015). Graduate Student Theses, Dissertations, & Professional Papers. 10784. https://scholarworks.umt.edu/etd/10784 This Dissertation is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. COEVOLUTION AND COSPECIATION IN A BARK-BEETLE FUNGAL SYMBIOSIS By RYAN RUSSELL BRACEWELL B.S. Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, 2002 M.S. Ecology, Utah State University, Logan, UT, 2009 Dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Forestry and Conservation Sciences The University of Montana Missoula, MT December 2015 Approved by: Sandy Ross, Dean of The Graduate School Graduate School Dr. Diana Six, Chair Department of Ecosystem and Conservation Sciences Dr. Jeffrey Good Division of Biological Sciences Dr. John McCutcheon Division of Biological Sciences Dr. Michael Schwartz USDA Forest Service/College of Forestry and Conservation Dr. Ylva Lekberg MPG Ranch/College of Forestry and Conservation ProQuest Number: 10096854 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. ProQuest 10096854 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, MI 48106 - 1346 Bracewell, Ryan, Ph.D., Fall 2015 Forestry and Conservation Science Coevolution and Cospeciation in a bark-beetle fungal symbiosis Chairperson: Diana L. Six Bark beetles in the genus Dendroctonus are some of the most important insects in forest ecosystems worldwide and are known to be involved in symbiotic relationships with fungi. However, we have a poor understanding of beetle-fungal coevolution and if the specificity we see in beetle-fungal relationships may translate to cospeciation over longer time frames. In this dissertation, I attempt to answer these questions by investigating the western pine beetle (Dendroctonus brevicomis)-fungal symbiosis, a beetle that consists of two putative cryptic species in the early stages of divergence on two susbspecies of ponderosa pine (Pinus ponderosa). In the first chapter, I describe research aimed at determining if the western pine beetle harbors the same species of mycangial fungi across its entire range. I found widespread fungal fidelity and that the beetle carries two species, Entomocorticium sp. B, and Ceratocystiopsis brevicomi. In the second chapter, I describe research aimed at determining if the western pine beetle is indeed in an obligate mutualism and is adapted to fungal isolates with a shared evolutionary history. I found that E. sp. B was crucial for the successful development of western pine beetles and found no significant difference in the effects of the natal (shared history) and non-natal (no shared history) isolate on beetle fitness parameters. However, brood adult beetles failed to incorporate the non-natal fungus into their mycangium indicating adaption by the beetle to particular genotypes of symbiotic fungi. In the third chapter I describe research exploring if the beetle, its two fungal symbionts, and the host tree are genetically structured in a similar fashion indicative of shared evolutionary history and cospeciation. I sequenced the genomes of the beetle and two fungal symbionts and conducted population genetic and genomic analyses for the host tree, beetle, and for the two fungal symbionts. I found congruent patterns of population genetic structure and phylogenetic relationships between multiple species. Taken together, my dissertation research suggests that the western pine beetle is in a tightly linked and evolving obligate mutualism with fungi and that the entire tree-beetle-fungi system is diverging and cospeciating in concert. ii TABLE OF CONTENTS ABSTRACT ........................................................................................................................ ii ACKNOWLEDGEMENTS ............................................................................................... iv DISSERTATION OVERVIEW...........................................................................................1 CHAPTER 1: Broadscale specificity in a bark beetle-fungal symbiosis: A spatio-temporal analysis of the mycangial fungi of the western pine beetle ................................................4 Abstract ............................................................................................................................5 Introduction ......................................................................................................................6 Methods ............................................................................................................................9 Results ............................................................................................................................14 Discussion ......................................................................................................................17 References ......................................................................................................................22 Tables .............................................................................................................................31 Figures ............................................................................................................................33 CHAPTER 2: Experimental evidence of bark beetle adaptation to a fungal symbiont ....39 Abstract ..........................................................................................................................39 Introduction ....................................................................................................................40 Methods ..........................................................................................................................43 Results ............................................................................................................................48 Discussion ......................................................................................................................50 References ......................................................................................................................55 Tables .............................................................................................................................62 Figures ............................................................................................................................64 CHAPTER 3: Cascading speciation among mutualists and antagonists in a tree-beetle- fungal interaction ..............................................................................................................68 Abstract ..........................................................................................................................68 Introduction ....................................................................................................................69 Results ............................................................................................................................72 Discussion ......................................................................................................................79 Methods ..........................................................................................................................82 References ......................................................................................................................97 Tables ...........................................................................................................................106 Figures ..........................................................................................................................109 iii ACKNOWLEDGEMENTS The research described herein would have been impossible without the help of a large number of people. I would first and foremost like to thank my primary advisor, Diana Six, who broadened my horizons and got me excited about symbioses and fungi. Her enthusiasm for science is infectious and her attention to detail was always appreciated. I would also like to make a special mention of all of the support and mentorship that Jeff Good has provided throughout my dissertation. He has had a tremendous impact on the way I think about science and conduct research and I will forever be grateful. I would
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