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University of Nevada, Reno Reconciling Western Toad University of Nevada, Reno Reconciling Western toad phylogeography with Great Basin prehistory A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geography by Pete M. Noles Dr. Jill S. Heaton/Thesis Advisor December, 2010 THE GRADUATE SCHOOL We recommend that the thesis prepared under our supervision by PETE M. NOLES entitled Reconciling Western toad phylogeography with Great Basin prehistory be accepted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Jill S. Heaton, Ph.D., Advisor Scott A. Mensing, Ph.D., Committee Member Kenneth E. Nussear, Ph.D., Committee Member C. Richard Tracy, Ph.D., Graduate School Representative Marsha H. Read, Ph. D., Associate Dean, Graduate School December, 2010 i ABSTRACT This study marks the first attempt to study historical processes that may be responsible for the contemporary geographic distribution and phylogeny of Great Basin Western toads (Anaxyrus boreas spp.). The dynamic aquatic history of the Great Basin was evaluated as a potential model for early toad dispersal into regions which would later become arid and isolated, affecting gene flow and eventually promoting allopatric speciation. This research was accomplished by exploring the spatial and historical relationships among Western toad clades and Great Basin drainages. Toad clades that are distributed over large areas, and are composed of many populations, tend to fall within the confines of regional, riverine drainages. Smaller, more genetically distant clades are generally harbored in small, riverless drainage basins. Dates of estimated evolutionary divergence among Western toad clades varied considerably using rates of molecular substitution that are reasonable for this organism. In addition, aquatic histories contain last known dates of interbasin connectivity that are well within the range of toad evolutionary divergence times reported here. Although the specific dates presented in this study encourage further refinement, this study suggests that the relative ages of Western toad clades are positively related with their geographic isolation. These results suggest that the evolutionary history of the Western toad may have been affected by prehistoric environments dominated by glacial cycles. This information can be used to inform strategies used by wildlife managers to catalog and protect unique biodiversity. ii ACKNOWLEDGEMENTS I would like to thank my advisor, Jill S. Heaton, and my advisory committee, Scott A. Mensing, Kenneth E. Nussear, and C. Richard Tracy for their intellectual contributions to this research. The previous field and lab studies that eventually led to this thesis was completed in collaboration with colleagues: Mo Beck, Bobby Espinoza, Robert Fisher, Matt Forister, John Gray, Bridgette Hagerty, Fran Sandmeier, and Eric Simandle. I would like to especially acknowledge Ken Adams, Brian Horton, Marith Reheis, Donald Sada, and Alan Wallace for participating in discussions that were invaluable to my understanding of Great Basin aquatic histories. The U.S. Fish & Wildlife Service, and the U.S. Geological Survey provided generous financial support. I would like to thank my friends and family for their support throughout my years in graduate school: my parents, Rick & Bonnie Noles, my grandparents, Richard & Patricia Noles, and Lily Mathieu, my brother, Garrett Noles, and my dear friends, Tim & Pam Alpers, Amy Barber, Ankur Goyal, Brigitte Peterson, Seth Taylor, and Stephanie Wakeling. The rural residents of Nevada also deserve recognition here for ensuring that "school didn't get in the way of my education", particularly: Shirley Harlan, Dave & Bobbie Murphey, Durk Pearson, Lina Sharp, and Dave Spicer. Finally, I would like thank my High School geometry teacher and friend, Mr. Tom Beveridge, for teaching me the meaning of perseverance. iii Table of Contents INTRODUCTION .............................................................................................................. 1 METHODS ......................................................................................................................... 5 Study Area ...................................................................................................................... 6 Clade Mapping ................................................................................................................ 7 Watershed Mapping ........................................................................................................ 8 Estimating Divergence Times ......................................................................................... 8 RESULTS ........................................................................................................................... 9 Clade Mapping ................................................................................................................ 9 Watershed Mapping ...................................................................................................... 10 1. The Northwest Basins ..................................................................................... 10 2. The Lahontan Basin ........................................................................................ 10 3. The Manly Basin ............................................................................................ 11 4. The Railroad Basin ......................................................................................... 11 5. Fish Lake Valley ............................................................................................. 11 Area of Sterile Basins ......................................................................................... 12 Closed Isolated Basins ....................................................................................... 12 Evolutionary Divergence Times ................................................................................... 13 Basin Histories .............................................................................................................. 13 The Mono Basin "Switching Yard" .......................................................................... 13 Dixie Valley & Fish Lake Valley ............................................................................. 15 The San Joaquin Connection .................................................................................... 16 Railroad Valley ......................................................................................................... 16 Oregon....................................................................................................................... 18 Isolated and Relict Dace Basins ................................................................................ 19 DISCUSSION ................................................................................................................... 19 Absolute vs. Relative Dates .......................................................................................... 19 Important Caveats to Analyses ..................................................................................... 20 Sampling Recommendations ........................................................................................ 23 Conclusions ................................................................................................................... 24 REFERENCES ................................................................................................................. 26 FIGURES AND TABLES ................................................................................................ 32 FIGURE 1: Western toad range in North America. ...................................................... 32 iv FIGURE 2: Great Basin Western toad clades. .............................................................. 34 FIGURE 3: Great Basin morphological regions. .......................................................... 36 FIGURE 4: Principal pluvial drainage basins. .............................................................. 38 FIGURE 5: The.Mono Basin switching yard ............................................................... 40 FIGURE 6: Southern expansion of Lake Lahontan towards Fish Lake Valley ............ 42 FIGURE 7:.Eastern expansion of Lake Lahontan into Dixie Valley............................ 44 FIGURE 8: Pre-Pleistocene Mono Basin to San Joaquin drainage link. ...................... 46 FIGURE 9:.Miocene corridors between Railroad Valley and the White River ........... 48 FIGURE 10:.Closed, isolated drainages around an "Area of Sterile Basins" ............... 50 FIGURE 11:.Relative clade ages vs geographic isolation ............................................ 51 TABLE 1:.Estimated Western toad evolutionary divergence times (slow rate) ........... 53 TABLE 2: Estimated Western toad evolutionary divergence times (fast rate) ............ 54 1 INTRODUCTION The Western toad species group (Anaxyrus boreas spp.), as currently recognized (Stebbins, 2003; Frost, 2007), is composed of two broadly distributed subspecies and three localized species. The geographic range of Anaxyrus boreas (Baird and Girard, 1852) extends from the eastern slopes of the Rocky Mountains to the Pacific Ocean, and from northern Baja California to Alaska and the Yukon (Figure 1). The subspecies A. b. boreas inhabits most of this range (Baird and Girard, 1852), and A. b. halophilus (Baird and Girard, 1852) is distributed in southern California (largely south of the Tehachapi Mountains) and
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