Pleistocene glacial cycles drove lineage diversification and fusion in the Yosemite toad (Anaxyrus canorus)

• Main Authors: Maier, Paul A., Vandergast, Amy G., Ostoja, Steven M., Aguilar, Andres, Bohonak, Andrew J.
• Format: Text
• Language: unknown
• Published: figshare 2019
• Subjects: Evolutionary Biology; FOS Biological sciences; 60411 Population, Ecological and Evolutionary Genetics; Ice Sheet
• Online Access: https://dx.doi.org/10.6084/m9.figshare.10260362; https://figshare.com/articles/Pleistocene_glacial_cycles_drove_lineage_diversification_and_fusion_in_the_Yosemite_toad_Anaxyrus_canorus_/10260362

Species endemic to alpine environments can evolve via steep ecological selection gradients between lowland and upland environments. Additionally, many alpine environments have faced repeated glacial episodes over the past two million years, fracturing these endemics into isolated populations. In this “glacial pulse” model of alpine diversification, cycles of allopatry and ecologically divergent glacial refugia play a role in generating biodiversity, including novel admixed (“fused”) lineages. We tested for patterns of glacial pulse lineage diversification in the Yosemite toad ( Anaxyrus [ Bufo ] canorus ), an alpine endemic tied to glacially influenced meadow environments. Using double‐digest RADseq on populations densely sampled from a portion of the species range, we identified nine distinct lineages with divergence times ranging from 18–724 ka, coinciding with multiple Sierra Nevada glacial events. Three lineages have admixed origins, and demographic models suggest these fused lineages have persisted throughout past glacial cycles. Directionality indices supported the hypothesis that some lineages recolonized Yosemite from east of the ice sheet, whereas other lineages remained in western refugia. Finally, refugial niche reconstructions suggest that low‐ and high‐elevation lineages have convergently adapted to similar climatic niches. Our results suggest glacial cycles and refugia may be important crucibles of adaptive diversity across deep evolutionary time.