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

Authors: MAIER, PAUL - San Diego State University; VANDERGAST, AMY - Us Geological Survey (USGS); Ostoja, Steven; AGUILAR, ANDRES - California State University; BOHONAK, ANDREW - San Diego State University

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2019
Publication Date: 10/29/2019
Citation: Maier, P.A., Vandergast, A., Ostoja, S.M., Aguilar, A., Bohonak, A. 2019. Pleistocene glacial cycles drove lineage diversification and fusion in the Yosemite toad (Anaxyrus canorus). Ecology and Evolution. 73(12):2476-2496. https://doi.org/10.1111/evo.13868.
DOI: https://doi.org/10.1111/evo.13868

Interpretive Summary: Amphibian persistence in the 21st century is affected by many anthropogenic impacts including habitat alteration, chemical toxicants, pandemic disease, and climate shifts. The Yosemite toad (Anaxyrus [Bufo] canorus) is a federally protected species of meadow-specializing amphibian endemic to the high-elevation Sierra Nevada Mountains of California. Up to 69% of its populations have recently been extirpated. Climate change is projected to have a major hydrological impact on the Yosemite Toad’s core meadow habitat, although future effects on meadow connectivity via tadpole recruitment and adult dispersal are poorly understood. As part of a field study and genetic analyses we found distinct environmental drivers of connectivity among four genetically unique (phylogeographic) lineages of toads. We also found that meadows with higher moisture regimes produce larger tadpoles and toads with higher site fidelity. Our results will have significant utility for prioritizing the future management and conservation of this California native species.

Technical Abstract: Amphibian persistence in the 21st century is beset by many anthropogenic impacts including habitat alteration, chemical toxicants, pandemic disease, and climate shifts. The Yosemite toad (Anaxyrus [Bufo] canorus) is a federally protected species of meadow-specializing amphibian endemic to the high-elevation Sierra Nevada Mountains of California. Up to 69% of its populations have recently been extirpated. Climate change is projected to have a major hydrological impact on the Yosemite Toad’s core meadow habitat, although future effects on meadow connectivity via tadpole recruitment and adult dispersal are poorly understood. In this study, we used a double-digest RADseq dataset along with numerous remotely-sensed habitat attributes in a landscape genetics framework to answer three primary questions: (1) Are meadows or clusters of meadows the best approximation of population boundaries? (2) Which environmental, topographic, and climatic attributes most facilitate meadow connectivity? (3) What are the environmental predictors of source-sink structure? We modified a gravity modeling approach that has benefits for modeling microevolutionary dynamics in patch-separated amphibian populations. Multiple analyses of genetic structure suggested that populations are typically circumscribed by a single meadow, however clusters of meadows are connected with source-sink structure, with large and flat “hub” meadows surrounded by smaller and rugged “satellite” meadows. Our results revealed distinct environmental drivers of connectivity among four phylogeographic lineages of toads. We also found that meadows with higher moisture regimes produce larger tadpoles and toads with higher site fidelity. Our results will have significant utility for prioritizing the future management and conservation of this California native species.