Pronounced Genetic Structure Associated with Differences in a Reproductive Trait and Climatic Barriers in Canadian Populations of Western Toads (Anaxyrus boreas)

Abstract

Identifying genetic groups within species is essential for understanding biodiversity, characterizing species' distributions, and for delineating conservation units. I aimed to characterize genetic structure for western toads (Anaxyrus boreas) in Canada where they are currently recognized as two legal conservation units (i.e. designatable units): a Calling population, which has a pronounced breeding call and vocal sac, and a Non-calling population, which lacks both these traits. I assess whether genetic differences exist between these populations and correspond to known phenotypic differences in calls. I additionally explore ecological differences between Calling and Non-Calling populations using ecological niche models. Genetic analyses revealed the Calling and Non-calling populations are genetically distinct, with a high concordance with the call phenotypes. The observed genetic boundary between these groups also aligns with ecological breaks in habitat suitability. In addition to differences between Calling and Non-Calling western toads, I found evidence of a third genetic group in southwestern Alberta and southeastern British Columbia, in what is known as the Crown of the Continent Ecosystem. Overall, my thesis suggests the continued recognition of the Calling and Non-calling populations as separate conservation units is warranted, and highlights the potential for northern latitudes to harbor biologically significant genetic structure.