Asynchrony of seasons rather than habitat type determines genetic differentiation in a Neotropical toad

We ask whether environment is a primary influence on the evolution of Rhinella granulosa, a widely distributed Neotropical toad, by evaluating the degree to which temporal variation in local climates (asynchrony of seasons) and spatial variation in habitat (environmental gradients) influence genetic diversity. We inferred genetic structure using single nucleotide polymorphisms after outlier detection and genome-environment association, selected the best demographic model for population diversification, and investigated the influence of habitat and climate in explaining genetic structure using linear discriminant models. Our results indicate that genetic diversity is distributed along a latitudinal gradient and not associated with habitat type. Stable populations have diverged in isolation during most of their evolutionary history, with demography being unrelated to historical habitat stability. Outlier loci recovered increased structure in a hierarchical way, which is poorly explained by habitat but well explained by monthly climatic variables. Due to the biology of this organism, precipitation likely mediates gene flow by causing extrinsic barriers to migration at climate transitions zones. This is consistent with natural selection promoting genetic differentiation, but because climates vary mostly in a temporal context, we propose selection not necessarily involves local adaptation. Reported differences at the advertisement call suggest premating isolation and reinforcement.