Population genomics reveals local adaptation related to temperature variation in two stream frog species: Implications for vulnerability to climate warming

Identifying populations at highest risk from climate change is a critical
component of conservation efforts. However, vulnerability assessments are
usually applied at the species level, even though intraspecific variation
in exposure, sensitivity, and adaptive capacity play a crucial role in
determining vulnerability. Genomic data can inform intraspecific
vulnerability by identifying signatures of local adaptation that reflect
population-level variation in sensitivity and adaptive capacity. Here, we
address the question of local adaptation to temperature and the genetic
basis of thermal tolerance in two stream frogs (Ascaphus truei and A.
montanus). Building on previous physiological and temperature data, we
used whole genome resequencing of tadpoles from four sites spanning
temperature gradients in each species to test for signatures of local
adaptation. To support these analyses, we developed the first annotated
reference genome for A. truei. We then expanded the geographic scope of
our analysis using targeted capture at an additional 11 sites per species.
We found evidence of local adaptation to temperature based on
physiological and genomic data in A. montanus and genomic data in A.
truei, suggesting similar levels of sensitivity (i.e., susceptibility)
among populations regardless of stream temperature. However, invariant
thermal tolerances across temperatures in A. truei suggests that
populations occupying warmer streams may be most sensitive. We identified
high levels of evolutionary potential in both species based on genomic and
physiological data. While further integration of these data is needed to
comprehensively evaluate spatial variation in vulnerability, this work
illustrates the value of genomics in identifying spatial patterns of
climate change vulnerability.