Local adaptation of redband trout in desert and montane environments

Natural populations that evolve under extreme climates are likely to diverge due to selection and adaptation to local environments.  To explore whether local adaptation has occurred in redband trout occupying differing climate regimes, we used a limited genome scan approach to test for candidate markers under selection in populations occurring in desert and montane streams.  Outlier methods generally lacked sensitivity to detect selection gradients among populations, however, linear regression of minor allele frequency with temperature revealed five candidate markers associated with temperature in this species (p < 0.01).  Literature reviews of these candidate genes provided strong corroboration for their role in thermal adaptation and response to heat stress.  Putatively neutral markers identified high genetic differentiation among warm populations relative to cooler sites, likely due to intermittent flows in desert streams.  Additionally, populations exhibited a highly significant pattern of isolation-by-temperature (p < 0.0001) and those adapted to the same environment had similar allele frequencies across the six candidate markers, indicating selection for differing climates.  These results implicate that many genes are involved in adaptation of redband trout to high temperature environments, and selection acts to reinforce localization.