Evolutionary change has been demonstrated to occur rapidly in human-modified systems, yet understanding how multiple components of global change interact to affect adaptive evolution remains a critical knowledge gap. We examined how regional climatic conditions and land use interact to affect genetically based color polymorphism in the eastern red-backed salamander (Plethodon cinereus). P. cinereus is a woodland salamander with two primary discrete color morphs (striped, unstriped) that have been associated with macroclimatic conditions. Unstriped individuals tend to be most common in warmer, drier regions, but morph frequencies can be variable within climate zones, suggesting that additional factors drive spatial variation in morph frequencies. Because forest cover alters microclimatic conditions experienced by salamanders at the forest floor, land use may mediate the effect of macroclimatic conditions on color morph variation. Here we analyzed morph frequencies among 238 591 individual salamanders across 1170 sites throughout the range of P. cinereus. We used path analyses to examine how morph frequencies were related to spatial variation in ambient temperature, precipitation, and forest cover, and we tested for a trend in morph frequencies.
Results/Conclusions
Frequency of striped individuals was positively related to forest cover in populations occurring in warmer regions (>7 °C annually), a relationship that was weak to nonexistent in populations located in colder regions (≤7 °C annually). Morph frequencies were not related to precipitation, and there was no evidence for a trend in morph frequencies across the range of P. cinereus despite climate warming. Our results suggest that directional selection imposed by climate warming at a regional scale may be amplified by forest loss and suppressed by forest persistence, with a mediating effect of land use that varies geographically. Our work highlights how the complex interaction of selection pressures imposed by different components of global change may lead to divergent evolutionary trajectories among populations.