Meeting Abstract
Most species consist of multiple genetically differentiated populations that undoubtedly experience different community contexts and forms of natural selection. This allows the interface of gene flow and selection to continuously shape the spatial patterning of population structure and adaptive variation across geographic space. Despite the importance of a population genetic perspective for understanding the evolutionary consequences of the geographic mosaic of coevolution, few studies have thoroughly characterized both the form and outcome of natural selection on population genetic structure across geographic mosaics of coevolution. Here, we quantify the phenotypic variation and population structure in the Sierra garter snake (Thamnophis couchii) using 26,121 SNPs to understand the geographic scale at which gene flow might be reduced among populations, and thus, allow for independent local adaptation in response to variation in the tetrodotoxin (TTX) defense of its Pacific newt prey (Taricha). We documented phenotypic variation in across the range, with snakes from the southern part of the distribution having much higher resistance. Phylogenetic analyses indicate that greater resistance evolved as Th. couchii colonized southern regions of its range. We documented surprisingly fine scale population genetic differentiation at the level of neighboring watersheds. Our results suggest that the geographic scale of the outcome of coevolutionary interactions is likely to be narrow, which could facilitate the evolution of adaptive variation across fine spatial scales.
