The effects of climate and demographic history in shaping genomic variation across populations of the Desert Horned Lizard (Phrynosoma platyrhinos)

Species often experience spatial environmental heterogeneity across their
range, and populations may exhibit signatures of adaptation to local
environmental characteristics. Other population genetic processes, such as
migration and genetic drift, can impede the effects of local adaptation.
Genetic drift in particular can have a pronounced effect on population
genetic structure during large-scale geographic expansions, where a series
of founder effects leads to decreases in genetic variation in the
direction of the expansion. Here we explore the genetic diversity of a
desert lizard that occupies a wide range of environmental conditions and
that has experienced post-glacial expansion northwards along two
colonization routes. Based on our analyses of a large SNP dataset, we find
evidence that both climate and demographic history have shaped the genetic
structure of populations. Pronounced genetic differentiation was evident
between populations occupying cold versus hot deserts, and we detected
numerous loci with significant associations with climate. The genetic
signal of founder effects, however, is still present in the genomes of the
recently expanded populations, which comprise subsets of genetic variation
found in the southern populations, and we found substantial evidence that
genetic diversity of lizards differs along the two colonization routes.