Data from: The effects of drift and selection on latitudinal genetic variation

Clinal variation is paramount for understanding the factors shaping
genetic diversity in space and time. During the last glacial maximum,
northern Europe was covered by glacial ice that rendered the region
uninhabitable for most taxa. Different evolutionary processes during and
after the recolonisation of this area from different glacial refugia have
affected the genetic landscape of the present-day European flora and
fauna. In this study, we focus on the common toad (Bufo bufo) in Sweden
and present evidence suggesting that these processes have resulted in two
separate lineages of common toad, which colonised Sweden from two
directions. Using ddRAD sequencing data for demographic modelling,
structure analyses and analyses of molecular variance (AMOVA), we provide
evidence of a contact zone located between Uppland and Västerbotten in
central Sweden. Genetic diversity was significantly higher in southern
Sweden compared to the north, in accordance with a pattern of decreased
genetic diversity with increasing distance from glacial refugia. Candidate
genes under putative selection are identified through outlier detection
and gene-environment association methods.  We provide evidence of
divergent selection related to stress response and developmental processes
in these candidate genes. The colonisation of Sweden by two separate
lineages may have implications for how future conservation efforts should
be directed by identifying management units and putative local
adaptations.