Landscape genomics of a widely distributed snake (Dolichophis caspius, Gmelin, 1789) across Eastern Europe and Western Asia

Across the distribution of the Caspian whipsnake (Dolichophis caspius),
populations have become increasingly disconnected due to habitat
alterations. To understand population dynamics and the adaptive potential
of this widespread but locally endangered snake, we investigated
population structure, admixture and effective migration patterns. We took
a landscape-genomic approach to identify selected genotypes associated
with environmental variables relevant to D. caspius. With double-digest
restriction-site associated DNA (ddRAD) sequencing of 53 samples resulting
in 17,518 single nucleotide polymorphisms (SNPs), we identified eight
clusters within D. caspius reflecting complex evolutionary patterns of the
species. Estimated Effective Migration Surfaces (EEMS) revealed
higher-than-average gene flow in most of the Balkan Peninsula and
lower-than-average gene flow along the middle section of the Danube River.
Landscape genomic analysis identified 751 selected genotypes correlated
with seven climatic variables. Isothermality correlated with the highest
number of selected genotypes (478) located in 41 genes, followed by annual
range (127) and annual mean temperature (87). We conclude that
environmental variables, especially the day-to-night temperature
oscillation in comparison to the summer-to-winter oscillation, may have an
important role in the distribution and adaptation of D. caspius.