Recent recolonisation of West Siberia and northern cryptic refugia in the grass snake Natrix natrix scutata (Pallas, 1771) (Squamata: Natricidae)

Abstract

Most of the geographic range of the grass snake Natrix natrix is occupied by the subspecies N. n. scutata, which occurs from Eastern Europe to East Siberia. This study addressed the phylogeography of this subspecies via analysis of variation of partial cytochrome b (cyt b) sequences from 135 individuals sampled at 91 localities across its range, in addition to species distribution modelling. A haplotype network was constructed and identified a major star-like haplogroup that harbours most of the analysed specimens and is considered the main source of recolonisation of vast territories of northern Eurasia after the Last Glacial Maximum (LGM). Most of this subspecies’ current range is occupied by haplotypes from a single haplogroup, with probable refugia in the south of the European part of Russia or the North Caucasus. The most frequent (ancestral) haplotype in this group is the only one discovered in West Siberia among 25 specimens from 13 sampling sites, indicating relatively recent colonisation of Siberia. According to species distribution modelling, no relatively suitable areas were present in Central Asia or Siberia during the LGM. Nonetheless, the only two specimens examined from the easternmost area of the species’ geographic range, near Lake Baikal, had unique haplotypes that differed from the most common haplotype by one and two substitutions. The most probable explanation for this pattern is that N. n. scutata colonised the area during a previous interglacial period and survived here during the last glacial. The Mugodzhar Range in western Kazakhstan also showed cyt b differentiation as compared to surrounding areas but warrants further sampling to test competing hypotheses.