Cytochrome b mitochondrial gene analysis-based phylogeography of a Sand lizard in the Crimea: ancient refugium at the peninsula, late expansion from the North, and first evidence of Lacerta agilis tauridica and L. a. exigua (Lacertidae: Sauria) hybridization

The contact zones of the distribution ranges of closely related reptile taxa are the source of valuable data on the microevolutionary processes in populations, the history of regional faunas origin, and the environmental preferences of the studied forms. Our study is focused on the genetic structure of the populations of sand lizard, Lacerta agilis Linnaeus, 1758, at the Crimean peninsula. This lacertid species inhabits the mountain (afforested) and plain (steppe) parts of the Crimea, being abundant or common in many areas. Lacerta agilis is represented in the Crimea by two subspecies: the widely distributed Eastern (L. a. exigua Eichwald, 1831) inhabiting a large part of Northern Eurasia, and the endemic (L. a. tauridica Suchow, 1927) residing in the Crimean mountains. Mitochondrial haplogroup affiliation corresponding to one of the subspecies (L. a. tauridica, L. a. exigua or L. a. chersonensis) was established for 225 L. agilis individuals from 81 localities in the Crimea and adjacent mainland territories. The nucleotide sequences of the complete cytochrome b gene of mitochondrial DNA (1143 bp) were studied in 75 L. agilis individuals from 68 localities. The genetic distance between both subspecies inhabiting the Crimea revealed by used molecular marker comprised 2.8%, which indicates their early divergence approximately at the transition of Early to Middle Pleistocene (ca. 1 Mya). L. a. tauridica is characterized by a comparatively deep genetic structure. Haplotypes occupying isolated positions on the phylogenetic tree of this subspecies were found in the south-western part of the Crimean Mountains, what might be explained by the localization of L. agilis microrefugia in areas least affected by the Late Pleistocene cooling. Genetic structure of L. a. exigua is more homogeneous. Another important result of our study was an identification of zones of haplogroups «exigua» and «tauridica» coexistence localized along the northern and eastern margins of the Crimean Mountains. The portion of the «exigua» haplogroup in local populations decreases southward and westward. The observed pattern of the spatial distribution of haplogroups seems to be a result of the hybridization zone formation between the sand lizard subspecies during the Holocene expansion of L. a. exigua. Ecological niches modeling for L. agilis subspecies and analysis of morphological variability of the lizards support the hypothesis of L. a. exigua and L. a. tauridica hybridization in the area of contact of their ranges in the eastern part of the Crimean Mountains.