Variation in morphological characters of the dice snake Natrix tessellata (Reptilia, Colubridae) in the Central and Southern Dnieper River Area

The dice snake Natrix tessellata (Laurenti, 1768) is one of the common snake species in the Southern Palaearctic and North Africa. In the Central and Southern Dnieper River basin the dice snake is one of the most numerous and characteristic species. Relative isolation and the varying influence of environmental factors are known to be a motive force behind epigenetic divergence between populations. In populations of N. tessellata this divergence can be manifest in the form of morphometric and phenetic peculiarities. Research into these parameters of dice snake populations in terms of anthropogenic influence on habitats along a latitude gradient is essential. In the Central and Southern parts of the Dnieper River basin such studies are of great importance for the monitoring of populations and for further indicative purposes. The aim of our study is to characterize the morphometric features of N. tessellata in this area and to determine the variability of these parameters in the snake populations under varying intensities of anthropogenic influence. The snakes were collected in 2013–2016 from the territory adjacent to the Prydniprovska Thermal Power Plant, from the Maiorova gully (Maiorka village, Dnipropetrovsk region) and the National Nature Park “Velykyi Lug” (Zaporizhia region). The following morphometric parameters were recorded: snout-vent length (SVL), tail length (TL), the number of ventral scales (V), and the number of subcaudal scales (SBC), the number of scale rows at mid-body (MBS), the number of supralabial scales (SLS), the number of temporal scales (TS), and the number of postocular scales (POS). All the tested parameters generally correspond to the limits known for this species from the literature. Nevertheless , some geographic peculiarities in variability of the tail length and number of subcaudal scales were identified. According to data from the literature, the southern populations of the dice snake are distinguished by an increase in the number of subcaudal scales . The studied dice snake populations were characterized by some sexual dimorphism in the snout-vent length, tail length and the number of subcaudal scales. A higher percentage of bilateral asymmetry in snakes from the population close to the Prydniprovska TPP was found. Such changes are usually considered to be an indicator of a certain destabilization of the embryogenesis.