Phylogeography and Contact Zones of the Common Grass Snake in Poland (Squamata: Natricidae: Natrix natrix )

Abstract

Until now, the genetic identity of common grass snakes ( Natrix natrix ) in Poland remained poorly understood. This study presents the first comprehensive phylogeographic analysis for Poland using mitochondrial DNA sequences ( cyt b and ND4 + tRNAs ) and 13 nuclear microsatellite loci. A total of 982 individuals from Poland and adjacent countries were analysed. Three mitochondrial lineages were identified, with partially overlapping distributions. A Bayesian cluster analysis of microsatellite data revealed three genetic clusters corresponding to distinct mitochondrial lineages and the subspecies N. n. natrix , N. n. vulgaris , and N. n. scutata , respectively, albeit with extensive admixture. The mitochondrial lineage of the nominotypical subspecies occurs in the centre and west of the country, the lineage of N. n. vulgaris mainly in the south and southeast, and the lineage of N. n. scutata mainly in the very east. However, Poland represents a complex hybrid zone, with widespread admixture and many individuals with mitonuclear discordance, indicating extensive gene flow. Nuclear genomic signatures of N. n. scutata were found to be widely distributed, also far beyond the occurrence of the respective mitochondrial lineage in eastern Poland. This provides evidence for a dynamic hybrid zone moving from the east to the west and for a westward expansion of N. n. scutata . The present phylogeographic pattern reflects complex postglacial range dynamics, namely the admixture of N. n. natrix , a Central European survivor during the last glaciation, with the postglacial invaders N. n. vulgaris from the southeast and N. n. scutata from the east.

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