Distribution and hybridisation of barred and common grass snakes (Natrix helvetica, N. natrix) in Baden-Württemberg, South-western Germany

Abstract

The distribution and hybridisation zone of the two grass snake species occurring in the German state of Baden-Württemberg are described, based on genetic data from maternally inherited mitochondrial DNA (mtDNA, up to 1983 bp) and biparentally inherited microsatellite DNA (13 loci). In agreement with previously published morphological evidence, the barred grass snake (Natrix helvetica) occurs in the Upper Rhine Valley and the Black Forest, while the common grass snake (N. natrix, ‘yellow lineage’) is distributed across the remaining, more eastern parts of Baden-Württemberg. Cline analyses across two transects running through the region of Karlsruhe and the Black Forest indicate that the hybrid zone is similarly narrow here as in the previously characterised stretch near Lake Constance. With respect to nuclear DNA, the Black Forest constitutes no impediment to gene flow in comparison with lowland regions (Karlsruhe, Lake Constance). However, on the eastern slope of the Black Forest, the abrupt replacement of mtDNA of N. helvetica by that of N. natrix indicates male-mediated gene flow and that the Black Forest represents a dispersal barrier for female grass snakes.

Transalpine dispersal: Italian barred grass snakes in southernmost Bavaria—This far but no further!

“…sicula that occurs also in Bavaria (lineage C; Table ). Except for 15 newly processed samples, these data were from previous studies (Kindler et al, 2013, 2014, 2017; Kindler & Fritz, 2018; Kindler, Graciá, et al, 2018; Schultze et al, 2019, 2020).…”

“…Two marker systems (mtDNA, microsatellite loci) were applied, which were previously used in other studies on grass snakes (Kindler et al, 2013, 2017; Kindler, de Pous, et al, 2018; Kindler & Fritz, 2018; Pokrant et al, 2016; Schultze et al, 2019, 2020). Two mtDNA fragments were sequenced, the cytochrome b ( cytb ) gene (1117 bp), and the partial ND4 gene plus adjacent DNA coding for tRNAs ( tRNA ‐ His , tRNA ‐ Ser , tRNA ‐ Leu ; 866 bp).…”

“…Recent studies based on mitochondrial and nuclear DNA changed this picture. Due to limited gene flow across geographic contact zones, three full species are now recognized (Asztalos et al, 2020; Kindler et al, 2017; Pokrant et al, 2016; Schultze et al, 2019, 2020; Speybroeck et al, 2020). These three species were previously identified with distinct subspecies (Kabisch, 1999; Mertens & Wermuth, 1960).…”

“…helvetica into N . natrix (Kindler et al, 2017; Schultze et al, 2019), and the genetic transition is paralleled by a sharp morphological transition (Thorpe, 1979). Further south another subspecies of the barred grass snake, Natrix helvetica sicula (Cuvier, 1829), hybridizes with N .…”

The valid scientific names of the barred grass snake and its subspecies from mainland Italy and Sicily

“…Based on molecular genetic investigations, the traditional concept (Mertens and Wermuth, 1960;Thorpe, 1979;Lanza, 1983;Kabisch, 1999) of a widely distributed polytypic species Natrix natrix (Linnaeus, 1758) was replaced by the insight that there are three genetically deeply divergent species of grass snake (Pokrant et al, 2016;Kindler et al, 2017). These parapatrically distributed taxa hybridize only rarely (N. astreptophora and N. helvetica;Pokrant et al, 2016) or in narrow hybrid belts (N. helvetica and N. natrix sensu stricto; Kindler et al, 2017;Schultze et al, 2019Schultze et al, , 2020. One of the three species, the barred grass snake N. helvetica (Lacepède, 1789), occurs in Western Europe north of the Pyrenees to the Rhine region, in Britain and on the Italian Peninsula, Sicily, Sardinia, and Corsica (Kindler et al, 2017;Schultze et al, 2020).…”