Hybridization patterns in two contact zones of grass snakes reveal a new Central European snake species

Abstract

Recent studies found major conflicts between traditional taxonomy and genetic differentiation of grass snakes and identified previously unknown secondary contact zones. Until now, little is known about gene flow across these contact zones. Using two mitochondrial markers and 13 microsatellite loci, we examined two contact zones. One, largely corresponding to the Rhine region, involves the western subspecies Natrix natrix helvetica and the eastern subspecies N. n. natrix, whereas in the other, more easterly, contact zone two lineages meet that are currently identified with N. n. natrix and N. n. persa. This second contact zone runs across Central Europe to the southern Balkans. Our analyses reveal that the western contact zone is narrow, with parapatrically distributed mitochondrial lineages and limited, largely unidirectional nuclear gene flow. In contrast, the eastern contact zone is very wide, with massive nuclear admixture and broadly overlapping mitochondrial lineages. In combination with additional lines of evidence (morphology, phylogeny, divergence times), we conclude that these differences reflect different stages in the speciation process and that Natrix helvetica should be regarded as a distinct species. We suggest a nomenclatural framework for presently recognized grass snake taxa and highlight the need for reconciling the conflicts between genetics and taxonomy.

A common toad hybrid zone that runs from the Atlantic to the Mediterranean

“…General features of the species contact zone are the absence of large areas of B. bufo-B. spinosus sympatry, its long, narrow and more or less linear aspect, with an overall geographical pattern similar to that of other species pairs, like Triturus cristatus and T. marmoratus (Arntzen and Wallis, 1991;Wielstra et al, 2014), or -not in France but more to the north and the east -Natrix grass snakes (Kindler et al, 2017). Some topographical correlates of the zone's position can tentatively be proposed.…”

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

“…Grass snakes were, until recently, thought to represent a widespread species distributed from North-western Africa and the Iberian Peninsula across much of Western, Central, Northern and Eastern Europe into Central Asia (Kabisch 1999). Genetic investigations revealed three deeply divergent genealogical lineages without or with very restricted, unidirectional gene flow and prompted the recognition of three distinct species (Kindler et al 2013(Kindler et al , 2014(Kindler et al , 2017(Kindler et al , 2018aPokrant et al 2016). According to these investigations, the red-eyed grass snake, Natrix astreptophora (Seoane, 1884), occurs in North-western Africa, the Iberian Peninsula and South-western France.…”

“…The barred grass snake hybridises in a narrow belt, largely corresponding to the Rhine region, with the common grass snake, Natrix natrix (Linnaeus, 1758), whose intraspecific systematics is poorly understood. There are many conflicts between traditionally recognised subspe-cies and genetic lineages and clusters (Kindler et al 2013(Kindler et al , 2017. Gene flow is mainly unidirectional from N. helvetica into N. natrix.…”

Genomewide SNP markers breathe new life into phylogeography and species delimitation for the problematic short‐necked turtles (Chelidae: Emydura) of eastern Australia

“…Where it deemed necessary, as a practical convenience rather than a reflection of biological reality, one could assign to species, the MDB OTU ( E. macquarii (Gray 1830)), the LEB OTU ( E. emmotti Cann et al., 2003), the Hunter River OTU ( E. gunabarra Cann, ) and a single coastal species E. krefftii Gray, 1871 with subspecies for the NE Coast (no available name), E Coast ( E. krefftii krefftii, as defined here), SE Coast ( E. krefftii signata Ahl 1932) and Fraser Island OTUs ( E. krefftii nigra McCord et al., ). Whatever operational decision is taken, it will be controversial, as the decision involves considerable subjectivity in imposing a classification on what is essentially a dynamic, sometimes reticulate, and incomplete evolutionary process (Kindler et al., ).…”