Phenotypic variability in the western grass snake Natrix astreptophora, with description of a new subspecies from Morocco

Based on a large sample of 920 Natrix astreptophora (López Seoane, 1884) from Western Europe and 32 specimens from North Africa, we examine phenotypic variation in this species. In agreement with genetic findings of previous phylogeographic studies, we distinguish three subspecies. The nominotypical subspecies is distributed in the European part of the distribution range.

Natrix astreptophora algerica (Hecht, 1930) lives in northeastern Algeria and northern Tunisia. Moroccan grass snakes represent Natrix astreptophora soumiafahdae subsp. nov., which is described here as new to science. All three subspecies differ in coloration and pattern and represent three deeply divergent genetic lineages as reflected by mitochondrial and nuclear DNA.

Natrix astreptophora soumiafahdae subsp. nov. is very rare and has a fragmented distribution range. It represents an evolutionarily significant conservation unit for which conservation measures are needed. In addition, across the distribution range of the nominotypical subspecies, three non-melanistic phenotypes can be distinguished that also differ in coloration and pattern.

One of these phenotypes is widespread across the whole European range, while two are geographically restricted to the north and west of the Iberian Peninsula, respectively, where they may co-occur with the other phenotypes. In addition, there is a clear correlation between the distribution of melanistic grass snakes and latitude; 45 of the 46 melanistic N. a. astreptophora were recorded from the northern and northwestern Iberian Peninsula.

There are no records for melanistic grass snakes in North Africa.