The distribution and biogeography of slow worms (Anguis, Squamata) across the Western Palearctic, with an emphasis on secondary contact zones

The slow-worm lizards (Anguis) comprise five species occurring throughout most of the Western Palearctic. Although these species are relatively uniform morphologically - with the exception of A. cephallonica, which exhibits a quite unique morphology - they are genetically deeply divergent. Here, we provide detailed distribution maps for each species and discuss their biogeography and conservation based on updated genetic data and a robust distribution database. We pay particular attention to the so called 'grey zone', which typically represents secondary contact zones and in some cases confirmed or presumed hybrid zones. Four of the five species live in parapatry, while only two species, A. cephallonica and A. graeca from the southern Balkans occur in partial sympatry. Further research should focus on the eco-evolutionary interactions between species in contact, including their hybridization rates, to reveal deeper details of the slow-worm evolutionary and natural history.

Automated summary

The slow-worm lizards comprise five species with relatively uniform morphology but deep genetic divergence. Four of the species live in parapatry, while only two species occur in partial sympatry in certain regions. Further research is needed to explore the eco-evolutionary interactions between these species, including their hybridization rates, to uncover more details about the slow-worm evolutionary and natural history.