Newts under siege:: range expansion of Triturus pygmaeus isolates populations of its sister species

The newt species Triturus marmoratus and Triturus pygmaeus are both present in central Portugal where they have parapatric distributions. We used four genetic markers to determine which species was present in 31 populations. In the centre of the study area we found a T. marmoratus enclave. Despite small interpopulation distances, hybridization is locally rare. We built several models to try to explain this distribution using environmental data. The best model, chosen by Akaike's Information Criterion, relates the presence of T. marmoratus with the temperature in July, the relief of the landscape, and a higher use of the land for orchards. The current distribution can best be explained by T. pygmaeus expanding north and replacing T. marmoratus, the latter only persisting where ecological conditions are relatively favourable.