Biogeography and Ecology of a dimorphic trait in Triturus alpestris (Amphibia, Caudata)

Paedomorphosis is an evolutionary process in which larval structures are retained in adult animals. In newts and salamanders, this heterochronic process is widely represented and concerns the retention of gill slits. Our aim was to find out whether habitat and geographical determinants may be associated with paedomorphosis in a European species of newt. To this end, we determined the main characteristics of the aquatic sites containing paedomorphic Alpine newts that have been described in the literature or discovered by one of us. Although metamorphs are widely distributed in Europe, paedomorphs were only found at the southern margin of the geographic range of the species: mainly in the Italian and Balkan peninsulas. They were recorded in 87 aquatic sites. No single trend was outlined for the analyzed ecological parameters of the aquatic and surrounding terrestrial habitats (e.g. altitude, maximum water depth, drying and presence of forest). These results show that paedomorphs can be found in both favorable aquatic habitats surrounded by hostile terrestrial landscapes, but also in temporary waters located in proximity to appropriate terrestrial environments. Models predicting paedomorphosis in varied environments are thus supported, but require complementary investigations on the costs and benefits of each alternative ontogenetic pathway. On the other hand, the southern limitation of the heterochronic phenomenon and the existence of favorable sites in northern and eastern Europe suggest a genetic basis for paedomorphosis in the studied species.