Taille et mélanisme chez Vipera aspis dans les Préalpes suisses et en Italie centrale et comparaison avec différentes populations alpines de Vipera berus

Abstract

In a contact zone of Vipera aspis and Vipera berus in the Swiss Bernese Prealps, V. berus is smaller than V. aspis. V. berus seems to be a dwarf mountainous form. The rate of melanism is higher in V. berus (49%) than in V. aspis (34%), probably a consequence of the difference in habitat use between the two species. Comparisons with other Swiss and Italian populations of both V. aspis and V. berus suggest that melanism is particularly advantageous in closed, forested areas. On the other hand, for both species and in all the studied populations, the rate of melanism is higher in females than in males, suggesting a higher advantage to be black for the females. In Switzerland, as well as in Italy, melanistic V. berus tend to be heavier and longer than cryptic ones, whereas in V. aspis the opposite is the case. In both species, growth rates are higher in melanistic morphs and we suggest that the larger body size of the cryptic V. aspis is related to their higher survival rate and higher mean age.