BODY-SIZE AND MELANISM IN VIPERA-ASPIS IN THE SWISS PREALPS AND CENTRAL ITALY AND COMPARISON WITH DIFFERENT ALPINE POPULATIONS OF VIPERA-BERUS

In a contact zone of Vipera aspis and Vipera berus in the Swiss Bernes e Prealps, V.berus is smaller than V.aspis. V.berus seems to be a dwar f mountainous form. The rate of melanism is higher in V.berus (49%) th an in V.aspis (34%), probably a consequence of the difference in habit at use between the two species. Comparisons with other Swiss and Itali an populations of both V.aspis and V.berus suggest that melanism is pa rticulary advantageous in closed, forested areas. On the other hand, f or both species and in all the studied populations, the rate of melani sm is higher in females than in males, suggesting a higher advantage t o be black for the females. In Switzerland, as well as in Italy, melan istic 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 ar e 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 h igher mean age.