Sexual size dimorphism, morphometry and phenotypic variation in the whip snake Hierophis viridiflavus from a central Mediterranean area

Animal populations living in different environments generally exhibit divergent phenotypic characteristics. In snakes, body size varies greatly among disjunct populations. The European Whip snake, Hierophis viridiflavus, is widely distributed in the western Mediterranean area, and on most of both small and large islands of the Tyrrhenian Sea. We compared biometrical patterns regarding ventral scalation, body size and head size among different samples from mainland, large islands and small islands. Sexual Size Dimorphism was very marked in the species, with males attaining larger body size and larger relative head size than females and a lower number of ventral scales. There was a clear evidence of a strong relationship between ventral scale number and the geographic origin, with smaller island snakes characterized by a significantly higher number of ventral scales. This relationship was true even when considering body size, with insular snakes significantly smaller than mainland ones. Our results clearly indicated a strong differentiation among the considered populations, and provided basis to clarify the relative importance of phenotype variation.