Sexual Size Dimorphism in Eastern Slow-Worm ( Anguis fragilis colchica , Reptilia: Anguidae)

Abstract

The direction and magnitude of inter-sexual differences in body and head size in one eastern slow-worm ( A. f. colchica ) population were investigated. We compared morphological measures of 92 male and 127 female adult A. f. colchica from a single population. In line with our expectations, we found that females were generally larger, but males had larger relative head size. At similar growth rate a disproportionate increase of head size in males and respectively of body size in females are pointed. The sexual difference in relative head size increased with the size (a proxy for age) of the animals. Our results fits well to the general theory, especially when studies of the reproductive biology of the species — reporting vigorous male-male combats, the presence of copulatory bites, and showing that female fecundity is size dependent — is taken into account. However, considering this generalist species, another common hypothesis suspecting dietary divergence between sexes behind sexual differences in relative head size is not likely to represent a strong evolutionary pressure in this case.