Sexual differences in caudal morphology and its relation to tail autotomy in lacertid lizards

Abstract

We hypothesized that the presence of the forked hemipenes, and associated musculature, at the base of the tail in male lizards should constrain the capacity to autotomize the tail. Thus, this hypothesis predicts that the non-autotomous base of the tail should be longer in male than in female lizards. We tested this hypothesis in four species oflacertid lizards. Males have on average one to two non-autotomous vertebrae more than females, and the sexual difference in length of the non-autotomous tail base remains constant over the entire body size range. In addition, the first functional autotomy plane in males is usually located on, or is distal to, the vertebrae from which two hemipenial muscles take origin. These observations support the view that functional demands of the male intromittent organs impose constraints on the abilities of tail autotomy. In a natural population of Lacerta vivipara, the proportion of tail breaks that occurred at very short distances from the base was highest in females, indicating that the small sexual difference in length of the non-autotomous tail part is of functional significance. Total length of the tail was largest in males. This can be interpreted as a compensation for the decline in autotomy capacities at the tail base, such that the length of the autotomous part remains similar in both sexes.