SEXUAL DIFFERENCES IN CAUDAL MORPHOLOGY AND ITS RELATION TO TAIL AUTOTOMY IN LACERTID LIZARDS

We hypothesized that the presence of the forked hemipenes, and associa ted musculature, at the base of the tail in male lizards should constr ain the capacity to autotomize the tail. Thus, this hypothesis predict s that the non-autotomous base of the tail should be longer in male th an in female lizards. We tested this hypothesis in four species of lac ertid lizards. Males have on average one to two non-autotomous vertebr ae more than females, and the sexual difference in length of the non-a utotomous tail base remains constant over the entire body size range. In addition, the first functional autotomy plane in males is usually l ocated on, or is distal to, the vertebrae from which two hemipenial mu scles take origin. These observations support the view that functional demands of the male intromittent organs impose constraints on the abi lities of tail autotomy. In a natural population of Lacerta vivipara, the proportion of tail breaks that occurred at very short distances fr om the base was highest in females, indicating that the small sexual d ifference in length of the non-autotomous tail part is of functional s ignificance. Total length of the tail was largest in males. This can b e 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.