SEXUAL DIMORPHISM OF TAIL LENGTH IN LACERTID LIZARDS - TEST OF A MORPHOLOGICAL CONSTRAINT HYPOTHESIS

Males of many lizard species have longer tails than similarly-sized fe males. We hypothesized that this dimorphism is induced by a longer non -autotomous tail part in males, which is associated with the presence of the copulatory organs at the tail base, and presumably reduces the males' ability to escape predation by tail shedding. A compensatory me chanism would be an increase of total tail length in males, to achieve equal lengths of the autotomous tail part in both sexes. A critical p rediction of this 'morphological constraint' hypothesis is that the ex tent of dimorphism in total tail length increases with the magnitude o f sexual differences in length of the non-autotomous tail base. We tes ted this prediction through a comparative study in a small clade of la certid lizards. Within each of nine species, sexual differences in len gth of the non-autotomous tail base and in total tail length do not ch ange with body size. All species, except one, exhibit a clear male-bia sed dimorphism in length of the non-breakable rail base. In all specie s studied, males have longer tails than females. We used the method of phylogenetically independent contrasts to explore the interspecific r elation between dimorphism in length of the tail base and sexual diffe rences in total tail length. Contrary to our prediction, we found no e vidence for a positive correlation between the extent of dimorphism in both traits. Thus, constraints imposed by the male copulatory organs on tail autotomy do not seem to be a significant factor in the evoluti on of dimorphism in tail length in this clade of lacertid lizards.