Geographic variation in sexual size dimorphism in the rock agama, Agama atra (Sauria: Agamidae)

Abstract

Significant sexual dimorphism in overall size occurs in the rock agama, Agama atra (Sauria; Agamidae), with males growing larger than females. Geographic variation in the degree of sexual size dimorphism also exists, males growing significantly larger than females in Namaqualand and Namibia compared to populations in other areas. Sexual differences in scaling of head, limb and tail dimensions were mainly the result of differential asymptotic sizes reached by the sexes. Head size was also influenced by a faster increase in head dimensions with increasing snout to vent length in males compared to females, probably as a result of sexual selection. In females, scaling of limb and tail dimensions was decreased compared to males, possibly a result of differential energy allocation to reproduction.

Key words: sexual size dimorphism, head size, limb size, tail size, scaling.