SEXUAL DIMORPHISM IN CORDYLID LIZARDS - A CASE-STUDY OF THE DRAKENSBERG CRAG LIZARD, PSEUDOCORDYLUS-MELANOTUS

In a high-altitude population of the Drakensberg crag lizard. Pseudoco dylus melanotus, most adult males, unlike adult females, are brightly coloured, and they are larger in body size and have relatively larger heads than females. Three basic colour phases can be distinguished amo ng the brightly coloured adult males. No apparent differences in repro ductive activity, number and differentiation state of the generation g lands and femoral pores, or scar frequency were noted among the three colour phases. In males the development of bright colours and the diff erentiation of the epidermal glands coincide with the onset of sexual maturity. Sexual dimorphism in head size of adults is due to a decreas e in female head size relative to juvenile head size as well as an inc rease in relative head size of males. Preliminary data indicate a soci al structure of territorial polygyny in P. melanotus and suggest that the dimorphism can partly be ascribed to sexual selection. There are a lso, however, indications of altitudinal variation in the expression o f sexual dimorphism, which may be explained in terms of differential e nergy allocation by females at different altitudes.