SEXUAL DIMORPHISM IN 2 GIRDLED LIZARD SPECIES, CORDYLUS-NIGER AND CORDYLUS-CORDYLUS

The extent of sexual selection in two girdled lizard species was evalu ated by measuring sexual dimorphism in those characters normally affec ted by sexual selection. Neither Cordylus niger, a cool-adapted specie s, nor C. cordylus, a warm-adapted species, displayed any notable sexu al differences in asymptotic body sizes, but both species displayed sl ight dimorphism in head size measurements. The C. niger sample contain ed more large males than large females, which may be attributed to a l ower growth rate in females. In the cool Saldanha area, females of bot h species lack generation glands. in the warmer Gansbaai area, these g lands are present in females of C. cordylus, but in lower numbers than in males. Sex ratios favouring females, have been recorded for both s pecies. The observed sexual dimorphism in the two species seems to be mainly the result of differential energy allocation by females, and no t of sexual selection per se.