Sexual Dimorphism and Sex Ratio in a Terrestrial Girdled Lizard, Cordylus macropholis

The large-scaled girdled lizard, Cordylus macropholis, uses the succulent Euphorbia caputmedusae as microhabitat in the dry western coastal regions of South Africa. Up to nine individuals were found to share the same plant shelter. No cases were recorded where two or more adult males shared a plant. Groups consisting of an adult pair and a varying number of juveniles predominated, but several cases were recorded where an adult male shared a plant with more than one adult female. The largest individuals in the sample were females. The axilla-groin length of adult females was significantly larger than in males, but males had larger heads and longer tails than females. Adult males had twice the number of femoral pores as females and also significantly more generation glands. Neonates had the same number of pores as adult males indicating that males and females are born with the same number of pores, but that the outer pores degenerate in females during maturation. The ratio of adult males to adult females was highly skewed towards females (1:2.39). This female-biased sex ratio was also observed in the juvenile size class (1:2.07). The scar incidence recorded for adult males was two times that recorded for adult females.