The cryptic significance of melanism in cordylid lizards: A case study ofCordylus nigerandC. polyzonus

CORDES, I.G., and P. le F. N. MOUTON. 1995. The cryptic significance of melanism in cordylid lizards: A case study of Cordylus niger and C. polyzonus. J. Herpetol. Assoc. Afr. 44: 16–21. The cryptic significance of melanism in two girdled lizard species, Cordylus niger and C. polyzonus, was evaluated by comparing the melanistic forms with closely related, non-melanistic forms. A simple photographic technique involving colour transparencies and a colour densitometer, was used. The degree of correspondence between the integral density of the dorsal body surface of each lizard and its associated substrate was taken as an indication of the degree of background colour-matching. Inland, non-melanistic populations of C. cordylus and C. polyzonus, were significantly more background colour-matched than a population of the melanistic species C. niger and a melanistic population of C. polyzonus, occurring at the coast. A darkly coloured C. cordylus population, occurring 2 km from the coast, was also less background colour-matched than the inland forms. The results show that the primary function of melanism in cordylid lizards is not a cryptic one. It is suggested that, although not selected for background colour-matching, a black body colour may be advantageous in the avoidance of predators, as it may blend in well with shadows when seen from a distance.