Sexual size dimorphism in montane cordylid lizards: a case study of the dwarf crag lizard, Pseudocordylus nebulosus

The aim of this study was to provide information on sexual size dimorphism (SSD) in Pseudocordylus nebulosus and to discuss the observed variation in SSD among montane cordylids. Data for P. nebulosus were recorded in the Landdroskop area in the Hottentots Holland Mountains, South Africa. The total sample of 87 lizards, consisted of 26 adult males, 49 adult females and 12 juveniles. Size at sexual maturity was determined as 60 mm snout–vent length (SVL) for both sexes. Generation glands were found to be present in males only and the number present was significantly correlated to body size. Both adult males and adult females possessed active femoral glands, but males had significantly more than females. Females were found to reach larger body sizes than males, but adult males had relatively larger heads than females. No significant difference in scar frequency was found between male and female samples. The female-biased SSD in P. nebulosus and its sister species, P. capensis, is tentatively ascribed to fecundity selection for offspring to be large at birth in order to survive in a predictable unfavourable environment at high altitudes. Variation in SSD among montane cordylids is discussed and the need for more comprehensive data is highlighted.