Sexual Dimorphism in Namibian Endemic Herero Nama Lizards ( Namazonurus pustulatus)

Abstract

Sexual dimorphism in lizards is broadly attributed to intrasexual differences in morphology that affect fitness. In the lizard family Cordylidae, commonly known as girdled lizards, sexual dimorphism is common. Differences in morphological traits (e.g., body and head size) between females and males are useful for describing sexual dimorphism, and examining other traits (e.g., scar frequencies and color) is useful for understanding the selective pressures driving sexual dimorphism in cordylids. Recent morphological studies in Cordylidae reveal sexual dimorphic biases where males have larger heads, but either sex may have larger bodies. In this study, we examined body size, head dimensions, and other traits that commonly differ between sexes to identify sexually dimorphic traits and understand selective pressures in the Namibian endemic cordylid Namazonurus pustulatus (Herero Nama Lizard). We measured 224 field and 10 museum specimens within the known distribution of N. pustulatus. Our results indicate that females were larger in snout-vent length (SVL), axilla-to-groin length, and mass, but males were larger in head width and head length. Allometric growth in juvenile head dimensions was greater than that in adults. Segmented regression analyses indicated a change in growth rate of approximately 68.3-70.0 mm SVL, which we associated with sexual maturity. Adults of both sexes were larger at low elevations (1200-1700 m above sea level) than adults at high elevations (2000-2500 m above sea level), but there was no difference in head height. Epidermal glands (generation glands and femoral pores) scaled with SVL. No differences in scar frequencies were identified, but frequencies were higher than any other cordylid species recorded to date. We attributed larger female size to fecundity selection and larger male head size to sexual selection. This work establishes the first detailed biometric characteristics of the species, fills the missing literature gap of sexual dimorphism information from a species in the Namazonurus clade, and is the first to examine sexual dimorphism in a Namibian endemic cordylid.