Comparative ecology of species in the Lizard Genus Vanzosaura (Squamata: Gymnophthalmidae)

Abstract

Species with broad distributions experience diverse environmental conditions and selective pressures across populations that can drive adaptive responses such as phenotypic plasticity and genetic differentiation. Vanzosaura (Gymnophthalmidae) is widely distributed across South America's open diagonal, occurring in the Cerrado, Caatinga, and Chaco regions of Brazil. We studied body size, sexual size dimorphism, reproduction, and diet in three Vanzosaura species from different ecosystems. Our goals were to evaluate the extent to which traits vary with environmental predictability and to test Boyce's hypothesis that body size is positively correlated with environmental stability. We predicted that species from the more climatically predictable Cerrado (V. rubricauda and V. savanicola) would show larger body size and seasonal reproduction whereas the Caatinga species (V. multiscutata) would exhibit smaller size and continuous reproduction. We found no significant dietary differences; all species consumed primarily Araneae, Orthoptera, and Plecoptera. Clutch size consisted of two eggs, a synapomorphy of gymnophthalmids. Vanzosaura multiscutata exhibited continuous reproduction with sequential clutches and smaller eggs, whereas V. savanicola and V. rubricauda had seasonal reproduction with larger eggs. Morphological analyses revealed sexual dimorphism in V. multiscutata with males being larger, consistent with ecological and reproductive adaptations related to environmental conditions. Vanzosaura savanicola was the largest species. Diet is evolutionarily conserved while ecological factors shape morphology and reproductive strategies. Our results corroborate theoretical predictions from Boyce's hypothesis, highlighting predictable environmental conditions that act as critical selective pressures shaping larger body sizes and associated ecological advantages. The differences in body size and reproductive strategies between Cerrado and Caatinga underscore the evolutionary significance of climatic predictability and resource stability.