Predictive Factors of Chemical and Visual Sensory Organ Size: The Roles of Sex, Environment, and Evolution

Abstract

Animals obtain environmental information using different sensory modalities, and sensory organ size allows inferences concerning the importance of these modalities, which depend on numerous evolutionary or ecological factors. Here, we test whether sex, different evolutionary processes and climatic factors explain chemical and visual sensory organ size in South American Liolaemus lizards as a model. We obtained snout volume (vomeronasal organ proxy), eye surface area, and counted the number of secretory precloacal pores in males and females of 61 species. For evolutionary processes, we tested phylogenetic signal, and different evolutionary models; as well as compared evolutionary rate changes on these traits. We also explored different climatic factors associated with changes in these traits. Our results showed the majority of studied traits had low phylogenetic signal and fit a variety of models. Number of precloacal pores showed greater phylogenetic signal in both sexes and best fit a model of evolution with differential rate transitions model, and have a more complex evolution in females versus males. In males, snout volume correlated positively with precipitation, solar radiation and temperature; while male eye surface area was negatively associated with precipitation, solar radiation and wind speed. However, females appear to be more influenced by intrinsic evolutionary processes whereas males were more influenced by climatic factors. This is the first study exploring the evolution of female precloacal pores in squamates reptiles in general and provides evidence that sex and sensory modality type are strong predictive factors of sensory organ size.