Testing the thermal melanism hypothesis for Cape Cobras (Naja nivea) using community science photographic data

Abstract

Animal colour is a highly adaptive phenotypic trait that can respond to several selection pressures, including those facilitated by variations in climate. The thermal melanism hypothesis predicts that for ectotherms, selection for darker phenotypes should be highest in cooler areas because darker pigmentation should provide thermoregulatory advantages. We tested whether intraspecific variation in colour distribution of Cape Cobras (Naja nivea) conforms to this hypothesis using a dataset of ∼800 georeferenced photographs of cobras available from community science platforms. We scored the dorsal colouration of snakes in each photograph and tested for associations between snake colours and climate variables at those locations. Our results provide strong evidence to suggest that temperature and solar radiation are important predictors of N. nivea colour occurrence, whereas elevation and precipitation are not. Overall, darker snakes have a significantly higher probability of occurrence in colder areas with low solar radiation than lighter snakes, which are more likely to occur in hotter areas with more solar radiation. Our study is the first to provide evidence for thermal melanism in a sub-Saharan African snake species, which was made possible by the availability of community science data.