Intra- and interspecific and elevational variation in keratinized spines on the head in two closely related Bufo species

Ecological factors such as environment, habitat, and accompanying gradients affect the morphological characteristics of species. Different environmental conditions may induce phenotypic dissimilarities in populations of a species or between closely related species causing character evolution, or they may cause phenotypic plasticity as a response to abiotic and biotic changes in living habitats. The family Bufonidae (Amphibia: Anura) contains stereotypical toads with basic phenotypic features like dry warty skin characterized by spinosity. Keratinized spines were handled in previous studies on the genus Bufo. The studies were focused on the morphological shape differences and mostly intra-specific variations, but ecological parameters were not sufficiently investigated. In this study, we tested the relationship between elevation and the intensity of keratinized spines for Bufo bufo and B. verrucosissimus species in Turkiye. We also assessed intra and interspecific variations for both species based on the spinosity. According to the results of a chi-squared test, a statistically significant difference was found in the intensity of keratinized spines between the sexes of B. bufo. Males mostly had smooth skin without spines, whereas most females had slightly keratinized spines. There was no difference in terms of intensity of keratinized spines between sexes in B. verrucosissimus species. For interspecific variations, we found that female specimens differed in terms of intensity of keratinized between species. Accordingly, all B. bufo females had heavily keratinized spines, whereas most of B. verrucosissimus females had smooth skin. We found statistically significant negative relationships between elevation and intensity of keratinized spines for both species. Accordingly, we assume that the observed disparity related to the intensity of spines demonstrates a species-specific character evolution between species. The differences between elevations might be associated with local climatic conditions and defense strategies against predators in the living space.