Relationships of mineralized dermal layer of mountain endemic miniature frogs with climate

Abstract

The mineralized dermal layer (MDL) is found in most terrestrial anurans. Its thickness represents on average up to 8% of that of the entire skin. It has been proposed that it may reduce body water loss, act on homeostasis, support skin structure, or conversely, it may be a currently functionless trait constrained by groups' evolutionary history. We described the MDL morphology of 11 Brachycephalus species, terrestrial, miniaturized and microendemic anurans, and tested for its relationship with climate of higher latitude regions of the Atlantic Rainforest of Brazil. All species presented MDL, described with two distinct morphological patterns: homogeneous or heterogeneous MDL, the latter distinguishable by MDL with dorsal or lateral expansion, sometimes up to the limit of the epidermis and comprising up to 50% of the thicknesses of the entire skin. Climate differed between locations by MDL morphological group, less rainy or seasonally less rainy where species with heterogeneous MDL occur. Our results indicate that the abundance of calcium in MDL and its heterogeneous condition suggest its adaptive function in reduce water loss. Such adaptations in anurans in very humid highlands reinforce the mountains' propensity for rapid loss of humidity, demystifying them as an extremely abundant source of water. This is the third study that tested the relationship between the MDL morphology and the environment where species occur and the first that correlated this structure with the climate of anurans of the same habit and distributed in a single habitat, the Atlantic Rainforest.