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.

Ladies in armor: A micro‐computed tomographic study of skin calcification in European toads (genus Bufo)

“…If we assume that ACDs have similar functional roles in homeostasis and protection from desiccation as the EK‐layer, the calcification of the skin might be related to the habitat (Elkan, 1968; Moss, 1972; Toledo and Jared, 1993a; Brito‐Gitirana and Azevedo 2005; Lillywhite 2006; Felsemburgh et al 2009; Mari et al, 2022) whereas Ponssa and coauthors (2017) noted a strong phylogenetic signal of EK‐layer thickness. Further research is necessary to determine whether ACDs are common to the genus Bufo and to discover how this trait evolved across bufonids.…”

“…The layer may vary in size and thickness depending on the body part as well as between species and individuals (Elkan, 1968; Toledo and Jared, 1993a; Mangione et al, 2011; Quinzio and Fabrezi, 2012; Ponssa et al, 2017). Calcification increases during ontogeny (Elkan, 1968; Quinzio and Fabrezi, 2012; Chammas et al, 2014) and varies between habitats (Toledo and Jared, 1993a; Barrionuevo, 2017; Mari et al, 2022). The EK‐layer is more abundant in the dorsal than in ventral skin (Elkan, 1968; Azevedo et al, 2005) and can be continuous or be distributed in patches.…”

“…The presence of the EK‐layer may be associated with terrestriality, especially in anurans from drier regions (Elkan, 1968; Toledo and Jared, 1993a, 1993b). It has been hypothesized that the EK‐layer has a role in protection against body water loss (Elkan, 1968; Toledo and Jared, 1993b; Lillywhite, 2006; Mari et al, 2022) and in mineral homeostasis (Moss, 1972; Verhaagh and Greven, 1982; Bentley, 1984).…”