Intraspecific variation of bone plates in the pumpkin-toadlet Brachycephalus darkside Guimarães et al. 2017 (Anura, Brachycephalidae).

Brachycephalus darkside is a species endemic to the north portion of the Mantiqueira mountain range at Minas Gerais state, Brazil. It was noticed that the population of Parque Estadual da Serra do Brigadeiro presents intraspecific variation on the shape of its external bone plates: frontoparietal, parotic, paravertebral and spinal plates. To recognize the morphological diversity of bone plates, 25 fixed adult specimens were visualized under a stereoscopic microscope, analyzed with ImageJ software and then digitally drawn. To decrease the variation due ontogenetics, we selected specimens of similar size. The posterior margin of the frontoparietal bone can vary in thee shapes: straight (n=12), bi lobed (n=9) or three lobed (n=4); the parotic plate varies being more or less projected posteriorly in relation to the posterior margin of frontoparietal bone; the paravertebral plate can vary in the lateral borders, which can be rounded (most frequently) or straight. The spinal plates vary in shape and number: in some individuals, the first spinal plate can be triangular, circular (both less frequent n=1/n=1 respectively) or trapezoidal (most frequent n=23); in number, the population presented two (n=24) or three (n=1) spinal plates anteriorly to the paravertebral plate. Some specimens presented only anterior spinal plates (n=7) and (n=18) present spinal plate both anterior and posterior to the paravertebral plate. The bone plates of B. darkside possess high level of variation. Some authors suggest that these bone plates may related to water balance, and recent research suggests a possible communication through bone fluorescence.