Boundaries of Morphological and Molecular Variation and the Distribution of a Miniaturized Froglet, Brachycephalus nodoterga (Anura: Brachycephalidae)

Abstract

Most miniaturized froglets of the genus Brachycephalus occur in isolation in slopes of mountain ranges at elevations varying from 600 to 1,800 m in the Atlantic Forest of eastern Brazil. For organisms such as Bracycephalus with spatially discontinuous distributions, a fundamental task is to determine whether observed patterns of variation are consistent with geographic differentiation among allopatric populations within a single species or are suggestive of a potential species boundary. We address this problem by focusing on continental and island population samples potentially assignable to Brachycephalus nodoterga (Anura: Brachycephalidae) from the perspective of variation in qualitative and quantitative morphological traits and DNA sequences. Population samples from continental and island populations share color characteristics, qualitative traits, and multivariate patterns of variation and covariation in cranial metric traits. Comparative analysis of DNA sequences showed the magnitude of molecular distances between B. nodoterga and Brachycephalus ephippium to be 1 order of magnitude larger than molecular distances within B. nodoterga and B. ephippium. We interpret the combined morphological and molecular evidence to indicate that continental and island population samples examined here are conspecific. Therefore, by defining species boundaries for B. nodoterga, we also established minimal estimates of its distribution.