Cryptic diversity and historical biogeography of a nurse- frog species complex (Allobates tinae)

Abstract

Amazonia continuously reveals outstanding biotic diversity and endemism, but our comprehension regarding their underlying processes has been impaired by knowledge gaps on cryptic taxonomic diversity. Here, we clarified the diversity and historical biogeography of nurse-frogs typical from Brazilian Southwestern Amazonia, the Allobates tinae species complex, using fine-scale population sampling and molecular-based analyses. Fieldwork was conducted at 23 localities across three major interfluves encompassing two well-recognized areas of endemism. Fragments of three mitochondrial DNA genes were sequenced and compared through phylogeographic and phylogenetic analyses. Based on these results, we estimated the species limits and inferred the historical biogeography. We found seven highly supported clades, which were considered as distinct species according to delimitation analyses. However, only two of these clades are taxonomically described, indicating a nearly threefold underestimation of the complex species richness. Major clades showed pronounced genetic distances, strong spatial structuring, and restricted or absent haplotype sharing. However, genetic structure was not predicted by geographic distance, and strong genetic structure among major clades was evident even at smaller geographical scales lacking evident physical barriers. Biogeographic analysis indicated diversification of the A. tinae complex most likely occurred through dispersals followed by speciations. These events started southward from the Guiana Shield during the Miocene, and were followed by sequential secondary northward dispersals along the Pliocene and Pleistocene. Our results indicate combined roles of historical (landscape dynamism) and ecological (environmental heterogeneity) factors driving biotic diversification in Brazilian Southwestern Amazonia.