Abstract
BackgroundAmphibians are rapidly vanishing. At the same time, it is most likely that the number of amphibian species is highly underestimated. Recent DNA barcoding work has attempted to define a threshold between intra- and inter-specific genetic distances to help identify candidate species. In groups with high extinction rates and poorly known species boundaries, like amphibians, such tools may provide a way to rapidly evaluate species richness.MethodologyHere we analyse published and new 16S rDNA sequences from 60 frog species of Amazonia-Guianas to obtain a minimum estimate of the number of undescribed species in this region. We combined isolation by distance, phylogenetic analyses, and comparison of molecular distances to evaluate threshold values for the identification of candidate species among these frogs.Principal FindingsIn most cases, geographically distant populations belong to genetically highly distinct lineages that could be considered as candidate new species. This was not universal among the taxa studied and thus widespread species of Neotropical frogs really do exist, contrary to previous assumptions. Moreover, the many instances of paraphyly and the wide overlap between distributions of inter- and intra-specific distances reinforce the hypothesis that many cryptic species remain to be described. In our data set, pairwise genetic distances below 0.02 are strongly correlated with geographical distances. This correlation remains statistically significant until genetic distance is 0.05, with no such relation thereafter. This suggests that for higher distances allopatric and sympatric cryptic species prevail. Based on our analyses, we propose a more inclusive pairwise genetic distance of 0.03 between taxa to target lineages that could correspond to candidate species.ConclusionsUsing this approach, we identify 129 candidate species, two-fold greater than the 60 species included in the current study. This leads to estimates of around 170 to 460 frog taxa unrecognized in Amazonia-Guianas.SignificanceAs a consequence the global amphibian decline detected especially in the Neotropics may be worse than realised.
Highlights
Amphibians are undergoing a drastic global decline [1,2,3,4,5,6,7]
Our analysis suggests that widespread Neotropical frog species do exist [38,39]
Our results clearly show that the number of species is highly underestimated in anurans from the Guianan and Amazonian regions
Summary
The number of amphibian species known to science is increasing with many new species discovered annually [8,9,10,11] These new species descriptions are not the result of changes in theoretical species concepts but rather are a consequence of (1) real first hand discoveries (e.g. phenotypically divergent taxa described using traditional taxonomic practices), due to the exploration of previously poorly known tropical areas [11], (2) diagnoses aided by molecular tools, and (3) the recent appreciation that a combination of slight differences in morphology and ecology (e.g. vocalisation) can be sufficient to characterize new species of amphibians [12] under both evolutionary and biological species concepts. Geographically distant populations belong to genetically highly distinct lineages that could be considered as candidate new species This was not universal among the taxa studied and widespread species of Neotropical frogs really do exist, contrary to previous assumptions. As a consequence the global amphibian decline detected especially in the Neotropics may be worse than realised
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