Looks can be deceiving: species delimitation reveals hidden diversity in the freshwater crab Aegla longirostri (Decapoda: Anomura)

Aegla is the most abundant and diversified genus of freshwater crabs from southern South America. Despite the high number of species described, their morphological diagnostic characters are not fully informative and exhibit little variation, which could result in cryptic species, as subtle interspecific differences can be easily overlooked. The aim of our study was to estimate the phylogenetic relationships and phylogeographic patterns of diversity of Aegla longirostri to test the hypothesis that this species represents a complex of cryptic species. We analysed 17 populations using three molecular markers. The analysis showed that A. longirostri constitutes a polyphyletic group; our trees suggest the presence of two major clades composed of many well-supported subclades that, despite being geographically close, are genetically distinct from each other. Surprisingly, species delimitation methods indicated the presence of at least 14 potential species. Our results suggest that the real diversity of aeglids may be largely underestimated and we discuss the conservation implications of cryptic diversity for this group. Given that prioritization of habitats for conservation often relies on estimation of species richness, endemism and conservation status coupled with the fact that several Aegla species are endangered, it is imperative to accurately quantify the hidden diversity of aeglids.