Unravelling genetic structure of the neotropical freshwater crab Sylviocarcinus pictus (Decapoda, Trichodactylidae) along the rapids-dwelling Xingu River, Amazon basin

Abstract

Sylviocarcinus pictus is a freshwater crab widely distributed across the Amazon basin and coastal basins of northern South America. In the Xingu River basin, Pará, Brazil, the species is found from its middle portion up to the confluence with the Amazon River. This extensive distribution led to questions about the influence of the Volta Grande do Xingu rapids on genetic diversification between populations above and below this area. To explore this hypothesis, 39 mitochondrial gene sequences (COI and 16S rRNA) from 22 samples collected from both areas were analysed in a phylogeographic context. Bayesian Inference and haplotype networks revealed at least two genetically distinct lineages of S. pictus in the Xingu River. The resulting genetic structure found within these populations raised questions about the taxonomic cohesion of the taxon and the potential existence of cryptic species that warrant further investigation. To the best of our knowledge, this is the first molecular study on the genetic structure of a Sylviocarcinus species from the Amazon basin. Given the novelty and the underestimated diversity in this region, we advocate for additional studies on morphological and taxonomic approaches about this taxon to contribute to a future understanding of the evolutionary history of the genus.