Structure and genetic diversity of Macrobrachium amazonicum complex

The present study evaluated the phylogenetic relationships and the population structure in the 'Macrobrachium amazonicum' species complex, including M. amazonicum and M. pantanalense based on Single Nucleotide Polymorphism (SNP) markers. We analyzed specimens from three main genetic lineages (Clade I: M. amazonicum - Santarém-PA; Clade III: M. amazonicum - Mosqueiro-PA; Clade II: M. pantanalense - Bela Vista de Goiás-GO) and one artificially isolated population (M. amazonicum - Tucuruí-PA). After ddRAD sequencing, a final set of 969 SNPs were genotyped for all populations/species. High levels of genetic structure were observed among the populations of M. amazonicum, particularly when individuals from inland freshwater habitats in Amazon were compared to those from coastal basins, reinforcing the morphophysiological differences among both groups. Moreover, differently from the phylogenetic inferences using mitochondrial DNA markers, all analyses by SNPs confirmed the taxonomic status of M. pantanalense as a distinct species from M. amazonicum. Therefore, we provided the first molecular evidence of speciation in this group, being useful to resolve the taxonomic uncertainties in M. pantanalense. This study also indicates a putative process of ongoing speciation involving the clades I and III of M. amazonicum, thus emphasizing the need for further studies to better assess the relationships between both lineages.