First identification of interspecies hybridization in the freshwater stingrays Potamotrygon motoro and P-falkneri (Myliobatiformes, Potamotrygonidae)

The stingrays Potamotrygon motoro and P. falkneri occurred in sympatry in the Paraguay, Lower and Middle Parana River, and belong to distinct ecomorphological groups. The construction of a hydroelectric dam in Itaipu in 1982 facilitated the invasion of Upper Parana River by both species with unpredictable ecological consequences. The aim of the present work was to evaluate the putative hybridization between these species, using mitochondrial (COI and CytB) and nuclear microsatellite markers. Diagnostic nuclear (Pm 21 and Pm 25 microsatellites) and mitochondrial (Hap1 present in P. motoro, Hap2 and Hap3 present in P. falkneri) DNA markers enabled us the evaluation of hybridization processes. Four individuals morphologically characterized as P. motoro but showing P. falkneri mtDNA haplotypes were suspected to be the result of hybridization and were further analyzed with microsatellites. These individuals showed the combination of diagnostic alleles for both species, thus demonstrating for the first time the occurrence of hybrids between species of stingrays.