Mitochondrial genetic variation of endemic stingray Potamotrygon magdalenae (Myliobatiformes: Potamotrygonidae) in the middle Magdalena River basin, Colombia

Potamotrygon magdalenae is the only freshwater stingray species reported to be endemic to Colombia, inhabiting the Magdalena-Cauca, San Jorge, Atrato, and Catatumbo River basins. While aspects of its ecology, reproduction, and biochemistry are well understood, its population genetics remain underexplored, particularly given the various threats it faces. To assess the population structure of P. magdalenae, we analyzed mitochondrial DNA sequences of the MT-CYB gene from 60 individuals sampled across three swamps in the middle Magdalena River basin. Our analysis of 693-bp sequences revealed 24 variable sites across 22 haplotypes (hd = 0.83277, π = 0.00246). Significant gene flow was observed between the swamps, supporting the hypothesis that P. magdalenae constitutes a single panmictic population (ΦST = -0.0083, p = 0.68035). Tajima’s D test (D = -1.62, p < 0.05) and Fu’s Fs-test (Fs = -4.59, p < 0.02) indicate a recent population expansion following a bottleneck event, likely due to habitat degradation, despite the limitations of molecular marker. No genetic differentiation was found across the 200 km study area, and genetic estimates were comparable to those of other fish species endemic to the Magdalena River.