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The chromosomes of two freshwater stingrays,  Potamotrygon motoro  and  Potamotrygon  sp., from the Amazon River basin in Brazil were investigated using integrated molecular (cytochrome c oxidase subunit 1) and cytogenetic analyses.  Potamotrygon motoro  presented intraspecific variation in the diploid number, with 2n=66 in the females and 2n=65 in the males, while  Potamotrygon  sp. had a karyotype with 66 chromosomes, in both sexes. The C-banding revealed the presence of heterochromatic blocks accumulated in the centromeric region of all the chromosomes in both species. The FISH assays with 18S DNA probes highlighted the terminal region of three or four chromosome pairs in  P. motoro  and seven chromosomes in  Potamotrygon  sp. The rDNA 5S sequences were found in only one chromosomal pair in both species. The interspecific genetic distance based on the COI sequences, between  P. motoro  and  Potamotrygon  sp .  from Amazon River was 10.8%, while that between the Amazonian  P. motoro  and  Potamotrygon amandae  from the Paraná River was 2.2%, and the genetic distance between  Potamotrygon  sp. and  P. amandae  was 11.8%. In addition to the new insights on the cytogenetics of the study species, the results of the present study confirmed the existence of heteromorphic sex-linked chromosomes in  P. motoro .

genetics and molecular biology

Cytogenetic and molecular characteristics of Potamotrygon motoro and Potamotrygon sp. (Chondrichthyes, Myliobatiformes, Potamotrygonidae) from the Amazon basin: Implications for the taxonomy of the genus