Allometric patterns in Potamotrygon motoro (Myliobatiformes: Potamotrygonidae): insights into sexual and ontogenetic variation

Potamotrygon is the most species-rich genus of Neotropical freshwater stingrays in the Potamotrygoninae, currently comprising 31 species primarily diagnosed by coloration patterns, dermal denticles, and body measurements. Although morphometric characters are fundamental for species descriptions, their growth patterns can vary throughout an individual’s life, especially due to sexual dimorphism and ontogenetic changes. However, these aspects have not been investigated in detail in potamotrygonins. This study aims to explore allometric growth patterns in Potamotrygon motoro, examining ontogenetic and sexual allometry across 25 body measurements. Our results reveal that pelvic fin width and the interocular distance exhibit distinct allometric patterns between males and females. Considering developmental stages, clasper structures in males grow 1.85 to 2.99 times faster in juveniles than in adults. Understanding these allometric patterns is particularly significant for P. motoro, and can aid in species identification and delimitation, given its broad distribution and notable polychromatism.