Quantifying Shape Variation in an Antisymmetrical Trait in the Tropical Fish Xenophallus umbratilis

Antisymmetry is a striking, yet puzzling form of biological asymmetry. The livebearing fish Xenophallus umbratilis exhibits antisymmetry in the male intromittent organ and provides a system that is well-suited for studying the nature of variation in antisymmetrical traits. Using geometric morphometrics, we test the hypothesis that because the gonopodium is critical to fitness there will not be significant differences in gonopodium shape between the two gonopodial morphs in this species. Our results are consistent with this prediction, though we found that gonopodium shape differed with gonopodium size.

Automated summary

This study investigates the symmetry of the male intromittent organ in the livebearing fish Xenophallus umbratilis. The results show that the shape difference in the genitalia is related to the size rather than the morphs.