Allometric and trophic effects on shell morphology of Pomacea canaliculata (Caenogastropoda, Ampullariidae) from a geometric morphometrics viewpoint.
Pomacea canaliculata, an invasive apple snail native to South America, is a serious pest of aquatic crops in several parts of the world. The origin of inter-population variation in shell shape is thought to be both genetic and environmental but the reaction norms to specific environmental factors are still poorly understood. Our aims were to analyze the existence of direct and indirect (allometric) effects of food availability (FA) on the shape of young adults of P. canaliculata. Full sibling hatchlings were reared under different levels of FA. Nine landmarks and 10 semi-landmarks were determined on photographs of mature shells and analyzed using geometric morphometrics. In both sexes significant allometry was found: a decrease in the spire height in both sexes, and an increase of the aperture size in males and of the last whorl in females. When this allometric component was removed a relationship between size-corrected shape and FA was found only in females, which were more globose and had a larger aperture when grown under high FA. This effect may be explained by the faster growth of the reproductive organs and the thinner shells of the best fed females.