Allometric growth and insight on sexual dimorphism in Pomacea canaliculata (Gastropoda: Ampullariidae)

The shape changes associated with increase in size and sexual dimorphism in Pomacea canaliculata are described using bivariate and multivariate statistical analysis. Allometric growth was found in the studied population, the shell becoming relatively more globose and both aperture and operculum becoming rounder as shell height increases. Related to this ontogenetic change in shell shape is a relative increase in body dry weight. Adult snails show sexual dimorphism, males having both aperture and operculum rounder than females. Because juvenile snails do not exhibit these differences in aperture form, shell dimorphism seems to be associated with sexual maturity; that is, it is possibly related to the development of the penial complex. In summer, adult females of any given shell height weigh significantly more than males of equivalent size; this being possibly due to the remarkable development of the albumen gland in this period. Shell dry weight shows great variability in similarly sized snails, this fact being partially ascribable to the seasonal growth pattern of Fl canaliculata in waters showing thermal seasonality.