Based upon the results, variations between sexes of P. canaliculata can be due
to differences in the height of the spire and differences in shell opening. The height of
the spire is related to the gastropod’s natural response for survival (Borra, 2006).
Differences in the shape of the shell opening could be attributed to predatory defense
of the snail. The shape of the shell opening or the aperture is the best way to prevent
shell entry as frequently performed by predators such as decapods (DeWitt, 2000).
Narrow apertures are a potentially important defense in freshwater. Conversely, wider
aperture indicates vulnerability to predation (Williams, 2005). It could be inferred that
predators may affect apertural shape of the freshwater snails.
Sexual dimorphism in P. canaliculata has been inferred on size differences
where females are larger than males (Estebenet and Cazzaniga, 1998). In addition to
size dimorphism, qualitative analysis revealed that there appears to be variation in the
shape of the aperture and operculum where females have broader mouth and a
concave operculum and the males a convex operculum (Cowie, 2006). Since theoperculum is located in the opening or the apertural portion of the shell it is argued to
be affecting its over-all shape patterns.
The results of the current study suggest the presence of sexual dimorphism in P.
canaliculata applying the quantitative methods of geometric morphometrics. These
methods are effective in the determination of sexual dimorphism in the shell shape of
P. canaliculata. The applications of GM tools are efficient in quantitatively describing
shape variations and differentiate between sexes of P. canaliculata. Describing sex
differences in the snail’s shell using various characters like the ventral/aperture,
dorsal, and top/whorl portion quantitatively are efficiently done using GM analysis.
This study indicates that geometric morphometric methods are useful in detecting
subtle differences between sexes and to understand the patterns of shell shape
variation and can be used to advance taxonomic and micro-evolutionary studies of
gastropods. Further studies using correlation of different shell shape characters is
highly recommended in order to determine sexual shell dimorphism in gastropods.