Shell geometric morphometrics in Biomphalaria glabrata (Mollusca: Planorbidae) uninfected and infected with Schistosoma mansoni

Abstract

Freshwater planorbid mollusks belonging to the genus Biomphalaria act as intermediate hosts for Schistosoma mansoni, the etiological agent of human intestinal schistosomiasis, in the Neotropical Region. Identification of Biomphalaria spp. are carried out based on morphological characters, and the Schistosoma infection are determined by the presence of cercariae (verified through microscope preparation and mounting). Recently, the geometric morphometrics has proven to be a useful tool for determining shape differences in disease vectors arthropods. Due to this, we used geometric morphometrics to determine Biomphalaria glabrata shell differences (shape and size) between uninfected and infected specimens. We digitalized 12 anatomical points over the shell left side (from umbilicus to the last whorl) by combining type I and II landmarks and sliding semilandmarks; the coordinates were aligned by generalized Procrustes analysis. Principal component analyses were implemented for examining main variation axes, and discriminant analysis for testing group membership significance. We found significant separation between infected and uninfected shell conformation. All specimens were 100% correctly classified. The main differences occur in the peristome. The Kruskal-Wallis test finds significant differences in shell isometric size among infected and uninfected specimens. These findings correspond to other studies of traditional morphometrics, that infected snails showed the reduction in shell size in contrast to those uninfected specimens