Phenotypic modulation by the substratum of shell sculpture in Semisulcospira reiniana (Prosobranchia: Pleuroceridae

Abstract

Effects of the substratum on shell sculpture in Semisulcospira reiniana were examined in the laboratory. The shell sculpture varied from ribbed to smooth type. Snails grown in a sand aquarium formed ribbed shell more frequently than did snails grown in a pebble aquarium. In one of two experiments, females with class 1 sculpture (having more than two clear ribs) produced higher percentage of ribbed than did females with class O sculpture (completely smooth, having faint ribs, or having one or two clear ribs). The maternal shell type, however, was correlated only with that of offspring's shell formed after birth, and not with that of the newborn shell. These results suggest that phenotypic variation of adult shell sculpture is controlled by environmental factors although it has a genetic basis, and that the sculptures of newborn shell and adult shell are controlled by different genes. Ribbed shells were more tolerant of a crushing load than were smooth shells with the same shell mass. The shell sculpture of S. reiniana may be an adaptation to shell-crushing predators, such as a carp, associated with fine substratum.