Sex-related differences in growth and morphology of blue mussels

The morphology and growth pattern of male and female blue mussels (Mytilus edulis) from the north Norfolk coast, UK, were studied. In allometric terms, the external shell parameters of females grew faster relative to shell length than those of males. In absolute terms, females also grew more quickly than males for all external shell parameters and for most internal body parts. At a given age, females are therefore larger than males. Females had a higher shell to tissue weight ratio and a relatively heavier foot than males. A discriminant function incorporating age, weight and shell length, width, and height correctly sexed 81% of individuals in the sample from which it was derived. Both natural and sexual selection may be involved in the evolution of sexual dimorphism in blue mussels.