Energy investment in nurse eggs and egg capsules in Crepidula dilatata Lamarck (Gastropoda, Calyptraeidae) and its influence on the hatching size of the juvenile

Abstract

In the marine gastropod Crepidula dilatata Lamarck, egg capsule height and width, the weight of the capsule wall, and the number of eggs per capsule increased with the female's shell length. However, since not all the eggs developed (some being nurse eggs), the number of embryos per capsule was independent of the shell length or dry tissue weight of the female parent, as were egg diameter and the number of capsules per brood. More than 90% of the energy invested in the egg mass was allocated to egg production, and less than 8% to constructing the capsules themselves. Small females produced embryos with a lower growth potential than that of embryos from larger females, because the larger the female, the more nurse eggs available to each embryo. The low energy investment in the production of capsule walls may be a consequence of `physical' parental care, because the female lays the capsules on the substratum and covers them with her shell throughout intracapsular development. The mean size of juveniles at hatching increased with the shell length of the female, because more nurse eggs were available to an embryo from a larger female than to an embryo from a smaller one. Larger juveniles may be at a competitive advantage in estuaries, where physical conditions vary over short time intervals and are often unfavourable.