Egg energetics, fertilization kinetics, and population structure in echinoids with facultatively feeding larvae

Larvae of marine invertebrates either arise from small eggs and feed during their development or arise from large eggs that proceed to metamorphosis sustained only from maternal provisioning. Only a few species are known to possess facultatively feeding larvae. Of about 250 echinoid species with known mode of development, only two, Brisaster latifrons and Clypeaster rosaceus, are known to develop through facultatively planktotrophic larvae. To obtain more information on this form of development and its consequences, we determined egg size and egg energetic and protein content of these two species. We found that eggs of B. latifrons resemble those of species with nonfeeding larvae in these characteristics more than those of C. rosaceus. We also compared DNA sequences of the cytochrome oxidase (COI) gene from the Caribbean C. rosaceus to those of the sympatric planktotrophic developer C. subdepressus and also to those of the eastern Pacific species C. europacificus to estimate the degree of divergence between species with different developmental modes. Comparison of COI sequences of C. rosaceus from Panama and Florida revealed that there is no geographic differentiation in this species. Cross-fertilization experiments between C. rosaceus and C. subdepressus indicated that bidirectional gametic incompatibility has evolved between the two species.