Coral individuality - confluence of change physical splitting and developmental ability of embryos.

Previous studies have suggested that blastomeres from the 2-, 4-, or 8-cell stage of corals have the ability to develop into normal primary polyps. However, it is still not known which developmental stage's blastomere produces which juvenile. In this study, we demonstrated that only the blastomeres with animal hemispheres have the capacity to develop into normal primary polyps. Individuality was evaluated using blastomeres isolated from the corals Acropora digitifera, A. intermedia, Dipsastraea lizardensis, and Favites chinensis. On commencement of embryo cleavage, the animal pole was marked using Neutral red staining, and at the 2-, 4-, and 8-cell stages, embryos were divided into individual blastomeres using glass needles. We found that the survival rate and percentage metamorphosis were higher in the larger-sized blastomeres with animal hemispheres. The vegetal hemisphere alone is incapable of developing into a normal primary polyp; however, a ball-shaped embryo with incomplete mesenteries and no pharynx developed in some cases. These results indicate that the animal hemisphere is needed for corals to develop into normal primary polyps, and that the individuality of corals is possibly determined by a combination of the chance physical splitting of embryos by waves and their innate developmental ability.