application/pdf 紀要論文 Many species of reef-building corals spawn gametes synchronously in the reef, and hybridization has been supposed in such mass-spawning events. We conducted crossing experiments and molecular phylogeny with a number of mass-spawning species in the major coral genus Acropora. Interspecific fertilization at high rates was observed in several combinations of particular species despite very different morphologies. The hybrid larvae developed normally, and contained two allelic sequences of a marker gene inherited from the parents in the Mendelian manner. Molecular phylogenetic analyses provided strong evidence that a DNA polymorphism is shared by the hybridizing species. These reproductive and genetic characteristics are consistent with a species complex under the separation or fusion processes predicted in reticulate evolution. Synchronous mass spawning may facilitate the unique evolutionary history in corals.