Fertilization mechanisms in hermaphroditic ascidians and nematodes: Common mechanisms with mammals and plants.

Most animals have male and female, whereas flowering plants are hermaphrodites. Exceptionally, a small population of invertebrates, including ascidians and nematodes, has hermaphrodite in reproductive strategies. Several ascidians exhibit strict self-sterility (or self-incompatibility), similar to flowering plants. Such a self-incompatibility mechanism in ascidian has been revealed to be very similar to those of flowering plants. Here, we describe the mechanisms of ascidian fertilization shared with invertebrates and mammals, as well as with plants. In the nematode Caenorhabditis elegans, having self-fertile hermaphrodite and male, several genes responsible for fertilization are homologous to those of mammals. Thus, novel proteins responsible for fertilization will be easily disclosed by the analyses of sterile mutants. In this review, we focus on the same or similar reproductive strategies by shedding lights on the common mechanisms of fertilization, particularly in hermaphrodites.