Hermaphroditism and intersexuality in <i>Clava multicornis</i> (Forsskеl, 1775) (Cnidaria: Hydrozoa)
The origin of different variants of animal and plant reproduction remains an actual problem of evolutionary research. The transitions between hermaphroditism and dioecy within the same group of organisms are of particular interest in understanding the evolution of sexual reproduction. Representatives of Cnidaria, the basal group of multicellular animals, are characterized by variety of both asexual and sexual reproduction. Therefore, members of this taxon seem to be promising objects for solving the mentioned problem. For the first time the hermaphroditic colonies of the littoral hydrozoan Clava multicornis (Forsskеl, 1775) from the White Sea were found in natural habitats. This species is characterized by development of gonophores (reduced medusae) upon the hydranths during the period of sexual reproduction and is traditionally considered to be dioecious. There are colonies which hydranths form only male gonophores and colonies which hydranths produce only female gonophores. Such colonies, as well as the hydranths themselves, are called male and female, respectively. We found hermaphroditic colonies with hydranths of different sexes within the same colony. Moreover, intersexual gonophores containing female and male gametes simultaneously were present in such hermaphroditic colonies. Details of the organization of intersexual gonophores were studied by methods of light and electron microscopy. Experimental fusion of hydranths taken from male and female colonies with gonophores at the initial stages of development resulted in emergence of chimeric organisms, in which one of the hydranths formed gonophores of the opposite sex, as well as intersex gonophores. This allowed suggesting that the development of hermaphroditic colonies of C. multicornis in nature occurs due to the fusion of closely growing colonies of different sexes.