SPERM CHEMOTAXIS IN THE HYDROMEDUSAE .1. SPECIES-SPECIFICITY AND SPERM BEHAVIOR

Egg extracts from 32 species of marine hydromedusae, siphonophores and sessile hydroids were tested for sperm attracting activity using the sperm of all species in both homo- and heterospecific combinations. Species-specific sperm chemotaxis could be demonstrated in nearly every species tested. Of the 1,024 possible combinations, 272 could not be attempted for lack of material. Of the 752 which were carried out, only 13 heterospecific cross-reactions were found. The bulk of these involved reactions which were either weaker in the heterospecific direction or unidirectional. The sperm behavior in response to both homospecific and heterospecific egg extracts is described. In the latter case, no changes in sperm motility or direction of movement were observed. In the former case, the sperm show turning behavior which brings them closer to the source of the extract. Since most of the Hydrozoa tested share the same habitat and are reproductively active at the same time of year, it appears that species-specific sperm chemotaxis may be a significant mechanism for both ensuring fertilization in an environment which subjects the gametes to massive dilution and preventing hybridization. © 1979 Springer-Verlag.