An Ecological Approach to Hydra-Cell Colonization by Algae - Algae/Hydra Symbioses

Abstract

All plants and animals host ecto- and endosymbionts. Living habitats thus outnumber abiotic ones, but their study has not received its due interest. I review data showing colonization, competition, territoriality and the resulting host/symbiont specificity in algae/hydra endosymbioses. In nature we find Chlorella sp./Hydra viridissima and Symbiococcum hydrae/Hydra magnipapillata symbioses. In the laboratory, 18 out of 46 strains of seven free-living species of Chlorella have successfully colonized cells of H. viridissima, and S. hydrae has colonized 15 strains of, in nature, nonsymbiotic hydra. If cultured in the dark, H. viridissima retain their symbiotic chlorellae while H. magnipapillata loose their symbiococci