Regulation of the Endosymbiotic Algae in Hydra by Digestive Cells and Tissue Growth

Endosymbiotic algae in hydra release photosynthetically fixedcarbon to the host which augments the animals nutrition duringstarvation. The algae may acquire metabolites from hydra asa source of nutrition when the animals are maintained in thedark. The kind of algae acquired by aposymbiotic hydra is determinedby a recognition phenomenon involving the hosts digestive cellsand potential endosymbionts. The size of the algal populationis related to the necessity of light for maximum algal multiplication,the rate of cell division in hydra, and the potential for heterotrophyby the algae.