Glycogen, protein, and lipid content of green, aposymbiotic, and nonsymbiotic hydra during starvation

Glycogen and protein levels during starvation were determined for symbiotic and aposymbiotic Hydra viridis, and for a brown hydra, H. littoralis. Glycogen content in green hydra increased over a 2‐week period; this appears to be the first report of an animal which accumulates a food reserve during prolonged starvation. These hydra also retained a greater proportion of tissue protein than either of the other groups. Relative utilization of glycogen was similar in aposymbiotic and brown hydra, although initial glycogen stores of brown hydra were ten times larger. Aposymbionts had a proportionately higher rate of protein loss than brown hydra. Food reserves of starving green hydra are augmented by photosynthetic products of symbiotic algae, while starving brown hydra rely on large stores of all reserves, including lipids.