Survival During Starvation of Symbiotic, Aposymbiotic, and Non-Symbiotic Hydra

Abstract

Many experimental studies on the benefit of endosymbiotic algae to their coelenterate hosts have utilized so-called “aposymbiotic” animals as controls. These individuals, although from a species which normally contains algal symbionts, have no algae. Algae-free individuals may be obtained through experimental treatment; aposymbiotic strains of Hydra viridis have been produced in culture by the use of 0.5 per cent glycerol (Whitney, 1907). Populations of aposymbionts may also be obtained through the culture of eggs of H. viridis which have not been infected with algae. Although these algae-free eggs are apparently produced in nature, no naturally occurring aposymbiotic H. viridis have been reported. Differential survival during starvation has been proposed as one factor which may favor symbiotic green hydra over aposymbiotic forms (Muscatine and Lenhoff, 1965).