Effects of food availability on asexual reproduction and stress tolerance along the fast-slow life history continuum in freshwater hydra (Cnidaria: Hydrozoa)

Life history theory predicts that reproduction and somatic maintenance are negatively related, but the strength of this relationship is expected to depend on food availability. In this study, we investigated asexual reproduction (budding rate) and oxidative stress tolerance as two opposing facets of life history trade-offs in 17 strains of five freshwater hydra species under experimentally simulated low, medium, and high food availability. Stress tolerance was quantified by exposing animals to exogenous H2O2, which mimics reactive oxygen species arising in vivo. The five species differed in life history traits (low budding rate and high stress tolerance in Hydra vulgaris and H. circumcincta and the opposite in H. oligactis and H. viridissima; low budding rate combined with relatively low stress tolerance in H. oxycnida). Stress tolerance and asexual reproduction increased with food, but there were clear interspecific differences in this relationship. Across all strains, stress tolerance and budding rate were significantly negatively related on the low and medium, but not the high food level. These results suggest that resource allocation trade-offs are involved in determining life history traits in hydra; populations/species can be broadly positioned on a fast-slow life history continuum, and response to variation in food varies along this continuum.