Have you ever wondered why everyone cultures Hydra at 18 °C? I have. Hydra does not live at a constant temperature as does E. coli. In the wild, the temperature that Hydra is exposed to varies by geographic location, season, and where Hydra is in the water column. Hydra has been found at the bottom of Lake Superior (Nalepa et al., 1987), where the temperature is 4 °C. We know that Hydra vulgaris begins expressing heat shock proteins at about 23-24 °C (Bosch et al., 1988), yet Hydra does fine when cultured at 24 °C. It would be interesting to search the literature to see when papers first began stating that Hydra was cultured in an incubator at 18 °C. The only reason now for everyone culturing at 18 °C is so that one can compare results from experiment to experiment. Then there is the question of culturing Hydra on a standard light/dark cycle and the more general question of how Hydra senses and responds to light. I’ll post on that at some point.

REFERENCES

Bosch, T.C., Krylow, S.M., Bode, H.R., and Steele, R.E. (1988). Thermotolerance and synthesis of heat shock proteins: these responses are present in Hydra attenuata but absent in Hydra oligactis. Proc. Natl. Acad. Sci. U. S. A. 85, 7927-7931.

Nalepa, T.F., Remsen, C.C., and Klump, J.V. (1987). Observations of Hydra from a submersible at two deepwater sites in Lake Superior. J. Great Lakes Res. 13, 84-87.