Behavioral hypothermia and survival of hypoxic protozoans Paramecium caudatum.

Hypoxia has been shown to elicit behavioral hypothermia in a number of different metazoan species, all with nervous systems. The protozoan, Paramecium caudatum, has no nervous system and was not expected to display behavioral hypothermia. However, this species was also found to select a lower temperature in a thermal gradient under hypoxic conditions. This response proved to be beneficial as survival of hypoxic paramecia was greatly increased at lower temperatures. This unicellular species may provide a useful model to investigate the cellular and molecular basis of adaptive thermoregulatory behavior.