Seasonal Variation in the Time Course of Thermal Acclimation in the Crayfish Orconectes rusticus

The time courses of thermal acclimation for heat tolerances (critical thermal maxima, CTMax) and cold tolerances (critical thermal minima, CTMin) were examined in winter and summer for the crayfish Orconectes rusticus. The CTMax and CTMin were monitored at various intervals during a low (5° C) to high (25° C) temperature transfer or a high (25° C) to low (5° C) temperature transfer (summer only). CTMax and CTMin were higher in summer than in winter throughout most of the low to high temperature time course. Additionally, the loss of cold resistance and the gain in heat resistance occurred more rapidly in summer than in winter. The loss in cold resistance and gain in heat resistance were faster than their counterpart gain and loss in the high to low temperature transfer. Certain of these resistances for O. rusticus approached its range of ecologically encountered temperatures, and these acclimation responses may thus be adaptively important. Furthermore, the seasonal adjustments of the time courses of thermal acclimation enhance the ability of this species to compensate for changes in its natural environment.