| Summary: | Hemigrapsus nudus and H. oregonensis, the experimental animals, are subjected to a wide range of temperature and salinity in their natural environment. The influence of seasonal change, and laboratory acclimation to various temperature-salinity combinations in both summer and winter, on heat tolerance was determined. There was a seasonal change in the 50 per cent survival temperature for 12 and 24 hours when summer and winter base lines were compared.
A definite species difference in thermal resistance was present, but both species reacted similarly to any particular temperature-salinity combination. Acclimation to a high temperature in the physiological temperature range generally increased the resistance to lethal temperatures and acclimation to low salinity generally decreased it. High temperature, high salinity was the most favourable acclimation combination to resist lethal temperatures. Gain in heat tolerance after a low temperature history was rapid, less than one week. The low tolerance found in winter animals at the low temperature series was not demonstrated in summer animals acclimated to these same conditions.
Small animals appeared to be slightly more resistant than larger ones. Moulting at the test tolerance temperature adversely affected the resistance. A certain density was necessary to prevent death from overcrowding at lethal temperatures. There was no difference in tolerance between
the sexes. === Science, Faculty of === Zoology, Department of === Graduate
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