VARIATION IN HEAT TOLERANCE IN INDIVIDUAL ASELLUS-AQUATICUS DURING THERMAL-ACCLIMATION

1. The thermal tolerance of adult Asellus aquaticus was determined during acclimation from 10 to 20-degrees-C and 20 to 10-degrees-C. 2. Thermal tolerance was established by imposing a temperature rise of 12-degrees-C/h. The temperature at which righting reflex was lost was considered to be the critical thermal maximum (CTMax). 3. This parameter can be determined repeatedly in the same individual, reliably and with constancy over time. 4. The CTMax increased by 4-5-degrees-C by acclimation at 20-degrees-C as compared with the same animals at 10-degrees-C, a change that was fully reversible by reacclimation to 10-degrees-C. The rate of attainment of acclimation was faster from 10 to 20-degrees-C than from 20 to 10-degrees-C. 5. No narrowing of the range of interindividual variation was found in the thermal acclimation of CTMax during the process of the gain or loss of acclimation. 6. No evidence was found to support the proposal [Ushakov B. P. and Pashkova I. M. (1984) J. therm. Biol. 9, 1-6] that a negative correlation occurred between the individual value of CTMax and the extent of its change during the process of acclimation.