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

1. The thermal tolerance of adult Asellus aquaticus was determined dur ing acclimation from 10 to 20-degrees-C and 20 to 10-degrees-C. 2. The rmal tolerance was established by imposing a temperature rise of 12-de grees-C/h. The temperature at which righting reflex was lost was consi dered to be the critical thermal maximum (CTMax). 3. This parameter ca n be determined repeatedly in the same individual, reliably and with c onstancy over time. 4. The CTMax increased by 4-5-degrees-C by acclima tion 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-degree s-C than from 20 to 10-degrees-C. 5. No narrowing of the range of inte rindividual variation was found in the thermal acclimation of CTMax du ring the process of the gain or loss of acclimation. 6. No evidence wa s found to support the proposal [Ushakov B. P. and Pashkova I. M. (198 4) J. therm. Biol. 9, 1-6] that a negative correlation occurred betwee n the individual value of CTMax and the extent of its change during th e process of acclimation.