Organisms are able to respond to their changing environment, and the extent of the response is thought to depend on the degree of variability and predictability of the environment. Furthermore, the form of this physiological phenotypic plasticity has formed the basis of numerous discussions. However, behavioural regulation of the environment can eliminate the need for physiological alterations and therefore phenotypic plasticity (the Bogert effect). Furthermore, these physiological responses should be investigated in a cost-benefit framework. First, because of the increasing realisation of the importance of cue reliability and variation of the environment for organism response, statistical measures of environmental variability and predictability were investigated. Microclimate temperature data from two localities were used (highly predictably and variable vs. unpredictable and less variable). The proportionate coefficient of variance was most suited to measure variability, whereas Fourier transformation technique seemed to be the most useful estimate of temperature predictability. Acclimation and hardening can often elicit physiological responses that may increase fitness. I investigated life-stage differences in acclimation and hardening ability in the lethal limits and supercooling ability in Paractora dreuxi. The extent of plasticity in both adults and larvae were surprisingly low. The lower lethal limit remained unaffected by acclimation, hardening, and the interaction between acclimation and hardening. However, in the upper lethal limits of adult P. dreuxi a low temperature acclimation significantly increased survival to that of above the warm acclimated individuals. Furthermore, a strong life-stage effect was evident in the supercooling points. While larvae did not show any plasticity, the acclimation*hardening interaction had a significant effect on adults SCP.

Submitted for the Degree of Doctor of Zoology