CR prepress abstract  -  doi: 10.3354/cr00870

ABSTRACT: Regular exposure to a given stressor poses selective pressure towards increased resistance. In high temperature environments this can be mediated through physiological and biochemical adjustments that lead to increased resistance to heat coma. Such adjustments may influence complex traits such as locomoter activity through cascading effects. Alternatively, changes in locomoter activity may change the exposure to the stressor and thereby the importance of the physiological and biochemical adjustments. In this experiment we analysed how selection for heat shock resistance may affect locomotor activity at high temperatures in Drosophila melanogaster. Thus, we compared two lines selected for heat (HS) and cold shock resistance (CS) at four constant high temperatures (range 28-38°C). We also tested the importance of Hsp expression by comparing locomotor activity at the same temperatures of a heat sensitive mutant line (Hsf⁰) where the heat shock factor (Hsf) is non-functional at high temperatures with that of a rescued mutant line (Hsf⁺) with a functional Hsf re-inserted. At moderately stressful temperatures (28 and 34°C) flies from the Hsf⁰ line were more active than flies from the Hsf⁺ line whereas this was reversed at higher temperatures. In the selection lines the CS flies were more active at 28°C but this was reversed at 34°C and 36°C whereas no difference was observed at the most stressful temperature (38°C). This suggests that the lines selected for increased cold tolerance were more stressed at moderately high temperatures and therefore more active in the attempt to escape the stress whereas at higher temperatures their locomotor activity was more compromised than flies from the lines selected for increased heat resistance.