Plastic responses to four environmental stresses and cross-resistance in a laboratory population of Drosophila melanogaster

1. Acclimation or hardening to one stress in arthropods can lead to a plastic response, which confers increased resistance to other stresses. Such cross-resistance may indicate shared physiological resistance mechanisms and a possibility of joint evolution for resistance traits. 2. In this study, we tested for cross-resistance using Drosophila melanogaster as a model system. Adult females were assayed for resistance to cold, heat, desiccation and starvation following cold acclimation, heat hardening, desiccation hardening and starvation acclimation, resulting in 12 pretreatment-by-test combinations for estimating potential cross-resistance effects. The acclimation / hardening regimes were chosen so that flies enhanced their resistance to the same type of stress as that used for the particular pretreatment. 3. Two cases of cross-resistance were found, with desiccation-hardened and starvation-acclimated flies being more resistant than control ones in heat and desiccation resistance tests, respectively. In four cases, no acclimation / hardening effect was observed, and for six pretreatment- by-test combinations, the effect of acclimation / hardening was negative. 4. We also revealed that heat and desiccation hardening as well as acclimation to starvation had a cost under non-stressful conditions leading to reduced longevity. Cold acclimation did not affect longevity, although its effect was difficult to estimate precisely: during pretreatment at a low temperature, biological ageing of the flies might be delayed. 5. The pattern of acclimation / hardening responses considered in the context of literature data on stress resistance indicates that expression of heat-shock proteins is not likely to contribute to the observed cross-resistance, but other probable general stress resistance mechanisms such as reduction of metabolic rate and accumulation of energy reserves might be involved. 6. The lack of cross-resistance induced by acclimation / hardening treatments suggests that in an environment with multiple stresses, evolution of shared protective systems associated with plastic responses may be constrained.