Effects of relative emergence time on heat stress resistance traits, longevity and hsp70 expression level in Drosophila melanogaster

Fast development is considered selective advantage in Drosophila as the pre-adult life stages can expect to be subjected to decreasing food quality and increasing larval competition with time. However, trade-offs between fast developmental time and other life history traits are known. Here, we investigated some environment-dependent trade-offs between relative emergence time and longevity, heat resistance and Hsp70 expression. The relative emergence time had large effects on these traits, and on average flies with intermediate emerging times were performing best. However, sex and environmental interactions were also found. The heat-shock survival and heat knock-down tests showed similar interactions with developmental conditions. Longevity and Hsp70 expression also showed similar environment-dependent interactions, but different from the heat resistance traits. The results suggest that emergence time not only can be correlated with size and fecundity, but also with stress resistance and probably other fitness traits. It is possible that individuals that have developed under low levels of stress benefit from the activation of the stress response system that has been shown to have impact on many traits. In a natural environment, which often will be stressful, selection might act upon this trade-off increasing general performance in the specific environment. (C) 2004 Elsevier Ltd. All rights reserved.