Lifespan extension of Drosophila melanogaster through hormesis by repeated mild heat stress.

We assessed the impact of repeated episodes of a mild heat stress on lifespan, fecundity, heat stress resistance and Hsp70 expression in Drosophila melanogaster. There was a significant increase in lifespan of females repeatedly exposed to a mild heat stress when measured in both a pair and a group situation. There was no effect on fecundity when the flies were first exposed to the mild heat stress at an age later than 3 days old, but when it did occur on day 3, there was a significant effect on cumulative fecundity levels over 18 days. The negative fitness effect appears to be the result of a direct cessation or reduction of oviposition during the first bout of stress exposure, and is influenced by the age at which this first exposure occurs. The mild heat stress had no impact on egg viability. The mild heat stress exposures increased resistance to potentially lethal heat stress and levels of Hsp70 expression in heat-exposed flies were higher than those in controls.