Functional Ecology, 8(6): 730-737 (Dec 1994)
Costs and Benefits of Activation of the Heat-Shock Response in Drosophila melanogaster

R. A. Krebs, V. Loeschcke


1. The costs of conditioning adult Drosophila melanogaster with a mild thermal stress that activates the genes for heat-shock proteins were examined by comparing the number of offspring produced by females maintained continuously at 25°C with females exposed to a non-lethal stress, 36°C for 75 min, once, twice or three times. The comparison was done under two nutritional treatments, with or without yeast added to the medium.

2. Benefits of conditioning adult D. melanogaster to thermal stress were examined by comparing survival after a severe stress (39°C for 100 min) among flies that were not conditioned with those conditioned once, twice or three times by exposure to 36°C for 75 min. Additional comparisons were made varying either the duration of conditioning or the time elapsed between conditioning and exposure to the severe stress.

3. Fewer offspring were produced by females receiving the conditioning treatment than for those not receiving it and the decrease in fecundity was greater for females conditioned more often. Proportional differences in fecundity were larger for the no-yeast treatment than for females held with yeast.

4. Survival after the severe stress was much greater for flies that were conditioned than for those not conditioned and survival increased with increasing number of conditioning bouts. Survival also was greater for flies conditioned closer to the exposure to severe stress, with the exception that survival for flies conditioned only 2 or 4 h before exposure to severe stress was less than that for those conditioned 8 h before.