Experimental manipulation of the cost of thermal acclimation in Drosophila melanogaster

Acclimation to environmental change can impose costs on organisms. One potential cost is the energy and nutrients consumed by a physiological response, e.g. the resources required for expression of heat-shock proteins (Hsps). We examined the significance of this cost by genetic manipulation. We isolated four isofemale lines from a Drosophila melanogaster population previously transformed with a hsp70-kcZ fusion. Lines were similar in Hsp70 expression but differed in P-galactosidase expression upon heat shock, and replicates of each line were reared on a high quantity and low quantity medium. Multiple heat shock reduced survival in all lines, but did not increase developmental time. Variation in expression of β-galactosidase among lines, which differed more than 4-fold in response to heat treatment, was unrelated to the decreased survival. Thus the predicted effects of β-galactosidase expression on components of fitness were not evident. The superimposition of costs upon those normal for acclimation had no effect on mortality or developmental time, even when resources were especially limiting.