A Drosophila melanogaster strain from sub-equatorial Africa has exceptional thermotolerance but decreased Hsp70 expression

Drosophila melanogaster collected in sub-equatorial Africa in the 1970s are remarkably tolerant of sustained laboratory culture above 30 degreesC and of acute exposure to much wanner temperatures, Inducible thermotolerance of high temperatures, which in Drosophila melanogaster is due in part to the inducible molecular chaperone Hsp70, is only modest in this strain. Express ion of Hsp70 protein and hsp70 mRNA is likewise reduced and has slower kine tics in this strain (T) than in a standard wild-type strain (Oregon R), The se strains also differed in constitutive and heat-inducible levels of other molecular chaperones. The lower Hsp70 expression in the T strain apparentl y has no basis in the activation of the heat-shock transcription factor HSF , which is similar in T and Oregon R flies. Rather, the reduced expression may stem from insertion of two transposable elements, H.M.S, Beagle in the intergenic region of the 87A7 hsp70 gene cluster and Jockey in the hsp70Ba gene promoter. We hypothesize that the reduced Hsp70 expression in a Drosop hila melanogaster strain living chronically at intermediate temperatures ma y represent an evolved suppression of the deleterious phenotypes of Hsp70.