Natural hyperthermia and expression of the heat shock protein Hsp70 affectdevelopmental abnormalities in Drosophila melanogaster

We demonstrate that natural heat stress on wild larval Drosophila melanogas ter results in severe developmental defects in >10% of eclosing adults, and that increased copy number of the gene encoding the major inducible heat s hock protein of D. melanogaster, Hsp70, is sufficient to reduce the inciden ce of such abnormalities. Specifically, non-adult D. melanogaster inhabitin g necrotic fruit experienced severe, often lethal heat stress in natural se ttings. Adult flies eclosing from wild larvae that had survived natural hea t stress exhibited severe developmental anomalies of wing and abdominal mor phology, which should dramatically affect fitness. The frequency of develop mental abnormalities varied along two independent natural thermal gradients , exceeding 10% in adults eclosing from larvae developing in warm, sunlit f ruit. When exposed to natural heat stress, D. melanogaster larvae with the wild-type number of hsp70 genes (n=10) developed abnormal wings significant ly more frequently than a transgenic sister strain with 22 copies of the hs p70 gene.