LERMAN, D.N.*; BETTENCOURT, B.R.; YI, C.H.; KIM, I.; FEDER, M.E.: Response of an hsp70 gene cluster to laboratory and natural selection in Drosophila melanogaster.

We investigated whether polymorphisms at the 87A7 hsp70 cluster, which includes 2 of the 5 genes encoding the inducible molecular chaperone/heat-shock protein Hsp70, respond to natural and laboratory thermal selection in Drosophila populations. Our principal foci were morphs originally reported by Goldschmidt-Clermont (1980, Nucleic Acids Res. 8) as clones 122 and 56H8, and detectable by PCR and RFLP analysis. Allele frequencies covaried with evolution temperature in Drosophila melanogaster lines that have been cultured at different temperatures for more than 20 years and that differ in Hsp70 expression and inducible thermotolerance. Replicate lines evolving at 28�C fixed the 56H8-type morph, while those evolving at 18�C and 25�C fixed the alternative allele. Populations selected for low knockdown temperature (Gilchrist & Huey, 1999, Heredity 83) also differed in 56H8-type allele frequencies from the control and high selected populations. To test if hsp70 allele frequencies covaries with temperature in natural Drosophila populations, we screened flies from “Evolution Canyon,” a small canyon in Israel (200 m wide at base) with north- and south-facing slopes (NFS and SFS, respectively). Allele frequencies in the NFS differed significantly from those in the SFS. Allele frequencies also covaried with collection latitude in Australian Drosophila populations from tropical to temperate (gift of Ary A. Hoffmann). These results suggest that alleles at the hsp70 87A7 cluster respond to thermal selection in both natural and laboratory environments. The functional significance of the alleles themselves (or of sequences linked to these markers) remains to be determined. Supported by NSF97-23298, 99-86158, BSF98-00443, and HHMI.