ACCLIMATION AND SELECTION FOR INCREASED RESISTANCE TO THERMAL-STRESS IN DROSOPHILA-BUZZATII

Direct selection for increased resistance to a heat shock (41.9 degree s for 90 min) was carried out using two replicate lines of Drosophila buzzatii that were derived from a large base population. Selected indi viduals were first acclimated to high temperature before selection, wh ile control individuals were acclimated but not selected, and selectio n was performed every second generation. Resistance to heat shock with acclimation increased in selected lines. Without acclimation, a corre lated smaller increase in heat-shock resistance was suggested. Surviva l of males was higher than that of females in all lines when tested wi th acclimation, but with direct exposure to high temperatures, surviva l of females was greater than that of males both in selection and cont rol lines but not in the base population. From analysis of reciprocal cross progeny between lines, one selection line was found to possess a dominant autosomal factor that significantly increased resistance of males much more than resistance of females. Also suggestive was recess ive traits on the X chromosome in both selection lines that increased thermotolerance. No cytoplasmic effects were found. After accounting f or other effects, survival of F-1 flies was intermediate, suggesting t hat additive variation is present for one or more of the autosomes.