STRESS TEMPERATURES AND QUANTITATIVE VARIATION IN DROSOPHILA-MELANOGASTER

Using an isofemale line analysis, we analysed the consequences of extr eme rearing temperatures for genetic variation in quantitative charact ers in Drosophila melanogaster. Three types of characters were used: l ife history (viability and developmental time), body size (thorax leng th and wing length) and meristic (number of sternopleural chaetae and number of arista branches). Phenotypic variation significantly increas ed under stress conditions in all morphological characters studied; fo r viability, it increased at the low stress temperature. Genetic varia tion, measured by the coefficient of intraclass correlation, was gener ally higher at both low and high stress temperatures for thorax length and sternopleural chaeta number. For wing length and viability, genet ic variation was higher at the low extreme temperature. No consistent trend was found for genetic variation in arista branch number and deve lopmental time. Our results agree with the hypothesis that genetic var iation is increased in stressful environments. A possible mechanism un derlying this phenomenon is briefly discussed.