EFFECTS OF POPULATION DENSITY AND TEMPERATURE CONDITION ON FITNESS IN DROSOPHILA MELANOGASTER

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Abstract
By using homozygous or heterozygous flies of 2 strains of D. melanogaster, the effect on fecundity (egg production) of adult density and fluctuating temperature were investigated. Fecundity was strongly influenced by adult density and by the temperature condition, i.e., egg production was lower in the higher density and under the fluctuating temperature (a 20.degree.-30.degree. C cycle per day) in both strains. The mean number of eggs laid by heterozygous flies was larger than that laid by homozygous flies. However, the decrease in oviposition under the fluctuating temperature was more pronounced for heterozygous flies than for homozygous ones of both strains. In order to examine the change of the daily egg production, the regression coefficients of mean number of eggs per day and the (c)-values were estimated under various conditions. The (c)-value and the absolute value of the regression coefficient were larger for homozygous flies, in the crowded condition and under the constant temperature than for heterozygous ones, in the uncrowded conditions and under the fluctuating temperature, respectively. Mortality was related to the regression coefficient of daily egg production. Therefore, mortality (longevity) can be predicted from this coefficient. Also, mortality was different between the sexes, and the difference was affected by temperature. The effect of the fluctuating temperature on fecundity and mortality was similar to that of fluctuating light.