Effects of Population Density and Temperature Condition on Fitness in Drosophila Melanogaster

Using the Oregon-R strain of Drosophila melanogaster, the pre-adult fitness components of developmental time and viability were estimated under various environmental conditions of larval density and temperature. The results show that: (1) The eclosion patterns acquired a circadian rhythm under fluctuating temperature conditions. (2) Developmental time was delayed not only by increasing larval density, but also by fluctuating temperature. (3) Though the pre-adult viability decreased with increasing larval density, it did not decrease with fluctuating temperature. (4) The correlations between developmental time and pre-adult viability under the constant and fluctuating temperatures were -0.55 and -0.31, respectively. (5) The coefficients of variation for pre-adult viability were larger than those for developmental time. Moreover, under the fluctuating temperature and in the low larval density, they were larger than under the constant temperature and in the high larval density.These results suggest that in general the pre-adult fitness components are strongly influenced by environmental conditions. The fitness components, therefore, must be carefully estimated by considering the effects of environmental conditions.