The proposed project will address the effect of relaxed selection on the accumulation of slightly deleterious mutations and the corresponding impact of this accumulation on population fitness in the fruit fly, Drosophila melonagaster. Sufficiently large populations of Drosophila melanogaster will be propagated for 30-40 generations using the "Middle class neighborhood" approach to shut down selection. For each generation all virgin flies will be randomly divided into pairs (female and male), each pair will be placed in a separate vial, the female will be allowed to lay only a few eggs, and a son and daughter will be chosen randomly from each vial to contribute to the next generation. Using this technique, selection will be absent because each individual will contribute the same number of offspring (two) into the next generation. The change in fitness-related traits (fecundity, mobility, longevity, and competitive ability) will be measured every 5 generations. Natural selection is relaxed in captive animal and civilized human populations, and, consequently, there is no barrier to the accumulation of new slightly deleterious mutations. The relaxation of selection is hypothesized to lead to a gradual decay of population fitness. Determining the rate of decay is important and will provide a basis for designing captive breeding programs in endangered species to reduce the effects of the accumulation of slightly deleterious muations.
