MODELING PROBLEMS IN CONSERVATION GENETICS USING DROSOPHILA - CONSEQUENCES OF FLUCTUATING POPULATION SIZES

Many natural populations fluctuate widely in population size. This is predicted to reduce effective population size, genetic variation, and reproductive fitness, and to increase inbreeding, The effects of fluct uating population size were examined in small populations of Drosophil a melanogaster of the same average size, but maintained using either f luctuating (FPS) or equal(EPS) population sizes.FPS lines were maintai ned using seven pairs and one pair in alternate generations, and EPS l ines with four pairs per generation. Ten replicates of each treatment were maintained. After eight generations, FPS had a higher inbreeding coefficient than EPS (0.60 vs. 0.38), a lower average allozyme heteroz ygosity (0.068 vs. 0.131), and a much lower relative fitness (0.03 vs. 0.25). Estimates of effective population sizes for FPS and EPS were 3 .8 and 7.9 from pedigree inbreeding, and 4.9 vs. 7.1 from changes in a verage heterozygosities, as compared to theoretical expectations of 3. 3 vs. 8.0. Results were generally in accordance with theoretical predi ctions. Management strategies for populations of rare and endangered s pecies should aim to minimize population fluctuations over generations .