Modelling problems in conservation genetics using Drosophila: consequences of fluctuating population sizes


  • This paper is a result of collaborative work between Richard Frankham, David Briscoe and Rod Nurthen (Macquarie, Biological Sciences) that began in 1990 to test theoretical predictions and model problems in conservation genetics using Drosophila. Lynn Wood worth and Meg Montgomery are pos tgradua te students now working on minimum viable populations to conserve endangered species and optimum genetic management for small pedigreed populations of endangered species.

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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 fluctuating population size were examined in small populations of Drosophila melanogaster of the same average size, but maintained using either fluctuating (FPS) or equal (EPS) population sizes.FPS lines were maintained using seven pairs and one pair in alternate generations, and EPS lines 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 heterozygosity (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 average heterozygosities, as compared to theoretical expectations of 3.3 vs. 8.0. Results were generally in accordance with theoretical predictions. Management strategies for populations of rare and endangered species should aim to minimize population fluctuations over generations.