Fitness of allozyme variants inDrosophila pseudoobscura: II. Selection at theEst-5, OdhandMdh-2loci

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Abstract
SUMMARY: We have studied the effects on fitness of allelic variation at three gene loci (Est-5, Odh, andMdh-2)coding for enzymes inDrosophila pseudoobscura. Genotype has a significant effect on fitness for all six parameters measured (female fecundity, male mating capacity, egg-to-adult survival under near-optimal and under competitive conditions, and rate of development under near-optimal and under competitive conditions). No single genotype is best for all six fitness parameters; rather, genotypes with superior performance during a certain stage of the life-cycle may have low fitness at some other stage, or in different environmental conditions. Heterozygotes are sometimes best when all fitness parameters are considered. There are significant interactions between loci. The various forms of balancing selection uncovered in our experiments may account for the polymorphisms occurring in natural populations ofD. pseudoobscuraat the three loci studied.