An experimental study of genetic drift for two quantitative traits in Tribolium

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Abstract
Genetic drift for two quantitative traits, pupal weight and reproductive fitness as measured by progeny numbers, was investigated in 48 populations of Tribolium castaneum randomly mated over 20 generations. The experiment involved 12 replicate populations for each of four constant sizes (5, 10, 25, and 50 pairs of parents) with both traits observed each generation on a random sample of offspring. Observed drift variances for both traits, calculated each generation as the variance among the means of replicate populations were significantly less than those theoretically expected from estimates for additive genetic variance and effective population size. Stabilizing selection, arising from an intermediate phenotype being favored by natural selection, appeared to be the major factor countering genetic drift.