| heal.abstract |
Previous studies have shown that natural populations of the olive fruit fly, Bactrocera oleae (Gmelin), segregate for 3 electrophoretically distinguishable alleles (allozymes S, F, and I) at the alcohol dehydrogenase (ADH) locus. Allele I is rare, but in colonies maintained on an artificial larval medium its frequency rapidly rises to ≈35%. Analysis of allelic frequency trajectories have suggested strong selection in favor of heterozygotes. Here we report on the results of an extensive study designed to estimate fitness components of the various genotypes at the ADH locus and to identify the stage in the life cycle of the insect at which selection pressure is most intense. Significant differences among genotypes were observed for egg hatchability, larva-to-pupa viability, pupa-to-adult viability, and for egg-to-pupation time. When combined into an overall fitness value, these differences produced clear evidence for heterozygote advantage. In addition, our results reinforce previous claims that selection acts directly on the ADH locus and narrows the time of selection to the early larval stage. The ADH system of B. oleae serves as a model case of a predictable and drastic genetic change that occurs in an insect colony as it adapts to an artificial environment. |
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