Selection at the alcohol dehydrogenase locus of the olive fruit fly dacus oleae under artificial rearing

Abstract

In colonies of the olive fruit fly Dacus oleae maintained on an artificial substrate, an allele of the ADH locus whose frequency in natural populations is about 1 per cent increases in frequency to about 40 per cent within 6 generations of artificial rearing; the allele most common in natural populations suffers a compensatory decrease from 65 per cent to 30 per cent; a third allele is only slightly affected. This rapid genetic change coincides with an initial negative population growth rate followed by gradually increasing rates, an indication that the selection associated with this change has a toll on the colony’s growth. Estimation of relative fitnesses shows that under artificial rearing, heterozygotes are on average twenty times as fit as homozygotes. These are probably the largest selection differentials reported for allozymes, and are comparable only to differentials for tolerance to heavy metals in plants. The hypothesis of linkages of the ADH alleles with other genetic elements (e.g., chromosomal inversions), which are the targets of selection, cannot be excluded. The study demonstrates the types of selection pressures that may operate on newly established colonies of “domesticated” insects and the genetic changes that may result from them. © 1982 The Genetical Society of Great Britain.