Oviposition-site preference in Drosophila following interspecific gene transfer of the Alcohol dehydrogenase locus

The preference of Drosophila females to lay eggs on substrates that do or do not contain alcohol is an excellent system to study the evolutionary genetics of behavior, because (1) there is variation in this behavior within and among species, (2) the behavior is amenable to laboratory investigation, and (3) the behavior presumably has a direct relationship to reproductive fitness. Moreover, a key genetic component of the system, the Alcohol dehydrogenase (Adh) locus, is arguably the most well characterized gene known. However, because the Adh gene and its genetic background are inseparable in reproductively isolated species, it is difficult to establish its role in behavioral divergence. By transgene coplacement, we created pairs of strains of D. melanogaster expressing an Adh allele from either D. melanogaster or D. affinidisjuncta, a Hawaiian species with very low levels of ADH in adults. When raised on ethanol-containing medium, the affinidisjuncta-Adh strains experience high mortality relative to the melanogaster-Adh strains. However, affinidisjuncta-Adh females show the same preference for oviposition on ethanol-containing medium as melanogaster-Adh females. Thus, preference for ethanol in these strains is not determined primarily by Adh genotype.