QUANTITATIVE GENETIC-VARIATION OF ODOR-GUIDED BEHAVIOR IN A NATURAL-POPULATION OF DROSOPHILA-MELANOGASTER

Quantitative genetic variation in behavioral response to the odorant, benzaldehyde, was assessed among a sample of 43 X and 35 third chromos omes extracted from a natural population and substituted into a common inbred background. Significant genetic variation among chromosome lin es was detected. Heritability estimates for olfactory response, howeve r, were low, as is typical for traits under natural selection. Further more, the loci affecting naturally occurring variation in olfactory re sponse to benzaldehyde were not the same in males and females, since t he genetic correlation between the sexes was low and not significantly different from zero for the chromosome 3 lines. Competitive fitness, viability and fertility of the chromosome 3 lines were estimated using the balancer equilibrium technique. Genetic correlations between fitn ess and odor-guided behavior were not significantly different from zer o, suggesting the number of loci causing variation in olfactory respon se is small relative to the number of loci causing variation in fitnes s. Since different genes affect variation in olfactory response in mal es and females, genetic variation for olfactory response could be main tained by genotype X sex environment interaction. This unusual genetic architecture implies that divergent evolutionary trajectories for olf actory behavior may occur in males and females.