Genetic analysis of Drosophila sechellia specialization: Oviposition behavior toward the major aliphatic acids of its host plant

Oviposition behavior of the four species in the Drosophila melanogaster com plex (D. melanogaster, D. simulans, D. mauritiana, D. sechellia) was invest igated versus natural morinda fruit (the normal resource of D. sechellia) a nd the two major aliphatic acids of this fruit (hexanoic acid, C6, and octa noic acid, C8). Two different experimental techniques were compared. When c ontrol and experimental food were set on the same egg laying plate, three s pecies (D. sechellia, D. mauritiana, D. melanogaster) exhibited a significa nt preference for morinda; with aliphatic acids, only D. sechellia manifest ed a preference. With separate oviposition sites, a preference was found in D. sechellia for morinda and acids, and a general avoidance behavior in th e three other species. Genetic analysis of the behavioral response toward C 6 and Cg was done with the two plates technique on D. sechellia, D. simulan s, Fl hybrids and backcrosses. Significant behavioral differences were obse rved with major effects due to genotype, concentration and their interactio n. Hybrid behaviors were intermediate between those of their parents. In se veral cases, a qualitative reversal from preference to avoidance was observ ed with increasing concentration. In Fl flies, a dominance reversal was obs erved with increasing Cs concentration. Different reaction thresholds in di fferent receptors might explain such observations.