Genetics of a nonoptimal behavior: oviposition preference of Drosophila mauritiana for a toxic resource.

Among three sibling species of the D. melanogaster subgroup, two are generalists (D. simulans and D. mauritiana), while the third, D. sechellia, specializes on a single toxic resource, the fruit of Morinda citrifolia. D. sechellia, resistant to the toxics, prefers to oviposit on morinda; D. simulans, which is very sensitive, is strongly repelled. D. mauritiana exhibits an aberrant behavior since it prefers to lay its eggs on morinda, where its embryos are killed. Oviposition behavior, studied in parental species, F1 hybrids, and backcrosses, was mostly an additive genetical trait. Further investigations were made with D. mauritiana and D. simulans carrying recessive markers. The X and second chromosomes had no effect, while a clear effect was found for chromosome 3. Since the toxicity of morinda is due to middle-length fatty acids, the behavior of the three species toward various acids was investigated. We found that D. sechellia exhibited a general oviposition preference for acids, while D. simulans was repelled by acids with at least four carbons. Surprisingly D. mauritiana exhibited behavior quite similar to that of D. simulans. Preference for morinda in D. sechellia and D. mauritiana could be mediated by different chemicals.