Bimodal distribution of oviposition preference for a novel food medium in Drosophila melanogaster

Bimodal distributions of oviposition preference within populations, are of interest as they may represent an early step towards host-race formation in nature. Oviposition preference for a novel food medium was assayed in 20 f ull-sib families of a laboratory population of Drosophila melanogaster, Sig nificantly greater variation in preference for the novel food was observed among families, compared to within families, indicating that the observed v ariation is, at least partly,under genetic control. The distribution of ovi position preference of individual females in the total Population was highl y bimodal; resulting in a low mean oviposition preference value as a conseq uence of high specificity (a measure of the strength of oviposition prefere nce) coupled with extensive variation in preference. The results confirm ea rlier reports of such bimodal distributions of preference in laboratory pop ulations of Drosophila and provide evidence for a genetic basis to this var iation, suggesting that this pattern of distribution of preference may be a n evolved response to some aspect(s) of the laboratory ecology of these Dro sophila cultures, Such an evolved response results in a partial delinking o f oviposition preference and specificity at the populational level, and pro vides an opportunity to study the genetic architecture of preference and sp ecificity in these populations.