Interocellar bristles in Drosophila melanogaster : Part 3: Response to disruptive selection.

A population of Drosophila melanogaster has been exposed to disruptive selection for interocellar bristle number for fifteen generations. Two different mating systems have been employed: quasi-random and mating-choice.The expected results of an increase in phenotypic variance and divergence of extreme mating groups were not found when the mating-choice system was used, while a clear divergence (2.04% of overlap) was found at the end of the experiment in one line where the quasi-random system (QR1) had been used.A possible explanation for our results, which is also suggested by those of several other authors, could be that of hybrid vigor. Thus, the reason for the absence of effect in MCh may be that the progeny of "hybrid" matings are likely to be less inbred and therefore have higher viability, mating ability and egg production.