The mating advantage of rare males in Drosophila.

The mating advantage of rare Drosophila males in tested using two eye color mutants. In one experiment, the flies remained for three hours in observation chambers containing 25 pairs; in another experiment they stayed for 24 hours in mass cultures of 200 individuals. The outcome of this latter experiment was followed for ten generations, with all competition other than that for mates eliminated. For initial frequencies of 80 per cent for the common and 20 per cent for the rare type, the frequencies converged to approximate equality because the rare males were favored as mates. When the formerly rare type increases in frequency, it loses its mating advantage, and a balanced equilibrium is eventually attained.