FREQUENCY-DEPENDENT SELECTION .1. RARE MALE PHENOMENON IN D-SUBOBSCURA DEPENDENT ON THE PROPORTION OF AMY GENOTYPES AND SUBSTRATE COMPOSITION

Analysis of the rare male mating advantage in D. subobscura, as a type of frequency dependent selection on maltose and starch media, was don e by applying different statistical approaches (chi(2), cross-product ratio, variance and regression analysis). They reveal that mating occu rs at random when proportions of prospective mates are equal, and that mating success of the males homozygous for Amy-locus genotypes (S/S a nd F/F) depends on their proportion. Regression analysis showed that t he F/F males are sexually more active (have higher vigour) than S/S ma les. Rare male effect is one-sided and appears in F/F males that parta ke in more heterogamic matings. Comparison of the number of observed a nd expected homo- and heterogamic matings shows that homogamic matings are more frequent. Multifactorial analysis of variance shows that the number of matings are different for nine pairs of lines and four poss ible mating types (SfSm, SfFm, FfSm, FfFm). The rare male phenomenon i s not dependent on different food composition, but is associated with variations in individual genotypes.