Frequency-dependent sexual selection among wild-type strains of Drosophila melanogaster

Frequency-dependent sexual selection was studied using three geographically isolated strains of Drosophila melanogaster. The Oregon-R and Canton-Special wild-type strains were essentially homogeneous, having been maintained in laboratories since 1925; the wild Macomb strain was relatively genetically heterogeneous, having been collected in September 1972, immediately prior to this investigation. allowing 2 hr observation possible double combinations of the three strains were placed in separate chambers of a modified Elens-Wattiaux observation apparatus at ratios of 5:20, 12:12, and 20:5. All time for each chamber, data were collected to detect mating preference between these strains. There was no sexual isolation between the strains. However, frequency dependence, where rare males have a definite mating advantage in a population, was exhibited by the strains studied. Sexual vigor appeared to be a factor when the heterogeneous Macomb strain was mated to either of the two homogeneous strains in equal numbers.