Frequency-dependent sexual selection among wild-type strains ofDrosophila melanogaster

Abstract

Frequency-dependent sexual selection was studied using three geographically isolated strains ofDrosophila 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. All 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. Allowing 2 hr observation 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.