A Model of Mating Behavior in Flies.

A model of mating behavior is developed to characterize geographic variation in flies. Normally distributed sexual vigor parameters [Formula: see text] and [Formula: see text] are defined for males and females, respectively. When there is no sexual isolation present, the success and duration of a courtship is determined by the linear difference between the vigors of courting pairs. Sexual isolation is represented as an angle (θ) separating the vigor vectors of courting pairs, and the effectiveness of the male vigor assumes its projection onto the female vector ([Formula: see text]), where cos θ is the correlation between the courtship patterns of the two populations. The corroboration of the basic tenets of mating success implicit in our formulation agrees remarkably well with extant data in percentage of copulations in single pairs, distribution of mating times, the balance between sexes, and the correspondence of the isolation parameter to quantitative differences in courtship patterns among competing genotypes. Sexual vigor, variability in vigor within populations, assortative mating, and duration of copulation interact in a complex manner to determine mating success in competitive circumstances. The model has considerable heuristic value in conceptually separating the oftenconfounded effects of sexual isolation and sexual selection (vigor) and allowing their separate estimation from observed matings within and among competing strains.