Disruptive sexual selection in Colias eurytheme butterflies.

Sexual selection on male pheromone composition in Colias eurytheme (Pieridae) butterflies has the remarkable effect of increasing the variability of this trait. Sexual selection on important traits is generally thought to have a strong stabilizing effect on intraspecific variation of those characters. In this species, however, the male courtship pheromone is highly variable in the relative proportions of its three chemical constituents. Stabilization and/or canalization of this polygenic character in a population is impeded by the disproportionate mating success of males in one portion of the character distribution with alba (white morph) females, and of those in the opposite portion with orange (colored morph) females.