Sexual selection and the nonrandom union of gametes: retesting for assortative mating by fitness in Drosophila melanogaster.

This article investigates whether the fruit fly *Drosophila melanogaster* engages in assortative mating based on body size, a trait linked to genetic quality, and examines the fitness consequences of such mating patterns. Using flies reared under standard culture conditions to preserve natural size variation, the study found no evidence of assortative courtship behavior but observed that individuals produced more offspring with mates of similar body size, indicating assortative union of gametes. Complementary assays revealed that assortative mating yielded equal or slightly higher offspring reproductive success compared to disassortative mating, suggesting indirect fitness benefits. These findings provide empirical support for theoretical models proposing that sexual selection via assortative mating can enhance the efficiency of natural selection by promoting adaptive evolution.