Genetic drift decouples Fisherian trait-preference coevolution from genetic correlations in finite populations

Abstract

A central mechanism of sexual selection theory is Fisher's process, which refers to the coevolution of male traits and female preferences, in which preference is indirectly selected through genetic association with male trait alleles built up via mate choice. However, empirical studies often fail to detect strong trait-preference genetic correlations, raising doubts about the importance of Fisherian selection in nature. Notably, the theoretical expectation that genetic correlations are essential for trait-preference coevolution through Fisherian selection derives largely from models assuming infinitely large populations, whereas real populations are finite. Using population genetic models, I show that interactions between Fisherian selection and genetic drift can fundamentally decouple trait-preference genetic correlations from the evolution of male traits and female preferences. Genetic drift generally reduces expected trait-preference correlations but simultaneously promotes the expected increase in female preference frequency beyond deterministic predictions. Consequently, in populations of realistic sizes, trait-preference correlations may often be weak or even negative, particularly when recombination among trait and preference loci is infrequent, but substantial trait-preference coevolution can still occur. Therefore, the strength of genetic correlations may be an unreliable indicator of the extent of trait and preference coevolution, offering a potential resolution to a longstanding dilemma in sexual selection theory.