Genetic Coupling of Mate Recognition Systems in the Genomic Era

, have identified genes in the sex determination pathway and in pheromonal communication where single loci can influence both signals and preferences. This may be based on isoform divergence, in which sex- and tissue-specific effects are facilitated by alternative spicing, or on regulatory divergence. Hence it is not clear that such examples provide compelling evidence of pleiotropy in the sense that "magic mutations" could maintain trait coordination. Rather, coevolution may be facilitated by regulatory divergence but require different mutations or coevolution across isoforms. Reconsidering the logic of genetic coupling, it may be that pleiotropy could actually be less effective than linkage if distinct but associated variants allow molecular coevolution to occur more readily than potentially "unbalanced" mutations in single genes. Genetic manipulation or studies of mutation order effects during divergence are challenging but perhaps the only way to disentangle the role of pleiotropy versus close linkage in coordinated trait divergence.