Phenotypic polymorphism via mate copying

Classical mate choice theories assume independent decision-making, yet mounting evidence shows that individuals often use social information and copy conspecifics' mate choices, a behavior termed mate copying. While this nonindependent mate choice has been documented across vertebrates and notably in Drosophila melanogaster, theoretical and experimental frameworks have been mainly restricted to binary choice scenarios, limiting our understanding of its evolutionary implications in natural populations. Here, we develop a theoretical model of mate copying applicable to populations with multiple morphs, incorporating both private (inherent) and public (cultural) information in mate choice decisions. The population dynamics of the different male morphs are driven by the differing intensities of conformist and anticonformist mate copying. We demonstrate that mate copying can lead to the fixation of low-quality morphs and identify the conditions necessary for the existence of a polymorphism consisting of all male morphs in the population. Furthermore, we identify a plausible mechanism that could maintain a stable polymorphism in the case of conformist mate copying with two morphs. Our findings provide a theoretical framework for understanding how social learning in mate choice can influence evolutionary trajectories and contribute to maintaining phenotypic diversity in populations, with potential implications for sexual selection and speciation.