The role of mate-choice copying in speciation and hybridization.

Mate-choice copying, a social, non-genetic mechanism of mate choice, occurs when an individual (typically a female) copies the mate choice of other individuals via a process of social learning. Over the past 20 years, mate-choice copying has consistently been shown to affect mate choice in several species, by altering the genetically based expression of mating preferences. This behaviour has been claimed by several authors to have a significant role in evolution. Because it can cause or increase skews in male mating success, it seems to have the potential to induce a rapid change of the directionality and rate of sexual selection, possibly leading to divergent evolution and speciation. Theoretical work has, however, been challenging this view, showing that copying may decelerate sexual selection and that linkage disequilibrium cannot be established between the copied preference and the male trait, because females copy from unrelated individuals in the population, making an invasion of new and potentially fitter male traits difficult. Given this controversy, it is timely to ask about the real impact of mate-choice copying in speciation. We propose that a solution to this impasse may be the existence of some degree of habitat selection, which would create a spatial structure, causing scenarios of micro-allopatry and thus overcoming the problem of the lack of linkage disequilibrium. As far as we are aware, the potential role of mate-choice copying on fostering speciation in micro-allopatry has not been tackled. Also important is that the role of mate-choice copying has generally been discussed as being a barrier to gene flow. However, in our view, mate-choice copying may actually play a key role in facilitating gene flow, thereby fostering hybridization. Yet, the role of mate-choice copying in hybridization has so far been overlooked, although the conditions under which it might occur are more likely, or less restricted, than those favouring speciation. Hence, a conceptual framework is needed to identify the exact mechanisms and the conditions under which speciation or hybridization are expected. Here, we develop such a framework to be used as a roadmap for future research at the intersection of these research areas.