The role of reinforcement in speciation: Theory and data

To assess the frequency and importance of reinforcement in nature we must begin by looking for its signature in the most likely places. Theoretical studies can pinpoint conditions that favor and inhibit reinforcement, and empirical studies can identify both how often these conditions occur and whether reinforcement results. We examine how well these tools have addressed these questions by searching for gaps and mismatches in theoretical and empirical studies of reinforcement. We concentrate on five areas: (a) a broad assessment of selection against interspecific mating, (b) the mode and genetic basis of nonrandom mating, (c) the geography of speciation, (d) divergent selection on mating cues, (e) and the genetics of reproductive isolation. We conclude that reinforcement has probably not been looked for where it is most likely to occur. We pinpoint however, many further areas of study that may ultimately provide a strong assessment of the importance of reinforcement in speciation.