Mate preference in sympatric and allopatric darters (genus Etheostoma): comparative evidence for a sex effect in reinforcement

Reinforcement is the strengthening of preference for conspecific mates as a byproduct of selection against hybrids. A hypothesis of reinforcement predicts that populations evolving in sympatry will have greater preferences for conspecific over heterospecific mates as compared to allopatric populations. In animals, this pattern was demonstrated across the genus Drosophila, however, most empirical evidence for reinforcement comes from studies of two or only a few species. To infer general patterns requires broader comparative analyses. We therefore compared mate preferences in sympatric and allopatric species of darters (genus Etheostoma). We performed a meta-analysis of 15 studies, encompassing 20 species. As expected, we found stronger preferences for conspecifics over heterospecifics across studies, species, and sexes. We further found the classic signature of reinforcement, with sympatric species showing on average stronger preferences for conspecifics than allopatric species. This was especially true for females, consistent with the idea that mate choice might be more costly for females than males.