Sexual imprinting and speciation in two Peromyscus species

Sexual isolation, a reproductive barrier, can prevent interbreeding between diverging populations or species. Sexual isolation can have a clear genetic basis; however, it may also result from learned mate preferences that form via sexual imprinting. Here, we demonstrate that two sympatric sister species of mice—the white-footed mouse (Peromyscus leucopus) and its closest relative, the cotton mouse (P. gossypinus)—hybridize only rarely in the wild despite co-occurring in the same habitat and lack of any measurable intrinsic postzygotic barriers in laboratory crosses. We present evidence that strong conspecific mate preferences in each species form significant sexual isolation. We find that these mating preferences are learned in one species but may be genetic in the other: P. gossypinus sexually imprints on its parents, but innate biases or social learning affects mating preferences in P. leucopus. Our study demonstrates that sexually imprinting contributes to reproductive isolation that reduces hybridization between otherwise inter-fertile species, supporting a previously underappreciated role for learning in mammalian speciation.