Subspecies recognition in the house mouse: a study of two populations from the border of a hybrid zone

Mate choice is the outcome of sexual preference for partners carrying specific signals. Thus, mating among conspecifics (homogamy) depends on the occurrence of species recognition systems. We asked what happens if populations diverge, and we investigated female sexual preference between two subspecies of the house mouse in populations from the borders of a hybrid zone ( Jutland, Denmark). We used choice tests to analyze the occurrence of recognition signals and to locate these signals in soiled bedding and urine. Our results show that populations of the two subspecies can be discriminated on the basis of urinary signals, suggesting that the latter have diverged. Additionally, these signals seem to have similar features in populations of different geographical origins, suggesting that subspecific differentiation occurs. This is the first demonstration that subspecific recognition through urinary signals occurs in the house mouse. However, while Mus musculus domesticus does not display a preference, we show that Mus musculus musculus females tend to mate with males of the same subspecies. We discuss the different factors that could explain these discrepancies between females of the two taxa: differences in signal perception, evolution at a different pace, or evolution under different selective pressures in their area of contact. Further, we propose that the divergence in male signal was at least partly initiated in allopatry and discuss different evolutionary scenario that may explain the patterns observed in Denmark and their relevance to isolation between the two taxa.