Does competitive interaction drive species recognition in a house mouse secondary contact zone?

Abstract

Miscommunication may induce a high risk of unnecessary escalated fights between competitors (populations to species), resulting in selection favoring signal divergence through agonistic character displacement (ACD). When signals allowing discrimination between competitors are also involved in mate recognition, ACD could explain reproductive character displacement (RCD). We tested interference competition between males as a potential driver of RCD (here, subspecies recognition) in a secondary contact zone between two mouse subspecies (Mus musculus musculus and Mus musculus domesticus) displaying asymmetric dominance. Since such asymmetry could create a conflict between subspecies (compatibility) and quality (dominance) recognition in the contact zone, we tested for geographic variation in female preference for dominant males in the subordinate subspecies, musculus. We assessed competition between males and tested ACD during dyadic encounters comparing behavior displayed during trials between heterosubspecifics originating from populations close to the secondary contact (“contact”) and further away (“allopatric”). We also compared behavior of contact versus allopatric males during homosubspecific versus heterosubspecific trials to test whether subspecies discrimination evolved under competitive interference. Although domesticus dominated most heterosubspecific trials regardless of geographic origin, agonistic behavior was more marked (i.e., lower attack latencies) during contact than allopatric encounters, suggesting that ACD occurred. Comparing behavior during homosubspecific and heterosubspecific encounters, only allopatric musculus displayed differences, that is, higher attack latencies toward heterosubspecifics, indicating that discrimination between competitors did not evolve with ACD. Finally, although allopatric musculus females seemed to prefer dominant males, their contact counterparts did not, suggesting that “compatibility” may have outweighed “quality” under a risk of hybridization.