Recognition of subspecies status mediated by androgen-binding protein (abp) in the evolution of incipient reinforcement on the european house mouse hybrid zone

Between 5000 and 10 000 years ago, two populations of European house mice, today characterized as the subspecies Mus musculus domesticus and M. M. musculus, made secondary contact, resulting in formation of the narrow hybrid zone running across Danish Jutland and down through central Europe from the Baltic to the Black Sea. Studies suggest that a mechanism(s) of postzygotic reproductive isolation maintains the European mouse hybrid zone; however, there is also evidence that one or more prezygotic isolation mechanisms may also contribute to the maintenance of this zone of secondary contact. The purpose of this chapter is to review the data that suggest that these two subspecies and the transition of their hybrids across the zone can recognize each other and that this may result in some degree of avoidance of mating with each other. This putative prezygotic reproductive barrier is a behavioural one and a proteinaceous pheromone, mouse salivary androgen-binding protein (ABP) has been proposed to be a signal that mediates subspecies recognition. We review the putative mouse proteinaceous pheromones described thus far and present the state of knowledge about ABP’s contribution to mouse communication. In so doing, we explore the relatively recent evidence that ABP-based recognition may be an incipient mechanism of reinforcement operating on the borders of the allopatric subspecies populations. Chemosensory detection in vertebrates Vertebrates possess two olfactory systems, the main olfactory system (MOS) and the accessory olfactory system (AOS). The structures and functions of these systems have been the subjects of many reviews (e.g. Dulac and Torello, 2003; Mombaerts, 2004; Baum and Kelliher, 2009; Tirindelli et al., 2009; Touhara and Vosshall, 2009) and will only be summarized here. Both the MOS and AOS are chemosensory systems that transduce chemical sensations into neural activity and both can detect semiochemicals (derived from ’semeon’, the Greek for ’signal’) – chemical substances that carry messages – either individually or as a mixture. In contrast to the MOS, which detects volatile chemicals, the AOS detects fluid-phase chemicals including proteinaceous pheromones. The main olfactory receptor neurons project to the main olfactory bulb (MOB), whose mitral/tufted cells project in turn to the olfactory cortex. The sensory receptors of the accessory olfactory system are located in the vomeronasal organ (VNO), where receptor neurons innervate the accessory olfactory bulb (AOB), located on the dorsal-posterior portion of the main olfactory bulb.