Linkage disequilibrium approaches for detecting hybrid zone movement: A study of the house mouse hybrid zone in southern bavaria
Introduction. In a series of papers spanning over a decade (e.g. Hewitt, 1975; Barton, 1979; Barton and Hewitt, 1985, 1989), Barton and Hewitt explored the nature of hybrid zones that are formed when genetically distinct populations overlap and reproduce (Barton and Hewitt, 1985, 1989). They viewed most hybrid zones as ‘tension zones’ (Key, 1968), i.e. clines maintained by a balance between dispersal and selection against hybrids, and they proposed that tension zones can be stationary or they can move across geographic space due to demographic differences between populations or as a result of asymmetric selection (Hewitt, 1975; Barton, 1979; Barton and Hewitt, 1985). Determining whether a hybrid zone is stationary or moving has important implications for understanding the evolutionary processes affecting interactions in hybrid populations. However, in a recent review of the hybrid zone literature, Buggs (2007) discussed the difficulties in detecting hybrid zone movement, especially from patterns of gene flow. For example, although a moving tension zone will leave a signature tail of neutral clines in its wake (Arntzen and Wallis, 1991), this pattern could also be interpreted as the adaptive introgression of alleles away from a stationary front. Buggs (2007) concluded that evidence for moving hybrid zones was not well established in the literature. The well–studied hybrid zone between genetically distinct populations of house mice, Mus musculus musculus and M. m. domesticus (also referred to in the literature as Mus musculus and Mus domesticus) (Hunt and Selander, 1973; Sage et al., 1986b; Vanlerberghe et al., 1986, 1988a, b; Tucker et al., 1992; Fel–Clair et al., 1996; Orth et al., 1996; Boissinot and Boursot, 1997; Prager et al., 1997; Munclinger et al., 2002; Payseur et al., 2004; Božiková et al., 2005; Raufaste et al., 2005; Macholán et al., 2007, 2008, 2011; Teeter et al., 2008, 2010), offers an opportunity to explore the possibility of hybrid zone movement. The hybrid zone is likely a tension zone with selection against hybrids due to genetic incompatibilities, including hybrid male sterility resulting from spermatogenic failure (Forejt, 1996; Storchová et al., 2004; Britton–Davidian et al., 2005; Good et al., 2008a, b, 2010; Vyskocilová et al., 2009), hybrid female sterility (Britton-Davidian et al., 2005), hybrid inviability (Sage et al., 1986a; Moulia et al., 1993), and reinforcement selection affecting mate choice preferences (Smadja and Ganem, 2005; Voslajerová Bimová et al., 2011).
