title: Properties of a hybrid zone between highly distinct chromosomal races of the house mouse (Mus musculus domesticus) in Northern Italy, and comparisons with other hybrid zones.
abstract: Here we provide the first detailed description of the hybrid zone between the Cremona chromosomal race of house mouse (ICRE; 2n = 22) and the standard all-telocentric race (40ST; 2n = 40), with full karyotypes of 106 individuals from 17 localities along a transect between the 2 races to the west of Lake Garda in Northern Italy. The ICRE race is characterised by 9 pairs of metacentric chromosomes in a homozygous state and we use the metacentric frequency data along the transect to fit tanh metacentric clines. The clines are narrow (5-8 km, standardised width) suggesting low hybrid fitness. However, the lack of occurrence of ICRE × 40ST F(1) hybrids and presence of other hybrid types suggests that the F(1) hybrids initially produced in this hybrid zone were at least partially fertile, despite having 9 meiotic trivalent configurations. We apply the same cline-fitting methodology to 3 previously studied hybrid zones between metacentric races and the 40ST race. Taken together with published clinal data on 4 further metacentric-40ST hybrid zones, we are able to make objective generalisations on the characteristics of such zones in the house mouse. Zones involving 22-chromosome races are narrower, on average, than other metacentric-40ST hybrid zones and do not show a tendency towards the generation of new races as found with zones where the metacentric race has a higher 2n. It appears that metacentric-40ST zones are unlikely to be sites of speciation (even when a 22-chromosome race is involved), although a mosaic structure to the hybrid zone may enhance this possibility. We make a comparison between metacentric-40ST zones and contacts between 2 metacentric races, for a comprehensive perspective of chromosomal hybrid zones in the house mouse.
authors.affiliation: Department of Biology, University of York, York, UK.
authors.forename: H C
authors.initials: HC
authors.lastname: Hauffe
authors.forename: M D
authors.initials: MD
authors.lastname: Giménez
authors.forename: R
authors.initials: R
authors.lastname: Vega
authors.forename: T A
authors.initials: TA
authors.lastname: White
authors.forename: J B
authors.initials: JB
authors.lastname: Searle
mesh_terms: D000818:Animals; D006824:Hybridization, Genetic; D007558:Italy; D007621:Karyotyping; D051379:Mice / Q000235:genetics*