Contact zones between chromosomal races of Mus musculus domesticus. 1. Temporal analysis of a hybrid zone between the CD chromosomal race (2n=22) and populations with the standard karyotype

Abstract

A temporal analysis of a hybrid zone between chromosomal races of Mus musculus domesticus was performed to evaluate its dynamics over a 20-year period. The transect chosen was one previously analysed by Spirito et al. (1980) across the hybrid zone between the chromosomal race CD 2n 22 (central Italy) and the surrounding populations with standard karyotype (2n 40). The results show that 20 years of hybridization have not had any signi®cant e ect on the position of this hybrid zone, nor on the location of its extreme margin, except for one site for which passive transport of mice may have been important. The absence of a signi®cant shift of the tension zone excludes a possible imbalance between the two cytotypes; a ®tness superiority of one homozygote greater than 0.01 would have produced an appreciable shift of the zone. The internal chromosomal structure of the zone shows a constant gradual increase in metacentric chromosome frequency towards the localities nearest the area inhabited by the 22-CD homozygote population. This contrasts with the previously reported data which indicated an irregular trend, particularly evident for the Rb(3.8), Rb(5.17) and Rb(6.13) chromosomes. For each Rb metacentric, we observed greater values of F ST in the past sample than in the present one. These di erences reveal a tendency towards the homogenization of adjacent populations, perhaps because of greater migration between adjacent demes resulting from increased commercial tra c. The Mantel test was performed for both temporal samples. A positive correlation between the geographical and chromosomal di erentiation was demonstrated.

Spatio-temporal variation in the structure of a chromosomal polymorphism zone in the house mouse

“…These results suggest that processes of introgression of animals, carrying diverse chromosomal combinations, towards the centre of polymorphism may alter the expected metacentric frequencies in the area. The arrival of allochthonous mice in the centre of a metacentric zone has also been reported in Rb populations from Italy (Franchini et al, 2007;Castiglia and Capanna, 1999) and Madeira (Nunes et al, 2005). In those cases, as may also occur in the Rb zone of Barcelona, the action of humans on the natural landscape has influenced the dynamics of commensal mice (Chatti et al, 1999;Castiglia and Capanna, 1999).…”

“…The arrival of allochthonous mice in the centre of a metacentric zone has also been reported in Rb populations from Italy (Franchini et al, 2007;Castiglia and Capanna, 1999) and Madeira (Nunes et al, 2005). In those cases, as may also occur in the Rb zone of Barcelona, the action of humans on the natural landscape has influenced the dynamics of commensal mice (Chatti et al, 1999;Castiglia and Capanna, 1999). Passive transport via vehicles, especially in farming areas, may have promoted introgression events independently of the common mouse dispersion (Cucchi et al, 2005;Franchini et al, 2007).…”

“…Several long-term spatio-temporal studies of Rb hybrid zones have been reported (Hauffe and Searle, 1993;Castiglia and Capanna, 1999;Faria and Navarro, 2010). However, the detection of gradual variations or rapid changes in a zone may be overlooked when the time scale is too long.…”

“…Hence, we carry out mid-term analysis focused on the detection of possible structural variations of the polymorphism area of Barcelona over the past 13 years. This period, in a temperate Mediterranean region, corresponds to nearly 50 generations of mice because of their reproductive characteristics (Castiglia and Capanna, 1999). Thus, we assume that this is time enough to reveal detailed variations, which will allow us to obtain a more accurate vision of the dynamics of the polymorphism area at longer time scales.…”

Contact zones between chromosomal races of Mus musculus domesticus. 3. Molecular and chromosomal evidence of restricted gene flow between the CD race (2n = 22) and the ACR race (2n = 24)

“…In fact, the absence of genetic differentiation can be interpreted as the presence of free gene flow between races or it could be due to the recent formation of the races (Britton-Davidian et al, 1989). Many studies have focused on the contact zones between Robertsonian races and the standard one (see Searle, 1993 for a review; Castiglia and Capanna, 1999a;Gundü z et al, 2001a). All these studies have found hybrids showing trivalents at diakinesis, with hybrid zone widths from 0.5 km (Chatti et al, 1999) to 30 km .…”