Mechanisms of Fixation and Accumulation of Centric Fusions in Natural Populations of Mus musculus L. I. Karyological Analysis of a Hybrid Zone Between Two Populations in the Central Apennines

Centric fusions seem to play a decisive role in the early stages of the speciation processes in Mus musculus and other rodents in accentuated conditions of isolation of the populations; in the house mouse this is demonstrated by the presence of numerous wild populations in which a high number of cen...

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Bibliographic Details
Published in:Evolution 1980-05, Vol.34 (3), p.453-466
Main Authors: Spirito, Franco, Modesti, Antonella, Perticone, Paolo, Cristaldi, Mauro, Federici, Roberto, Rizzoni, Marco
Format: Article
Language:English
Subjects:
Chromosomes
Evolution
Evolutionary genetics
Heterozygotes
Hybridity
Metacentric chromosomes
Mice
Population genetics
Population structure
Speciation
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Summary:Centric fusions seem to play a decisive role in the early stages of the speciation processes in Mus musculus and other rodents in accentuated conditions of isolation of the populations; in the house mouse this is demonstrated by the presence of numerous wild populations in which a high number of centric fusions are independently fixed and accumulated. A cytogenetic analysis was carried out on the hybrid zone between two populations of Mus musculus L.: a normal one (2n = 40 telocentric chromosomes) and the so-called CD population (Capanna et al., 1973) with nine centric fusions in homozygosis (2n = 22 chromosomes, of which 18 are metacentrics). Our goals were to define the degree of isolation of the two populations and the genetical dynamics under way in the hybrid zone. The hybrid zone turned out to be made up of local populations situated along a gradient with respect to the number of metacentric chromosomes, with an irregular course of the variations in frequency of the configurations of individual chromosomes from one station to the other and a consistent frequency of heterozygotes. These results show the absence of mechanisms of premating isolation and the past and present intense dynamics of genetic exchanges in the hybrid zone. It is not possible to define the particular adaptive values for the different fusions. These observations are in agreement with the hypothesis that the two populations are in an early phase of the cladogenetic process. The fixation and accumulation of centric fusions are the first stage, probably determined by the peculiar structure of the chromosomes concerned, by the partial sterility of the heterozygotes, the original conditions of isolation of the populations concerned, and the limited deme size.
ISSN:0014-3820
1558-5646
DOI:10.1111/j.1558-5646.1980.tb04835.x