title: Asymmetric and differential gene introgression at a contact zone between two highly divergent lineages of field voles (Microtus agrestis).
abstract: Secondary contact zones have the potential to shed light on the mode and rate at which reproductive isolation accumulates during allopatric speciation. We investigated the population genetics of a contact zone between two highly divergent lineages of field voles (Microtus agrestis) in the Swiss Jura mountains. To shed light on the processes underlying introgression, we used maternally, paternally, and bi-parentally inherited markers. Though the two lineages maintained a strong genetic structure, we found some hybrids and evidence of gene flow. The extent of introgression varied with the mode of inheritance, being highest for mtDNA and absent for the Y chromosome. In addition, introgression was asymmetric, occurring only from the Northern to the Southern lineage. Both patterns seem parsimoniously explained by neutral processes linked to differences in effective sizes and sex-biased dispersal rates. The lineage with lower effective population size was also the more introgressed, and the mode-of-inheritance effect correlated with the male-biased dispersal rate of microtine rodents. We cannot exclude, however, that Haldane's effect contributed to the latter, as we found a marginally significant deficit in males (the heterogametic sex) among hybrids. We propose a possible demographic scenario to account for the patterns documented, and empirical extensions to further investigate this contact zone.
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland. mathias.beysard@ iee.unibe.ch
authors.forename: M
authors.initials: M
authors.lastname: Beysard
authors.forename: N
authors.initials: N
authors.lastname: Perrin
authors.forename: M
authors.initials: M
authors.lastname: Jaarola
authors.forename: G
authors.initials: G
authors.lastname: Heckel
authors.forename: P
authors.initials: P
authors.lastname: Vogel
mesh_terms: D000818:Animals; D003411:Arvicolinae / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000737:chemistry; D005260:Female; D051456:Gene Flow; D049810:Genetic Speciation; D006239:Haplotypes; D006824:Hybridization, Genetic; D008297:Male; D018895:Microsatellite Repeats; D011156:Population Density; D011157:Population Dynamics; D060047:Reproductive Isolation; D017422:Sequence Analysis, DNA; D012737:Sex Factors; D014998:Y Chromosome / Q000737:chemistry
chemical_list: D004272:DNA, Mitochondrial