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Abstract:
Background: The mechanistic basis of speciation and in particular the contribution of behaviour to the completion
of the speciation process is often contentious. Contact zones between related taxa provide a situation where selection
against hybridization might reinforce separation by behavioural mechanisms, which could ultimately fully isolate the taxa.
One of the most abundant European mammals, the common vole Microtus arvalis, forms multiple natural hybrid zones
where rapidly diverging evolutionary lineages meet in secondary contact. Very narrow zones of hybridization spanning
only a few kilometres and sex-specific gene flow patterns indicate reduced fitness of natural hybrids and incipient
speciation between some of the evolutionary lineages. In this study, we examined the contribution of behavioural
mechanisms to the speciation process in these rodents by fine-mapping allopatric and parapatric populations in the
hybrid zone between the Western and Central lineages and experimental testing of the partner preferences of
wild, pure-bred and hybrid female common voles.
Results: Genetic analysis based on microsatellite markers revealed the presence of multiple parapatric and largely
non-admixed populations at distances of about 10 km at the edge of the area of natural hybridization between
the Western and Central lineages. Wild females from Western parapatric populations and lab-born F1 hybrids preferred
males from the Western lineage whereas wild females of Central parapatric origin showed no measurable preference.
Furthermore, wild and lab-born females from allopatric populations of the Western or Central lineages showed no
detectable preference for males from either lineage.
Conclusions: The detected partner preferences are consistent with asymmetrical reinforcement of pre-mating
reproductive isolation mechanisms in the European common vole and with earlier results suggesting that hybridization
is more detrimental to the Western lineage. As a consequence, these differences in behaviour might contribute to a
further geographical stabilization of this moving hybrid zone. Such behavioural processes could also provide a
mechanistic perspective for frequently-detected asymmetrical introgression patterns in the largely allopatrically
diversifying Microtus genus and other rapidly speciating rodents.
