In yellow-necked mouse, Apodemus flavicollis, B chromosomes are present in almost all populations in a wide range of frequencies that are often stable from year to year, but contribution of Bs to genetic and phenetic structure and their maintenance in the absence of accumulation mechanism, are poorly explored in general. Therefore, we intend to analyse population structure across ecologically different habitats and those situated at the altitude edges of species distribution. Genetic profile of populations will be obtained using molecular markers while phenetic structure will be attained from skull shape analyses, as well as from life-history traits.

Adaptive variation will be investigated by measuring variation at highly polymorphic molecular markers. In the context of genetic structure and presence of Bs, prevalence and intensity of macro parasites dominant for this species, as well as virus's presence, will be monitored. We suppose that obtained data, together with data from analysis of Bs transmission from cages, will allow understanding the contribution of B chromosome polymorphism to genetic diversity and adaptability of species across different environments. Further understanding of mechanism of Bs maintenance in populations is also expected.