Habitat quality and B chromosomes in the yellow-necked mouse Apodemus flavicollis

The correlation between frequency of B chromosomes and quality of habitat was analysed in 680 specimens of yellow-necked mice, Apodemus flavicollis, collected at six localities in Serbia. Animals with B chromosomes were present at all localities in frequencies ranging from 0.23 to 0.40. Quality of habitat was judged from an index of overall body size (BSI). At the studied localities, the frequency of animals with Bs was negatively correlated with the index of overall body size (r = -0.93), indicating that B chromosomes in this species are mentioned due to the effects that they exert at the level of populations. This finding supports the heterotic model of maintenance of B chromosomes.