Nuclear and mitochondrial patterns of introgression into native dark bees (Apis mellifera mellifera) in Poland

The genetic diversity of the north and western European subspecies of honey bee, Apis mellifera mellifera (the dark bee) is severely endangered due to hybridization with introduced bees of evolutionary branch C. Genetic variability of native honey bees in the north-eastern part of Poland, including a special isolated breeding zone in the Augustow Forest, has been investigated using mitochondrial DNA and nuclear microsatellites. These involve analysis for alien haplotypes of the tRNA(leu)-COII region and presence of diagnostic alien alleles respectively, in conjunction with a Bayesian model based approach. We found that approximately 10 to 30% of the nuclear gene pool and 3 to 50% of mitochondria in the studied populations were derived from non-native bees. Our data revealed the presence of hybrids in populations formerly considered to be the most pure populations of dark bees in Poland. We suggest that the Bayesian analysis of admixture based on nuclear microsatellites provides a reliable tool for measuring introgression in dark bees, which should be routinely used for evaluation during conservation programmes.