Conservation of the dark bee (Apis mellifera mellifera): estimating C-lineage introgression in Nordic breeding stocks

Displacement and admixture are threatening the survival and genetic integrity of the European dark bee, Apis mellifera mellifera. Studies on the phenotype-genotype map and genotype by environment interactions in honey bees are demonstrating that variation at subspecies level exists and is worth conserving. SNP-based tools for monitoring genetic integrity in bees have been developed, but are not yet widely used by European dark bee breeders. We used a panel of ancestry informative SNP markers to assess the level of admixture in Nordic dark bee breeding stocks. We found that bee breeders falsely classified admixed stocks based on morphometry as purebred and vice versa. Even though most Nordic A. m. mellifera breeding stocks have low proportions of C-lineage ancestry, we recommend to incorporate genotyping in Nordic dark bee breeding programmes to ensure that minimal genetic diversity is lost, while the genetic integrity of the subspecies is maintained.We are greatly indebted to the participating bee breeders for allowing us to include their samples in this study and for providing the samples. We sincerely thank Dr. Stefan Fuchs for providing the morphological reference data. This project would not have been possible without the help of João Costa from the Genomics Unit of the Instituto Gulbenkian de Ciência, Portugal, who carried out the genotyping for us. We thank the two anonymous reviewers who helped greatly to improve the manuscript. This research was partly funded by the Norwegian Agriculture Agency 17/3472.