Genetic integrity of the Dark European honey bee (Apis mellifera mellifera) from protected populations: a genome-wide assessment using SNPs and mtDNA sequence data

The recognition that the Dark European honey bee, Apis mellifera mellifera, is increasingly threatened in its native range has led to the establishment of conservation programmes and protected areas throughout western Europe. Previous molecular surveys showed that, despite management strategies to preserve the genetic integrity of A. m. mellifera, protected populations had a measurable component of their gene pool derived from commercial C-lineage honey bees. Here we used both sequence data from the tRNAleu-cox2 intergenic mtDNA region and a genome-wide scan, with over 1183 single nucleotide polymorphisms (SNPs), to assess genetic diversity and introgression levels in several protected populations of A. m. mellifera, which were then compared with samples collected from unprotected populations. MtDNA analysis of the protected populations revealed a single colony bearing a foreign haplotype, whereas SNPs showed varying levels of introgression ranging from virtually zero in Norway to about 14% in Denmark. Introgression overall was higher in unprotected (30%) than in protected populations (8%), and is reflected in larger SNP diversity levels of the former, although opposite diversity levels were observed for mtDNA. These results suggest that, despite controlled breeding, some protected populations still require adjustments to the management strategies to further purge foreign alleles, which can be identified by SNPs.Pint

Estimating introgression in Apis mellifera siciliana populations: are the conservation islands really effective?

Apis mellifera siciliana is a honey bee subspecies prone to be conserved. Conservation measures include maintaining colonies on different islands to serve as parental lines for outcrossing. Molecular diversity and genetic structure of honey bees from Sicily (main island) and Vulcano and Filicudi (conservation islands) were analysed with mitochondrial and microsatellite markers to assess the efficacy of the ongoing conservation effort. Samples from continental Italy and Sardinia island were included for comparison. All the samples of the conservation islands were included in the African (A) evolutionary lineage, while western and northern (M) and eastern (C) European evolutionary lineages were also detected in colonies from the main island (17.1% and 22% respectively), thus highlighting introgression at the mitochondrial level. Nuclear data from conservation and main island populations were compared to evaluate the proportion of admixed honey bees. A higher level of hybridization was found in the central and eastern areas of Sicily main island. Our data describe the efficacy of the conservation islands, and suggest where and how to manage mating stations to further improve the present conservation strategy by recovering additional residual genetic variability of A. m. siciliana. We also propose the establishment of a European network of conservation islands to preserve honey bee subspecies and to implement research studies of adaptation to peculiar climatic conditions.Depto. de Biodiversidad, Ecología y EvoluciónFac. de Ciencias BiológicasTRUEpu