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

1. 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. 2. 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. 3. 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. 4. 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. 5. 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. 6. 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.