Origin and Maintenance of Genetic Diversity in Northern European Sheep

The Nordic and Baltic countries and North-western Russia have >20 old native sheep breeds. These together with recently synthesized breeds and local populations of international breeds make up the northern European sheep diversity. Changes in agriculture threaten to erode genetic diversity in sheep. Molecular genetic variation was assessed to understand genetic diversity in northern European sheep. Distribution of maternal lineages were studied based on mitochondrial control region variation in 76 sheep breeds in northern Europe and in a wide neighbouring area extending to the Caucasus and Central-Asia. Autosomal microsatellite variation was studied in 37 northern European breeds, and autosomal blood protein variation was studied in six Finnish and Russian breeds. Four distinct maternal lineages were observed in Eurasian sheep. Their distribution agrees with sheep expansion starting from the Near East. Two most common distinct lineages were recorded in northern Europe. Majority of northern sheep have the lineage, which predominates in other parts of Europe. Results suggest that the main maternal origin of northern sheep is in the south. However, rare "Asian" lineage was observed in several old northern European breeds. The rare type in the Nordic sheep is descendant to the type observed in the Middle Volga region, which suggest that some sheep were brought to northern Europe from the east. Microsatellites showed clustering of geographically neighbouring sheep, when breed locations are corrected for the recent transportations. The analysis separated long and short-tailed sheep, although this macroscale structure explains a small proportion of breed differences. Differentiation among the northern European breeds is stronger than typically observed in sheep. Many native breeds are less inbred than the local populations of the international breeds, but some rare breeds and subpopulations of divided unofficial strains were inbred. Some breeds require more careful maintenance due to recent population size reduction. Maintaining prolificacy in breeds such as the Finnsheep and the Romanov may require efficient avoidance of inbreeding. The breeds were ranked for conservation using simultaneously within-breed variation and breed divergence. Set of important breeds included seven rare old native breeds or strains which merit efficient conservation measures urgently.