Ancient human mitochondrial genomes from Bronze Age Bulgaria: new insights into the genetic history of Thracians

One of the best documented Indo-European civilizations that inhabited Bulgaria is the Thracians, who lasted for more than five millennia and whose origin and relationships with other past and present-day populations are debated among researchers. Here we report 25 new complete mitochondrial genomes of ancient individuals coming from three necropolises located in different regions of Bulgaria – Shekerdja mogila, Gabrova mogila and Bereketska mogila – dated to II-III millennium BC. The identified mtDNA haplogroup composition reflects the mitochondrial variability of Western Eurasia. In particular, within the ancient Eurasian genetic landscape, Thracians locate in an intermediate position between Early Neolithic farmers and Late Neolithic-Bronze Age steppe pastoralists, supporting the scenario that the Balkan region has been a link between Eastern Europe and the Mediterranean since the prehistoric time. Spatial Principal Component Analysis (sPCA) performed on Thracian and modern mtDNA sequences, confirms the pattern highlighted on ancient populations, overall indicating that the maternal gene pool of Thracians reflects their central geographical position at the gateway of Europe.