Ancient DNA reveals prehistoric habitat fragmentation and recent domestic introgression into native wild reindeer

Introgression and admixture from domestic or foreign conspecifics into wild populations are of great concern in wildlife conservation. The issue is of particular interest in ungulates where translocations and re-introductions have been common practice. In Europe, the only large remaining wild populations of reindeer (Rangifer tarandus L.) are found in the mountainous habitats of southern Norway. These populations have during the last centuries been exposed to extensive habitat modifications and periods of contact with domestic reindeer. Through analyses of ancient and extant mitochondrial DNA (mtDNA) we document extensive intra- and inter-population genetic changes during the last millennium. Our data indicate population reduction within a short time interval during the 11th-12th century during a period when mass trapping of reindeer was common. Significant differentiation between the ancient herds suggests an ancient genetic structuring of the reindeer herds in southern Norway, although not as strong as between modern herds. Two different mtDNA lineages characterized the ancient herds. A Bayesian approach to reconstruct the recent evolutionary history suggests that the reindeer herds in southern Norway originate from two populations separated in different refugia during the last glacial period. The presence of two additional extant lineages, characteristic of domestic herds, suggests substantial introgression into the native wild reindeer. The putatively different refugial origins of the lineages represented by the extant herds in Rondane/Dovre, Hardangervidda and those with a mainly domestic origin may well reflect different adaptations to environmental conditions, including degree of human interference. Further research on this issue would provide important insights for conservation priorities and a sustainable and flexible management strategy for the remaining wild reindeer herds in the Scandinavian mountains.