Localization of a Contact Zone between Two Highly Divergent Mitochondrial DNA Lineages of the Brown Bear Ursus arctos in Scandinavia.

Abstract

In Europe the brown bear (Ursus arctos) is represented by two different mitochondrial DNA (mtDNA) lineages, which probably diverged about 0.85 million years ago. Scandinavia has been colonized by representatives of both lineages, from the north (eastern lineage) and from the south (western lineage), and now bears occur primarily in four main regions called female concentration areas. For management purposes the localization of the contact zone between these two genotypes is important. Using hairs as a source of DNA, 127 individual brown bears from throughout the Scandinavian populations were assayed for lineage assignment. A part of the mtDNA control region was amplified via the polymearase chain reaction, and the product was either sequenced (14 individuals) or digested with two diagnostic restriction endonucleases (113 individuals). Fifty-six and 71 bears were assigned to the western and eastern lineages, respectively. The geographic distribution of the two genotypes allowed precise localization of the contact zone. Only two males from each lineage had crossed the border between the two lineages. We used dispersal data from bears radiomarked as yearlings to determine whether potential mtDNA introgressions agreed with the dispersal behavior of bears. The males in the "wrong" areas were all within the 95th-percentile dispersal distance from the "correct" area. Females were more philopatric than males, and none were found in the wrong areas. The two female concentration areas flanking the contact zone were 134 km apart. Thus, radiotelemetry results on dispersal distances could explain the occurrence of the males in the wrong genetic area. In the absence of information concerning possible male-mediated gene flow, a conservative management approach would be to consider the southern and the three northern female concentration areas as two distinct conservation units. Localización de una zona de contacto entre dos linajes de ADN mitocondrial muy divergentes del oso pardo Ursus arctos en Escandinavia.