Admixture and Gene Flow from Russia in the Recovering Northern European Brown Bear (Ursus arctos)

Abstract

Large carnivores were persecuted to near extinction during the last centuries, but have now recovered in some countries. It has been proposed earlier that the recovery of the Northern European brown bear is supported by migration from Russia. We tested this hypothesis by obtaining for the first time continuous sampling of the whole Finnish bear population, which is located centrally between the Russian and Scandinavian bear populations. The Finnish population is assumed to experience high gene flow from Russian Karelia. If so, no or a low degree of genetic differentiation between Finnish and Russian bears could be expected. We have genotyped bears extensively from all over Finland using 12 validated microsatellite markers and compared their genetic composition to bears from Russian Karelia, Sweden, and Norway. Our fine masked investigation identified two overlapping genetic clusters structured by isolation-by-distance in Finland (pairwise FST = 0.025). One cluster included Russian bears, and migration analyses showed a high number of migrants from Russia into Finland, providing evidence of eastern gene flow as an important driver during recovery. In comparison, both clusters excluded bears from Sweden and Norway, and we found no migrants from Finland in either country, indicating that eastern gene flow was probably not important for the population recovery in Scandinavia. Our analyses on different spatial scales suggest a continuous bear population in Finland and Russian Karelia, separated from Scandinavia.

Evidence of rapid change in genetic structure and diversity during range expansion in a recovering large terrestrial carnivore

“…The average latitude of both subpopulations shifted northwards during the study period by 18 latitude, which corresponds to a linear distance of approximately 110 km, or an average of 7.4 km per year. Further, the proportion of individuals that was not clearly assigned to either subpopulation, possibly due to advanced admixture and gene flow from neighbouring populations [31], was found further north as time progressed. Previous studies and meta-analyses have summarized the speed of range shifts.…”

“…These included tissue samples from 772 legally harvested bears (271 females, 500 males, one unknown sex), and 47 bears (20 females, 27 males) that had been sampled non-invasively. Thus, we analysed a total of 819 bears (figure 1c), collected annually during 1996 through 2010, of which 333 samples from 2005 to 2010 were used previously in spatial genetic analyses [31,32].…”

Y chromosome haplotype distribution of brown bears (Ursus arctos) in Northern Europe provides insight into population history and recovery

“…We used DNA samples of verified male individuals, analysed and stored in the course of regional and national monitoring programmes conducted in Sweden and Norway, as well as during previous studies conducted in Finland (Kopatz et al . , ; Schregel et al . ; Hagen et al .…”

“…; Kopatz et al . ). These differential recovery histories and the low connectivity between the eastern and western parts of the species’ range offer an opportunity for applying Y‐chromosomal markers to study the impact of male gene flow in the recovering brown bear populations in Northern Europe.…”

“…Recently, using autosomal STRs, Kopatz et al . () documented that the demographic recovery, that is the increase of population size after the bottleneck, of the brown bears in Finland was supported by immigration from Russia, whereas in Sweden and Norway, brown bear numbers increased from near extinction without significant immigration of eastern bears. In addition, genetic connectivity between the eastern (Finland, Russia) and western (Norway, Sweden) subpopulations (Fig.…”