Limited gene flow among brown bear populations in far Northern Europe? Genetic analysis of the east-west border population in the Pasvik Valley.

Noninvasively collected genetic data can be used to analyse large-scale connectivity patterns among populations of large predators without disturbing them, which may contribute to unravel the species' roles in natural ecosystems and their requirements for long-term survival. The demographic history of brown bears (Ursus arctos) in Northern Europe indicates several extinction and recolonization events, but little is known about present gene flow between populations of the east and west. We used 12 validated microsatellite markers to analyse 1580 hair and faecal samples collected during six consecutive years (2005-2010) in the Pasvik Valley at 70°N on the border of Norway, Finland and Russia. Our results showed an overall high correlation between the annual estimates of population size (N(c) ), density (D), effective size (N(e) ) and N(e) /N(c) ratio. Furthermore, we observed a genetic heterogeneity of ∼0.8 and high N(e) /N(c) ratios of ∼0.6, which suggests gene flow from the east. Thus, we expanded the population genetic study to include Karelia (Russia, Finland), Västerbotten (Sweden) and Troms (Norway) (477 individuals in total) and detected four distinct genetic clusters with low migration rates among the regions. More specifically, we found that differentiation was relatively low from the Pasvik Valley towards the south and east, whereas, in contrast, moderately high pairwise F(ST) values (0.91-0.12) were detected between the east and the west. Our results indicate ongoing limits to gene flow towards the west, and the existence of barriers to migration between eastern and western brown bear populations in Northern Europe.

Reproductive success in reindeer males in a herd with varying sex ratio.

In polygynous species, male reproductive success is often correlated with dominance status of individual males and sex ratio in the population. Reindeer, Rangifer tarandus, is a polygynous species, and here we compared the variation in male reproductive success and dominance status during two successive years in a herd with a male:female sex ratio of 1:7 and 1:3. Copulations were recorded, together with data on male dominance hierarchy and size of mating groups. Male reproductive success was estimated by paternity analysis of calves using microsatellite DNA markers. The distribution of reproductive success among the males was highly skewed for both years with the most dominant male also being the most successful. The largest mating group was established in the herd with the least skew in sex ratio. In this herd some of the adult males present were less reproductively successful than some of the more subordinate younger males. Estimates of the mating group size of males, correcting for dominance status when more than one male is present in the groups, gave good prediction of individual males' reproductive success.