A bear-y strong comeback: Investigating temporal genomic consequences of a recent demographic bottleneck in the Scandinavian brown bear

The Scandinavian brown bear went through a severe bottleneck due to human actions in the early 1900’s that reduced the population to low numbers. After protective measures were taken, the population recovered and today it consists of around 3000 individuals. Such loss of genetic variation can have long-lasting effects on population viability even as populations recover, and is therefore important to consider in the management and conservation of species. Previous studies investigating the genetic effects of the bottleneck based on genetic markers, such as microsatellites and mitochondrial DNA, have rendered inconclusive results. Here, whole-genome sequencing of historical and contemporary bears was used to estimate heterozygosity, inbreeding and mutational load in the pre- and post- bottleneck population. Surprisingly, a significant increase in heterozygosity was found in the contemporary population and no significant increase in inbreeding over time was found. However, mutational load was higher in the contemporary subpopulation in the south of Sweden compared to the subpopulation in the north, and the southern subpopulation seems to have lost unique genetic variation after the bottleneck. The results indicate that although the population was negatively affected by the bottleneck, a following increase in gene flow could have contributed to successful recovery of the population