Isabelle Sofie Feinauer

After the last ice age, species migrated into a newly deglaciated Scandinavia. Brown bear recolonization is thought to have occurred from two directions—from the south and the northeast—resulting in a nonoverlapping distribution of two distinct mitochondrial clades. A contact zone in central Sweden separates populations with mitochondrial clade 1a in the south from those with clade 3a in the north. However, a paucity of brown bear subfossils in Scandinavia has limited testing of this prevailing model using ancient DNA. Here, we present a high-coverage brown bear mitogenome (231×) and nuclear genome-wide data (0.05×) extracted from lake sediment dated to 9.6 cal. ka BP from northern Sweden, representing the oldest known record of brown bear in the region. At this point in the Early Holocene, the Fennoscandian Ice Sheet was in its final stages of recession. Surprisingly, our analyses suggest that this environmental genome represents one male individual carrying clade 1a and with southern brown bear nuclear ancestry, despite being found far north of the contact zone. This suggests the individual was a migratory bear and had dispersed northward from its birthplace. Our finding adds to the scarce genomic record of Early Holocene brown bears and highlights the use of sedimentary ancient DNA as a powerful source of genomic information.

After the last ice age, the brown bear (Ursus arctos) recolonized Scandinavia, likely from two different source populations, resulting in two subpopulations with distinct mitochondrial haplogroups. In the early 1900s, human persecution led to a severe bottleneck that reduced the overall population size from around 5000 to approximately 130 individuals. After protective measures were taken, the population recovered and today it comprises roughly 3000 individuals. Such bottlenecks can lead to loss of genetic variation, which can have long-lasting effects on population viability and population recovery. In this study, we generated whole-genome data of seven historical and 21 contemporary Scandinavian brown bears to estimate heterozygosity, inbreeding and mutational load, as well as population structure in the pre- and post-bottleneck subpopulations. Surprisingly, no significant decrease in heterozygosity and no significant increase in inbreeding and mutational load were found when comparing the historical and modern subpopulations. However, analyses of population structure and admixture suggest that the southern subpopulation has lost most of its genetic uniqueness, except in the mitochondrial genome. Our results indicate that the bottleneck led to an increase in male-driven gene flow from the north to the south, which maintained the subpopulation’s genome-wide diversity and may have contributed to its successful recovery.

The Norwegian lemming ( Lemmus lemmus ) is a small rodent distributed across the Fennoscandian mountain tundra and the Kola Peninsula. The Norwegian lemming likely evolved during the Late Pleistocene and inhabited Fennoscandia shortly prior to the Last Glacial Maximum. However, the exact timing and origins of the species, and its phylogenetic position relative to the closely related Siberian lemming ( Lemmus sibiricus ) remain disputed. Moreover, the presence of ancient or contemporary gene flow between both species is largely untested. The Norwegian lemming displays characteristic phenotypic and behavioral adaptations (e.g., coat color, aggression) that are not present in other Lemmus species. We generated a de novo genome assembly for the Norwegian lemming and resequenced nine modern and two ancient Lemmus spp. genomes. We show that all Lemmus species form distinct monophyletic clades, with concordant topology between the mitochondrial and nuclear genome phylogenies. The Siberian lemming is divided into two distinct but paraphyletic clades, one in the east and one in the west, where the western clade represents a sister taxon to the Norwegian lemming. We estimate that the Norwegian and western Siberian lemming diverged shortly before the Last Glacial Maximum, making the Norwegian lemming one of the youngest known mammalian species. We did not find any indication of gene flow between L. lemmus and L. sibiricus , suggesting postglacial isolation of L. lemmus . Furthermore, we identify species-specific genomic differences in genes related to coat color and fat transport, which are likely associated with the distinctive coloration and overwintering behavior observed in the Norwegian lemming.

Our understanding of prehistoric societal organization at the family level is still limited. Here, we generated genome data from 32 individuals from an approximately 3,800-y-old burial mound attributed to the Bronze Age Srubnaya-Alakul cultural tradition at the site of Nepluyevsky, located in the Southern Ural region of Central Eurasia. We found that life expectancy was generally very low, with adult males living on average 8 y longer than females. A total of 35 first-degree, 40 second-degree, and 48 third-degree biological relationships connected 23 of the studied individuals, allowing us to propose a family tree spanning three generations with six brothers at its center. The oldest of these brothers had eight children with two women and the most children overall, whereas the other relationships were monogamous. Notably, related female children above the age of five were completely absent from the site, and adult females were more genetically diverse than males. These results suggest that biological relationships between male siblings played a structural role in society and that descent group membership was based on patrilineality. Women originated from a larger mating network and moved to join the men, with whom they were buried. Finally, the oldest brother likely held a higher social position, which was expressed in terms of fertility.