A chromosome-level genome assembly of the common eider, Somateria mollissima (Linnaeus, 1758).

The common eider, Somateria mollissima mollissima (Chordata; Aves; Anseriformes; Anatidae), is a large sea duck with a circumpolar distribution. We here describe a chromosome-level genome assembly from an individual female. The haplotype-resolved assembly contains one pseudo-haplotype spanning 1205 megabases (with both Z and W sex chromosomes) and one pseudo-haplotype spanning 1080 megabases. Most of these two assemblies (91.13% and 93.18%, respectively) are scaffolded into 32 autosomal chromosomal pseudomolecules plus Z and W for pseudo-haplotype one. The BUSCO completeness scores are 94.0% and 89.9%, respectively, and gene annotations of the assemblies identified 17,479 and 16,315 protein coding genes. Annotation of repetitive sequences classify 17.84 % and 14.62 % of pseudo-haplotype one and two, respectively, as repeats. The genome of the common eider will be a useful resource for the widely distributed northern species in light of climate change and anthropogenic threats.

Adaptation to the High-Arctic island environment despite long-term reduced genetic variation in Svalbard reindeer.

Typically much smaller in number than their mainland counterparts, island populations are ideal systems to investigate genetic threats to small populations. The Svalbard reindeer (Rangifer tarandus platyrhynchus) is an endemic subspecies that colonized the Svalbard archipelago ca. 6,000-8,000 years ago and now shows numerous physiological and morphological adaptations to its arctic habitat. Here, we report a de-novo chromosome-level assembly for Svalbard reindeer and analyze 133 reindeer genomes spanning Svalbard and most of the species' Holarctic range, to examine the genomic consequences of long-term isolation and small population size in this insular subspecies. Empirical data, demographic reconstructions, and forward simulations show that long-term isolation and high inbreeding levels may have facilitated the reduction of highly deleterious-and to a lesser extent, moderately deleterious-variation. Our study indicates that long-term reduced genetic diversity did not preclude local adaptation to the High Arctic, suggesting that even severely bottlenecked populations can retain evolutionary potential.