oliverke

• Ellis, Gabrielle N.; Kersten, Oliver Sven; Vetter, Eric; Smith, Craig R.; Drazen, Jeffrey C. & Goetze, Erica (2026). Along the Benthic to Holoplanktonic Continuum: Seafloor Affinity Increases Distance-Decay Rates Among Abyssal Communities. Global Ecology and Biogeography. ISSN 1466-822X. 35(8). doi: 10.1111/geb.70287. Full text in Research Archive
• Dierickx, Katrien Alfred C; Kersten, Oliver Sven; Falahati-Anbaran, Mohsen; Sollid, Eirik; Szpak, Paul & Seiler, Martin Thomas [Show all 14 contributors for this article] (2026). The morphology, isotopic ecology, and phylogeny of walrus, Odobenus rosmarus (Pinnipedia: Odobenidae) populations. Zoological Journal of the Linnean Society. ISSN 0024-4082. 207(1). doi: 10.1093/zoolinnean/zlag077. Full text in Research Archive Show summary

  Walruses are classified into nine extant and two extirpated populations across their circumpolar distribution. While there are hints that these differ morphologically, thus far there has been no in-depth comparison of their morphology and ecology, limiting insights into their conservation and evolutionary status. Here, we investigate regional differences in walrus morphology and ecology during the 17th–21st centuries ce by integrating morphometric analysis of crania (N = 188) and mandibles (N = 193), multi-isotope analysis of bone collagen (δ13C, δ15N, and δ34S; N = 142), and genetic analysis (N = 115). The Pacific and Atlantic subspecies show morphological and isotopic distinctions. Distinct regional selection pressures on males and females can be inferred. This was most visible in the extirpated Maritimes walrus, where females had a unique cranium shape. Regional isotopic and genetic differences were also observed; we found regional differences in δ13C, δ15N, and δ34S, and identified multiple genetic clades coinciding with geographic populations. Overall, the comparative insight into the morphological, ecological, and genetic characteristics of different walrus populations sets a frame of reference for conservation management and from which to understand how each has been impacted by human exploitation and environmental changes in the past.

• Furness, Lydia Hildebrand; Sabin, Richard; Torvanger, Marianne Strand; Kersten, Oliver Sven; Barrett, James Harold & Star, Bastiaan (2025). Historical Collections of Tropical Marine Mammals Are an Excellent Resource for Ancient DNA. Molecular Ecology Resources. ISSN 1755-098X. 25(7), p. 1–16. doi: 10.1111/1755-0998.70015. Full text in Research Archive Show summary

  ABSTRACT The ability to predict ancient DNA sequencing success in natural history collections is critical to reducing the amount of destructive sampling of a finite resource. So far, studies investigating such success have predominantly focused on taxa with ranges restricted to temperate or cold environments at northern latitudes, which likely aids DNA preservation. Here, we report remarkably high aDNA sequencing success in Sirenia , herbivorous marine mammals of which the distribution is currently constrained to the global tropics. We investigate 91 samples from 85 specimens comprising all four contemporary species and one extinct species, comparing different sample types (cranial/post‐cranial bone, skin and cartilage), species, collections, and material age. We obtained remarkably high (e.g., > 20%) endogenous DNA preservation for the majority (e.g., ~57% percent) of samples. Sequencing success was linked to sample type, with cranial bones (including petrous and tympanic bones) yielding significantly higher endogenous DNA. Additionally, we obtained variable, but potentially superior DNA results for preserved cartilage and hide samples that can be associated with historical bone. Although such tissue is not always present, this type of material is easy to sample, with very limited destructive impacts on the associated bones, and we therefore highlight its untapped potential as a source of DNA. Overall, our results show the high success of ancient DNA retrieval from historical collections of species with a tropical distribution, expanding on the types of specimens that are available for temporal genomic analyses.

• Kersten, Oliver Sven; Star, Bastiaan; Anker-Nilssen, Tycho; Strøm, Hallvard; Jakobsen, Kjetill Sigurd & Boessenkool, Sanne (2025). Single Nucleotide Polymorphisms, Structural Variants, and Short Tandem Repeats Capture Distinct Signals of Adaptive Divergence in the Atlantic Puffin. Genome Biology and Evolution (GBE). 17(9), p. 1–17. doi: 10.1093/gbe/evaf162. Full text in Research Archive Show summary

  The Arctic has been the scene for (re)colonization, diversification, and adaptation of boreal and Arctic fauna. As anthropogenic warming of the Arctic environment increases the extinction risk for peripheral populations, understanding patterns of local adaptation is imperative. The Atlantic puffin (Fratercula arctica) comprises multiple genetically and morphologically distinct populations with an Arctic-boreal distribution. Yet, patterns of adaptation between these populations remain poorly understood. Here, we investigate potential adaptive divergence between High Arctic (F. a. naumanni) and boreal (F. a. arctica) puffin subspecies using whole-genome sequence data. We analyze different types of intraspecific DNA variation, including single nucleotide polymorphisms (SNPs), structural variants (SVs) and short tandem repeats (STRs). Patterns of elevated levels of genetic divergence vary across these types, with STRs uncovering the largest unique proportion (47.2%) of genomic outlier loci. Notably, 94.5% of all outlier genes are exclusive to one type of variation and several such genes are linked to phenotypic differences observed between these subspecies, including body size, skeletal development, adipose tissue accumulation and the sensory system. Our observations indicate that F. a. naumanni harbors unique genetic diversity within puffins suggesting adaptation to its Arctic environment. Importantly, we show that SNPs, SVs, and STRs capture distinct signals of adaptive divergence, underscoring the importance of integrating multiple genomic markers to fully understand the complexity of local adaptation. These results offer a broader perspective on genomic patterns of adaptive divergence in Arctic fauna and can inform conservation strategies aimed at preserving genetic diversity in the Atlantic puffin.

• Dierickx, Katrien Alfred C; Kersten, Oliver Sven; Hurk, Youri van den; Frasier, Brenna A.; Sabin, Richard & Star, Bastiaan [Show all 7 contributors for this article] (2025). Ontogenetic changes and sexual dimorphism in the cranium and mandible of the Atlantic walrus (Odobenus rosmarus rosmarus L.). The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology. ISSN 1932-8486. p. 1–29. doi: 10.1002/ar.70050. Full text in Research Archive Show summary

  Abstract Walruses have been an important subsistence and cultural resource for humans and have been exploited for millennia across their distribution. This exploitation has contributed to severe declines in several populations and local extirpations. The study of walrus remains from archaeological sites can provide insights into past exploitation strategies and contribute to improving current conservation practices. The ability to differentiate disarticulated skeletal remains by age and sex can provide insights into past herd compositions. While sexing is a well‐established approach for mandibles, a clear morphological key to determine such differentiation in crania is currently lacking. Here, linear measurements and geometric morphometrics of mandibles ( n  = 121) and crania ( n  = 116) of the Atlantic walrus ( Odobenus rosmarus rosmarus ) are used to describe the age and sex differences. Suture fusion states are strongly associated with age. There are clear size and shape differences between adults and neonates, with juveniles showing a gradual transition between states. Sexual dimorphism is clearly present in adults, but not detected in juveniles and neonates. Linear discriminant analysis successfully assigned sexes to 19 out of 21 (90.5%) DNA‐sexed adult test specimens. Comparatively, only two out of five juvenile test specimens were correctly sexed using morphometrics. We suggest that aging specimens using suture fusion states, followed by classification between adult males and females, provides the most accurate results. This classification technique will facilitate future osteological studies on walruses, for example, to understand their ecomorphology and to provide insight into historical age‐ and sex‐based exploitation and population impacts through time.

• Eriksen, Emma Falkeid; Andrews, Adam Jon; Nielsen, Svein Vatsvåg; Persson, Per; Malca, Estrella & Onar, Vedat [Show all 19 contributors for this article] (2025). Five millennia of mitonuclear discordance in Atlantic bluefin tuna identified using ancient DNA. Heredity. ISSN 0018-067X. 134, p. 175–185. doi: 10.1038/s41437-025-00745-1. Full text in Research Archive Show summary

  Mitonuclear discordance between species is readily documented in marine fishes. Such discordance may either be the result of past natural phenomena or the result of recent introgression from previously seperated species after shifts in their spatial distributions. Using ancient DNA spanning five millennia, we here investigate the long-term presence of Pacific bluefin tuna (Thunnus orientalis) and albacore (Thunnus alalunga) -like mitochondrial (MT) genomes in Atlantic bluefin tuna (Thunnus thynnus), a species with extensive exploitation history and observed shifts in abundance and age structure. Comparing ancient (n = 130) and modern (n = 78) Atlantic bluefin MT genomes from most of its range, we detect no significant spatial or temporal population structure, which implies ongoing gene flow between populations and large effective population sizes over millennia. Moreover, we identify discordant MT haplotypes in ancient specimens up to 5000 years old and find that the frequency of these haplotypes has remained similar through time. We therefore conclude that MT discordance in the Atlantic bluefin tuna is not driven by recent introgression. Our observations provide oldest example of directly observed MT discordance in the marine environment, highlighting the utility of ancient DNA to obtain insights in the long-term persistence of such phenomena.

• Andrews, Adam Jon; Eriksen, Emma Falkeid; Star, Bastiaan; Præbel, Kim; Natale, Antonio Di & Malca, Estrella [Show all 19 contributors for this article] (2025). Ancient DNA suggests a historical demographic decline and genetic erosion in the Atlantic bluefin tuna. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 122(21). doi: 10.1073/pnas.2409302122. Full text in Research Archive Show summary

  Overexploitation has depleted fish stocks during the past century; nonetheless, its genomic consequences remain poorly understood for most species. Characterizing the spatiotemporal patterns of these consequences may provide baseline estimates of past diversity and productivity to aid management targets, help predict future dynamics, and facilitate the identification of evolutionary factors limiting fish population recovery. Here, we evaluate human impacts on the evolution of the iconic Atlantic bluefin tuna (Thunnus thynnus), one of the longest and most intensely exploited marine fishes, with a tremendous cultural and economic importance. We sequenced whole genomes from modern (n = 49) and ancient (n = 41) specimens dating up to 5,000 y ago, uncovering several findings. First, we identify temporally stable patterns of population admixture, as bluefin tuna caught off Norway and in the eastern Mediterranean share a greater degree of ancestry with Gulf of Mexico bluefin tuna than western and central Mediterranean bluefin tuna. This suggests that Atlantic spawning areas are important mixing grounds for the genetic diversity of Mediterranean bluefin tuna. We model effective population size to show that Mediterranean bluefin tuna began to undergo a demographic decline by the year 1900 to an extent not observed across the previous millennia. Coinciding with this, we found that heterozygosity and nucleotide diversity were significantly lower in modern (2013 to 2020) than ancient (pre-1941) Mediterranean bluefin tuna, suggesting that bluefin tuna underwent a genetic bottleneck. With this work, we show how ancient DNA provides unique perspectives on ecological complexity with the potential to inform the management and conservation of fishes.

• Furness, Lydia Hildebrand; Kersten, Oliver Sven; Boilard, Aurélie; Keith-Diagne, Lucy; Brito, Cristina & Barrett, James Harold [Show all 11 contributors for this article] (2024). Population structure of Dugong dugon across the Indo-Pacific revealed by historical mitogenomes. Royal Society Open Science. 11(8). doi: 10.1098/rsos.240599. Full text in Research Archive Show summary

  Sirenia, an iconic marine taxon with a tropical and subtropical worldwide distribution, face an uncertain future. All species are designated ‘Vulnerable’ to extinction by the IUCN. Nonetheless, a comprehensive understanding of geographic structuring across the global range is lacking, impeding our ability to highlight particularly vulnerable populations for conservation priority. Here, we use ancient DNA to investigate dugong (Dugong dugon) population structure, analysing 56 mitogenomes from specimens comprising the known historical range. Our results reveal geographically structured and distinct monophyletic clades characterized by contrasting evolutionary histories. We observe deep-rooted and divergent lineages in the East (Indo-Pacific) and obtain new evidence for the relatively recent dispersal of dugongs into the western Indian Ocean. All populations are significantly differentiated from each other with western populations having approximately 10-fold lower levels of genetic variation than eastern Indo-Pacific populations. Additionally, we find a significant temporal loss of genetic diversity in western Indian Ocean dugongs since the mid-twentieth century, as well as a decline in population size beginning approximately 1000 years ago. Our results add to the growing body of evidence that dugong populations are becoming ever more susceptible to ongoing human action and global climate change.

• Tørresen, Ole K.; Kersten, Oliver Sven; Garmann-Aarhus, Benedicte; Helberg, Morten; Tooming-Klunderud, Ave & Skage, Morten [Show all 8 contributors for this article] (2024). A chromosome-level genome assembly of the common eider, Somateria mollissima (Linnaeus, 1758). Journal of Heredity. ISSN 0022-1503. doi: 10.1093/jhered/esae042. Full text in Research Archive Show summary

  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 1,205 megabases (with both Z and W sex chromosomes) and one pseudo-haplotype spanning 1,080 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.

• Kersten, Oliver Sven; Star, Bastiaan; Krabberød, Anders Kristian; Atmore, Lane; Tørresen, Ole K. & Anker-Nilssen, Tycho [Show all 12 contributors for this article] (2023). Hybridization of Atlantic puffins in the Arctic coincides with 20th-century climate change. Science Advances. 9(40). doi: 10.1126/sciadv.adh1407. Full text in Research Archive Show summary

  The Arctic is experiencing the fastest rates of global warming,leading to shifts in the distribution of its biota and increasing the potential for hybridization. However, genomic evidenc eof recent hybridization events in the Arctic remains unexpectedly rare. Here, we use whole-genome sequencing of contemporary and 122-year-old historical specimens to investigate the origin of an Arctic hybrid population of Atlantic puffins(Fratercula arctica) on Bjørnøya, Norway. We show that the hybridization between the High Arctic, large-bodied subspecies F.a. naumanni and the temperate, smaller-sized subspecies F.a. arctica began as recently as six generations ago due to an unexpected southward range expansion of F.a. naumanni. Moreover, we find a significant temporal loss of genetic diversity across Arctic and temperate puffin populations.Our observations provide compelling genomic evidence of the impacts of recent distributional shifts and loss of diversity in Arctic communities during the 20th century.

• Leigh, Deborah M.; Kersten, Oliver Sven; Star, Bastiaan; Anker-Nilssen, Tycho; Burnham, Kurt & Johnson, Jeff [Show all 8 contributors for this article] (2022). Sympatry of genetically distinct Atlantic Puffins (Fratercula arctica) in the High Arctic. IBIS. ISSN 0019-1019. 165(3), p. 1022–1030. doi: 10.1111/ibi.13153. Full text in Research Archive Show summary

  Across its range, the Atlantic Puffin Fratercula arctica is divided into four separate genetic clusters that correspond with geography and/or size differences. However, in the Western Atlantic High Arctic, there is a Puffin colony (Thule) that comprises two discrete size phenotypes. Using whole genome sequencing data of six Thule individuals from these two phenotypes, we found that Thule consists of three distinct genetic clusters, with no signs of recent interbreeding. Our results suggest the beginnings of a potential northward shift of boreal Atlantic Puffins in the West Atlantic, consistent with responses to a warming High Arctic climate. climate change, genomics, Greenland, seabird

• Kersten, Oliver; Star, Bastiaan; Leigh, Deborah M.; Anker-Nilssen, Tycho; Strøm, Hallvard & Danielsen, Jóhannis [Show all 17 contributors for this article] (2021). Complex population structure of the Atlantic puffin revealed by whole genome analyses. Communications Biology. 4. doi: 10.1038/s42003-021-02415-4. Full text in Research Archive Show summary

  The factors underlying gene flow and genomic population structure in vagile seabirds are notoriously difficult to understand due to their complex ecology with diverse dispersal barriers and extensive periods at sea. Yet, such understanding is vital for conservation management of seabirds that are globally declining at alarming rates. Here, we elucidate the population structure of the Atlantic puffin (Fratercula arctica) by assembling its reference genome and analyzing genome-wide resequencing data of 72 individuals from 12 colonies. We identify four large, genetically distinct clusters, observe isolation-by-distance between colonies within these clusters, and obtain evidence for a secondary contact zone. These observations disagree with the current taxonomy, and show that a complex set of contemporary biotic factors impede gene flow over different spatial scales. Our results highlight the power of whole genome data to reveal unexpected population structure in vagile marine seabirds and its value for seabird taxonomy, evolution and conservation.

• Guellil, Meriam; Rinaldo, Natascia; Zedda, Nicoletta; Kersten, Oliver; Muro, Xabier Gonzalez & Stenseth, Nils Chr. [Show all 8 contributors for this article] (2021). Bioarchaeological insights into the last plague of Imola (1630–1632). Scientific Reports. 11(1), p. 1–12. doi: 10.1038/s41598-021-98214-2. Full text in Research Archive Show summary

  Abstract The plague of 1630–1632 was one of the deadliest plague epidemics to ever hit Northern Italy, and for many of the affected regions, it was also the last. While accounts on plague during the early 1630s in Florence and Milan are frequent, much less is known about the city of Imola. We analyzed the full skeletal assemblage of four mass graves (n = 133 individuals) at the Lazaretto dell’Osservanza, which date back to the outbreak of 1630–1632 in Imola and evaluated our results by integrating new archival sources. The skeletons showed little evidence of physical trauma and were covered by multiple layers of lime, which is characteristic for epidemic mass mortality sites. We screened 15 teeth for Yersinia pestis aDNA and were able to confirm the presence of plague in Imola via metagenomic analysis. Additionally, we studied a contemporaneous register, in which a friar recorded patient outcomes at the lazaretto during the last year of the epidemic. Our multidisciplinary approach combining historical, osteological and genomic data provided a unique opportunity to reconstruct an in-depth picture of the last plague of Imola through the city's main lazaretto.

• Ferrari, Giada; Cuevas, Angelica; Wyrozemska, Agata Teresa; Ballantyne, Rachel; Kersten, Oliver & Palsdottir, Albina Hulda [Show all 18 contributors for this article] (2021). The preservation of ancient DNA in archaeological fish bone. Journal of Archaeological Science. ISSN 0305-4403. 126(105317). doi: 10.1016/j.jas.2020.105317. Full text in Research Archive Show summary

  The field of ancient DNA is dominated by studies focusing on terrestrial vertebrates. This taxonomic bias limits our understanding of endogenous DNA preservation for species with different bone physiology, such as teleost fish. Teleost bone is typically brittle, porous, lightweight, and is characterized by a lack of bone remodeling during growth. All of these factors potentially affect DNA preservation. Using high-throughput shotgun sequencing, we here investigate the preservation of DNA in a range of different bone elements from over 200 archaeological Atlantic cod (Gadus morhua) specimens from 38 sites in northern Europe, dating up to 8000 years before present. We observe that the majority of archaeological sites (79%) yield endogenous DNA, with 40% of sites providing samples containing high levels (>20%). Library preparation success and levels of endogenous DNA depend mainly on excavation site and pre-extraction laboratory treatment. The use of pre-extraction treatments lowers the rate of libraries that can be sequenced, although — if successful — the fraction of endogenous DNA can be improved by several orders of magnitude. This trade-off between library preparation success and levels of endogenous DNA allows for alternative extraction strategies depending on the requirements of down-stream analyses and research questions. Finally, we do not find particular bone elements to yield higher levels of endogenous DNA, as is the case for denser bones in mammals. Our results highlight the potential of archaeological fish bone as a source for ancient DNA and suggest a possible role of bone remodeling in the preservation of endogenous DNA.

• Laroche, Oliver; Kersten, Oliver; Smith, Craig R. & Goetze, Erica (2020). From sea surface to seafloor: A benthic allochthonous eDNA survey for the abyssal ocean. Frontiers in Marine Science. 7, p. 1–16. doi: 10.3389/fmars.2020.00682. Full text in Research Archive Show summary

  Environmental DNA (eDNA) metabarcoding could facilitate rapid and comprehensive biotic surveys in the deep ocean, yet many aspects of the sources and distribution of eDNA in the deep sea are still poorly understood. In order to examine the influence of the water column on benthic eDNA surveys in regions targeted for deep-sea polymetallic nodule mining, we investigated the occurrence of pelagic eDNA across: (1) two different deep-sea habitat types, abyssal plains and seamounts, (2) benthic sample types, including nodules, sediment, and seawater within the benthic boundary layer (BBL), and (3) sediment depth horizons (0–2 and 3–5 cm). Little difference was observed between seamounts and the adjacent abyssal plains in the proportion of legacy pelagic eDNA sampled in the benthos, despite >1,000 m depth difference for these habitats. In terms of both reads and amplicon sequence variants (ASVs), pelagic eDNA was minimal within sediment and nodule samples (<2%), and is unlikely to affect benthic surveys that monitor resident organisms at the deep seafloor. However, pelagic eDNA was substantial within the BBL (up to 13% ASVs, 86% reads), derived both from the high-biomass upper ocean as well as deep pelagic residents. While most pelagic metazoan eDNA found in sediments and on nodules could be sourced from the epipelagic, protist legacy eDNA sampled on these substrates appeared to originate across a range of depths in the water column. Some evidence of eDNA degradation across a vertical sediment profile was observed for protists, with higher diversity in the 0–2 cm layer and a significantly lower proportion of legacy pelagic eDNA in deeper sediments (3–5 cm). Study-wide, our estimated metazoan sampling coverage ranged from 40 to 74%, despite relatively large sample size. Future deep-sea eDNA surveys should examine oceanographic influences on eDNA transport and residence times, consider habitat heterogeneity at a range of spatial scales in the abyss, and aim to process large amounts of material per sample (with replication) in order to increase the sampling coverage in these diverse deep ocean communities.

• Laroche, Olivier; Kersten, Oliver; Smith, Craig R. & Goetze, Erica (2020). Environmental DNA surveys detect distinct metazoan communities across abyssal plains and seamounts in the western Clarion Clipperton Zone. Molecular Ecology. ISSN 0962-1083. 29(23), p. 4588–4604. doi: 10.1111/mec.15484. Full text in Research Archive Show summary

  The deep seafloor serves as a reservoir of biodiversity in the global ocean, with >80% of invertebrates at abyssal depths still undescribed. These diverse and remote deep‐sea communities are critically under‐sampled and increasingly threatened by anthropogenic impacts, including future polymetallic nodule mining. Using a multigene environmental DNA (eDNA) metabarcoding approach, we characterized metazoan communities sampled from sediments, polymetallic nodules and seawater in the western Clarion Clipperton Zone (CCZ) to test the hypotheses that deep seamounts (a) are species richness hotspots in the abyss, (b) have structurally distinct communities in comparison to other deep‐sea habitats, and (c) that seafloor particulate organic carbon (POC) flux and polymetallic nodule density are positively correlated with metazoan diversity. eDNA metabarcoding was effective at characterizing distinct biotas known to occur in association with different abyssal substrate types (e.g., nodule‐ and sediment‐specific fauna), with distinct community composition and few taxa shared across substrates. Seamount faunas had higher overall taxonomic richness, and different community composition and biogeography than adjacent abyssal plains, with seamount communities displaying less connectivity between regions than comparable assemblages on the abyssal plains. Across an estimated gradient of low to moderate POC flux, we find lowest taxon richness at the lowest POC flux, as well as an effect of nodule size on community composition. Our results suggest that while abyssal seamounts are important reservoirs of metazoan diversity in the CCZ, given limited taxonomic overlap between seamount and plains fauna, conservation of seamount assemblages will be insufficient to protect biodiversity and ecosystem function in regions targeted for mining.

• Guellil, Meriam; Kersten, Oliver; Namouchi, Amine; Luciani, Stefania; Marota, Isolina & Arcini, Caroline [Show all 17 contributors for this article] (2020). A genomic and historical synthesis of plague in 18th century Eurasia. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 117(45), p. 28328–28335. doi: 10.1073/pnas.2009677117. Full text in Research Archive Show summary

  Plague continued to afflict Europe for more than five centuries after the Black Death. Yet, by the 17th century, the dynamics of plague had changed, leading to its slow decline in Western Europe over the subsequent 200 y, a period for which only one genome was previously available. Using a multidisciplinary approach, combining genomic and historical data, we assembled Y. pestis genomes from nine individuals covering four Eurasian sites and placed them into an historical context within the established phylogeny. CHE1 (Chechnya, Russia, 18th century) is now the latest Second Plague Pandemic genome and the first non-European sample in the post-Black Death lineage. Its placement in the phylogeny and our synthesis point toward the existence of an extra-European reservoir feeding plague into Western Europe in multiple waves. By considering socioeconomic, ecological, and climatic factors we highlight the importance of a noneurocentric approach for the discussion on Second Plague Pandemic dynamics in Europe.

• Kersten, Oliver; Vetter, Eric W.; Jungbluth, Michelle J.; Smith, Craig R. & Goetze, Erica (2019). Larval assemblages over the abyssal plain in the Pacific are highly diverse and spatially patchy. PeerJ. 7, p. 1–36. doi: 10.7717/peerj.7691. Full text in Research Archive Show summary

  Abyssal plains are among the most biodiverse yet least explored marine ecosystems on our planet, and they are increasingly threatened by human impacts, including future deep seafloor mining. Recovery of abyssal populations from the impacts of polymetallic nodule mining will be partially determined by the availability and dispersal of pelagic larvae leading to benthic recolonization of disturbed areas of the seafloor. Here we use a tree-of-life (TOL) metabarcoding approach to investigate the species richness, diversity, and spatial variability of the larval assemblage at mesoscales across the abyssal seafloor in two mining-claim areas in the eastern Clarion Clipperton Fracture Zone (CCZ; abyssal Pacific). Our approach revealed a previously unknown taxonomic richness within the meroplankton assemblage, detecting larvae from 12 phyla, 23 Classes, 46 Orders, and 65 Families, including a number of taxa not previously reported at abyssal depths or within the Pacific Ocean. A novel suite of parasitic copepods and worms were sampled, from families that are known to associate with other benthic invertebrates or demersal fishes as hosts. Larval assemblages were patchily distributed at the mesoscale, with little similarity in OTUs detected among deployments even within the same 30 × 30 km study area. Our results provide baseline observations on larval diversity prior to polymetallic nodule mining in this region, and emphasize our overwhelming lack of knowledge regarding larvae of the benthic boundary layer in abyssal plain ecosystems.

• Ottoni, Claudio; Guellil, Meriam; Ozga, Andrew; Stone, Anne; Kersten, Oliver & Bramanti, Barbara [Show all 8 contributors for this article] (2019). Metagenomic analysis of dental calculus in ancient Egyptian baboons. Scientific Reports. 9, p. 1–10. doi: 10.1038/s41598-019-56074-x. Full text in Research Archive Show summary

  Dental calculus, or mineralized plaque, represents a record of ancient biomolecules and food residues. Recently, ancient metagenomics made it possible to unlock the wealth of microbial and dietary information of dental calculus to reconstruct oral microbiomes and lifestyle of humans from the past. Although most studies have so far focused on ancient humans, dental calculus is known to form in a wide range of animals, potentially informing on how human-animal interactions changed the animals’ oral ecology. Here, we characterise the oral microbiome of six ancient Egyptian baboons held in captivity during the late Pharaonic era (9th–6th centuries BC) and of two historical baboons from a zoo via shotgun metagenomics. We demonstrate that these captive baboons possessed a distinctive oral microbiome when compared to ancient and modern humans, Neanderthals and a wild chimpanzee. These results may reflect the omnivorous dietary behaviour of baboons, even though health, food provisioning and other factors associated with human management, may have changed the baboons’ oral microbiome. We anticipate our study to be a starting point for more extensive studies on ancient animal oral microbiomes to examine the extent to which domestication and human management in the past affected the diet, health and lifestyle of target animals.

• Guellil, Meriam; Kersten, Oliver; Namouchi, Amine; Bauer, Egil Lindhart; Derrick, Michael & Jensen, Anne Østergaard [Show all 8 contributors for this article] (2018). Genomic blueprint of a relapsing fever pathogen in 15th century Scandinavia. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 115(41), p. 10422–10427. doi: 10.1073/pnas.1807266115. Full text in Research Archive Show summary

  Louse-borne relapsing fever (LBRF) is known to have killed millions of people over the course of European history and remains a major cause of mortality in parts of the world. Its pathogen, Borrelia recurrentis, shares a common vector with global killers such as typhus and plague and is known for its involvement in devastating historical epidemics such as the Irish potato famine. Here, we describe a European and historical genome of B. recurrentis, recovered from a 15th century skeleton from Oslo. Our distinct European lineage has a discrete genomic makeup, displaying an ancestral oppA-1 gene and gene loss in antigenic variation sites. Our results illustrate the potential of ancient DNA research to elucidate dynamics of reductive evolution in a specialized human pathogen and to uncover aspects of human health usually invisible to the archaeological record.

• Namouchi, Amine; Guellil, Meriam; Kersten, Oliver; Hänsch, Stephanie; Ottoni, Claudio & Schmid, Boris Valentijn [Show all 16 contributors for this article] (2018). Integrative approach using Yersinia pestis genomes to revisit the historical landscape of plague during the Medieval Period. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 115(50), p. E11790–E11797. doi: 10.1073/pnas.1812865115. Full text in Research Archive Show summary

  Over the last few years, genomic studies on Yersinia pestis, the causative agent of all known plague epidemics, have considerably increased in numbers, spanning a period of about 5,000 y. Nonetheless, questions concerning historical reservoirs and routes of transmission remain open. Here, we present and describe five genomes from the second half of the 14th century and reconstruct the evolutionary history of Y. pestis by reanalyzing previously published genomes and by building a comprehensive phylogeny focused on strains attributed to the Second Plague Pandemic (14th to 18th century). Corroborated by historical and ecological evidence, the presented phylogeny, which includes our Y. pestis genomes, could support the hypothesis of an entry of plague into Western European ports through distinct waves of introduction during the Medieval Period, possibly by means of fur trade routes, as well as the recirculation of plague within the human population via trade routes and human movement.

• Kersten, Oliver; Smith, Craig R. & Vetter, Eric W. (2017). Abyssal near-bottom dispersal stages of benthic invertebrates in the Clarion-Clipperton polymetallic nodule province. Deep Sea Research Part I: Oceanographic Research Papers. ISSN 0967-0637. 127, p. 31–40. doi: 10.1016/j.dsr.2017.07.001. Full text in Research Archive Show summary

  Growing interest in polymetallic nodule mining has intensified the need to characterize the abundance, community structure and vertical flux of meroplankton in the Clarion-Clipperton Zone (CCZ) to facilitate the estimation of larval supply and potential connectivity of benthic populations. These ecological parameters are essential to predict recolonization processes following the expected large-scale, high intensity disturbances associated with nodule extraction. Here, we present the first description of the composition, abundance, temporal variability, and mesoscale distribution of dispersing stages of the benthos in two study areas in the eastern CCZ. Samples from free-vehicle plankton pumps showed little variation in meroplankton diversity and abundance over scales of 30–100 km for time scales of days to weeks. However, sediment-trap samples revealed high temporal variability in vertical flux over weeks to months. Larval abundances and fluxes measured in the abyssal CCZ are ~ 1–2 orders of magnitude lower than observed at deep-sea ridge and hydrothermal-vent habitats. We found significantly higher downward larval fluxes at 11 m above the bottom (mab) than at 146 mab, indicating accumulation or retention of meroplankton within the Benthic Boundary Layer (BBL). The high abundance of meroplankton in the BBL emphasizes its importance to dispersing stages and suggests that the creation of large sediment plumes in the BBL during nodule mining could compromise the dispersal and recruitment abilities of the abyssal benthos, potentially slowing rates and altering patterns of benthic community recovery following mining disturbance.

• Ajani, Penelope A.; Armbrecht, Linda H.; Kersten, Oliver; Kohli, Gurjeet S. & Murray, Shauna A. (2016). Diversity, temporal distribution and physiology of the centric diatom Leptocylindrus Cleve (Bacillariophyta) from a southern hemisphere upwelling system. Diatom Research. ISSN 0269-249X. 31(4), p. 351–365. doi: 10.1080/0269249X.2016.1260058. Full text in Research Archive

View all works in NVA

• Kersten, Oliver Sven; Schult, Anna Lisa; Randel, Kristin Ranheim; Johansen, Kristin & Vedvik, Stine (2026). Årsrapport for Tarmscreeningprogrammet 2025. Full text in Research Archive Show summary

  Resultatene for 2025 viser at Tarmscreeningprogrammet holder god kvalitet på nasjonalt nivå. Nasjonale måltall ble oppnådd for de fleste kvalitetsindikatorene, og koloskopikvaliteten var gjennomgående høy. For enkelte indikatorer varierte resultatene mellom helseforetakene. Noen helseforetak hadde fortsatt et begrenset tallgrunnlag, noe som gir større usikkerhet i resultatene. Nytt i årets rapport er resultater for bruk av sedasjon og analgesi ved koloskopi og for andelen koloskopier utført av prekvalifiserte skopører. Blant dem som fikk tilsendt prøvesett i 2025, sendte 52 % inn en prøve innen seks måneder. Deltakelsen var lavere blant menn enn blant kvinner, henholdsvis 48 % og 57 %. Deltakelsen er fortsatt lavere enn ønsket. Programmet arbeider kontinuerlig med å øke deltakelsen, og flere tiltak ble satt i gang i 2026. Svartidene for rutineprøver i patologitjenesten bedret seg i 2025 til tross for økt prøvevolum. I 2025 ble det også etablert en digital løsning som gir screeningsentrene løpende tilgang til egne kvalitetsdata.

• Kersten, Oliver Sven; Schult, Anna Lisa; Randel, Kristin Ranheim; Johansen, Kristin & Vedvik, Stine (2025). Årsrapport for Tarmscreeningprogrammet 2024. Full text in Research Archive Show summary

  Tarmscreeningprogrammet ble landsdekkende i 2024 og tilbyr screening med test for blod i avføringen til menn og kvinner fra 55 års alder. Ved påvist blod henvises man til koloskopi på sykehus. Målet er å redusere dødelighet ved å oppdage kreft tidlig og fjerne forstadier før de utvikler seg. Dette er den første årsrapporten for Tarmscreeningprogrammet og viser resultater for 2024. Rapporteringen er basert på forhåndsdefinerte kvalitetsindikatorer for Tarmscreening-programmet, som er beskrevet i programmets kvalitetsmanual. I 2024 deltok 53 % av de inviterte ved å sende inn en avføringsprøve. Det var høyere deltakelse blant kvinner (58 %) enn menn (48 %). Nasjonalt er det tilfredsstillende måloppnåelse på kvalitetsindikatorer for koloskopi. Samtidig ser vi variasjoner mellom regioner og helseforetak på enkeltindikatorer. Screeningsentrene får jevnlig tilgang på egne kvalitetsdata, og er ansvarlige for å følge opp manglende måloppnåelse med tiltak for forbedring. Kreftregisteret har tett dialog med sentrene for å sikre god innrapportering og datakvalitet, samt bidra til kvalitetsforbedring både gjennom monitorering, rapportering og oppfølging og via Endoskopiskolens kurstilbud.

• Kersten, Oliver Sven & Star, Bastiaan (2025). Analyse av eldgammelt DNA viser opprinnelsen til elfenbein fra atlanterhavshvalross/ Tracing the origins of Atlantic walrus ivory through ancient DNA analyses. doi: https:/www.ntnu.no/documents/10476/1308180283/Havets_elfenbein_Sea_Ivories_ebook_v1.pdf/dda3a918-b2cd-b729-755e-69e495e610e7?t=1750678216606. Full text in Research Archive
• Kersten, Oliver Sven; Garcia, Lourdes Martinez; Pulido, Angélica; Ferrari, Giada; Baalsrud, Helle Tessand & Helmerson, Cecilia [Show all 18 contributors for this article] (2024). Long-term population dynamics of Atlantic cod revealed by Ancient DNA and Genomics. Full text in Research Archive
• Kersten, Oliver Sven (2023). Sea Parrot Genomics: Linking Past and Present Population Structure of the Atlantic Puffin (Fratercula arctica). Full text in Research Archive
• Palsdottir, Albina Hulda; Kersten, Oliver; Star, Bastiaan; Nistelberger, Heidi Maria; Kantanen, Juha & Hallsson, Jón Hallsteinn [Show all 7 contributors for this article] (2021). Genetic history of sheep in the North Atlantic from the Viking Age to modern breeds. Full text in Research Archive Show summary

  Sheep were vital to subsistence in the newly settled lands of the Norse in the Faroes, Iceland and Greenland during the Viking Age. Sheep are multi-product animals and were reared for wool, milk, meat, skins and horns, and large number of sheep bones have been found in archaeological excavations in the region. Despite their importance, the origins of local sheep breeds and their development since the 9th century are poorly understood. Here we obtained whole genome sequences of 27 ancient sheep from archaeological excavations in Iceland, Greenland, the Faroe Islands, Norway and the UK dating from 800-1700. For comparison we also analysed both newly generated and previously published modern genomes from North Atlantic, European and Asian sheep breeds. We trace the introduction of sheep to the Faroes, Iceland and Greenland in a clear stepping stone pattern, but ancient UK and Norwegian sheep form an overlapping cluster. Moreover, our data shows a large reduction in genomic diversity of sheep in the North Atlantic from the Viking and Medieval period to the modern sheep breeds in the region.

• Kersten, Oliver Sven (2021). Complex population structure of the Atlantic puffin revealed by whole genome analyses. Full text in Research Archive
• Palsdottir, Albina Hulda; Kersten, Oliver Sven; Star, Bastiaan; Nistelberger, Heidi Maria; Kantanen, Juha & Hallsson, Jón Hallsteinn [Show all 7 contributors for this article] (2021). The tangled history of sheep in the North Atlantic revealed through ancient DNA. Full text in Research Archive Show summary

  Sheep played a vital role in the settlement of the North Atlantic in the Viking Age, providing wool for clothing and the sails of Viking ships in addition to milk, meat, skins and horns. Despite their importance we know little about how the rapid settlement of the North Atlantic shaped the population structure and genetic diversity of sheep and how the local breeds in the North Atlantic region have changed through a thousand years of isolation. We sequenced over 80 ancient sheep bones from archaeological excavations in the North Atlantic resulting in 28 ancient sheep genomes (800-1700 CE) with average coverage of 3,7X and eight genomes from modern landrace breeds present in the region. The population history of sheep in the North Atlantic is more complicated than previously thought with some evidence of admixture of sheep from Norway and the UK during the founding of the Icelandic sheep population. The sheep population in Norse Greenland is clearly founded from Iceland. In Greenland we observe a loss of heterozygosity and increases in inbreeding over time, probably related to population decline associated with the collapse of the Norse settlement in Greenland. Our data shows a large reduction in genomic diversity of sheep in the North Atlantic from the Viking and Medieval period to the modern sheep breeds in the region, specifically in Iceland and the Faroe Islands.

• Namouchi, Amine; Guellil, Meriam; Kersten, Oliver Sven; Hänsch, Stephanie; Ottoni, Claudio & Schmid, Boris Valentijn [Show all 16 contributors for this article] (2020). Correction for Namouchi et al., Integrative approach using Yersinia pestis genomes to revisit the historical landscape of plague during the Medieval Period. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 17(22). doi: 10.1073/pnas.2007983117. Full text in Research Archive
• Kersten, Oliver; Star, Bastiaan; Anker-Nilssen, Tycho; Strøm, Hallvard & Boessenkool, Sanne (2019). Genomic population structure of the Atlantic Puffin – insights into the species’ taxonomy. Full text in Research Archive
• Kersten, Oliver (2016). Yersinia pestis genomes from medieval Europe and Asia during the 2nd plague pandemic. Full text in Research Archive
• Kersten, Oliver Sven (2023). Sea Parrot Genomics: Linking past and present population structure and demography of the Atlantic puffin (Fratercula arctica ). Universitetet i Oslo. Full text in Research Archive Show summary

  Seabird populations worldwide have been declining dramatically over the last decades as a result of a range of environmental and anthropogenic stressors. Nevertheless, management of threatened seabirds is arguably hampered by the severe underutilization of whole genome sequencing (WGS) combined with a limited understanding of the interplay of complex ecological factors affecting population connectivity and contributing to the genetic population structure. By providing detailed genomic data, WGS allows to assess levels of connectivity and gene flow between distinct breeding populations and, thus, helps to identify relevant conservation units for seabirds. Atlantic puffins (Fratercula arctica) have been designated as vulnerable to extinction globally and listed as endangered in Europe. A lack of genetic data for puffins at all spatial scales obstructs efforts towards an assessment of dispersal barriers, limits our understanding of cause-and-effect dynamics between population trends, ecology and the marine ecosystem, and hinders the development of adapted large-scale conservation actions. Here, I present the first whole genome analysis of population structure, gene flow, demographic history and structural DNA variation of a pelagic, North Atlantic seabird. The analysis of 13 Atlantic puffin colonies throughout the majority of the species’ breeding range revealed four large, genetically distinct clusters, which broadly overlap with the currently recognized taxonomy that includes three subspecies (F. a. naumanni, F. a. arctica and F. a. grabae) (Paper I). Additionally, I found a hybrid population in the High Arctic resulting from interbreeding between the High Arctic, large-bodied subspecies F. a. naumanni and the temperate and smaller subspecies F. a. arctica (Paper I & Paper III). Using whole genome data from contemporary and museum specimens, I provide evidence that this hybridization started as recent as six to seven generations ago resulting from a southward range shift of F. a. naumanni and coinciding with a period of rapid ecological change in the Arctic (Paper III). The presence of a hybrid population may also be a forecast of future scenarios throughout other parts of the Arctic illustrated by the sympatry of genetically distinct, but nonadmixing, puffin subspecies within a single High Arctic colony on the west coast of Greenland (Paper II). While genomic-based demographic reconstructions suggest that F. a. naumanni and F. a. arctica diverged due to climatic oscillations in the Pleistocene (Paper III), our understanding of the genomic basis of puffin subspecies differentiation and potential adaptive divergence is limited. Hence, I used single nucleotide polymorphisms, structural variants and short tandem repeats to identify genomic outlier loci that potentially contribute to intraspecific gene flow barriers and phenotypic differences between the subspecies (Paper IV). The results of this thesis highlight the importance of historical and modern whole genome data in understanding population structure and gene flow in seabirds, as well as the genomic basis of intraspecific, phenotypic differences and local adaptation. In light of a global biodiversity loss occurring at unprecedented rates, these findings should have implications for future seabird research and conservation management.

View all works in NVA