Biology subjects

Kersten, O.

Publications and source records attributed to Kersten, O..

6 recordsLinked to original sources

bioRxiv2026

Of bone and ivory: Eastern Atlantic sources of the medieval European walrus ivory trade discovered by ancient mitochondrial and nuclear DNA

Previous molecular archaeological research has made the surprising discovery that almost all studied European walrus finds dating between the 11th and 14th centuries CE seemed to be traded from the Norse colony of Greenland. But why has almost no walrus ivory from the Barents Sea region been detected in medieval Europe, despite its closer proximity and being mentioned in historical accounts? Here, we show that the full spatial extent of medieval Atlantic walrus hunting has been underestimated in previous analyses that targeted modified walrus skulls (rostra) with which pairs of attached tusks were traded, because destructive sampling of ivory artefacts is not always practicable. By analysing workshop offcuts from medieval Sigtuna, Sweden, we directly compare the geographical sources of walrus ivory with rostra, and show that isolated tusks were traded in different ways. We first resolve the genome-wide trans-Atlantic walrus population structure, discovering significant genome-wide nuclear differentiation between western and eastern Atlantic walrus populations. By employing spatially diagnostic nuclear SNPs (n = 144,986), we then use low-coverage sequence data to classify historical walrus rostrum and tusk specimens to either western or eastern Atlantic origin, and thus overcome previous limitations when provenancing walruses based on mitochondrial DNA alone. We find that all medieval walrus rostra are assigned exclusively towards the western Atlantic. In contrast, half of the medieval ivory specimens from Sigtuna are assigned to eastern Atlantic sources including Iceland and the Barents Sea region. Moreover, the objects of eastern origin precede those from Norse Greenland in time, suggesting sequential exploitation. Our observations resolve a discrepancy between earlier molecular inference and historical evidence and imply a significantly broader extent and impact of medieval ecological globalisation in the Arctic.

evolutionary biology↗

bioRxiv2024

Ancient DNA reveals historical demographic decline and genetic erosion in the Atlantic bluefin tuna

Overexploitation has depleted fish stocks during the past century, nonetheless its genomic consequences remain poorly understood. Characterising 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 5000 years ago, uncovering several novel 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 was significantly lower in modern (2013-2020), than ancient (pre-1941) Mediterranean bluefin tuna, suggesting bluefin tuna underwent a genetic bottleneck. With this work we show how ancient DNA provides novel perspectives on ecological complexity with the potential to inform the management and conservation of fishes. SignificanceAchieving the aim of the current UN Ocean Decade to "protect and restore ecosystems and biodiversity" is stymied by a lack of historical knowledge on how human exploitation has impacted and therefore what should be restored. Here, we sequence DNA in ancient fish bones to evaluate the historical diversity of the Atlantic bluefin tuna; which has been of great commercial importance for centuries. We find that bluefin tuna began to undergo demographic decline by 1900, 70 years earlier than currently recognised. Correspondingly, we find modern bluefin tuna had lower levels of genetic diversity than historical ones. This suggests that human impacts on the diversity of marine fishes are likely to have begun earlier and be more complex than previously thought.

ecology↗

bioRxiv2024

Five millennia of mitochondrial introgression in Atlantic bluefin tuna identified using ancient DNA

Mitogenomic (MT) introgression between species is readily documented in marine fishes. Such introgression events may either be long-term natural phenomena or the result of human-driven shifts in spatial distributions of previously separated species. Determining the drivers behind MT introgression is stymied by the difficulty of directly observing patterns of interbreeding over long timescales. Using ancient DNA spanning five millennia, we here investigate the long-term presence of MT introgression from Pacific bluefin tuna (Thunnus orientalis) and albacore (Thunnus alalunga) into Atlantic bluefin tuna (Thunnus thynnus), a species with extensive exploitation history and observed shifts in abundance, and demographic distribution. Comparing ancient (n=130) and modern (n=78) mitogenomes of specimens covering most of the range of Atlantic bluefin tuna we detect no significant spatial or temporal population structure. This lack of spatiotemporal genomic differentiation is indicative of ongoing gene flow between populations and large effective population sizes over millennia. Moreover, we identify introgressed MT genomes in ancient specimens up to 5000 years old and find that this rate of introgression has remained similar through time. We therefore conclude that MT introgression in the Atlantic bluefin tuna is to date unaffected by anthropogenic impacts. By providing the oldest example of directly observed MT introgression in the marine environment, our results highlight the utility of ancient DNA to obtain temporal insights in the long-term persistence of such phenomena.

evolutionary biology↗

bioRxiv2020

Complex population structure of the Atlantic puffin revealed by whole genome analyses

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.

genomics↗

bioRxiv2020

From sea surface to seafloor: a benthic allochthonous eDNA survey for the abyssal ocean

Diverse and remote deep-sea communities are critically under-sampled and increasingly threatened by anthropogenic impacts. 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 cm, 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 an > 1000 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), deriving both from the high biomass upper ocean as well as deep pelagic residents. While most pelagic eDNA found in sediments and on nodules could be sourced from the epipelagic for metazoans, 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.

ecology↗

bioRxiv2020

The preservation of ancient DNA in archaeological fish bone

The field of ancient DNA is taxonomically dominated by studies focusing on mammals. This taxonomic bias limits our understanding of endogenous DNA preservation for vertebrate taxa with different bone physiology, such as teleost fish. In contrast to most mammalian bone, teleost bone is typically brittle, porous, lightweight and is characterized by a lack of bone remodeling during growth. 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 that contain 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 library success, 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 find that -- in contrast to mammalian bones -- different fish bone elements yield similar levels of endogenous DNA. Our results highlight the overall suitability of archaeological fish bone as a source for ancient DNA and provide novel evidence for a possible role of bone remodeling in the preservation of endogenous DNA across different classes of vertebrates.

evolutionary biology↗