Biology subjects

Olsen, M. T.

Publications and source records attributed to Olsen, M. T..

8 recordsLinked to original sources

bioRxiv2026

Contemporary hybridization and localized genomic differentiation between grey seal subspecies

Grey seals are divided into two subspecies, Halichoerus grypus grypus in the Baltic Sea and H. grypus atlantica in the North Atlantic Ocean. Historically, intense hunting caused local extinctions of grey seals across their range and promoted geographical isolation of the subspecies. However, recent population recovery and recolonization have renewed their overlap in a contact zone in Danish and Swedish waters. Here, using whole-genome sequencing data from 119 individuals, we investigate the demographic history of grey seals, the divergence of the subspecies, and genomic signatures of local adaptation and potential hybridization in the contact zone. We estimate that divergence began approximately 10,000 years ago, with gene flow ceasing 2000 years ago. We detect peaks of high genetic differentiation near genes with putative functions in osmo- and thermoregulation, consistent with salinity and temperature differences between the Baltic Sea and the North Atlantic. As evidence of the geographic isolation breaking up, we report a hybrid individual in the southwest Baltic contact zone, with Baltic maternal and Atlantic paternal ancestry, and identify a migrant of Baltic origin in the North Sea. Our study illustrates how local environmental variation and long-term hunting pressure have contributed to divergence between mammal subspecies over a short evolutionary timescale, with recent population recovery, recolonization and hybridization reshaping gene flow dynamics. Broadly, our work emphasizes the importance of studying evolutionary processes amid anthropogenic influences, including both disturbances and conservation successes, where demographic fluctuations, range shifts, altered gene flow, and adaptation to changing environments interact in complex, potentially consequential ways.

evolutionary biology↗

bioRxiv2025

Deep origins and distinct adaptations indicated for a glacial relict seal

Isolated populations of postglacial relicts are known from many regions and are typically found on mountains for terrestrial species and in lakes for aquatic species. Among the few aquatic mammalian relicts, the Saimaa ringed seal (Pusa hispida saimensis) has been landlocked in Lake Saimaa, Finland, for the last 10,000 years. Saimaa ringed seals show genetic, behavioral, and morphological differences to the other ringed seal subspecies, but the extent these differences stem from the end of the last glacial period remains unclear. Here, we demonstrate with comprehensive sampling and state-of-the-art genomic methods that the Saimaa ringed seals are much older than the lake they inhabit, having formed a separate evolutionary branch for at least 60,000 years. This deep evolutionary origin of the Saimaa ringed seals is further underscored by our ecomorphological analyses revealing adaptively distinct features in their dentition and tongue. Overall, glacial relicts, many threatened by extinction, may harbor a richer selection of evolutionary history than might be expected from their recent isolation history alone.

zoology↗

bioRxiv2024

Palaeoproteomic identification of a whale bone tool from Bronze Age Heiloo, the Netherlands

Identification of the taxonomic origin of bone tools is an important, but often complicated, component of studying past societies. The species used for bone tool production provide insight into what species were exploited, potentially how, and for what purpose. Additionally, the choice of species may have important implications for the place of the tool within the larger toolkit. However, the taxonomic identification of bone tools is often unsuccessful based on morphology. Here we apply three palaeoproteomic techniques, ZooMS, SPIN-like data analysis and a targeted database search to narrow down the taxonomic identification of an unusually large Bronze Age bone tool from Heiloo, the Netherlands, to the North Atlantic right whale (Eubalaena glacialis). Additionally, the tool was investigated for use-wear, which showed that it was likely used for the processing of plant fibres. The assignment of the tool as whale bone adds support to the exploitation of whales by coastal Bronze Age populations, not just for meat, as previously suggested, but also for bone as a resource for tool production. We know of no other parallel of a bone tool such as this in terms of size, use, hafting, and taxonomic identity.

evolutionary biology↗

bioRxiv2022

Genomic differentiation among European perch in the western Baltic Sea reflects colonization history and local adaptation

Environmental variation across the distribution of wild species can lead to local adaptations. The Baltic Sea was formed when the Fenno-Scandian ice sheet retreated around 12 thousand years ago, creating a new brackish water habitat colonised by both marine and freshwater fish species. The European perch (Perca fluviatilis) is a predatory freshwater fish with a large geographical distribution across Eurasia, where it inhabits a wide range of environmental niches. In the Baltic Sea region it has even developed a specialised brackish water phenotype that can tolerate environmental salinity levels, which are lethal to the ancestral freshwater phenotype. However, very little is known about the colonisation history and underlying genomic mechanisms facilitating the colonisation and adaptation of perch to the Baltic Sea. Here, we use Genotyping-By-Sequencing data from six freshwater and six brackish water localities to disclose the evolutionary relationship between the freshwater and brackish water phenotype. Our results show that the brackish water perch phenotype occurs in multiple distinct genetic clusters. We find that gene flow between brackish water phenotypes with full access to the sea likely led to lower levels of differentiation and higher diversity than in freshwater phenotypes. Selection analyses suggest that genomic adaptation played a role in the colonisation of the Baltic Sea and that the top three regions under selection harbour salinity tolerance genes. We also find a link between the historic salinity of the Baltic Sea and the demographic history of the brackish water phenotypes and go on to discuss the implications of our findings for management of brackish water perch in the western Baltic sea. HighlightsO_LIGBS data from 12 perch populations, six with brackish and six with freshwater origin C_LIO_LIColonisation history and differentiated gene flow shaped the current population structure C_LIO_LIThe brackish water ecotype was found in all three major genetic clades C_LIO_LITop three regions under selection harboured salinity tolerance genes C_LIO_LISalinity influenced Ne during the formation of the Baltic Sea C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/516742v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@29e5dforg.highwire.dtl.DTLVardef@b2b35borg.highwire.dtl.DTLVardef@1d3457org.highwire.dtl.DTLVardef@1574e46_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2022

Holistic monitoring of freshwater and terrestrial vertebrates by camera trapping and environmental DNA

The anthropogenic impact on the worlds ecosystems is severe and the need for non-invasive, cost-effective tools for monitoring and understanding those impacts are therefore urgent. Here we combine two such methods in a comprehensive multi-year study; camera trapping (CT) and analysis of environmental DNA (eDNA), in river marginal zones of a temperate, wetland Nature Park in Denmark. CT was performed from 2015 to 2019 for a total of 8,778 camera trap days and yielded 24,376 animal observations. The CT observations covered 87 taxa, of which 78 were identified to species level, and 73 were wild native species. For eDNA metabarcoding, a total of 114 freshwater samples were collected from eight sites in all four seasons from 2017 to 2018. The eDNA results yielded a total detection of 80 taxa, of which 74 were identified to species level, and 65 were wild native species. While the number of taxa detected with the two methods were comparable, the species overlap was only 20 %. In combination, CT and eDNA monitoring thus yielded a total of 115 wild species (20 fishes, four amphibians, one snake, 23 mammals and 67 birds), representing half of the species found via conventional surveys over the last ca. 20 years (83% of fishes, 68 % of mammals, 67 % of amphibians, 41 % of birds and 20 % of reptiles). Our study demonstrates that a holistic approach combining two non-invasive methods, CT and eDNA metabarcoding, has great potential as a cost-effective biomonitoring tool for vertebrates.

zoology↗

bioRxiv2022

Airborne environmental DNA captures terrestrial vertebrate diversity in nature

The current biodiversity and climate crises highlight the need for efficient tools to monitor terrestrial ecosystems. Here, we provide evidence for the use of airborne eDNA analyses as a novel method to detect terrestrial vertebrate communities in nature. Metabarcoding of 143 airborne eDNA samples collected during three days in [A]mosen Nature Park, Denmark yielded 64 bird, mammal, fish and amphibian taxa, representing about a quarter of the around 210 wild terrestrial vertebrates that have been registered in the greater [A]mosen area through years of compiling observational data. We provide evidence for the spatial movement and temporal patterns of airborne eDNA and for the influence of weather conditions on vertebrate detections. This study demonstrates airborne eDNA for high-resolution biomonitoring of vertebrates in terrestrial systems and elucidates its potential to guide global nature management and conservation efforts in the ongoing biodiversity crisis.

ecology↗

bioRxiv2021

Airborne environmental DNA for terrestrial vertebrate community monitoring

Assessing and studying the distribution, ecology, diversity and movements of species is key in understanding environmental and anthropogenic effects on natural ecosystems. Although environmental DNA is rapidly becoming the tool of choice to assess biodiversity 1-3 there are few eDNA sample types that effectively capture terrestrial vertebrate diversity and those that do can be laborious to collect, require special permits and contain PCR inhibitory substances, which can lead to detection failure. Thus there is an urgent need for novel environmental DNA approaches for efficient and cost-effective large-scale routine monitoring of terrestrial vertebrate diversity. Here we show that DNA metabarcoding of airborne environmental DNA filtered from air can be used to detect a wide range of local vertebrate taxa. We filtered air at three localities in Copenhagen Zoo, detecting mammal, bird, amphibian and reptile species present in the zoo or its immediate surroundings. Our study demonstrates that airDNA has the capacity to complement and extend existing terrestrial vertebrate monitoring methods and could form the cornerstone of programs to assess and monitor terrestrial communities, for example in future global next generation biomonitoring frameworks 4,5.

molecular biology↗

bioRxiv2019

Sex identification of ancient pinnipeds using the dog genome

Determining the male and female representation in zooarchaeological material from hunted animal species is essential, to fully investigate the effects and means of prehistoric hunting practices, and may further provide valuable biological information on past animal life-history, behaviour and demography. However, the fragmented nature of the zooarchaeological record and a lack of clear diagnostic skeletal markers, often prevents such inference. Here, we test the usability of the dog nuclear genome (CanFam3.1) for sex identification of pinnipeds. First, a contemporary sample set (n=72) of ringed seals (Pusa hispida), with known sex was used to test the genetic sex identification method. By quantifying the proportion of X chromosome reads, as the chrX/chr1 ratio, the ratios clustered in two clearly distinguishable sex groups. Of the 72 individuals, 69 were identified to the accurate sex, which proves a high reliability of the genetic method. Second, random down sampling of a subset of the ringed seal samples to different read number, suggests at least 5000 DNA sequence reads mapped to the reference genome as the lower limit for which this method is applicable. Finally, applying this standard, sex identification was successfully carried out on a broad set of ancient pinniped samples, including walruses (Odobenus rosmarus), grey seals (Halichoerus grypus) and harp seals (Pagophilus groenlandicus), which all showed clearly distinct male and female chrX/chr1 ratio groups.

genomics↗