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Hans AhlgrenForskningsingenjör

Publikationer

I urval från Stockholms universitets publikationsdatabas

  • The Baltic grey seal – a 9,000-year history of presence and absence

    Hans Ahlgren (et al.).

    The grey seal (Halichoerus grypus) has been part of the Baltic Sea fauna for more than 9,000 years and has ever since been subjected to extensive human hunting, particularly during the early phases but also in the early 20th century. In order to study the temporal genetic structure and investigate whether there has been a genetically continuous grey seal population in the Baltic, we generated mitochondrial control region data from skeletal remains from ancient grey seals from the archaeological sites Stora Förvar (Sweden) and Neustadt (Germany) and compared this with modern grey seal data. We found that the majority of the Mesolithic grey seals represent haplotypes that are now extinct, indicating that the Baltic Sea population has passed through a genetic bottleneck or maybe even local extinction, with a following recolonization from the North Sea. Finally, we suggest that here has been genetic continuity in the grey seals in the Baltic Sea at least from the Bronze Age but maybe longer.

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  • Prehistoric human impact on wild mammalian populations in Scandinavia

    2021. Hans Ahlgren.

    Avhandling (Dok)

    This thesis aims to study the interactions of pre-agricultural societies in Scandinavia with wild mammals, for example in terms of hunting and translocation. More specifically, the aim is to investigate the possibility of identifying examples of overexploitation, targeted hunting or translocation of wild mammals in prehistoric Scandinavia, and to discuss the implications this could have had for both the wild animals and the humans. The thesis also studies translocation to evaluate the feasibility of using it as a proxy for prehistoric human mobility, and to understand the motivation for this action. 

    Although the focus is on the animals in this thesis, the ultimate purpose is to study humans and their interactions with animals in prehistory. The thesis applies genetic analyses to zooarchaeological material of various mammalian species from different Scandinavian sites, in order to study whether the genetic structures have changed in these species over time, and to assess whether these changes were induced by different human actions. The species studied in this thesis were selected on the basis of the importance they are considered to have had for prehistoric people.

    The dissertation comprises five studies. The first study investigates the occurrence of mountain hares on the island of Gotland, and discusses how they got there and where they came from. The second study explores the temporal genetic structure of the grey seal in the Baltic Sea, and discusses whether humans and/or climate were the drivers for the sudden disappearance of grey seals from the island of Stora Karlsö. The third study concerns a shift where moose apparently became less important as prey in northern Sweden at the end of the Neolithic period, and discusses whether humans targeted female moose in hunting. The fourth study analyses and discusses the history of the harp seal in the Baltic Sea. The fifth study is a methodological paper which involves identifying seals according to sex, using the dog genome.

    The overall result of the different case studies shows that there were major population fluctuations over time in all the species studied, and that in some cases, humans are likely to have contributed to this, e.g. through overhunting and translocation. The study also shows that the population fluctuations often occurred in connection with certain climatic events, though it was not possible to separate climatic effects from human impact in terms of the cause.

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  • Multiple prehistoric introductions of the mountain hare (Lepus timidus) on a remote island, as revealed by ancient DNA

    2016. Hans Ahlgren (et al.). Journal of Biogeography 43 (9), 1786-1796

    Artikel

    Aim: The majority of the non-volant mammals now present on the island of Gotland, Sweden, have been introduced in modern times. One exception is the mountain hare (Lepus timidus), which was present on the island more than 9000 years ago. This paper investigates the origins of the Gotland hares and temporal changes in their genetic structure, and considers how they may have reached the island.

    Location: The island of Gotland, Sweden (57°30′ N, 18°20′ E).

    Methods: Two fragments of the mitochondrial D-loop 130 + 164 base pairs in length from skeletal remains from 40 ancient mountain hares from Gotland, 38 from the Swedish mainland and five from Lithuania were analysed and compared with 90 modern L. timidus haplotypes from different locations in Eurasia and five haplotypes of the Don-hare (Lepus tanaiticus) morphotype.

    Results: The Mesolithic hares from Gotland (7304 bc–5989 bc) cluster with modern hares from Russia, Scotland, the Alps and Fennoscandia whereas the Gotland hares from the Neolithic and onwards (2848 bc–1641 ad) cluster with Neolithic hares from the Swedish mainland and modern hares from Fennoscandia. The Neolithic haplotypes from Lithuania and the Don-hare haplotypes were dispersed within the network. The level of differentiation (FST) between the Mesolithic and Neolithic hares on Gotland was twice as great as that observed on the mainland.

    Main conclusions: The ancient hares on Gotland fall into two haplogroups separated in time, indicating that the mountain hare became extinct at one point, with subsequent re-colonization events. In view of the isolated location of Gotland, it is probable that the hares were brought there by human means of transport.

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  • Moose genomes reveal past glacial demography and the origin of modern lineages

    2020. Nicolas Dussex (et al.). BMC Genomics 21 (1)

    Artikel

    Background: Numerous megafauna species from northern latitudes went extinct during the Pleistocene/Holocene transition as a result of climate-induced habitat changes. However, several ungulate species managed to successfully track their habitats during this period to eventually flourish and recolonise the holarctic regions. So far, the genomic impacts of these climate fluctuations on ungulates from high latitudes have been little explored. Here, we assemble a de-novo genome for the European moose (Alces alces) and analyse it together with re-sequenced nuclear genomes and ancient and modern mitogenomes from across the moose range in Eurasia and North America.

    Results: We found that moose demographic history was greatly influenced by glacial cycles, with demographic responses to the Pleistocene/Holocene transition similar to other temperate ungulates. Our results further support that modern moose lineages trace their origin back to populations that inhabited distinct glacial refugia during the Last Glacial Maximum (LGM). Finally, we found that present day moose in Europe and North America show low to moderate inbreeding levels resulting from post-glacial bottlenecks and founder effects, but no evidence for recent inbreeding resulting from human-induced population declines.

    Conclusions: Taken together, our results highlight the dynamic recent evolutionary history of the moose and provide an important resource for further genomic studies.

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  • Predicting sample success for large-scale ancient DNA studies on marine mammals

    2021. Xénia Keighley (et al.). Molecular Ecology Resources 21 (4), 1149-1166

    Artikel

    In recent years, non-human ancient DNA studies have begun to focus on larger sample sizes and whole genomes, offering the potential to reveal exciting and hitherto unknown answers to ongoing biological and archaeological questions. However, one major limitation to the feasibility of such studies is the substantial financial and time investments still required during sample screening, due to uncertainty regarding successful sample selection. This study investigates the effect of a wide range of sample properties including latitude, sample age, skeletal element, collagen preservation, and context on endogenous content and DNA damage profiles for 317 ancient and historic pinnipedsamples collected from across the North Atlantic. Using generalised linear and mixed-effectmodels, we found that a range of factors affected DNA preservation within each of the species under consideration. The most important findings were that endogenous content varied significantly according to context, the type of skeletal element, the collagen content and collection year. There also appears to be an effect of the sample’s geographic origin, with samples from the Arcticgenerally showing higher endogenous content and lower damage rates. Both latitude and sample age were found to have significant relationships with damage levels, but only for walrus samples. Sex, ontogenetic age and extraction material preparation were not found to have any significantrelationship with DNA preservation. Overall, the skeletal element and sample context were found to be the most influential factors and should therefore be considered when selecting samples for large-scale ancient genome studies.

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  • Genomic insights on the extinct Baltic harp seal population

    Maiken Hemme Bro-Jørgensen (et al.).

    The harp seal is a cold adapted seal species, which requires a suitable formation of pack ice during winter and spring to secure successfully breeding. Today harp seals live in sub-Arctic regions and the North Atlantic, but during the middle Holocene Period, a breeding population existed in the Baltic Sea. In order to investigate the genetic affinity and faith of the now extinct Baltic harp seal population we analysed contemporary and ancient mitogenomes from across the species contemporary and ancient range. Ancient mitochondrial genomes were generated for a total of 49 Baltic harp seals ranging from Late Mesolithic to the Iron Age, together with five Neolithic samples from the White Sea and two Neolithic samples from the Northwest Atlantic Ocean. The ancient data was compared to published modern harp seal data assigned to the present breeding populations around Newfoundland, the Greenland Sea and the White Sea. Surprisingly only limited phylogenetic resolution was found among the ancient and modern localities. The statistical measures for genetic differentiation, however, identified significant levels of population genetic differentiation between the Baltic harp seal population and all modern populations, which suggest an independent breeding population in the Baltic Sea. The low level of genetic differentiation to the White Sea population indicate a shared ancestry between the Baltic and White Sea. The generated Skyline plot suggest second wave of colonization after a hiatus in the Baltic Sea. Interestingly, the genetic diversity in the Baltic harp seal population was significantly higher than in any of the modern populations. However, a drastic decrease in genetic diversity is observed from the Bronze Age to the Iron Age, which might be linked to effects of high hunting pressure and climatic changes towards the final extirpation of harp seals in the Baltic. 

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