University of Groningen
Hunting Ancient Walrus Genomes
Keighley, Xenia
DOI:
10.33612/diss.157287059
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Publication date:
2021
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Keighley, X. (2021). Hunting Ancient Walrus Genomes: Uncovering the hidden past of Atlantic walruses
(Odobenus rosmarus rosmarus). University of Groningen. https://doi.org/10.33612/diss.157287059
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Propositions
1. Traditionally academic research in walruses has been segregated by discipline, with history and archaeology focuses on long-term human uses (such as food and trade), and biologists looking closer at walrus behaviour and ecology. Much deeper and varied insights can be gained by integrating methods and knowledge from both social and natural sciences in interdisciplinary studies. For example, ancient DNA offers a bridge between archaeology and biology to understand past human-walrus interactions.
2. The interdisciplinary use of ancient DNA can be used to test hypotheses around the existence, genetic affinity, demographic characteristics and fate of walrus populations in geographic regions where they are no longer found. Place names, skeletal finds and historical records suggest that walruses were concentrated on the west coast of Iceland, with radiocarbon dating suggesting a near-continuous occupation from at least 9000-800 years before present.
3. Ancient DNA methods confirm that there was a genetically distinct population of walruses on Iceland. Shortly after the arrival of the Norse to Iceland at the end of the 9th century, this local population of walruses disappeared. The local extinction of walruses from Iceland is therefore one of the earliest
examples of international commercial trade driving local faunal population extirpation.
4. On a broader scale, ancient DNA analyses of nearly 200 walruses were also able to reveal past population structure, levels of genetic diversity and potential environmental triggers for key divergence events. Specifically, the presence of two main clades in Atlantic walruses was supported with both nuclear and mitochondrial DNA. These clades appear to have diverged around 20 000 years ago, as the (sub)Arctic regions of the North Atlantic began to emerge from the Last Glacial Maximum. Finer-scale population structure within each clade was likely shaped by the interaction between climatic oscillations and human activities
5. The use of destructive sampling techniques are currently required to perform ancient DNA analyses. As sample material is limited and precious, it would be a major advantage to be able to predict the quantity and quality of DNA preserved in a sample prior to drilling. Despite theories surrounding the gradual degradation of DNA over time and under specific environmental conditions DNA preservation in nearly 300 pinniped zooarchaeological specimens could not be estimated from any single measure such as sample age, geographic origin or skeletal element.
6. Although not universal, in walruses there is a trend for teeth, tusks and portions of the skull have higher yields of DNA than more porous bones such as ribs. This offers promise in untangling past human hunting, trade and craftmanship of walrus ivory as tusk fragments and worked ivory pieces are likely to be more successfully sequenced than many other bones.
7. Determining the sex of a zooarchaeological bone or piece of cultural material made from animal tissue can help inform our understanding of past hunting strategies and the demographic composition of certain animal populations. However, it is often impossible to sex identify juvenile or fragmentary bones based upon morphological examination alone. Genetic sex identification can be performed on a substantial proportion of historic and ancient pinniped bone samples by comparing the number of reads that align to the x chromosome, and an autosome of similar size. As an annotated, chromosome-level assembly is not yet available for walruses, correct sex identification can be obtained by aligning reads to the closely related dog genome.
