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Palaeoproteomics was used to confirm the earliest specimen of domesticated sheep (Ovis aries) arrived to South Africa around 2000 BP.
Domestic sheep (Ovis aries) currently reside all over the world alongside humans, but originally came from the Middle East and Central Asia (Reavill et al. 2000). Sheep were originally hunted as wild animals, but their presence began to rapidly decrease and humans therefore shifted to a more controlled hunting style to avoid complete extinction. Over time, controlled hunting transitioned to breeding and management of herds. This then led to domestication around 9500 BP (Atavliyeva and Tarlykov 2018).
After domestication, sheep were introduced to other continents. Sheep were undoubtedly imported to Africa, however the time frame in which they reached southernmost Africa is debated (Coutu et al. 2021). Early studies had to rely on dating by association or conventional radiocarbon dating to age samples. These methods were not very exact or required large samples from bones, which could be hard to come by when working with ancient bone samples (Levick 2011). Also, once bones of animal were found they had to be confirmed as to which species they belonged to. Early identification strategies relied on morphological criteria, rather than DNA from bone samples. However, this could very easily lead to mismatching bones to incorrect species. Domesticated sheep closely resemble other animals found during the same time period: the springbok, the grey rhebok, and the grey duiker. Therefore, early methods of dating and identification made it difficult to pinpoint when domesticated sheep made it to southern Africa.
New methods of species identification are being used and involve biomolecular methods to reliably determine what species a bone sample is. With new methods available, scientists decided to return to the debated issue of when domesticated sheep were imported to South Africa.
Zooarchaeology by Mass Spectrometry is widely used to identify hominid and zooarchaeological remains based on ancient protein samples. Protein fragments from collagen are collected from bone samples to find unique variations in amino acids that are commonly seen in specific species. These amino acid variations, referred to as “fingerprints”, can then be used to identify the species the bone samples are from. This method uses collagen rather than DNA because it is preserved longer and a smaller sample of collagen is needed to obtain the same results. Smaller samples are important because the precious specimen can remain intact, compared to sometimes destructive tactics of obtaining DNA from samples (Coutu et al. 2021).
With Zooarchaeology by Mass Spectrometry now available to researchers, the scientists in this paper had three goals. First, they wanted to identify the fingerprints that would distinguish sheep from African mammals of similar size and morphology. Second, the researchers aimed to find specific fingerprints in the remains that were currently thought to be those of domesticated sheep. And lastly, they wanted to test this method of extracting collagen from bone samples to understand if it could be a sustainable alternative to use in future studies. All in all, the researchers were looking to confirm the previous theory that believed domesticated sheep were imported to southernmost Africa around 2105 BP.
Through Zooarchaeology by Mass Spectrometry, the researchers were able to identify a fingerprint in the peptide sequence that differed in springbok, grey rhebok, grey duiker, and domesticated sheep (specifically, Namaqua Afrikaner sheep). The group used reference sequences to confirm which footprints belonged to each animal. From these findings the researchers were able to conclude that the specimen believed to be the earliest domesticated sheep did in fact have peptides conducive to Namaqua Afrikaner sheep. They were also able to distinguish these four similar African mammals from each other through identification of species specific fingerprints.
Also from this data the scientists learned ten out of eleven of their collagen samples provided a spectra that was good enough to use for identification. To additionally confirm results, they tested for contamination by looking at deamidation levels of the peptides. Deamidation is a chemical reaction of two amino acids, asparagine and glutamine, and are associated with aged proteins. Therefore, deamidation can help ensure the proteins the researchers are looking at are authentic, rather than due to modern contamination. The data from Zooarchaeology by Mass Spectrometry and from deamidation studies shows that this new method of extracting collagen from bones could be a less destructive alternative to collecting samples from old bones.
This study was able to use proteomics to confirm the earliest specimen that was initially identified based on morphology. There is now high confidence that domesticated sheep were introduced into South Africa around 2000 BP. This study was also able to successfully take collagen samples from bone samples, which proved to be less destructive and equally successful. Further evaluation should go into the most effective method of sampling; however, this study does provide some answers that help move sampling in the right direction. Identification methods that require DNA need larger samples, which can sometimes be difficult when working with small bone fragments. Collecting collagen requires smaller samples and preserves the bone, so that it can keep the original shape it was found in. Also, collagen sampling runs into less ethical concerns about preserving history and leaving the bones unchanged. This can help with further morphological identification and can protect the bone for the sake of history. Animal remains from the past are a very limited resource, therefore it is important to preserve them (Pálsdóttir et al. 2019). Research will continue to look for less destructive methods, so that history and the samples can be maintained.
References
1. Reavill, C. Ovis aries (mouflon). Animal Diversity Web https://animaldiversity.org/accounts/Ovis_aries/.
2. Atavliyeva S., Tarlykov P. Genetic History of Sheep Domestication. Eurasian Journal of Applied Biotechnology (2018).
3. Coutu, A. N. et al. Palaeoproteomics confirm earliest domesticated sheep in southern Africa ca. 2000 BP. Scientific Reports 11, 6631 (2021).
4. Dating Methods | Archaeology of East Oxford. http://www.archeox.net/fact-sheets/chronology/dating-methods.html.5. Pálsdóttir, A. H., Bläuer, A., Rannamäe, E., Boessenkool, S. & Hallsson, J. H. Not a limitless resource: ethics and guidelines for destructive sampling of archaeofaunal remains. Royal Society Open Science6, 191059.
© Copyright 2020 Department of Biology, Davidson College, Davidson, NC 28036.
Article written by Anna Montgomery at Davidson College, anmontgomery@davidson.edu.
