Holy Cow : Unveiling Domestic-Wild Hybridization Dynamics in Cattle Over Time

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Genomic Sequencing Reveals Hybridization Events between Iberian Cattle and Auroch during the Neolithic period

Cattle has been an essential way of human development as it produces high-value protein to meet human nutritional demands. Cattle was essential in Europe during the Neolithic period or the beginning of a settled human lifestyle. Aurochs are an extinct cattle species that was considered to be the wild ancestor of what we call modern domestic cattle. Aurochs went extinct during the 17^th century as a result of habitat loss and hunting (Günther, Torsten, et al). Although they went extinct, there is still many genetic ancestry correlations between them and domestic cattle breeds.

A group of scientists led by Torsten Günther performed a bioarcheological analysis which is a branch of archaeology that uses biological material from animals to address a panel of questions related to human life, of 24 taurine cattle that dated back from the Mesolithic to the Roman period (Liaison Groups). To investigate the extent of domestic-wild hybridization overtime, Gunter and his team attempted 50 DNA extractions that were successfully extracted from the 24 individuals identified as domestic cattle (taurine) and aurochs that were previously excavated from four pre-historic sites in Iberia. The DNA was extracted from bones and Teeth using A DREMEL!  Since these DNA extractions were historic, a UDG treatment had to be used. UDG treatments protect genomic information integrity by catalyzing the excision from DNA of Uracil nucleobases resulting from spontaneous cytosine deamination. This deamination occurs from animals decaying.  To detect the age of a sample individual, researchers used Radiocarbon dates. This method provides the individual an age estimate for carbon-based materials that originated from living organisms. To process the data, researchers used single- end reads of 35 base pairs length which were then mapped to the cattle reference genome.  

Researchers assigned different mitochondrial haplogroups, 9 were assigned to mitochondrial p1, one to haplogroup t1, one to haplogroup t4, and 13 to haplogroup t3. Since mitochondrial DNA is inherited through maternal lineage, researchers decided to use haplogroups. Haplogroups are mitochondrial DNA sequence polymorphism variations that occurred over more than 150,000 years and correlate with specific geographic regions used again to trace population maternal lineages(Kenney, M. Cristina).

Based on the number of reads that corresponded to the x chromosome, 13 individuals were identified as female and 11 as male. This data however was low-medium coverage at an average of 4.7x. Out of the haplogroups, T3 had direct correlation with the Neolithic samples meaning that there was evidence for domestic cattle in northern Iberia during this time. Furthermore, the ecology of the samples were also looked into using stable isotope analysis of bone collagen. In other words, through the measurement of ratios of different isotopes found in the bone collagen researchers were able to determine past diets and migration patterns (Matthew.D). T1 individual was an interesting finding in the Iberian pre-historic sites since this individual is usually found between Iberia and Africa. Additionally, the presence of t4 individual suggest that this haplogroup must have been distributed across western Europe, at very low frequencies.

Both groups show signs of frequent hybridization, that started as early as the neolithic age. These results can reflect the transition from hunting and herding to predominantly herding.  The reduced level of aurochs ancestry on X chromosome suggests that it was mostly males who contributed wild ancestry to now modern domestic herds. The possibility of a wild bull inseminating a domestic cow without becoming part of the herd suggests that some level of incidental interbreeding was possible. It seems that Iberian Lidia breed is no exception for the modern cattle ancestry of the aurochs for their aggressiveness. The isotope results suggested that wild and domestic groups did not specialize in a particular area in the Iberian Peninsula, however through mtDNA it was found that aurochs did change their areas over time. With these results, it is hypothesized that aurochs had flexibility in their areas of vegetation depending of the change of environment.  

This study collected valuable new information for the hypothesis of the admixture of domestic and wild animals specifically the aurochs. While this study attempted to answer the significance of aurochs’ ancestry in domestic herds, many limitations made the researcher’s conclusions unstable. The author emphasized that mtDNA only reflects on the maternal line of ancestry concluding that they do not represent the exact extent of interbreeding in their dataset. Additionally, this study raises ethical questions about who should be concerned about studies involving ancient subjects, particularly given how easily contaminated these materials might be (Martin). Overall, this research enhances our understanding of human settlement, and migration in the Neolithic period.

References

Johana Monzon

jomonzon@davidson.edu

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Department of Biology, Davidson College, Davidson, NC 28036.