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The influence of stress in the bones and teeth of great apes

Periodic Reporting for period 1 - SiBaToGA (The influence of stress in the bones and teeth of great apes)

Reporting period: 2018-09-01 to 2020-08-31

This project aimed to measure stress markers in the bones and teeth of great apes. Two studies measured the degree of asymmetry in the faces of human and nonhuman apes. Three studies characterized dental defects that form in response to stressors like malnutrition, injury, and illness during early life. The beneficiary created a method that makes three-dimensional maps of the tooth surface in order to analyze these features quantitatively, and applied it to nonhuman ape as well as human and Neanderthal teeth. Finally, this project analyzed thin sections of teeth to study their microscopic development in different species, including pigs, humans, and nonhuman great apes. Beyond biological anthropology, these results are relevant to conservationists interested in understanding how and when apes are stressed in early life, as well as clinicians, dentists, and orofacial surgeons who encounter (and correct) these features in their work. The project results will continue to be shared with the public for years to come, helping them to better understand their own anatomy and relationships with other species.
In the first part of the project, two studies focused on facial asymmetry, which was more pronounced in humans that grew up in disadvantaged populations, as well as in gorillas that are very inbred. These results highlight the complex nature of facial asymmetry and the fact that “stress” can take many forms, ranging from external, environmental factors to genetics. The manuscript on gorillas is currently in submission, while the manuscript on humans (led by a supervisee of the beneficiary) is in preparation. In the second part of the project, the beneficiary and her colleagues found that flanged male orangutans, or those with large pouches on their cheeks, have more severe dental defects than males stuck in arrested development. Previous studies showed that flanged males have higher stress hormones than unflanged males, and these results suggest that enamel defect severity might be a reliable indicator of physiological stress experienced in early life. This manuscript was been accepted in the American Journal of Physical Anthropology. The second of the 3D dental studies showed that wild-captured apes exhibit very severe defects in their teeth, while the last study showed that Neanderthals have similarly severe defects compared to different human groups, including those that lived just after the Neanderthals went extinct. The latter manuscript is currently in press in Scientific Reports, while the former manuscript is in preparation. In the third part of the project, all of the species examined (pigs, humans, nonhuman apes) were found to exhibit microscopic signs of stress inside the growth layers of their teeth, and ongoing work will shed light on the significance of these stress markers for our interpretation of the fossil and archaeological record. One manuscript on pig teeth was published in Chemical Geology, while two others on human teeth are in preparation. In total, three peer-reviewed papers have been published, six others are in preparation, and seven conference presentations were given as a result of this project. Two Master’s students were co-supervised by the beneficiary and a total of 10 mentees gained training in research techniques as a result of this project.
This project allowed the beneficiary to further develop the 3D microscopy method she uses to analyze dental defects, and share the results widely within and beyond the biological anthropology research community. Six more papers (either led or coauthored by the beneficiary) are expected to be published in peer-reviewed journals within the next 1-2 years, all of which include trainees that benefitted from this project. This project prepared the beneficiary for a research career in biological anthropology, and she has already begun another position back in the US. The results have the potential to be exploited by primatologists, conservationists, and clinicians by helping them to better understand the development of their study subjects. The results highlight the importance of preserving historical skeletal collections, but also the gravity of the ethical considerations in human and nonhuman ape research. Results show that socially-mediated access to resources and opportunities affect developmental outcomes, which could support efforts for social justice in medicine, public health, and related fields. Other results suggest that problems like inbreeding can be gleaned from the facial skeleton, opening up new avenues for researchers to retrospectively assess health within historical collections. The beneficiary is heavily involved in outreach within her community and she will continue to share the results of this project in museums, K-12 schools, and universities across the US.