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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Tamsin O'Connell, Archaeology


Brief summary: 
To examine the reliability of a novel technique for quantitative trophic position estimation that is fast rising in popularity, but may have some shaky underpinnings of untested assumptions.
Importance of the area of research concerned: 
Trophic connections among producers and consumers contribute to ecosystem structure, function, and stability. Isotopic values of body proteins have been used to identify individuals’ trophic position across a range of fields, particularly archaeology and (palaeo)ecology. Analyses of bulk tissues have proved informative, yet compound-specific measurements potentially offer greater precision, particularly amino acid nitrogen isotopic values. With new methodologies, it is imperative that they are built on firm foundations. Whilst the general concept behind amino acid nitrogen isotopic analysis seems to be robust, published studies hint that nitrogen isotopic patterning in amino acids is not as simple or consistent as first suggested. Work has shown that various factors influence amino acid isotopic values and the degree to which they change with increasing tropic level, particularly at the inter-species level. Less attention has been paid to intra-individual variability, although this has long been observed in different bulk tissue and amino acid isotopic values. If we don’t understand what is driving our measured signal, this is a major limitation in the technique’s use.
Project summary : 
This project will examine the effect of intra-individual variability on amino acid nitrogen isotopic values, and its potential implications for the accuracy of isotopic trophic biomarker estimates. It will compare bulk and compound-specific nitrogen isotopic values of different tissues of individuals from archived specimens of a range of species, comprising birds, mammals and fish. The aim is to identify key factors that drive patterns of isotopic difference across different tissues, as well as testing the effect of different dietary intakes and habitats. Part of the project will be to test better ways to interrogate the multi-dimensional dataset that we generate. Typically, studies measure at least 10 amino acid nitrogen isotopic values per tissue, and then ignore most of it, comparing only two, glutamate and phenylalanine. This is a waste of information, and again a limitation.
What will the student do?: 
The student will learn about isotopic ecology, and the utility of the technique. They will prepare bulk tissues and amino acids from different tissues from a range of archived specimens, and will then run the samples using isotope ratio mass spectrometry. They will test different ways of modelling and interrogating the multi-dimensional dataset using a range of statistical tools. They will consider the ways that such data can provide insights into the underlying metabolic mechanisms by which such isotopic variation occurs.
References - references should provide further reading about the project: 
Boecklen, W. J., C. T. Yarnes, B. A. Cook and A. C. James (2011). "On the use of stable isotopes in trophic ecology." Annual Review of Ecology, Evolution, and Systematics 42: 411-440. doi: 10.1146/annurev-ecolsys-102209-144726
Matthews, C. J. D., R. I. Ruiz-Cooley, C. Pomerleau and S. H. Ferguson (2020). "Amino acid δ15N underestimation of cetacean trophic positions highlights limited understanding of isotopic fractionation in higher marine consumers." Ecology and Evolution 10(7): 3450-3462. doi: 10.1002/ece3.6142
O'Connell, T. C. (2017). "‘Trophic’ and ‘source’ amino acids in trophic estimation: a likely metabolic explanation." Oecologia 184(2): 317-326. doi: 10.1007/s00442-017-3881-9
You can find out about applying for this project on the Department of Archaeology page.
Dr Tamsin O'Connell
Department of Archaeology Graduate Administrator