A new method for hormone research in wildlife
Quantifying the by-products of hormone degradation in urine and faeces is crucial for studies in wildlife conservation. Scientists from the German Leibniz Institute for Zoo and Wildlife Research (IZW) established a new method that allows comparison of such measurements over long periods of time and between different laboratories. The results of this study have been published in the scientific journal “Methods in Ecology and Evolution”.
How do we learn about animals that are extremely shy, dangerous or that live in places that are difficult to access? A well-established method is to examine what such animals leave behind them. Indeed, scientists can now derive most secret details about an animal’s social and sexual life or its physiological response to disturbance from measuring the concentration of hormone by-products (metabolites) in its faeces or urine.
Hormone metabolite concentrations are quantified using enzyme immunoassays. Specific antibodies bind to the metabolite of interest, and the quantity of bound antibodies provides an estimation of the metabolite concentration in a sample of faeces or urine. However, the accuracy of an enzyme immunoassay is influenced by certain properties of the metabolites and modifications in laboratory conditions, and this may lead to a bias between measured and true hormone concentrations. Such a bias is negligible if it is constant for all samples and if the main focus of a study is to understand relative differences in metabolite concentrations between animals. But if the accuracy of measurements varies considerably, results are not comparable and combining them in a statistical analysis would lead to misinterpretations. Previously, the only way to solve this problem was to re-analyse all samples together in one batch, but this is costly in time and money and may not always be feasible, especially when data sets are large and samples are no longer available.
The behavioural ecologists Eve Davidian and Sarah Benhaiem, and their colleagues from the IZW developed a mathematical method that allows the comparison of measurements when the accuracy of an enzyme immunoassay varies by re-analysing only a subset of samples. The scientists collected nearly 500 faecal samples from spotted hyaenas in the Ngorongoro Crater in Tanzania as part of a long-term study initiated in 1996. The accuracy of faecal cortisol (the so-called ‘stress’ hormone) metabolite concentrations varied during different periods of examination. The new method however rendered all measurements comparable with each other by using a subset of only 27 samples. “Our procedure standardises the concentration of hormone metabolites in a simple and inexpensive way, and can be applied to a variety of species, sample types and hormones”, comment the authors.
Their new method is particularly useful for long-term studies that deal with large data sets and for international collaborative projects that share the laboratory workload between different facilities and are likely to experience variation in enzyme immunoassay accuracy. The procedure should thus ultimately contribute to a better understanding of complex processes, such as interactions between hormones, behaviour and diseases. “We can now get more comprehensive information to protect and conserve wild animals”, emphasises Eve Davidian.
Publication:
Davidian E*, Benhaiem S*, Courtiol A, Hofer H, Höner OP, Dehnhard M (2015): Determining hormone metabolite concentrations when enzyme immunoassay accuracy varies over time. METHODS ECOL EVOL. doi:10.1111/2041-210X.12338.
* contributed equally to this work
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Background information:
The Leibniz Institute for Zoo and Wildlife Research (IZW) investigates the vitality and adaptability of wildlife populations in mammalian and avian species of outstanding ecological interest that face anthropogenic challenges. It studies the adaptive value of traits in the life cycle of wildlife, wildlife diseases and clarifies the biological basis and development of methods for the protection of threatened species. Such knowledge is a precondition for a scientifically based approach to conservation and for the development of concepts for the ecologically sustainable use of natural resources. The IZW belongs to the Forschungsverbund Berlin e.V. (www.fv-berlin.de)
The Leibniz Association connects 89 independent research institutions that range in focus from the natural, engineering and environmental sciences via economics, spatial and social sciences to the humanities. Leibniz Institutes address issues of social, economic and ecological relevance. They conduct knowledge-driven and applied basic research, maintain scientific infrastructure and provide research-based services. The Leibniz Association identifies focus areas for knowledge transfer to policy-makers, academia, business and the public. Leibniz Institutes collaborate intensively with universities – in the form of “WissenschaftsCampi” (thematic partnerships between university and non-university research institutes), for example – as well as with industry and other partners at home and abroad. They are subject to an independent evaluation procedure that is unparalleled in its transparency. Due to the institutes’ importance for the country as a whole, they are funded jointly by the Federation and the Länder, employing some 17,500 individuals, including 8,800 researchers. The entire budget of all the institutes is approximately 1.5 billion EUR.