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Scientists have created an evolutionary model to predict how animals should react in stressful situations.
Almost all organisms have fast-acting stress responses, which help them respond to threats, but being stressed consumes energy and chronic stress can be harmful.
The new study by an international team, which includes researchers from the universities of Bristol and Exeter, suggests that most animals remain stressed for longer than they are optimal after a stress-inducing accident.
The reasons for this are unclear, but one possibility is that there is a limit to how quickly the body can remove stress hormones from the circulation.
“Although the physiological basis of the stress response system has been extensively studied, we have previously understood very little of why this system has evolved,” said Dr. Sian English of the School of Biological Sciences of the University of Bristol.
“We have shown that considering both hormone elimination mechanisms and the characteristics of the environment – how predictable the threat is over time – can help explain the universal response to stress and how it varies.
“Our findings are all the more relevant today, when we live in such uncertain times and stress is a topic of daily discussion.”
Dr. English has worked with mathematical modeling experts, including Bristol professor John McNamara and Dr. Tim Fawcett of the University of Exeter, to develop the conceptual framework and consider the broader implications for stress in fish, birds and mammals.
“We created one of the first mathematical models to understand how organisms evolved to cope with stressful events,” said Dr. Fawcett.
“It combines existing research on the physiology of stress in a variety of organisms with the analysis of optimal responses that balance the costs and benefits of stress.
“We know that stress responses vary enormously between different species and even between individuals of the same species, as we see in humans.
“Our study is one step closer to understanding why stress responses are so variable.”
Researchers define stress as the process of an organism responding to stressors (threats and challenges in their environment), including both sensing and the response to stress itself.
A key point highlighted in the study is the importance of how predictable the threats are.
The model suggests that an animal living in a dangerous environment should have a high “baseline” stress level, while an animal in a safer environment would benefit from the ability to raise and lower stress levels rapidly.
‘Our approach reveals environmental predictability and physiological limits as key factors determining the evolution of stress responses,’ said lead author Professor Barbara Taborsky of the University of Bern.
“More research is needed to advance the scientific understanding of how this fundamental physiological system has evolved.”
The study was conducted by the universities of Bern, Exeter, Bristol, Stockholm and Turku and by the Brain Mind Institute of the École polytechnique fédérale de Lausanne.
Funding was provided by the Swiss National Science Foundation.
Paper:
“Towards an Evolutionary Theory of Stress Responses”, by Taborsky, B., English, S., Fawcett, TW et al.; in Trends in Ecology & Evolution.
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