Imagine leaning forward over the edge of a precipice. Lurching back to safety, you picture the forest hundreds of metres below. Is your heart racing? Are your palms sweating? Our body’s stress response to an ever-changing environment enables us to survive and flourish.
Physiologists play a crucial role in developing our understanding of the mechanisms involved. To highlight the exciting work that they do, our 2017 theme is ‘Making Sense of Stress’. Follow the conversation on Twitter using #YearOfStress.
Launching the theme will be Dr Kimberley Bennett’s talk, ‘Making sense of stress in the wild’, at the Association for Science Education’s (ASE’s) Annual Conference on 6 January 2017. Read a teaser to her talk below!
Coping with stress is a major issue in modern society, but it’s easy to forget that wildlife experiences stress too. Without enough water, plants wilt and die and whole crops fail; without the right habitat, a small population of rare animals dwindles and dies out, causing extinction of the species; a whole coral reef bleaches when the water temperature gets too high, causing catastrophe for the ecosystem, and massively increasing flooding risk for people living by the coast. We really need to pay attention to stress in the wild because the consequences can herald disaster.
Stress is the biological response to a major challenge, whether it’s at the whole organism or cell level. A gazelle in the Serengeti chased by a lion experiences the same stress responses that we do – a surge of adrenaline and cortisol that cause increased heart rate and blood pressure and a release of glucose. These changes make sure there is enough fuel and oxygen to cope with increased demand at the tissue and cell levels. Sudden change or mismatch in the supply of oxygen and fuel leads to increased production of reactive molecules called ‘free radicals’ that can damage cells. If the temperature gets too hot too fast or if the acidity of the cell changes too much, proteins (the molecules that catalyse reactions, transport substances and provide structure) can fall apart or unravel. So cells have to increase their defence mechanisms too. Cellular defences include antioxidants that mop up the free radicals, and heat shock proteins, which refold damaged proteins and stop them forming a sticky mess inside the cell.
The old adage that what doesn’t kill you makes you stronger is often true: short term ‘good stress’ builds up these defences and makes organisms better able to deal with stress later on. However, sometimes defences can be overwhelmed or can’t be maintained for long periods. The organism then experiences the same sorts of problems as people under chronic stress: lower immunity, altered metabolism, anxiety and tissue damage (like ulcers). In wildlife, this can have major consequences for breeding success or even survival. By affecting whether organisms survive and thrive, stress dictates which individuals contribute to the next generation. Stress shapes population dynamics, lifestyle and adaptations, and is therefore a powerful agent of natural selection.
I work on seals, top marine predators that are used to stress as a normal part of their existence. Their individual and population level health is an indicator of ecosystem health. Seals are air breathing mammals that feed underwater, but need to come to the surface to breathe, and to come ashore to rest, breed and moult. Diving on a single breath hold means they need to conserve oxygen; to do this, blood flow is restricted mostly to the heart and brain, so that other tissues may experience free radical production while oxygen levels are low. On land, seals need to fast, often while they are doing energy-demanding activities i.e. shedding and replacing hair, producing milk, defending pups or territory, or undergoing rapid development. Injury and infection can occur from skirmishes or trampling. Seals may have to reduce their defences to deal with all these demands on their energy when food is not available. In addition to their ‘lifestyle stressors’, seals face stress from competition for access to fish, disturbance on haul out or displacement from foraging grounds as a result of human activity, and the accumulation of contaminants in their blubber.
We need to understand natural and man-made causes of stress in wild populations, distinguish good stress from bad stress, and understand how multiple stressors at the same time can create problems. That means we have to have effective tools to measure stress and its consequences in organisms that can’t tell us how they feel. But can we measure stress responses in wildlife? What do they mean in context? And can they help in managing stress in the wild?
I will address all these questions and more at the ASE’s Annual Conference on Friday 6 January 2017, as part of the annual Biology in the Real World (#BitRW) lecture series. Please drop by the Knight Building, LT 135, at the University of Reading, at 1.30pm to find out more!
Dr Kimberley Bennett, Abertay University