Iguana study sheds light on wildlife response to disasters
May 27, 2010 § Leave a comment
by Romero, L. M. and Wikelski, M
Scientists from Germany and the US have gained new insights into the effects of the stress hormone corticosterone on animals. Their study, published in the online issue of the Proceedings of the Royal Society B, shows that the more quickly an animal can shut down the release of corticosterone (which is similar to cortisol in humans), the more likely it is to survive a stressful situation.
The study is extremely timely since it could help predict how wildlife will react to the pollution caused by the massive oil spill in the Gulf of Mexico. ‘As animals encounter the spill, they will have a robust release of corticosterone to help them cope with the consequences of the oil,’ says Dr L. Michael Romero of Tufts University in Medford, US, who is a co-author of the study. ‘However, those animals that can best turn off their corticosterone response once the initial danger from the oil has passed will probably be the most likely to survive.’
Dr Romero and his colleague, Professor Martin Wikelski from the Max Planck Institute for Ornithology in Radolfzell in Germany, base their findings on their study of Galápagos marine iguanas (Amblyrhynchus cristatus).
In 2002, shortly before El Niño struck, the researchers had captured 98 male iguanas and injected some of them with a synthetic hormone that lowers natural corticosterone levels via a negative feedback process.
When the researchers sought out the animals again after the El Niño event, 23 of them had starved to death and 75 had survived. The only difference between the survivors was their ability or inability to turn off the stress response.
The continued stress response triggered elevated levels of corticosterone. As a result, these animals used up all of their protein reserves and grew increasingly weak. Hence, a food shortage impacted them harder than their counterparts that had been able to switch off their stress response.
‘The results from the iguanas indicate that the better an individual is at coping with stress – by turning off the response as soon as possible – the better the chance they have to survive,’ comments Dr Romero.
Marine iguanas are found only on the Galápagos archipelago, where they live on the rocky shores of the islands. The lizards are ideal for this kind of study as their living conditions are rather predictable: They feed exclusively on marine algae growing in the seas surrounding the islands. The risk of starvation due to food shortages regularly caused by El Niño-related global climate events is virtually the only natural threat or source of stress. This makes it possible to exclude other stress factors by and large.
They also have a relatively long lifespan and tend to stay in the same area for most of their life. As a result, they are an excellent model for study in general and determining the ultimate function of a stress hormone response in particular.
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