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The impact of global warming on the metabolism of mosquitoes could further complicate predictions of how climate change will affect malaria, according to scientists.

Scientists have for the first time estimated how warmer climate will affect the metabolism of cold-blooded animals, such as mosquitoes, on a global scale. Such animals depend on outside temperature to regulate their body's metabolism. 

The study, published today (7 October) in Nature, says that the effect of temperature on metabolism is non-linear, affecting animals in warm regions disproportionately more than those in cold regions.

"At high temperatures, very small [temperature] changes have huge effects," said lead researcher Michael Dillon, an assistant professor of zoology and physiology at the University of Wyoming, United States.

Although the temperature has so far risen less rapidly in the tropical regions, the researchers say these areas will actually see the most drastic changes in metabolic rates of cold blooded animals.

The changes are also strongest in smaller animals, meaning that mosquitoes are among those most likely to be affected.

"Over the last 30 years we've seen significant changes in metabolic rate," said Dillon. "If we continue on the track that's predicted, it's only going to get worse."

But it is still unclear what effects this might have on diseases spread by mosquitoes, such as malaria.

He said the effects of warmer weather on malaria might be threefold: higher metabolic rates shorten gestation periods boosting the numbers of mosquitoes as successive generations hatch more frequently;  longer periods of warmth would allow the mosquitoes to be active for longer; and the metabolic rate of malaria parasites might increase as well leading to higher parasite numbers carried by the mosquitoes.

Combined, these three temperature effects could increase the potential for malaria infection in tropical regions. But whether this will actually occur is an "incredibly complicated" question, said Dillon.

Other factors might mean such an increase in metabolic rate could have little effect on malaria. For example, availability of other resources could limit mosquito population growth, or they simply might not sustain the higher metabolic rates. "They may just burn themselves out," he said.

Tarekegn Abeku, senior technical specialist for disease prevention at the Malaria Consortium, said that while short-term temperature changes in regions such as the East African highlands have increased malaria transmission rates, we do not know how gradual warming will influence the disease. "The long-term effects in general are not very clear," he added.

Paul Parham, a research fellow at the Grantham Institute for Climate Change, United Kingdom, said that when these new findings are put into existing disease transmission models, "small changes in the metabolic rates will have potentially quite large effects on disease transmission".

Link to full paper in Nature

References

Nature, 467, 704 (2010)

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