Animals that like it hot can be left in the cold and vice versa. Some species may have only one chance to adapt to global climate changes – and that might not be enough. If the climate fluctuates unpredictably, then it can be impossible for some species to survive.

Adaptation is a mechanism that may help many plant and animal species make their way through continuing climate changes. However, if the climate fluctuates unpredictably, adaptation will not necessarily be able to follow suit. This has been shown to be the case for certain fly species and may well count for other animals.

For the past three years, scientists from the Faculty of Agricultural Sciences (DJF) and the Faculty of Science at the University of Aarhus have been exchanging Drosophila flies with colleagues at the University of Melbourne in Australia. Their aim was to determine how the flies fare in hotter or colder conditions than the ones the flies are accustomed to. The scientists found that, although certain fly species can adapt once to climate change, if the environment changes again, the fly survival rates plummet.

The researchers cold-treated young and adult Drosophila flies - otherwise known as vinegar flies - in the laboratory in order to fast-track their adaptation to a colder climate. The flies were then released into the field in order to assess their survival rates in the hot Australian and cold Danish climates.

For both the developing and adult flies’ cold acclimation had enormous benefits at low temperatures in the field; in the coldest releases only cold-acclimated flies were able to find a food resource.

However, this adaptation came at a huge cost. When the cold-treated and untreated flies were released in mild or hot conditions, they were 36 times less likely to find a food resource than the ones that were not cold-acclimated. The reverse applied as well. Heat-adapted flies fared poorly under cool conditions.

- One way animals can counter the effects of climatic extremes is via physiological acclimation, but acclimating to one extreme decreases performance under different conditions, says project scientist Torsten Nygård Kristensen from the Department of Genetics and Biotechnology at the Faculty of Agricultural Sciences, University of Aarhus.

- If temperatures fluctuate, then organisms acclimated to cold or hot conditions can suffer a decrease in fitness as temperatures move to the middle or to the opposite extreme.

The scientists tested how physiological adaptation through cold acclimation changes the individuals’ ability to perform in a situation where many external stimuli such as humidity, predators or competitors are present in addition to thermal stimuli.

These factors were not evident in the laboratory tests where the scientists found no reduction in heat survival of the cold-acclimated flies. Field release studies, therefore, reveal the huge costs of cold and hot acclimation.

- Species have problems coping with fluctuating environments. This is an important problem at a time when climatic conditions are becoming more variable, Torsten Nygård Kristensen points out.

- It is therefore important to evaluate costs and benefits of acclimation and other responses under field conditions by using assays relevant to field performance. Our next step is to perform further field trials with a greater variety of species, he says.

Results from the study have recently been published in the highly respected international journal Proceedings of the National Academy of Sciences of the United States of America.

For further information please contact: Project scientist Torsten Nygård Kristensen, Department of Genetics and Biotechnology, Faculty of Agricultural Sciences, University of Aarhus, telephone: + 45 8999 1076 / +45 8942 3135, e-mail: Torsten.Nygaard@agrsci.dk

Photo: Torsten Nygård Kristensen