The researchers at the University of Leeds worked with soil mites that were collected from the wild and then raised in 18 glass tubes. Forty per cent of adult mites were removed every week from six of the glass tubes.
Lead author Dr Tom Cameron said "We saw significant evolutionary changes relatively quickly. The age of maturity of the mites in the tubes doubled over about 15 generations, because they were competing in a different way than they would in the wild. Removing the adults caused them to remain as juveniles even longer because the genetics were responding to the high chance that they were going to die as soon as they matured. When they did eventually mature, they were so enormous they could lay all of their eggs very quickly."
The initial change in the mites' environment—from the wild into the laboratory—had a disastrous effect on the population, putting the mites on an extinction trajectory.
Dr Cameron said: "The genetic evolution that resulted in an investment in egg production at the expense of individual growth rates led to population growth, rescuing the populations from extinction. This is evolutionary rescue in action and suggests that rapid evolution can help populations respond to rapid environmental change." The study has been published in the journal Ecology Letters.
Professor Tim Benton, of the University of Leeds' Faculty of Biological Sciences, said: "This demonstrates that short-term ecological change and evolution are completely intertwined and cannot reasonably be considered separate. We found that populations evolve rapidly in response to environmental change and population management. This can have major consequences such as reducing harvesting yields or saving a population heading for extinction."
Short-term ecological responses to the environment—for instance, a reduction in the size of adults because of lack of food—and hard-wired evolutionary changes were separated by placing mites from different treatments into a similar environment for several generations and seeing whether differences persisted.
Professor Benton said: "The traditional idea would be that if you put animals in a new environment they stay basically the same but the way they grow changes because of variables like the amount of food. However, our study proves that the evolutionary effect—the change in the underlying biology in response to the environment—can happen at the same time as the ecological response. Ecology and evolution are intertwined."
The size at which cod in the North Sea mature is about half that of 50 years ago and this change has been linked to a collapse in the cod population because adult fish today are less fertile than their ancestors.
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