Species' rapid evolution encouraged by drastic environmental change

A study has revealed that changes to their environment can influence species to undergo “rapid evolution” as they adopt traits to cope with the new conditions, according to reports from the BBC, NBC News, and Health24.

According to the findings published in the Ecology Letters journals, soil mites grown in a laboratory have doubled their age of maturity in just over 20 generations.

This goes against the previously held notion that evolutionary change only occurs gradually and over extensive periods of time ranging from thousands to millions of years.

“The implicit assumption has always been, from Darwin onwards, that evolution works on long timescale and ecology works on short timescales,” said Tim Benton, co-author of the research article and population ecology professor at the University of Leeds. “The thinking was that if you squash a population or you change the environment then nothing will happen from an evolutionary point-of-view for generations and generations, for centuries.”

The study also shed more light on the link between evolution and ecology, and what this can mean for the future of many species.

“This demonstrates that short-term ecological change and evolution are completely intertwined and cannot reasonably be considered separate,” Benton said. “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.”

Circumventing extinction

The research team collected the soil mites from four UK locations, then raised them in 18 test tubes in the laboratory.

Every week, about 40 percent of adult mites were removed from six test tubes, while 40 percent of juveniles were also taken from the other six tubes. The mites in the remaining tubes were left untouched.

At first, these drastic changes in the mites’ environment proved disastrous to their population and even brought them close to extinction. In every population that experienced continuous harvesting, however, the number of mites began to swell again after only a number of generations.

“We saw significant evolutionary changes relatively quickly,” said Dr. Thomas Cameron, lead author of the research. “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.

“Those mites with the genes selecting for the slowest growth had the highest fecundity and so we see that, in the long term, the reason that the population recovered was that there was selection for increased fecundity, increased number of offspring per individual,” Dr. Cameron expounded further.

Simply put, the laboratory environment was selecting slow-growing mites because, under the competitive conditions in the tubes, these particular mites were more fertile when they matured and could thus produce more offspring.

“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,” said Dr. Cameron. “This is evolutionary rescue in action and suggests that rapid evolution can help populations respond to rapid environmental change."

Real-world applications

Benton said that population management schemes, such as the conservation of endangered species, would benefit from the information revealed by the results of their experiment.

“For example, if you think about the challenges of climate change and nature reserves, where do you put the reserves?” he said. “The way that animals move across the landscape, their dispersal behavior is likely to evolve as a result of climate change.

“Do you put the nature reserves just 10 miles apart because that is how far the animals travel now? But in 50 years' time, they might disperse five miles.”

In the management of fisheries, human decisions can cause severe changes to an entire population’s environment. This has caused unexpected and sometimes disastrous evolutionary adaptations. For instance, the mature North Sea cod is now about half the size of its ancestors 50 years ago. Today’s adult cods are also less fertile, which has led to a decline in their population.

“The big debate has been over whether this is an evolutionary response to the way they are fished or whether this is, for instance, just the amount of food in the sea having a short-term ecological effect,” said Benton.

“Our study underlined that evolution can happen on a short time scale and even small 1-percent to 2-percent evolutionary changes in the underlying biology caused by your harvesting strategy can have major consequences on population growth and yields. You can't just try to bring the environment back to what it was before and expect everything to return to normal.” — BM, GMA News