Speedy evolution reported in a controlled experiment

A new study challenges the widely held belief that evolutionary changes in living organisms take place slowly, over hundreds, thousands or millions of years.

Researchers have found evidence species can evolve much more quickly when in response to environmental change.

Tim Benton studies how living organisms respond to changes in their environment. In a paper published in Ecology Letters, the professor of biological sciences at the University of Leeds in England examines why marine species, for example, have declined so rapidly in size and number over the past 50 years.

“Is this a response that is due to them having less food or the temperature of the water changing from climate change or is it a response that is due to natural selection working and evolutionary biology happening?” Benton said.

To find out, Benton’s team of researchers conducted a series of laboratory experiments with soil mites, tiny spider-like creatures that, among other things, reproduce rapidly.

“We brought them in from the wild and put them in test tubes, where each test tube maintained about 1,000 individuals in a free running population. Every day, we just put in a little bit of food,” he said. “And in some of the populations we took out juveniles and in other populations we harvested adults. And then we just left them to it over about 100 weeks.”

That’s normally long enough for about 20 generations of soil mites. In their new test tube environments, the tiny creatures competed for food, sex and survival in different ways than they would have in the wild. And in charting the mites’ growth rates, genetics and reproduction over this relatively brief span of time, the scientists observed that natural selection produced significant evolutionary changes. For example, Benton said, the length of time the mites needed to reach adulthood doubled during the course of the experiment.

“Because it is taking them so much longer to grow up, then that means that the population responds to changes in a different way,” he said. “Population growth rate is slower, which means that there are very large changes in population dynamics, the way the population size responds to environmental change in itself.”

According to Benton, the mite study suggests there is a powerful interplay between environmental and evolutionary change.

“And one or two more complementary studies like ours in different groups, then people will quite happily accept, I think, the force of evolutionary change in ecological time,” he said. “So over a single human life time, 100 years, there are likely to be very large changes and if we don’t start thinking about the evolutionary changes as well as the changes in the environment then the things we put in place to protect the species we want to manage won’t actually work.”

One place where this might have a critical impact is in fisheries management.

“Given that we are harvesting large animals all the time, that’s what we do when we go out fishing,” he said. “The phenotypic response that we see in the reduction of size is likely to be an evolutionary response and that’s what we found in our laboratory study. So what that means is, if you stop fishing because your stock is getting depleted and the animals are increasingly smaller and smaller and smaller, there is no necessity that they will be able to recover because you’ve had a hard-wired evolutionary change. So they won’t just be able to spring back.”

There’s no guarantee that they will again grow larger and larger.

Benton added that environmentally-induced evolutionary changes could also have serious implications for other wildlife conservation efforts, as well as for disease and pest control programs.

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