Evolution is a game changer in the short term

Cod fish in ice
The size at which North Atlantic cod are maturing now is about 50 per cent of the size at which they were maturing after World War II, and there has been a question mark over whether that is down to evolution. We have shown that evolution of that kind of magnitude does happen in around that number of generations.
Professor Tim Benton
Evolution is a potent force that needs to be reckoned with in the short term, according the results of a study led by University of Leeds researchers, alongside colleagues from the University of Aberdeen. The research, which was funded by the Natural Environment Research Council (NERC), focused on soil mites as a model organism, but the authors believe the findings to be widely applicable and of particular relevance for disease and pest control, population management and conservation programmes.

Reported in the journal Ecology Letters yesterday, this study is the first to confirm a link between rapid genetic evolution and population dynamics in an experimental setting, and reinforces previous indications of the connection between short-term changes in physical characteristics and evolution.

In an interview with ScienceOmega.com, Tim Benton, Professor of Population Ecology in the Faculty of Biological Sciences at the University of Leeds, commented on the intertwining of ecology and evolution that is demonstrated in the paper. He began by explaining that the perception of evolution as a very slow and gradual process stretches back to Darwin and even pre-Darwinian times.

"Looking at the characteristics of species over time, as in the fossil record, any changes in diversity will of course take hundreds of thousands or millions of years to work through," Professor Benton said. "Coupled with Darwin’s argument about natural selection giving rise to adaptations such as the eye, this makes it difficult to imagine such changes arising over anything other than many thousands of generations. It’s because of this expectation that people have tended not to look for genetic evolution over shorter periods."

Along with lead author Dr Tom Cameron, previously a postdoctoral fellow at Leeds and now based at Umeå University in Sweden, Professor Benton and the team collected soil mites from the wild and raised them in glass tubes. From six of the 18 tubes, 40 per cent of adult mites were removed each week. In six other tubes the same proportion of juvenile mites were also removed, and in the remaining tubes no ‘harvesting’ was undertaken.

Although there many studies have been conducted in the wild that have pointed towards evolution as a consequence of environmental change, these have very rarely been able to look at the combination of all three elements considered here; genetics, biology, and population dynamics.

"We chose the soil mite because it is a small but nonetheless representative animal in that it grows up and lays eggs in the same way a bird or a fish would," explained Professor Benton. "As it reproduces relatively quickly, we were able to carry out proper experiments in a laboratory setting and follow the population dynamics of the soil mite and the way its life history and genetics changed, according to the changes we brought about in its environment."

In just 15 generations, the researchers observed a doubling in the age at which the soil mites matured as they adapted to the conditions of captivity. In the tubes from which adults harvested, individuals remained as juveniles for even longer due to the higher likelihood of dying as they reached maturity. The competitive environment of the glass tubes favoured those mites that grew more slowly and were more fertile when mature.

"When we put the animals into the test tubes, at first they seemed to be evolving towards extinction because it was a foreign environment which they didn’t like and weren’t well-suited to," related Professor Benton. "Due to the evolutionary changes that occurred, they recovered, and that’s one of the positive messages to come out of this study."

That positive message is that evolution may help animals cope with environmental change, but Professor Benton was quick to caution that the impact could also be negative depending on how change is managed. Despite its relatively small scale, the study has its roots in finding the answers to other, perhaps more familiar, problems. There is mounting evidence that fish are evolving in response to harvesting and over-fishing around the world, as the professor explained.

"The size at which North Atlantic cod are maturing now is about 50 per cent of the size at which they were maturing after World War II, and there has been a question mark over whether that is down to evolution," he said. "We have shown that evolution of that kind of magnitude does happen in around that number of generations."

"The consequences are twofold. First, if you stop harvesting, they’re not going to go back to how they were before. Then, if they have evolved in a certain direction, they might evolve themselves into an extinction scenario, a situation where they’re not economically important anymore, or where they’re sufficiently small to be eaten by other predators and so the population crashes."

While there are researchers conducting similar experiments with small populations of fish in tanks, a further four or five other examples which reinforce the results of this study would go a long way towards confirming the robustness of the findings made by Professor Benton and his colleagues.

In a fast-changing world, many issues that we need to deal with as humans are relevant to ecology, whether it’s the number of fish we take from the sea, the way we cope with pests and diseases, or our dealings with ecosystem services that we rely on, such as pollinators.

"We need to think about how we manage ecology in the face of a changing world," Professor Benton stressed. "And it’s not just about ecology, because as the world is changing, species are also evolving much more rapidly than we would’ve thought possible 10 or 15 years ago."

In terms of managing biodiversity in nature reserves, for example, Professor Benton asserted that natural selection can often be based on dispersal behaviour. Nature reserves could be established now at a distance of 20 miles apart because that is the distance over which a species disperses at the moment. In 100 years, however, they might only disperse 10 miles, in which case there would be no habitat to go to and the species would be driven to extinction.

"The question of evolution is really important for population management in anything more than a five year window, and all attempts at population management have to cope with those longer term windows," he remarked.

As Professor Benton pointed out, many topical issues at the moment are directly relevant to the evolution of the tiny soil mites in their glass tubes. Antibiotic resistance is an evolutionary question; so is the rise of bird flu in South-east Asia, and the advance of various pests and diseases alongside climate change.

"The speed at which the environment is changing and how it might, through evolution, impact upon us and challenge us will raise many, many questions that we will need to answer in due course."

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The question that should also be asked : did these changes occur by evolution or by other older, dormant genes previously adapted for different environment? i.e. genes already present that are being expressed under the now present environmental conditions.

Paul Record - United Kingdom
It is good to see such a well-written article that shows just how permaculture can be used to help ourselves and others. I hope lots of people read this and are inspired, especially those who can fund projects/do this themselves.

Commented Alida Bedford on
Permaculture: overcoming the challenges of climate change

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