03 Aug 2009

First Comes Global Warming, Then an Evolutionary Explosion

In a matter of years or decades, researchers believe, animals and plants already are adapting to life in a warmer world. Some species will be unable to change quickly enough and will go extinct, but others will evolve, as natural selection enables them to carry on in an altered environment.
By carl zimmer

In 1997, Arthur Weis found himself with an extra bucket of seeds. Weis, who was teaching at the University of California at Irvine at the time, had dispatched a student, Sheina Sim, to gather some field mustard seeds for a study. When Sim was done with her research, Weis was left with a lot of leftover seeds. For no particular reason, he decided not to throw the bucket out. “We just tossed it in a cold, dry incubator,” said Weis.

Weis is glad they did. When a severe drought struck southern California, Weis realized that he could use the extra bucket of seeds for an experiment. In 2004 he and his colleagues collected more field mustard seeds from the same sites that Sim had visited seven years earlier. They thawed out some of the 1997 seeds and then reared both sets of plants under identical conditions. The newer plants grew to smaller sizes, produced fewer flowers, and, most dramatically, produced those flowers eight days earlier in the spring. The changing climate had, in other words, driven the field mustard plants to evolve over just a few years. “It was serendipity that we had the seeds lying around,” says Weis.

Weis is convinced that his experiment is just a harbinger of things to come. Global warming is projected to drastically raise the average global temperature, as well as producing many other changes to the world’s climate, such as more droughts in California. And in response, Weis and other researchers contend, life will undergo an evolutionary explosion.

“Darwin thought evolution was gradual, and that it would take longer than the lifetime of a scientist to observe even the slightest change,” says Weis, who is now at the University of Toronto. “That might be the average case, but evolution can also be very rapid under the right conditions. Climate change is going to be one of those things where the conditions are met.”

Over the past decade, conservation biologists have published a string of studies demonstrating that global warming is changing the face of nature. Red squirrels in Canada breed earlier in the spring, for
David K. Skelly/Yale University
Research by Yale University’s David K. Skelly suggests that the wood frog is capable of extremely fast evolved responses to changing thermal environments.
example. Feral sheep in Scotland are getting smaller. Many populations of birds, animals, and plants are shifting their ranges, as well. Species that live on mountains are moving uphill; other species are shifting away from the equator and toward the poles.

There are two things that can cause these sorts of changes. One is known as plasticity. In many plant species, genetically identical individuals will grow short in windy conditions and tall in calm ones. Humans are plastic, too. Over the past two centuries, for example, people in industrialized countries have become much taller than their ancestors, mainly due to the extra protein and better health they’ve enjoyed (and the extra protein and better health their mothers have enjoyed while they were pregnant).

Plasticity can help animals and plants thrive as conditions change. Insects, for example, emerge from cocoons in the spring as they sense the days getting longer. Their clock is genetically encoded, but they are also plastic enough to emerge ahead of schedule if the plants they feed on start growing sooner.

On the other hand, genes themselves can change, too. When the environment changes, individuals with certain genetic variations may be more likely to survive than others and have more offspring. They pass down their own genes to the next generation, and over time the entire population changes thanks to natural selection.

Yet conservation biologists have only rarely looked into which cause — plasticity or natural selection — has been responsible for the climate-driven changes they’ve documented. “People really weren’t thinking about evolution at all,” says David Skelly, a professor of ecology at the Yale School of Forestry & Environmental Studies. “They thought it happened on thousand-year time scales.”

But in recent years, evolutionary biologists have demonstrated that natural selection can move swiftly in response to manmade events — including changes in climate. Skelly studies wood frogs that live in Connecticut ponds. Over the past few decades, these ponds have been changing. Forests growing on abandoned farmland have been casting once-sunny ponds into cool shade. Beavers have been creating new ponds in open fields, creating ponds that get lots of light.

Skelly and his colleagues have collected wood frog eggs from sunny and shady ponds and have reared them under identical conditions in his lab. Even though the frogs were close relatives, they had quickly diverged in
Natural selection can move swiftly in response to man-made events.
many ways. Frogs from beaver-created wetlands could survive in warmer water than ones from shady ponds. The shady ponds tended to dry up sooner than the sunny ones in Skelly’s study, and that difference in timing had an effect on the development of the frogs. “The animals we collected from heavily-shaded ponds grew faster than frogs in sunny ponds that were literally a rock’s throw away,” says Skelly.

This changing view of evolution has led some researchers to look for evidence that global warming is driving evolution. William Bradshaw and Christina Holzapfel at the University of Oregon, for example, have studied a mosquito that lays its eggs inside carnivorous pitcher plants. The larvae hatch in the spring and feed on the dead insects that fall in. Bradshaw and Holzapfel have demonstrated that the mosquitoes have experienced natural selection, causing them to open sooner than they did a quarter-century ago.

In some cases, natural selection is working in a straightforward way. Weis, for example, had predicted that droughts would make field mustard plants bloom earlier. In wet years, it pays for plants to grow big before they flower, so that they can make more seeds. But in dry years, they run out of water before they can reap the benefit. Instead, earlier flowering plants have more luck. “What we saw was exactly what the theoretical model predicted,” says Weis.

But there are also many complexities to climate-driven evolution that scientists don’t understand very well yet. Red squirrels in Canada breed 18 days earlier in the spring, but the shift is not just a matter of natural selection or plasticity. Both forces are at work at the same time. In other words, all the squirrels are responding to the changing climate by moving up their breeding schedule, and genes associated with an early timetable are spreading through the population.

In other cases, a warming climate is changing animals by making natural selection weaker, not stronger. Among the feral sheep of Scotland, larger lambs used to be more likely to survive the harsh winters. Now that the winters are milder, small lambs don’t pay such a heavy price for their size. As a result, the average size of sheep is dwindling.

Juha Merilä of the University of Helsinki warns that in a lot of cases in which natural selection seems to be at work — some involving climate change, some not — there may not be any natural selection at all. Merilä and his colleagues have studied a colony of red-billed gulls in New Zealand
Some scientists believe that evolution will speed up as temperatures rise.
that have been gradually losing weight over the past 50 years. But when the scientists analyzed the pedigree of 16,520 birds, they found no evidence that the population was slimming because smaller birds were having more chicks than bigger ones. Something in their environment is causing the birds to develop to smaller sizes, regardless of their genes. “There are a multitude of possibilities,” he says, such as a dwindling food supply.

Merilä urges his fellow biologists to use rigorous methods like those employed by Weis and his colleagues on field mustard plants to look for natural selection. “It’s probably happening, but the methods we’re using aren’t up to the rigorous standards I would like to see,” he says.

If life is indeed evolving in response to climate change now, a number of scientists argue that this evolution will speed up in decades to come as temperatures rise and other changes emerge.

“Evolution is going to be important in the future,” says Andrew Hendry of McGill University in Montreal. That means that conservation biologists need to take evolution into account when they try to project what happens to the world’s biodiversity as the planet warms.

More from Yale e360

Biodiversity in the Balance
Paleontologists and geologists are looking to the ancient past for clues about whether global warming will result in mass extinctions. What they're finding is not encouraging, Carl Zimmer writes.

As Climate Warms, Species
May Need to Migrate or Perish

With global warming pushing some animals and plants to the brink of extinction, conservation biologists are now saying that the only way to save some species may be to move them.
The Intergovernmental Panel on Climate Change’s latest report warns that roughly a quarter of all species may be committed to extinction by global warming. The IPCC based that estimate on studies on the ranges of species. Researchers calculate the conditions to which a species is adapted — temperature, rainfall, and so on — and then project where that range will be in the future. In some cases, the range shifts faster than the species can move. In other cases, the suitable range shrinks. In either case, a species will be trapped in a dwindling habitat and become more likely to become extinct.

But these studies assume that species can only cope with climate change by moving, not by evolving. And scientists already know that some species have started evolving in response to global warming already. “Evolution is going to save a number of species from extinction,” Hendry predicts.

Yet Hendry doesn’t consider evolution an ecological Get-Out-Of-Jail-Free card. While some species may be able to evolve quickly, some will evolve slowly — if, for example, they take many years to mature. “They may not evolve quickly enough to forestall extinction,” says Hendry.

Hendry also points out that natural selection can hit biological walls. “There are just some limitations that organisms can’t overcome. We’re never going to be able to walk around at -273 degrees Celsius,” says Hendry. Likewise, some species may not be able to adapt to the new climate.

Unfortunately, scientists may not be able to appreciate the full scope of evolution’s effects for decades. Weis is now laying the groundwork for that research with something he and his colleagues call the Resurrection Initiative. They are starting to gather seeds and put them in storage.

“Fifty years from now, botanists can draw out ancestors from this seed bank and do much more sophisticated experiments on a much bigger scale,” says Weis. “It will answer some very nitty-gritty details about the evolutionary process itself. We want to take the serendipity out of it.”


Carl Zimmer writes about science for The New York Times and a number of magazines. A 2007 winner of the National Academies of Science Communication Award, Zimmer is the author of six books, including Microcosm: E. coli and the New Science of Life. In other articles for Yale Environment 360, he has written about the high-tech search for a cleaner biofuel alternative and about using assisted migration to save species threatened by climate change.

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It's an interesting article, but the reality is that the current background rate of extinctions far, far exceeds any compensation from increased evolutionary processes. This seems to be the equivalent of looking at the positive aspect of the flowerbed in your garden growing better because it gets more sunlight because your house has just burnt down.

The rate of species extinction is only going to increase if planetary warming, deforestation, desertification and ocean acidification continues on the current trajectory. It's irresponsible of the author to ignore this. It's also just a little careless to ignore the fact that the climate is leaving the range that allowed human society to flourish and that will result in the death of millions or billions in the coming decades.

And, sadly, this article - especially the title, which is all that most of them will read - will be eagerly embraced by global warming deniers / delayers - "See! Global warming will be good for plants and animals because they will evolve faster! Drill, baby, drill!"
Posted by DavidCOG on 03 Aug 2009

DavidCOG, how can you claim that the extinction rate far exceeds anything? The absurd numbers of extinctions per year are based on extreme hyperspeciation (to a degree that would classify the Mr. Smith and the Mr. Jones as different species) and estimations of unique species destroyed per acre of rainforest. There is no evidence that a single species has become extinct due to climate change, and there is no evidence that this will change in the foreseeable future.

The number of documented extinctions are small, and almost all have been due to invasive wildlife, chiefly rats on European ships taking the Pacific Isles by storm. The rest of the extinctions are due to poaching.

The reason for this is that life is amazingly tenacious.

It is common sense that plants and animals will adapt easily to a 1-degree-C per century increase in temperatures (they experience ten times that change every year). That leaves rainfall changes and ocean acidification as potential problems. The changes in rainfall are so unpredictable that a magic 8-ball is as useful a climate model, and the ocean acidification argument is an embarassment to anyone with rudimentary knowledge of buffers.

If you can name a single species that has been driven to extinction due to climate change in the past 30 years, I will apologize and concede the point. I do not expect this to happen.
Posted by Ben on 04 Aug 2009

Ben -- it took me, literally, less than 3 minutes to find this:,23739,24742053-952,00.html

This is thought to be the first mammal species to have gone extinct due to anthropogenic climate change. Yes, of course, as the article notes it's possible that some individuals may still be found -- but you are the one demanding evidence from a tiny 30-year timeframe. Note too that the article mentions that scientists believe other species have already gone extinct due to recent climate change.

Good enough for you?
Posted by Dave Harmon on 05 Aug 2009

Another variable worth devoting some cpu time to is just how astonishingly well the fourth cycle of eccentricity matches up with hominid evolution.

“An examination of the fossil record indicates that the key junctures in hominin evolution reported nowadays at 2.6, 1.8 and 1 Ma coincide with 400 kyr eccentricity maxima, which suggests that periods with enhanced speciation and extinction events coincided with periods of maximum climate variability on high moisture levels.”

state Trauth, et al (2009) in Quaternary Science Reviews. There is just nothing quite like having such a natural fly land in your climate change soup. As it turns out, periods of wet maximum climate variability (in modern lingo, global warming correctly re-branded as climate change), cook up the larger braincases. We went from 500-550cc braincases 2.8 mya to the average of about 2,500cc today in the most rapid encephalization of any mammal in the fossil record.

Posted by Sentient on 06 Aug 2009

From Wikipedia:

[The white lemuroid possum] was officially declared extinct in 2009. However since then 3 possums have been found.

Looks like reports of its death were a little premature...
Posted by Jon Jermey on 07 Aug 2009

Scientists were astounded at how quickly the ecosystem rebounded after Mount St. Helens blew up. We can't cap and trade volcanoes and it turns out we don't need to. The environment is a verb, not a noun, and all species evolved or died out via the insensitive "arms race" of natural selection. Humans are unique only in being aware of the process. Ironically, the environmental movement places special responsibilities upon humans, which is a Biblical perspective. The advent of humans is part of the same evolutionary processes. Ultimately, you can't much change human behavior, but you can get rid of lots of them, if that's the only way to "save the planet." Environmentalists are essentially misanthropic.
Posted by vealham on 11 Aug 2009

With levels of CO2 continuing to rise, areas of the world that currently have a tropical climate will be much warmer and drive vegetation and animal life north. These changes would lead to the spreading of Malaria northward, more catastrophic natural disasters and overall greater human health risks.
Posted by frasi on 13 Aug 2009

Are there any examples of tropical climate species that—beyond moving out of their current zone as the climate warms—have actually stopped flourishing, living, or reproducing in their original range? It is a claim that is made often, actual examples would move it from the alarmist to the actual.

In the case of the lemuroid, is it really the case that the paleoclimate record shows no temperatures in that area that exceeded the stated maximum survivable temperature? How was that temperature established, through inference or direct observation?

In the case of this article's conclusion, how was an epigenetic effect ruled out? This is not clear in the paper or this article.
Posted by Carlos on 14 Aug 2009

Good article. I've wondered if evolution didn't work at a higher pace of change than has been taught. It makes sense that if the environment doesn't change, plants and animals would have no 'incentive' to evolve. Only when the environment changes does the true pace of evolution arise.
Posted by bill on 24 Sep 2009

DavidCOG, how can you claim that the extinction rate far exceeds anything? The absurd numbers of extinctions per year are based on extreme hyperspeciation (to a degree that would classify the Mr. Smith and the Mr. Jones as different species) and estimations of unique species destroyed per acre of rainforest. There is no evidence that a single species has become extinct due to climate change, and there is no evidence that this will change in the foreseeable future.

Posted by Forex on 02 Feb 2011



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