Global Warming Fuels Speedy Evolution
Feb. 22, 2006 ?- Don't look now, but your backyard is evolving. It's no joke. There's a growing body of evidence that evolution is no longer something only seen either in this year's flu virus or Cretaceous tyrannosaur bones. It's happening everywhere, right now, and charging full-steam ahead.
Research on toads, frogs, salamanders, fish, lizards, squirrels and plants are all showing evidence that some species are attempting to adapt to new conditions in a time frame of decades, not eons, say biologists.
What's more, one of the biggest reasons for all this evolution right now may be that human-induced changes to climate and landscapes give species few other options.
Move, Adapt or Die
"Basically, a species can do three things," said the University of Sydney's Richard Shine: "go extinct, move or adapt."
The first two have kept conservation biologists working day and night, to the exclusion of the third, he said. But that's changing as real-time evolution is hitting the news wires and getting more attention.
The highest-profile case yet was made public by Shine and his colleagues in the Feb. 16 issue of Nature: the case of toxic cane toads at the forefront of a seven-decade Australian invasion. Measurements over the years prove that the leading toads have evolved significantly longer legs.
It appears that hopping further and faster rewards long-legged toads with the first crack at lush virgin territory, and therefore more offspring to perpetuate their athleticism.
Behind that story are even more cases of rapid evolution, says Shine, an evolutionary ecologist. Already he's seeing changes in native Australian snakes. First they tried to eat the toads, and died. Now, Shine says, the surviving snakes have modified jaws which make them unable to eat the toads and therefore safe from their toxin.
"Invasive species are a nice model," Shine said.
They hint at the rates of evolution that might be expected as species feel the increasing pressure of global warming. They also draw the attention of conservation biologists, who are often on the front lines of battles to save habitats and individual species.
"In the past 20 years, essentially all evolutionary biologists have come to widely recognize the importance and prevalence of (what's) often called 'rapid evolution,'" wrote evolutionary biologist Andrew Hendry of McGill University, who responded to questions via email from the Galapagos Islands. "Many conservation biologists have recently come to the same realization and I expect that the rest will soon follow."
Rapid evolution is good news for conservation biologists. It implies that the number of species that might go extinct will be less than some current estimates, which predict as many as one-third of all species alive today will be wiped out by 2050.
The first known case of a mammal responding genetically to warmer climate warming is the red squirrel of the Yukon Territory.
Canadian scientists have discovered that red squirrels are giving birth about 18 days earlier than their great-grandmothers. It's the early squirrel that gets the nut, after all: natural selection in action.
Frogs In Hot Spots
"Climate change is going to be a massive agent of evolution," said ecologist and rapid evolution researcher David Skelly of Yale University.
The case of the North American wood frog brought Skelly to study rapid evolution. It's a world champion adaptor, he says, because it manages to thrive in ponds as far flung as Alaska and Georgia.
To figure out the wood frog's secret, Skelly and his colleagues raised warm pond tadpoles and cold pond tadpoles from the same forest alongside each other at the same temperature. They were shocked to discover the cold pond tadpoles grew 15 percent faster, as if they had evolved a ramped-up growth rate to compensate for the slower growth rates normally found in cold water.
Next, they tested the tadpoles in a trough with warm water at one end and icy water on the other. Oddly, the cold water wood tadpoles swam toward the warmer water and the warm water tadpoles showed no preference. It's exactly what you'd expect if the cold-water frogs had adapted to living in cold ponds by always seeking the warmest possible spot.
On the other hand, the warm-water frogs never needed that trick, since their water was fine, so they hadn't evolved any preference to warm water.
"When I tell conservation biologists this story, they are astounded," said Skelly.
The wood frogs show how resilient and adaptable frogs can be, he says. Contrary to popular portrayals of frogs as the environmental canaries in the coal mine, most frogs are "fairly bullet proof," he said.
That's why when the frogs disappear, as they are in places like the Monteverde Cloud Forest of Costa Rica, there's all the more reason to be concerned about how drastic climate is changing, he said.
Good Ol' Evolution
Finally, rapid evolution also has something to say about what happened in the past, something about which dusty fossils are silent.
For a long time, paleontologists thought everything always evolved very slowly. But in 1972, Niles Eldridge and Steven J. Gould proposed that sometimes, when there is pressure to change, species evolve much more quickly.
Their "Punctuated Equilibrium" hypothesis explained why Eldridge would find layer upon layer of one sort of trilobite in rocks, "then BOOM, another kind of trilobite," said Spencer Lucas, curator of paleontology and geology at the New Mexico Museum of Natural History and Science.
Where did the new trilobite come from?
"Either it came from elsewhere or it evolved there," said Lucas.
If it evolved rapidly, the odds are against the few intermediate forms also be luckily preserved as fossils, and so the new species would seem to just pop into existence, as read in the rocks. The same holds true of many other sudden appearances of changed versions of animals and plants in the fossil record.
Of course, the rocks don't usually divulge whether it was 100 years or 10,000 years between the an old and new species.
"Even though the fossil record suggests most species take thousands of years to evolve, there's a lot of reason to believe that things happen very rapidly," said Lucas.
So it's not entirely surprising to a paleontologist to hear that biologists are discovering cases of rapid evolution, he said.
"Still," said Lucas, "It's kind of exciting."
