"We replicated what happened at the end of the last ice age," Barrett said in a telephone interview. Barrett and several colleagues collected wild saltwater sticklebacks along the Canadian coast and after a brief period of adjustment in the lab, the wild fish were introduced in three ponds. They started during the summer, when the water was reasonably warm, and progressed through colder and colder seasons over a three year period.
"The initial colonists produced thousands and thousands of babies, so we had quite a large population heading into the first winter," Barrett said. "There was massive mortality in the winter, and a lot of die-offs," he said, but enough survived for the experiment to continue. The second and third years were similar -- many died, but enough survived. Since the lifespan of a stickleback is one year, the researchers ended up with third generation progeny.
"We took a sample into the lab and ran them through a protocol which essentially just involved lowering the temperature (in the aquarium,)" he said. The temperature dropped so low that the fish became "ecologically dead because they couldn't forage for food and they couldn't escape predation."
At that point, the temperature was 4.5 degrees lower than what their ancestors -- just three generations before -- could have survived in the wild. So somehow, the last survivors had made a radical adaptation to a very different climate. How did they do it?
Natural selection is normally thought of as the acceptance of a genetic mutation that gives the organism an advantage over its cohorts.
"The time required for mutations to arrive that are beneficial for a particular trait, say cold tolerance, are so rare that it would normally take at least hundreds of years before you would see the right mutations arriving in a population," Barrett said. Yet these fish adapted in only three years.
"It's quite likely that the genes that are important for temperature tolerance almost certainly were brought into the ponds with the original colonists," he added. So the fish probably had the genetic equipment they needed all along, possibly left over from a previous epoch when they lived in a colder climate.
Once in a cooler pool, those genes expressed themselves, thus adapting the fish to their new environment.
So is it possible that many creatures have genes that can help out during the difficult years ahead? Barrett cautions that no one knows yet.
"That's not to say that all species are going to be fine and we can do whatever we want because they will adapt to whatever we throw at them," because even in the best of circumstances many will die during evolutionary processes, and even if a few survive they may not be numerous enough to sustain the population. All of the sticklebacks in this experiment eventually died.
So at this point scientists are drowning in a pool of unanswered questions. Barrett argues that potential evolutionary changes need to be brought into the equation but those changes are understood in very few cases, at least for now. We don't really know which animals, and plants, are most likely to survive. They're left with an old battle plan - migration being the first line of defense - which Barrett outlined like this:
"You move, and if you can't move you adapt, and if you can't adapt you die."