"In mosquito, a small tale of climate change"

From the Boston Globe

UNORGANIZED TERRITORIES, Maine -In a woodsy bog on the road between Millinocket and Baxter State Park, a mosquito that can barely fly is emerging as one of climate change's early winners.

The insect, which lives in the carnivorous purple pitcher plant, is genetically adapting to a warming world. By entering hibernation more than a week later than it did 30 years ago, the Wyeomyia smithii mosquito is evolving to keep pace with the later arrival of New England winters.

Along with Canadian red squirrels and European blackcap birds, the mosquito -- a non biting variety found from Florida to Canada -- is one of only five known species that scientists say have already evolved because of global warming.

The unobtrusive mosquito's story illustrates a sobering consequence of climate change: The species best suited to adapting may not be the ones people want to survive. Scientists say species with short life cycles -- Wyeomyia smithii lives about eight weeks -- can evolve quickly and keep up with changing environmental conditions as a result. Rodents, insects, and birds, some carrying diseases deadly to humans, are genetically programmed to win. Polar bears and whales, which take years to reproduce, are not.

"Rapid climate change is actually now driving the evolution of animals -- that is a dramatic event," said Christina M. Holzapfel, who, with her husband, William E. Bradshaw, has documented genetic changes in hundreds of thousands of mosquitoes at their University of Oregon lab in Eugene. The couple, both evolutionary geneticists, began collecting the mosquitoes at the bog here and in other New England locations more than 30 years ago while at Harvard University.

Until now, the effects of climate warming had been most noticeable in the Arctic, as glaciers melt. But dramatic changes are also being seen in northern temperate zones such as New England, where the average winter temperature has risen 4.4 degrees Fahrenheit over the last 30 years. Growing seasons have lengthened, winter is arriving later, and the weather has become more erratic...

Timing of hibernation is a life or death decision for the mosquito: If it begins hibernating too early, it will use up limited nutritional reserves when it doesn't need to and reduce its chance of surviving the winter. If it starts too late, it will freeze to death.

The experiment favors individual mosquitoes in each generation that, because of genetic variation, start hibernating later than the rest of the population. More of these late-hibernating mosquitoes survive the winter and then pass on that later-hibernation genetic trait to the next generation. The process continues until most of the population is hibernating at the best time to ensure they survive the winter...

Nearly every species reacts to changes in the weather. Lilacs bloom earlier if a spring is particularly warm. Mice populations boom in years when winter temperatures are warm enough for them to reproduce.

Yet these responses aren't necessarily genetic: Most species, including humans, have a built-in flexibility -- scientists call it phenotypic plasticity -- that allows them to adjust to temporary environmental conditions. It is partly why we can withstand Boston's frigid winters and steamy summers.

But when the changes are all in the same direction and continue for a long time -- such as the warming taking place in New England -- Charles Darwin's natural selection can take over: Individuals with certain characteristics better suited to the changed environment survive in greater numbers than others in the population. Those individuals then pass on those favorable genetic characteristics to their offspring, eventually leading to evolutionary change in the entire population...

"The moral of the story is that things are going to be different," said Kevin Emerson, a graduate student in the Bradshaw-Holzapfel lab. "Whether we know exactly what is going to be different . . . I don't think we can say. But people have to accept that things are changing."