For the first time, scientists have detected an impact from global warming on the genes of an organism. New research shows that over the last 30 years, a genetically controlled trait--the winter dormancy period--of a species of mosquito has shrunk as Earth has warmed up.
The mosquito Wyeomyia smithii completes its early development in the water-filled leaves of the pitcher plant. Larvae become dormant before dangerous cold weather hits and awake in the spring after the threat of frost has passed. In order to anticipate future temperature, the mosquitoes monitor day length. In the early 1970s, biologist William Bradshaw at the University of Oregon in Eugene demonstrated that the day length at which the larvae hibernate and wake up is programmed in their genes.
Now Bradshaw and his Oregon colleague Christina Holzapfel have shown that global warming has shifted the mosquito's threshold. In the 6 November early edition of the Proceedings of the National Academy of Sciences, they report data compiled from experiments over 30 years in which they collected dormant mosquito larvae from the wild. In the lab, they were bred and then, after they had entered dormancy, exposed to artificial light of various lengths to determine how much daylight they needed to sense before waking up. Comparisons between identical experiments conducted in 1972 and 1996 showed that the daylight the mosquitoes judged as sufficient to wake up in the spring shortened by 14 minutes over 25 years. That means the mosquitoes had compensated for spring weather that arrived earlier in 1996 than in it did 1972.
Global warming is affecting creatures great and small, says biologist D. Liane Cochran-Stafira at Saint Xavier University in Chicago, but most organisms just adapt to the warmer climates without genetic changes. She says Bradshaw's study is "very impressive" because it ties a clear genetic trait to global warming. "The really amazing feature of this is that they had all these years of data available to do these comparisons," she says.