The Heat Is Online

Warming Linked to Genetic Change in Mosquitoes

Mosquito evolves because of global warming
The Associated Press
, Nov. 7, 2001

WASHINGTON (AP) -- A tiny mosquito that lives in the pitcher plant is evolving in response to global warming, researchers report.

In a study appearing Tuesday in the Proceedings of the National Academy of Sciences, researchers at the University of Oregon in Eugene found that global warming is leading the pitcher plant mosquito, a tiny, fragile species that seldom bothers people, to delay when it breeds and develops.

The pitcher plant mosquito is not considered a pest. But experts say the study suggests that global warming also could lead to genetic changes in troublesome insects.

William E. Bradshaw of Oregon, the first author of study, said the pitcher plant mosquito bases its lifestyle on the length of day. When days grow shorter, it is genetically programmed to hibernate and settles in to spend the winter comfortably protected inside the pitcher plant, he said.

However, a subgroup within the pitcher plant mosquito population has slightly different genes that cause them to develop and reproduce later into the season. Global warming, by causing a longer growing season, favors this subgroup, Bradshaw said.

"The temperature changes caused by global warming are increasing the length of the season in which the animal can grow, develop and reproduce," he said. "As a result, animals that reproduce later in the season have a greater opportunity to leave their genes in the population."

As a result, global warming allows those mosquitoes to dominate others, Bradshaw said.

The pitcher plant mosquito, which lives mostly on nectar, is found in eastern North America, from Canada to Florida. Along its southern range, it is found as far west as Mississippi.

It is the southern type of pitcher plant mosquito that is adapted to a longer growing season, Bradshaw said. The study showed that this southern adaptation, favored by the effects of global warming, is now moving north.

In laboratory experiments, the Oregon researchers showed that this genetic adaptation can come to dominate a mosquito population in as little as five years.

"This is an important finding because it shows the genetic population of the mosquito was modified by global warming," said Marina Caillaud, a Cornell University genetic researcher who commented on Bradshaw's paper. "This suggests that this type of genetic adaptation could happen in other species also."

For instance, she said, other mosquitoes that are pests to humans might adapt so that the troublesome mosquito season could grow longer and expand further north.

Copyright 2001 Associated Press. All rights reserved.

Global warming changes mosquitoes' genetic "off" switch

By James Randerson

The New Scientist

The genetic switch that tells the tiny pitcher-plant mosquito when to bed down for the winter has shifted, US scientists have discovered.

"This is the first example of a change in a real trait of known function that has been directly related to changes in seasonality," says William Bradshaw of the University of Oregon.

Many previous studies suggest the warming of the global climate is forcing animals and plants to adapt. In the UK, for example, migratory birds are flying south later and butterfly populations are shifting northwards.

But all of these changes can be attributed to the responses of individuals to the environment rather than genetic changes, according to Bradshaw and Christina Holzapfel at the University of Oregon.

The mosquitoes they collected in 1996 went into dormancy 9 days later than in those from 1972. The scientists were also able to detect a change in the switch time between mosquitoes collected in 1988 and 1993, indicating that swift greenhouse climate change is being tracked by rapid genetic changes.


Critical timing

The mosquitoes (Wyeomyia smithii) are widely distributed across eastern North America, from the Gulf of Mexico to Canada. They lay their eggs in carnivorous pitcher-plants, where the larvae develop to adulthood.

The larvae must enter a dormant phase to survive the winter, but timing is crucial. If dormancy begins too early, valuable feeding time is missed, if dormancy begins too late, the risk of damaging cold temperatures rises.

The researchers collected mosquitoes from 1972 to 1996 and brought them into the lab. Using artificial chambers with a programmed light cycle, but a constant temperature, they tested the day-length that prompted the larvae to enter dormancy.

By rearing them in a controlled environment, explains Bradshaw, "we were able to factor out environmental effects and isolate genetic changes."

Over 24 years, the critical day-length that sent the insects to sleep has shortened by just over half an hour. If the mosquitoes had been using this day length in 1972, they would have been killed by winter weather, says Bradshaw.

Journal reference: Proceedings of the National Academy of Sciences (vol 98, no 23)