Since arriving in the United States from Japan in 1985, the invasive Asian tiger mosquito has spread across the country's eastern reaches, providing a natural demonstration of adaptive evolution. Peter Armbruster at Georgetown University in Washington DC and his colleagues report that over roughly 20 years, the insect (Aedes albopictus) has adapted to differences in the timing of winter onset across roughly 15° of latitude.

The authors measured the day length required to induce winter-time dormancy in mosquitoes across various latitudes in the US and Japan between 2005 and 2008, and compared the measurements with those taken about 20 years earlier. They found a response to seasonal change that is among the fastest documented adaptation in nature.

Other traits, such as body size, did not show a pattern of adaptation in either country. The findings support the idea that, in a changing climate, animals evolve mainly by adapting to changes in seasonal shifts.

Am. Nat. http://dx.doi.org/10.1086/664709 (2012)