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Weeds evolve fast in cties

March 5, 2008

Weed’s seeds evolve quickly in the city : Nature News  Annotated

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Plants have become more likely to drop seeds into their home patch of ground.

This weed's relatives won't travel far from home.This weed’s relatives won’t travel far from home.Gilles Przetak

Urbanization is forcing plants to evolve quickly, but their form of evolution could ultimately put them in danger of dying out.

The daisy-like annual weed Crepis sancta has two types of seed — big, heavy ones that tend to drop straight down, and light, floaty ones that can be caught on the wind and spread farther afield. Weeds growing in patches of soil around trees in the French city of Montpellier have evolved over a period of just 12 years to produce more of the big seeds than the flighty far-reaching ones, says Pierre-Olivier Cheptou from the CNRS in Montpellier who publishes his research team’s findings in the Proceedings of the National Academy of Sciences 1.

Cheptou first noticed the trend in the ‘field’ of a real urban environment. To find out whether it was due to a genetic change, rather than environmental cues, Cheptou took seeds from both rural and urban environments and grew them in a greenhouse. The two plant types were allowed to be pollinated only by similar plants, and once they flowered, the different types of seeds were collected and counted.

The researchers found that the plants grown from urban seeds produced about 14% heavy seeds, compared with 10% heavy seeds produced by the plants from the countryside. Using a mathematical model, Cheptou worked out that the change had happened over about 10 generations of the plant.

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