Urban lizards have gene mutations that help them adapt to city life

Lizards in three cities in Puerto Rico have evolved a similar set of genetic changes to help them adapt to urban life.

The Puerto Rican crested anole (Anolis cristatellus) is abundant in cities, but living in them presents challenges. There are fewer dense bushes to hide in, glass and metal surfaces are much smoother and harder to climb than tree bark and much of their diet consists of human garbage rather than the berries and insects they are used to in the forest.

Kristin Winchell at New York University and her colleagues have already discovered that the city lizards have longer limbs to run faster across open spaces and larger, stickier toe pads than the rural lizards, to help them climb smooth surfaces . But the team wanted to know how these changes were happening at the genetic level.

To find out, they collected tissue samples from lizards in three cities in Puerto Rico, as well as in the surrounding countryside, and compared their DNA. They found that, even though the three urban populations were genetically distinct, each had mutations in the same groups of genes – a textbook case of parallel evolution.

“No matter how we looked at it, urban lizards keep experiencing the same changes,” says Winchell, which shows that this species of lizard, at least, will adapt to deal with the pressures of urban life in predictable ways, rather than randomly hitting on a new solution.

The groups of genes involved were also notable. One was associated with immune function and metabolism, which makes sense, says Winchell, since urban lizards have a different diet and are exposed to more injuries and parasites than rural ones. Another was associated with limb and skin development, probably contributing to the city-dwellers’ longer legs and specialised toe scales adapted to smooth surfaces.

The latter set of genes proved more interesting still. “When we looked at the function of these genes, our jaws dropped,” says Winchell. Many of them, when they are mutated in humans, tend to result in limb and skin diseases and deformities.

We don’t yet know the precise effects of the mutations in the lizards, but Kevin de Queiroz at the Smithsonian National Museum of Natural History in Washington DC says they give us an insight into the trade-offs of evolution. “The lizards that can adapt to the city are kind of messed up,” he says. “It shows that some of the things that can give an adaptive advantage are not great overall.”

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