Genetic Mutations Could Help Lizards Survive City Life

Urban Puerto Rican crested anoles show genetic changes related to immune function, metabolism and limb and skin development

a lizard on a pole
An Anolis cristatellus lizard in Puerto Rico. Kristin Winchell via NYU

Urbanization transforms landscapes dramatically, often harming local wildlife. But some species can adapt to live in these unfamiliar environments. New research suggests city lizards in Puerto Rico have genetic changes distinct from their forest-dwelling counterparts, allowing them to thrive in the city. 

Previous studies from Kristin Winchell, a biologist at New York University, have shown that urban lizards have certain physical differences, including larger toe pads with scales that help them cling to smooth surfaces and longer limbs to run faster across open areas. But now, in a study published Thursday in Proceedings of the National Academy of Sciences, Winchell and her colleagues describe the genetic basis for these differences.

“Urbanization impacts roughly two-thirds of the Earth and is expected to continue to intensify, so it’s important to understand how organisms might be adapting to changing environments,” Winchell says in a statement. “In many ways, cities provide us with natural laboratories for studying adaptive change, as we can compare urban populations with their non-urban counterparts to see how they respond to similar stressors and pressures over short periods of time.”

Winchell and her colleagues examined 96 Puerto Rican crested anoles from three cities in Puerto Rico and the surrounding forests. They first confirmed that the populations of city-dwelling lizards were genetically different from each other, so they could point to urbanization for any similarities. Next, the team took new measurements to confirm that city lizards have longer limbs and larger toe pads.

After examining the animals’ genomes, they found 33 genes specifically linked to urbanization, including some related to metabolism and immune function. Another analysis showed 93 genes in urban lizards that are important for limb and skin development.

“You can hardly get closer to a smoking gun,” Wouter Halfwerk, an evolutionary ecologist and professor at Vrije University Amsterdam who was not involved in the study, tells Dánica Coto of the Associated Press. “The ultimate goal within the field of urban adaptive evolution is to find evidence for heritable traits and their genomic architecture.”

Previous research provides evidence that city lizards get injured more often, have more parasites and eat human food, so differences in their wound healing abilities, immunity and metabolism make sense, Winchell says in the statement. And the genes related to limb and skin development could explain the stickier toe pads and longer limbs of urban anoles.

But another set of genes they found was linked to diseases in humans and mice that involve shortened and deformed limbs.

“When we looked at the function of these genes, our jaws dropped,” Winchell tells New Scientist’s Brian Owens. 

With these traits, the lizards might be evidence of how evolving to match certain stressors can come with trade-offs. “It shows that some of the things that can give an adaptive advantage are not great overall,” Kevin de Queiroz, a zoologist at the Smithsonian’s National Museum of Natural History who was not involved in the research, tells New Scientist.

Still, more research is needed to fully understand the findings. With a sample of only adult male lizards, the scientists haven’t yet nailed down whether females experience the same changes or when the changes appear.

But understanding how animals respond to urbanization could help with conservation efforts in the future. 

“If urban populations are evolving with parallel physical and genomic changes, we may even be able to predict how populations will respond to urbanization just by looking at genetic markers,” Winchell says in the statement.

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