SAN JUAN, Puerto Rico (AP) — Lizards that once inhabited the forests but now scuttle through urban areas have been genetically mutated to survive life in the city, researchers have found.
The Puerto Rican crested anole, a brown lizard with a bright orange throat fan, has sprouted special scales to better adhere to smooth surfaces like walls and windows and has evolved larger limbs for running across open areas, scientists say.
“We’re watching evolution as it unfolds,” said Kristin Winchell, a professor of biology at New York University and lead author of the study published Monday in the Proceedings of the National Academy of Sciences.
As urbanization intensifies around the world, it’s important to understand how organisms adapt and how humans can design cities in ways that support all species, Winchell said.
The study analyzed 96 Anolis cristatellus lizards, comparing the genetic makeup of forest dwellers with those living in Puerto Rico’s capital, San Juan, as well as in the northern city of Arecibo and the western city of Mayagüez. The scientists found that 33 genes within the lizard’s genome were repeatedly associated with urbanization.
“You can hardly get close to a smoking gun!” said Wouter Halfwerk, an evolutionary ecologist and professor at Amsterdam’s Vrije University who was not involved in the study.
He said he was impressed that scientists could detect such a clear genomic signature of adaptation: “The ultimate goal within the field of urban adaptive evolution is to find evidence for heritable traits and their genomic architecture.”
Winchell said the lizards’ physical differences appeared to be reflected at the genomic level.
“If urban populations are evolving with parallel physical and genomic changes, we can even predict how populations will respond to urbanization simply by looking at genetic markers,” he said.
Changes in these lizards, whose lifespan is about 7 years, can occur very quickly, within 30 to 80 generations, allowing them to escape predators and survive in urban areas, Winchell added. Larger limbs, for example, allow them to run faster across a hot parking lot, and special scales allow them to cling to much smoother surfaces than trees.
“They can’t get their claws into it. … (O) squirrel around the rear,” she noted.
The scientists chased dozens of lizards for their study, catching them barehanded or using fishing rods with a small snare to catch them.
“It takes some practice,” Winchell said.
Sometimes they had to ask permission to catch lizards in people’s houses.
Among Winchell’s favorite finds was a rare albino lizard. He also found a 3-inch (8-centimeter) one, quite large for the species, which he nicknamed “Godzilla.”
The study focused on adult male lizards, so it’s unclear whether females are changing in the same way or at the same rate as males, and at what point in a lizard’s life the changes occur.
Halfwerk, whose own research showed how one species of frog changed its mating call in urban areas, said scientists should next look for possible constraints on the evolutionary response and how morphology relates to mating behaviour.
“Ultimately, to take advantage of adaptive traits for survival, they must lead to increased reproduction,” he said.