SAN JUAN, Puerto Rico (AP) — Scientists have discovered that lizards that once inhabited forests but now roam urban areas have genetically evolved to survive city life.
Scientists say the Puerto Rican crested anole, a brown lizard with a bright orange fan on its throat, grew special scales to better cling to smooth surfaces such as walls and windows, and grew larger limbs to run around open spaces.
“We’re seeing evolution unfold,” said Kristin Winchell, a professor of biology at NYU and lead author of the study published Monday in 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 make-up of forest dwellers with those of Puerto Rico’s capital, San Juan, as well as the northern city of Arecibo and the western city of Mayaguez. Researchers found that 33 genes in the lizard genome were repeatedly linked to urbanization.
“It’s hard to get close to a smoking gun!” said Wouter Halfwerk, an evolutionary ecologist and professor at Vrije University in Amsterdam, who was not involved in the research.
He said he was impressed that scientists were able to detect such a clear genomic signature of adaptation: “The ultimate goal in the field of urban adaptive evolution is to find evidence of heritable traits and their genomic architecture.”
Winchell said the lizards’ physical differences appear to be reflected at the genomic level.
“If urban populations evolve with parallel physical and genomic changes, we may be able to predict how populations will respond to urbanization simply by looking at genetic markers,” she said.
Changes in these lizards, which have a lifespan of about 7 years, can occur very quickly, over 30 to 80 generations, enabling them to escape predators and survive in urban areas, Winchell added. For example, their larger limbs allow them to run faster in a hot parking lot, and special scales cling to surfaces much smoother than trees.
“They can’t get their claws into it. … (Or) a squirrel on the ass,” she noted.
Scientists chased dozens of lizards for their study by grabbing them with their hands or using fishing rods with a small lasso to catch them.
“It takes some practice,” Winchell said.
Sometimes they had to ask for permission to catch lizards outside people’s homes.
Among Winchell’s favorite finds was a rare albino lizard. She also found an almost 8-inch (20-centimeter) long, quite large for a species she named “Godzilla.”
The study focused on adult male lizards, so it’s not clear if females change 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 the mating call in urban areas, said scientists should then look at the possible limits of the evolutionary response and how morphology relates to mating behavior.
“Ultimately, to monetize adaptive traits for survival, they must lead to higher reproduction,” he said.