Why the house lizards came home

House lizards that once lived in forests but now occupy urban areas are very familiar to anyone who lives in Thailand. House lizards are common throughout the tropics, but what makes one species into a house lizard and other… dead?

The Puerto Rican crested anole, a brown lizard with a bright orange throat fan, unique to the island, has sprouted special scales like a gecko to help cling to smooth surfaces like walls and windows and its legs have grown longer, making it faster across open areas, and harder for a cat to catch.

Kristin Winchell, a biology professor at NYU, said…

“We are watching evolution as it’s unfolding.”

As urbanisation increases around the world, it’s important to understand how organisms adapt, and humans can design cities in ways that support other species.

The study analysed 96 Anolis cristatellus house lizards, comparing the genetic makeup of forest dwellers to those living in Puerto Rico’s capital, San Juan, as well as the northern city of Arecibo and the Western city of Mayaguez. Scientists found that 33 genes within the lizard genome were repeatedly associated with urbanisation.

Wouter Halfwerk, an evolutionary ecologist and professor at Vrije University Amsterdam, said…

“You can hardly get closer to a smoking gun!”

Scientists were able to detect a clear genomic signature of adaptation. The house lizards’ physical differences were mirrored at the gene level.

The changes in the lizards, whose lifespans are roughly seven years, occur very quickly, within 30 to 80 generations, enabling them to escape from predators and survive in urban areas.

The scientists chased dozens of lizards for their study, catching them with their hands or using fishing poles with a tiny lasso. Among the findings was a rare albino lizard.