Surprisingly Swift Evolution Observed in Lizard Species

A green anole lizard (Anolis carolinensis) stands on a green leaf in the early morning sun. Jeff R Clow/Getty Images

Evolution takes time. But just how much time it takes is the issue. How long, for instance, did it take theropod dinosaurs to evolve into modern birds? Tens, if not not hundreds of millions of years. But since the turn of the last century, when American biologist Hermon Bumpus noticed that individual sparrows in a population became larger as the result of one huge snowstorm, scientists have been observing instances of short bursts of evolutionary progress over a significantly brief period of time.

Definitive instances of rapid evolution are tough to come by, though, even in these days of advance genetic testing. But a recent study published in the journal Science finds that, over the course of just a few months, green anole lizards (Anolis carolinensis) living in the area of the Mexico-Texas border evolved a rapid genetic tolerance to cold weather after an unusually frigid winter.

Green anoles are warm-weather reptiles that evolved on the Caribbean island of Cuba. They found their way to the mainland long ago, but a prolonged and extreme cold snap can really put the hurt on a population of anoles. The winter of 2013 did just that. Before that year's famed polar vortex hit, however, the research team collected anoles in August to find out just how cold one of these lizards could get before its motor function was compromised — that is, it couldn't right itself when knocked over.

They collected anoles from five different sites across Texas, and found that when gradually cooled in a chamber in the lab, the individuals from the southernmost site became uncoordinated at around 52 degrees F (11 degrees C), but the ones collected from the northernmost site became unable to right themselves at around 43 degrees F (6 degrees C).

Because the scientists already had genetic samples from the lizards in the first study, when, a few months later, temperatures plummeted to lows that hadn't been seen in 15 years, the researchers went out and collected some of the surviving lizards from all five sites. They placed them in the same cooling chambers and found the southernmost anoles exhibited much more cold resistance than the ones that had been collected back in the summer — they could now stand strong in the face of 43 degrees F (6 degrees C) temperatures. RNA sequencing before and after the cold front also revealed significant differences between individuals from the southern genomic regions before and after the weather event.