Almost by chance, researchers have observed lizards evolve over a matter of months. They found that a group of green anoles living in southern Texas evolved to survive at lower temperatures after a dramatic cold snap hit the region in 2014. They were even able to track the changes in their genes.
The recording of the rapid evolution was actually the result of a bit of luck. Since it is difficult to predict extreme weather events, it's hard to study how animals evolve in response to them. However, one of the researchers had already been testing how green anole lizards respond to cold throughout their range in Texas when the 2014 cold snap hit.
The authors were initially looking at how the lizards in the far north of their Texan range could still operate even when the temperature dropped to a chilly 6°C (43°F), while on the southern border with Mexico, the lowest temperature they can cope with is a much toastier 11°C (52°F). Over several years, they tested their response to air temperature, and even managed to identify differences in gene activity between the more cold-tolerant population in the north and the lizards living in the warmer south.
So when winter storms hit Texas, the researchers were perfectly placed to see what happened to the anoles in response to the sudden and dramatic drop in temperature. The polar vortex that hit meant that even on the border with Mexico, the region experienced frigid temperatures.
They found that the surviving lizards in the south, which before the cold snap were not able to function below 11°C, were now able to deal with temperatures as low as 6°C, just like those in the colder north. Not only that, but when the researchers then looked at their genes, they found that this shift was reflected in their DNA.
This neat example of natural selection in action is one of the most comprehensive studies delving into the subject to date. The researchers were in a unique position to record genetic changes in the lizards before, during, and after the weather event. It is not often that you get that sort of coverage in a study on evolution.