Einstein Science Reporting for Kids
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When lizards invade, it's time to evolve -- quick!

Anolis caroliensis.
[Credit: Dr. Todd Campbell]

You might think of evolution as something that takes millions and millions of years to happen—and yes, sometimes it does take that long for an animal or plant species to change. But scientists watching two species of lizards got a chance to see one of those lizard species evolve in just 10 years—a biological blink of an eye.

Yoel Stuart, a researcher at the University of Texas, Austin and his fellow scientists describe this rapid evolution in the 24 October issue of Science. They saw green anole lizards evolve after brown anole lizards invaded the greens' territory. Scientists have long thought that this kind of competition between close-cousin species can make evolution happen fast, but it's a rare thing to see happen in the wild.

Before the invasion, the green lizards were living on a group of small islands in Florida, where they liked to hang out on the trunks and lower branches of trees. But that all changed when the brown lizards came to the islands. The brown lizards also liked those lower branches, and they pushed the green lizards up into the higher tree branches.

The green lizards were used to clinging to the rough and wide low branches in the trees, and now they found themselves barely hanging on to the smoother, narrower high branches. Something had to change if their species was going to survive on the islands.

Ten years after the brown lizards invaded, Stuart and the other scientists noticed that green lizards' feet had changed over that decade. The green lizards had developed wider and stickier toepads, which helped them cling on to their new, higher perches. The changes only happened in places where the green lizards battled the brown lizards for tree space. On islands with no brown lizards, the green lizards' toes didn't change.

It's interesting to see that evolution can happen so fast, the scientists said, because some species may need to change fast in the future. Some animals and plants might find themselves competing with all kinds of other invaders, or they might need to evolve quickly to survive when the Earth's climate changes around them.