Part of the reservoir created by the Serra da Mesa Dam.
Part of the reservoir created by the Serra da Mesa Dam. Felipe Venâncio/CC BY 2.0

Thanks to the Serra da Mesa Dam in central Brazil, close to 300 islands were created in the span of just two years. More than 650 square miles of the Cerrado region were inundated by the reservoir, which finished filling in 1998. The region is considered a biodiversity hotspot. By so altering the landscape, the dam and reservoir threaten that, but by creating new environments and isolating species, they’re showing how life adapts to all the changes we throw at it.

The hilltops that became islands were once home to a variety of lizards that eat termites, and isolation impacted different varieties of lizards in different ways. Larger species died out (though they survive on the mainland) because they couldn’t find enough termites on their islands maintain large body size. So Gymnodactylus amarali, a small gecko, inherited a whole termite buffet.

There was just one problem. For most of the G. amarali geckos, the termites were too big to eat—bigger than their mouths. But some of the individual lizards were lucky enough to have slightly larger heads. So they gobbled up termites, thrived, and passed the large-head trait on to their offspring. When scientists from Brazil and the United States compared the island-dwelling lizards with their mainland relatives—separated by only 15 years and a short stretch of water—the researchers found the island lizards had heads that are about four percent larger. The researchers write in their report that the shift is “astonishing” because it was so rapid and the lizard populations on the five islands they studied evolved the same trait independently of each other.

It is possible, Science reports, that the larger head size isn’t a result of evolution, but rather better growth thanks to the new environment and altered diet. However, the researchers believe evolution explains the size difference, and plan to check for genetic changes in the future.