Scientists are marvelling at the mysteries of rapid evolution after finding that a dam in central Brazil has caused geckos in the region to grow bigger heads in just 15 years.
They say adaptation lets geckos eat a wider assortment of insects made available by the dam’s creation.
But they also warn that it signals other rapid evolutionary changes around the world as humans continue alter the natural landscape.
Starting in 1996 the dam flooded a series of valleys in Brazil’s Cerrado region, creating nearly 300 islands out of what was once high ground.
Larger lizards disappeared because there wasn’t enough food to support them. But a small, dragonfly-sized gecko, a termite-eater called Gymnodactylus amarali, survived on some islands.
With the big lizards gone bigger termites could now be had, but the geckos’ heads were only 1cm wide, the same size as the termites.
To find out what was going on, scientist Mariana Eloy de Amorim, an evolutionary ecologist at the University of BrasÃlia, and colleagues collected some animals on five of the islands in 2011 and compared them with geckos collected at non-flooded areas.
They measured the size of the geckos and, after euthanizing them, cut open their stomachs to inspect what they had been eating, reports the magazine, Science.
Despite the short time span, they were startled to find, the island-bound geckos had heads that were 4% larger. With a larger mouth, the geckos were able to eat larger termites, giving them a more varied diet.
The team published their findings in a paper in the Proceedings of the National Academy of Sciences.
"You don’t get results like this every day," Thomas Schoener, an ecologist at the University of California, Davis, and a study author, told Science. "It’s kind of this eureka moment when you find a result that actually does back up your expectations about how something should work."
But he said more work should to be done to confirm that evolution was responsible for the change, and not "phenotypic plasticity" – growth trajectories, not caused by genetic change.
Image: Not the type studied, this is a giant leaf-tail gecko, Uroplatus fimbriatus, clinging to glass (TimVickers/Creative Commons)