Team uses whole islands to test survival of the fittest

Posted by Emma Woollacott

For some people, fruit flies and a tank just aren't enough. Two Dartmouth biologists have been using whole islands in the Caribbean to investigate evolution in lizards.

The researchers wanted to see whether natural selection through competition was as important as natural selection through predation.

So they covered a number of small islands in the Bahamas with bird-proof netting to keep predatory birds at bay. Other islands were left open.

On a third group, the researchers added snakes to the mix, so that the lizards had to face both bird and snake predators.
 
Next, they tracked the lizards over the summer to record which lizards lived and which died on the different islands.

"We found repeated evidence that death by predators occurred at random with respect to traits like body size and running ability," said Robert Cox, a post-doctoral researcher at Dartmouth.

"But we also found that increasing the density of lizards on an island consistently created strong natural selection favoring larger size and better running ability."

In high-density populations, he says, there's a greater level of competition for food, space and other resources.

Part of the point of the study, though, was to show that it's possible to investigate evolution on a large scale.

"Many people are skeptical of evolutionary biology because they perceive it as a purely historical science that can't be tested experimentally," said assistant professor of biology Ryan Calsbeek.
 
"Here, we're providing a real experimental test of natural selection as it happens in the wild. That's an exciting way for us to advance the public's perception of evolution."