ENN — A discovery that remarkably similar lizard communities have evolved independently on different islands in the Caribbean is shedding new light on the science of evolution and genetics.

A team of scientists, led by Jonathan B Losos, PhD, associate professor of biology in Arts and Sciences at Washington University, examined DNA of 56 species found throughout large Caribbean Islands of Puerto Rico, Cuba, Jamaica and the Greater Antilles to test theories on evolutionary history of the Anoles.

The study reveals a perfect example of an evolutionary concept known as “convergence”, where species evolve in similar adaptations to the environment despite living geographically apart.

Although evolutionary convergence has been taken as evidence for the working of natural selection, the study is unique in showing that entire communities have converged. This goes against the grain of most evolutionary thought which stresses that random events — a meteorite striking Earth or a hurricane wiping out island species — play unpredictable roles that send evolutionary diversification down different pathways.

The studies show that while the species evolved separately, they adapted to use different parts of the environment by evolving differences in limb length, toepad size and other characteristics in a strikingly similar manner.

For example, in Puerto Rico’s Luquillo Forest, different anole species have adapted to use different parts of the environment.

One has extremely short legs and crawls slowly on narrow twigs; another has long legs and runs rapidly on the ground; a third lives in the grass.

Moreover, species that live high in the trees tend to have big toepads, important for clinging, whereas those that are more terrestrial have small toepads.

The interesting thing is that Cuba has the same set of habitat specialists, yet none of them are the same species as the set of specialised species in Puerto Rico. This holds true, for the most part, on all four islands.

Losos and his colleagues published the results of their study in an issue of Science magazine.

In Science, Losos and his colleagues report that the Anolis evolutionary tree shows the habitat specialists from the different islands genetically are not closely related, despite exact similarities in their physical traits.

“Our results are very clear-cut that similar communities on the different islands have evolved independently,” Losos said.

“The same habitat specialists on different islands are not closely related, and that’s very interesting because it suggests that there is something about the environment on these islands that elicits similar evolutionary responses on each island. This is rare proof of a community convergence, in which each component of the community on the different islands is identical.”

The study is believed to be the first well-documented case that shows both communities and components of the communities to be similar, a very difficult thing to find in nature.

For example, there are various parts of the world where the Mediterranean climate occurs — South Africa, Chile, Southern California and parts of Australia, as well as Mediterranean regions.

Botanists studying plants have long searched to find exact plant communities, with the exact components and distribution patterns, but in most cases the plants and their communities evolved differently in the various regions, despite having the same warm, generally wet climate.

“The lizard populations on the islands not only have very similar communities, but they are composed of identical components, and that’s really unique,” said Losos.

“The biggest surprise of our result is that it is opposite to a general trend in evolutionary biology in which evolution proceeding in different areas or times lead to very different results.”