From National Geographic News: Brown anole lizards on tiny islands in the Bahamas were enjoying the good life, untroubled by a lizard predator found on larger islands nearby.

But all that changed when biologist Jonathan Losos of Harvard University in Cambridge, Massachusetts, appeared on the scene.

Losos's team experimentally introduced predatory curly-tail lizards onto six islands where the ground-dwelling anoles had been living free of predators, sparking a see-saw year of natural selection.

For the smaller anole lizards, a trait that was advantageous in November - six months after the introduction - had become a liability by May.

...The evolutionary experiment, reported in tomorrow's issue of the journal Science, reveals that, even though evolution can seem like a slow process, its driving force - natural selection - can shift like the wind.

...The study also supports a somewhat controversial idea in biology: Animals' behavior in response to environmental change can spur evolutionary adaptations.

"In most cases in evolutionary biology, you have to look back and speculate what might have happened," Cameron Ghalambor said.

"[Losos's study] captures the changes as they occur. We're getting a window into what is actually happening in the very early stages of evolutionary change."

The new perspective may help biologists better understand evolution in the lizard genus Anolis, which contains about 400 species including the brown anole.

A number of Anolis species are tree-dwellers with small hind limbs.

Losos says that at least some of this diversity may be the result of a process similar to the one his team observed.

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Based on the Science paper:

Rapid Temporal Reversal in Predator-Driven Natural Selection

Jonathan B. Losos, Thomas W. Schoener, R. Brian Langerhans, David A. Spiller

Science 17 November 2006:

Vol. 314. no. 5802, p. 1111

DOI: 10.1126/science.1133584

As the environment changes, will species be able to adapt? By conducting experiments in natural environments, biologists can study how evolutionary processes such as natural selection operate through time. We predicted that the introduction of a terrestrial predator would first select for longer-legged lizards, which are faster, but as the lizards shifted onto high twigs to avoid the predator, selection would reverse toward favoring the shorter-legged individuals better able to locomote there. Our experimental studies on 12 islets confirmed these predictions within a single generation, thus demonstrating the rapidity with which evolutionary forces can change during times of environmental flux.

Read Jonathan Losos' paper "Adaptation and speciation in Greater Antillean anoles" (Open Access/Free)

Opening paragraph

This section first reviews the evidence that both speciation and adaptation played important roles in anole diversification, focusing primarily on the anoles of the Greater Antilles (Cuba, Hispaniola, Jamaica, and Puerto Rico). It then addresses the extent to which the two processes are intimately linked. The theory of adaptive speciation presents one mechanism by which the two processes might occur in an integrated fashion, but there are other possibilities. In part this requires a discussion of what constitutes a species of Anolis, so that it is possible to recognize when two lineages have diverged to the level of different species. Finally, this section addresses some exciting new developments that affect our understanding of the processes important in anole adaptive radiation.

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See "Model of an Internal Evolutionary Mechanism" (Draft)