A slender, dusky lizard clings to a spray of brush. Another, stout and brown, nearly disappears against a lichen-covered tree branch, its mobile eyes protruding. A third—large, lime green, and majestic, with an icing-drizzle pattern—flashes a ruddy dewlap from atop a matching spear of agave.

A look at just three species of Anolis lizard of the Greater Antilles hints at the incredible diversity to be found there. More than 100 species of Anolis inhabit the islands of Jamaica, Hispaniola, Cuba, and Puerto Rico. According to a new study in the journal Evolution, they did not tiptoe into this diversity, but took the islands by evolutionary storm.

Like Darwin's famous finches of the Galapagos islands, the Greater Antilles anoles are a textbook case of island biodiversity. Small dots of land hemmed in by ocean can exhibit startling levels of speciation compared to the nearby mainland, every pocket of habitat playing host to a new and different subset of a common group. While examples of islands as crucibles of speciation abound, it is much harder to reconstruct the timeline for how the process unfolded. Darwin's finches comprise 15 species sporting a cornucopia of beak shapes and body sizes. They all likely descended from an unremarkable mainland tanager, perhaps what birders like to call an LBJ or "little brown job." But did this explosion in diversity happen the moment the ancestral birds arrived and encountered a host of new niches? Or did they remain generalists for ages, slowly shuffling into specialist lifestyles one by one as real estate got tight? Recent work on the Antilles' anole populations suggest the former.

Researchers from Harvard University, the University of Rochester---New York, and the National Evolutionary Synthesis Center in Durham, North Carolina took DNA samples from Anolis species across the islands and compared body proportions from scores field-collected and museum specimens with the animals phylogenetic (family) tree to reconstruct the lizards' evolutionary paths on the islands.

Their results show that this was not a case of a slowly diverging tree at all, but a rapidly branching bush of diversity, with lizards spreading out into wildly different lifestyles and body types soon after reaching the islands. The pioneers touched down to find an open season on habitat types and no reptilian LBJs with which to compete. But very rapidly, lizards began to favor the brushy fringes, trunks, or stout tree branches to hunt for their food. Notes researcher Luke Mahler of Harvard, "Each body type is specialized for using different parts of a tree or bush." With dainty lizards finding their fellows in one place, and likewise for the larger, within a short span of evolutionary time the many major divisions had formed. But after the initial blitzkrieg, the habitat options narrowed and diversification slowed, said study author Liam Revell of the National Evolutionary Synthesis Center. "Ancient evolutionary changes in body proportions were large, but more recent evolutionary changes have been more subtle."

Richard Glor, University of Rochester

Jonathan Losos, Harvard University