When invading species land on new shores, they must face an alien landscape with a limited gene pool, which in theory should make it hard to survive. Yet many invaders thrive. Now genetic studies of a tropical lizard help explain this paradox, suggesting that multiple landfalls can help invaders stay both genetically diverse and adaptable.
From its ancestral range in the Caribbean, the brown anole lizard (Anolis sagrei) has traveled from Cuba to Florida, then on to Hawaii and Taiwan. Jason Kolbe of Washington University in St. Louis, Missouri, and colleagues examined the mitochondrial DNA of anoles around the world to study their diversity. Each native population in Cuba was genetically distinct. But animals that had migrated appeared to have ancestors belonging to many different Cuban populations.
Then the scientists retraced how the reptiles spread. Distinct gene mutations indicated that lizards from southern and southeastern Florida largely hailed from western Cuba. But animals from central and northern Florida were more likely to have ancestors from eastern Cuba and even Belize, suggesting that the brown anole landed on the Florida mainland many times. Such intermingling helps genetic diversity flourish, says Kolbe.The findings, reported in the 9 September issue of Nature, also help explain a common invasion phenomenon called the lag phase. The anole was first reported in the Florida Keys around the 1880s, only spreading to the rest of the state in the 1950s. People thought such invaders needed time to adapt to new conditions or attain a critical population size. But the anole's expansion coincides with the arrival of new lizard species, which brought additional genetic diversity.Other scientists say the findings make good sense. "When you enhance genetic variation, you're creating superlizards," says evolutionary ecologist Thomas Smith of the University of California, Los Angeles. "It could dramatically increase the likelihood of some individual being fit for the new environment." However, Craig Moritz, an evolutionary biologist at the University of California, Berkeley, cautions that more work is needed to definitively prove that this genetic mixing explains the success of an invasive species.