CAMBRIDGE, Mass. -- Some Caribbean lizards' strong sexual dimorphism allows them to colonize much larger niches and habitats than they might otherwise occupy, allowing males and females to avoid competing with each other for resources and setting the stage for the population as a whole to thrive. The finding, reported this week in the journal Nature, suggests sex differences may have fueled the evolutionary flourishing of the Earth's wildly diverse fauna in a way not previously appreciated by scientists.
Conducted at Harvard University, the University of Hawaii, and Washington University in St. Louis, the research is the first to investigate the role of sexual dimorphism -- which can yield differences between sexes as substantive as those seen between entirely separate species -- in adaptive radiation, the phenomenon by which species diverge from a single ancestor.
"Humans are keenly aware of the differences between the sexes, and such sexual dimorphism is widespread in the animal kingdom," says Jonathan B. Losos, professor of organismic and evolutionary biology in Harvard's Faculty of Arts and Sciences and curator in herpetology at the Harvard Museum of Comparative Zoology. "Evolutionary biologists have studied the much larger antlers of male deer, the showy plumage of male birds, and many other traits for decades. This extensive body of research has helped us understand why the sexes of particular species have evolved differences, but this sort of work has not previously been put into a broader context to understand how significant sexual dimorphism is in the grander scheme of evolutionary diversification."
Found across the West Indies, the Anolis lizards studied by Losos, zoologist Marguerite A. Butler, and mathematician Stanley A. Sawyer represent a classic case of adaptive radiation, having evolved independently after arriving on Cuba, Hispaniola, Jamaica, and Puerto Rico. On each island, species have evolved traits suited to th
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