Diversity among Mainland/Island Lizards

Anole lizard lifestyle, one of seven ecomorphs, is evidence for convergent evolution.

Brown, skinny lizard with black splotches along back on background of dead leaves

Ground-dwelling lizard A. tandai.

Ivan Prates

With over 400 species of anoles (Anolis) scattered from Florida to Bolivia, these slen­der lizards, widely sold in pet stores, have long been model subjects in evolutionary biology—keys to ecomorphology, adaptive radiation, and convergent evolution. Yet there is still much to discover about them. 

Jonathan Huie, a doctoral candidate at George Washington University, while an intern at the Smithsonian’s National Muse­um of Natural History, set out to determine whether the less-studied anoles of main­land Central and South America have evolved the six ecomorphs—forms adapted to microhabitats, from treetops to trunks to undergrowth—recognized in the much-studied species found on Caribbean islands. 

Huie examined 347 anoles preserved in four natural history museums; they represented 205 spe­cies, 99 of them from the mainland clade. He mea­sured thirteen morpho­logical traits associated with habitats and modes of locomotion, including the lengths of tails, bodies, snouts, heads, hands, feet, and limb bones and the width of the toe and finger pads anoles use to cling to vertical surfaces. After averaging these values for each species and correct­ing for body size, he plotted their positions in a multidimensional “morphospace.” He tested their resultant assignments to eco­morphs against available field data. 

Mainland anoles were previously consid­ered less ecologically diverse than their Ca­ribbean cousins. But Huie’s findings suggest they occupy all of the same microhabitats; the two groups underwent similar radia­tion—i.e., convergent evolution—over the approximately 30 million years since anoles from the islands recolonized the mainland. He also found evidence of a previously un­recognized ground-dwelling ecomorph in both groups. 

Why was this mainland diversity over­looked? Perhaps because it is much easier to study anoles on the islands, which are celebrated evolutionary hotbeds where, with fewer predators, they are more abundant and visible. “Mainland anoles are a lot more secretive and inhabit more complex envi­ronments, such as heavy forest,” Huie noted. 

Huie suggests the methods he and his coauthors developed could be applied to study “the relationships between form and function” in other morphological features of organisms, whether plant leaves, frog limbs, or the pharyngeal jaws of fish—especially cichlids, the fast-evolving, highly diverse piscine counterparts of anoles. (Biological Journal of the Linnaean Society

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