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Lizards seen evolving in just 15 years

Oct. 23, 2014
Courtesy of the University of Texas at Austin
and World Science staff

Sci­en­tists have doc­u­mented the ev­o­lu­tion of a na­tive Flor­i­da liz­ard spe­cies in as lit­tle as 15 years as a re­sult of pres­sure from an in­vad­ing liz­ard.

Since Dar­win’s time, bi­ol­o­gists as­sumed that ev­o­lu­tion takes cen­turies, or long­er, but re­cent find­ings have be­gun to change that view.

The left hind foot of Ano­lis car­o­li­nen­sis, or green anole. (Cred­it: Yoel Stu­art)


In Flor­i­da, re­search­ers found that af­ter con­tact with the in­va­sive spe­cies, the na­tive liz­ards be­gan perch­ing high­er in trees. Then, genera­t­ion af­ter genera­t­ion, their feet evolved to be­come bet­ter at grip­ping the thin­ner, smooth­er branches found high­er up.

Ev­o­lu­tion oc­curs when ec­o­log­i­cal con­di­tions fa­vor the sur­viv­al and re­pro­duc­tion of or­gan­isms with some traits, over those with oth­er traits. This leads the fa­vored traits to spread through a popula­t­ion over genera­t­ions. Given enough time, a whole spe­cies can change dramatically, or branch off into mul­tiple new species.

In the liz­ards, the sci­en­tists found that change oc­curred at an as­ton­ish­ing pa­ce: With­in a few months, na­tive liz­ards had be­gun shift­ing to high­er perch­es, and over 15 years and 20 genera­t­ions, their toe pads had be­come larg­er, with stickier scales on the feet.

“We did pre­dict that we’d see a change, but the de­gree and quick­ness with which they evolved was sur­pris­ing,” said Yoel Stu­art, a post­doc­tor­al re­search­er at The Uni­vers­ity of Tex­as at Aus­tin and lead au­thor of the study ap­pear­ing in the Oct. 24 edi­tion of the jour­nal Sci­ence.

“To put this shift in per­spec­tive, if hu­man height were evolv­ing as fast as these liz­ards’ toes, the height of an av­er­age Amer­i­can man would in­crease from about 5 foot 9 inches to­day to about 6 foot 4 inches with­in 20 genera­t­ion­s—an in­crease that would make the av­er­age U.S. male the height of an NBA shoot­ing guard,” said Stu­art. “Although hu­ma­ns live long­er than liz­ards, this rate of change would still be rap­id in ev­o­lu­tion­ary terms.”

Green anoles (left) and brown anoles (right). (Cre­dit: Todd Camp­bell and Adam Al­gar)


The na­tive liz­ards stud­ied, known as Car­o­li­na anoles or green anoles, are com­mon in the south­east­ern U.S. The in­va­sive spe­cies, Cu­ban anoles or brown anoles, are na­tive to Cu­ba and the Ba­ha­mas. Brown anoles first ap­peared in South Flor­i­da in the 1950s, pos­sibly as stow­aways in ag­ri­cul­tur­al ship­ments, and have since spread across the south­east­ern U.S. and have even jumped to Ha­waii.

This lat­est study is one of only a few well-doc­u­mented ex­am­ples of what ev­o­lu­tion­ary bi­ol­o­gists call “char­ac­ter dis­place­men­t,” in which si­m­i­lar spe­cies com­pet­ing with each oth­er evolve dif­fer­ences to take ad­van­tage of dif­fer­ent ec­o­log­i­cal niches. A clas­sic ex­am­ple comes from the finches stud­ied by Charles Dar­win. Two spe­cies of finch in the Galá­pa­gos Is­lands di­verged in beak shape as they adapted to dif­fer­ent food sources.

The re­search­ers spec­u­late that the com­pe­ti­tion be­tween brown and green anoles for the same food and spa­ce may be driv­ing the adapta­t­ions of the green anoles. Stu­art al­so not­ed that the adults of both spe­cies are known to eat the hatch­lings of the oth­er spe­cies. “So it may be that if you’re a hatch­ling, you need to move up in­to the trees quickly or you’ll get eat­en,” said Stu­art. “Maybe if you have big­ger toe pads, you’ll do that bet­ter than if you don’t.”


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Scientists have documented the evolution of a native Florida lizard species in as little as 15 years as a result of pressure from an invading lizard. Since Darwin’s time, biologists assumed that evolution takes centuries, or longer, but recent findings have begun to change that view. In Florida, researchers found that after contact with the invasive species, the native lizards began perching higher in trees. Then, generation after generation, their feet evolved to become better at gripping the thinner, smoother branches found higher up. Evolution occurs when ecological conditions favor the survival and reproduction of organisms with some traits, over those with other traits. This leads the favored traits to spread through a population over generations. In due course, a whole species can change noticeably. In the lizards, the scientists found the change occurred at an astonishing pace: Within a few months, native lizards had begun shifting to higher perches, and over the course of 15 years and 20 generations, their toe pads had become larger, with more sticky scales on their feet. “We did predict that we’d see a change, but the degree and quickness with which they evolved was surprising,” said Yoel Stuart, a postdoctoral researcher at The University of Texas at Austin and lead author of the study appearing in the Oct. 24 edition of the journal Science. “To put this shift in perspective, if human height were evolving as fast as these lizards’ toes, the height of an average American man would increase from about 5 foot 9 inches today to about 6 foot 4 inches within 20 generations — an increase that would make the average U.S. male the height of an NBA shooting guard,” said Stuart. “Although humans live longer than lizards, this rate of change would still be rapid in evolutionary terms.” The native lizards studied, known as Carolina anoles or green anoles, are common in the southeastern U.S. The invasive species, Cuban anoles or brown anoles, are native to Cuba and the Bahamas. Brown anoles first appeared in South Florida in the 1950s, possibly as stowaways in agricultural shipments, and have since spread across the southeastern U.S. and have even jumped to Hawaii. This latest study is one of only a few well-documented examples of what evolutionary biologists call “character displacement,” in which similar species competing with each other evolve differences to take advantage of different ecological niches. A classic example comes from the finches studied by Charles Darwin. Two species of finch in the Galápagos Islands diverged in beak shape as they adapted to different food sources. The researchers speculate that the competition between brown and green anoles for the same food and space may be driving the adaptations of the green anoles. Stuart also noted that the adults of both species are known to eat the hatchlings of the other species. “So it may be that if you’re a hatchling, you need to move up into the trees quickly or you’ll get eaten,” said Stuart. “Maybe if you have bigger toe pads, you’ll do that better than if you don’t.”