AboutZoos, Since 2008


Lizards show evo­lu­tion is predictable

pub­lished 20 July 2013 | mod­i­fied 30 May 2014

If you could hit the reset but­ton on evo­lu­tion and start over, would essen­tially the same species appear? Yes, accord­ing to a study of Caribbean lizards by researchers at the Uni­ver­sity of Cal­i­for­nia, Davis, Har­vard Uni­ver­sity and the Uni­ver­sity of Mass­a­chu­setts. The work is pub­lished on 19 July in the jour­nal Sci­ence.

Lizards CaribbeanThe pre­dictabil­ity of evo­lu­tion over timescales of mil­lions of years has long been debated by biol­o­gists, said Luke Mahler, a post­doc­toral fel­low at UC Davis and first author on the paper. For exam­ple, the late Stephen Jay Gould pre­dicted that if you “rewound the tape” on evo­lu­tion and started over, you would get an entirely dif­fer­ent out­come, argu­ing that small events – a storm that wiped out a par­tic­u­lar pond, a poor sea­son for insects – could have a dis­pro­por­tion­ate effect.

On the other hand, there are a num­ber of exam­ples of species in sim­i­lar habi­tats that evolve inde­pen­dently into similar-​looking forms, such as the cich­lid fishes of African lakes.

It’s a big ques­tion in evo­lu­tion­ary biol­ogy [the pre­dictabil­ity of evo­lu­tion, Moos], but very hard to test
Luke Mahler, lead author, UC Davis »

Mahler found his test sub­jects in the Anole lizards that live on four neigh­bour­ing islands – Cuba, His­pan­iola (the coun­tries of Haiti and the Domini­can Repub­lic), Jamaica and Puerto Rico. Anoles began colonis­ing these islands, all sim­i­lar in cli­mate and ecol­ogy, about 40 mil­lion years ago, and once there, they began to mul­ti­ply, result­ing in a diver­sity of species on each.

The researchers stud­ied 100 of the 119 Anole lizard species from the islands, tak­ing mea­sure­ments of their bod­ies from wild and museum spec­i­mens and com­par­ing them across islands. They found a strik­ing degree of con­ver­gence – on each island, evo­lu­tion had pro­duced a set of very similar-​looking lizards occu­py­ing sim­i­lar envi­ron­men­tal niches.

“The adap­tive radi­a­tions match on all four islands – with few excep­tions, each species on an island has a match on the other islands,” Mahler said.

A ter­ri­to­r­ial male Anolls mar­canoi pho­tographed in the Domini­can Repub­lic, dis­plays by extend­ing its dewlap and bob­bing its head. This species is typ­i­cally found perched on rocks or tree trunks, and will jump to the ground to for­age on pass­ing insects. Videog­ra­phy by Lucas Mahler/​UC Davis:

By com­bin­ing the body-​form data with a fam­ily tree of the Anoles, Mahler and col­leagues were able to con­struct an “adap­tive land­scape” for the lizards. An adap­tive land­scape is a fun­da­men­tal con­cept in evo­lu­tion­ary biol­ogy but dif­fi­cult to show in prac­tice. Peaks on an adap­tive land­scape rep­re­sent var­i­ous com­bi­na­tions of fea­tures that will be favoured by nat­ural selec­tion, whereas val­leys are just the oppo­site. Species with sim­i­lar habits will tend to clus­ter on the same peak.

For Anole lizards, their niche might be liv­ing on tree-​trunks, or among twigs high in a tree, or down in the grasses on the ground. Each calls for dif­fer­ent adap­ta­tions, and cre­ates a dif­fer­ent adap­tive peak.

The adap­tive land­scapes of all four islands are very sim­i­lar, the researchers found. Look­ing back at the lizards’ evo­lu­tion­ary his­tory, they were able to deter­mine when a par­tic­u­lar peak was colonised, or when a species hopped from one peak to another. The land­scape dri­ves con­ver­gence, they discovered.

“The cool part is that we now have a way of mod­el­ling the adap­tive land­scape that explains this con­ver­gence,” Mahler said.

(Source: UC Davis news release, 19.07.2013)

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