Imagine a hungry group of youngsters bursting into a candy store where sweets are free for the taking—no cashiers asking for money, no one at the counter putting lids on the candy jars. Children flock to all corners of the store. They spread out so each child can claim an entire row of candy jars as their own. As more and more children flood into the shop, they fill the open spaces, packing themselves ever tighter until each child is left with control of just a single jar of candy, not an entire row. As available candy jars dwindle, fewer and fewer children come into the candy store.
The first anole lizards who made their way from South America to the islands of the Caribbean forty thousand years ago encountered their own version of such a candy store.
Anoles, a group of lizards most closely related to iguanas, are among the most diverse groups of reptiles. There are more than 400 species of anoles and of those, nearly 100 species inhabit the islands of the Caribbean.
The islands of the Caribbean offered those first anole immigrants a smorgasbord of easy-to-catch food and plentiful available habitats. Consequently, they spread out across the spectrum of habitats and feasted on a variety of food resources.
Over time, the Caribbean anoles evolved different body shapes and sizes so each species became suited for specific habitats and feeding zones. Anoles that fed in the forest canopy evolved shorter limbs. Those that foraged on tree trunks developed long limbs.
Although scientists knew of the vast diversity of anole species throughout the Caribbean, no one knew the details of exactly how such diversity came about. No one, that is until now.
In the April 29 issue of the journal Evolution, Luke Mahler of Harvard University and his colleagues from University of Rockester, Harvard University, and the National Evolutionary Synthesis Center report their findings from a study of how anoles in the Greater Antilles diversified over time.
The Greater Antilles is one of three island groups in the Caribbean Sea. The Greater Antilles comprises Cuba, Hispaniola (an island that consists of two countries, Haiti and the Dominican Republic), Jamaica, and Puerto Rico.
Mahler's team reconstructed how the anoles evolved in the Greater Antilles by comparing DNA and body measurements for thousands of museum specimens. They determined the pace of anole diversification—how fast the anoles were changing shape and size so they could occupy different niches.
Mahler's team found that the first anoles to arrive to the islands of the Caribbean diversified rapidly. Those early anoles evolved the widest array of shapes and sizes. Then, as resources became increasingly scarce and as anole species poured into more and more available niches, diversification slowed. The anoles were forced to slice and dice their niches into ever smaller portions. Changes in the body size and limb length among anoles species—once rapid when niches were plentifu—now slowed as niches grew scarce.
References
Mahler, D., Revell, L., Glor, R., & Losos, J. (2010). Ecological Opportunity and the Rate of Morphological Evolution in the Diversification of Greater Antillean Anoles Evolution DOI: 10.1111/j.1558-5646.2010.01026.x
Photo (top) © Luke Mahler / Harvard University. Anolis fowleri, a rare anole from the Dominican Republic. Photo (bottom) © Luke Mahler / Harvard University. Anolis alutaceus, a grass-bush anole from Cuba.
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