Anolis is a speciose group of mostly arboreal lizards, represented by thirteen genera and more than 650 species. They are widely distributed throughout South America, Mexico, up into southern North America, the West Indies, and even occur as invasives in places such as Hawaii. Most researchers follow classification of this group by Frost, although several formal criticisms have been made (e.g. Lazell 1992, Schwenk 1994, Macey et al 1997), so I will not touch base on that topic for now.
Studying the different species of anoline lizards in the Antillean region, the first observation normally made is the occurence of similar ecological types, called ecomorphs (see Rand and Williams 1969 and Williams in 1972) on each of the seperate islands of the archipelago. In '72 Williams described to science 6 ecomorphs, then divided those between dry and wet habitats. In 1983, however, he revisted the area and added to his list of ecomorphs not in existence previously a few more. With the addition of a few newly discovered ecomorphic types, those known to occur at this point in time are: Trunk-Crown Giant, Trunk-Crown Dwarf, Twig, Trunk, Trunk-Ground, Boulder, Rockface-Cave, Bush-Grass, Bush, Aquatic, and Leaf Litter.
Most researchers believe Trunk-Crown or arboreal ancestors were the precursor of all other ecomorphs in anolines, as the treetops and canopies tend to have the greatest diversity of arthropoda. It has been suggesting that after some time of evolution to fill a specialist niche in the canopy, successive anolines came to compete with the arboreal species, which forced them through competition to evolve and radiate from the canopy, where the greatest source of food occured, to other areas like the tree's trunk, the ground, or the leaf litter, for example.
It has been proven through recent genetic research that these groups are totally unrelated to corresponding similar ecomorphs throughout the archipelago, evolving seperately from unrelated anolines, and as many have begun to note, from mainland South America in particular:
"Phylogenetic studies using mitochondrial DNA, conducted by Todd Jackman, in collaboration with Allan Larson and Kevin de Queiroz of the Smithsonian's National Museum of Natural History, clearly indicate that members of the same ecomorph class on different islands are not closely related. Hence, the similar assemblages on each island are the result of convergent evolution."-Losos Laboratory
It would be fascinating to study the Trunk-Crown Ecomorphs of the mainland to discover a mitochondrial similarity between it and all other species of the West Indies/Antilles region. Finding that one lizard whose genetic diversity is higher than the others (or even interconnected with a great many other Anolis), would also be a milestone in anoline studies. Gathering evidence not only from wild specimen data, but from long-gone specimens trapped in amber, would be a fascinating study to conduct. I wonder what conclusion would such a hypothesis reach? What results would this have in the future of the phylogenetic tree of Anolis?
