Breaking Up (Anolis) Is Hard to DoPosted: October 4, 2012
The “Anolisphere” is all abuzz with a recent paper by Nicholson et al. published in the journal Zootaxa with the inviting title, “It is Time for a New Classification of Anoles”. The authors propose two important and potentially disruptive changes to some widely-accepted features of the study of Anolis lizards:
1) The currently recognized genus Anolis is actually comprised of eight ancient lineages that are so divergent it is justified to break Anolis into eight genera (Dactyloa, Deiroptyx, Chamaelinorops, Anolis, Xiphosurus, Ctenonotus, Audantia, and Norops).
2) The widely accepted “ecomorph” hypothesis, which states that several independent lineages of Anolis lizards underwent convergent adaptive radiations on Caribbean islands (I wrote about this in a previous post), is not supported by the evidence. The authors therefore suggest a looser-fitting “ecomode”model, which simply describes similar ecological adaptations without having to invoke any deterministic process.
Jonathan Losos of Harvard University has referred to this paper as “undoubtedly the most important paper on anoles to be published in the last several years”. Nonetheless, these intriguing ideas will require long and heated debate before they are to be accepted by the scientific community as a whole. The editors of the anole-themed blog Anole Annals have already staked out a position as being strongly opposed to the changes. It has already been suggested that the Anolis community need not be compelled to formally adopt the new classification, and that it would be disruptive and confusing for future researchers, given the long body of work in which Anolis is referred to as a single large genus. There are also mounted defenses of the new paper as well. Check out what’s happening on the blog this week.
In my opinion, we should keep the single-genus status of Anolis, and here’s why. Pretty much everyone in evolutionary biology agrees that Linnean classifications (the binomial system which assigns genus and species names, as well as higher order classifications such as family, class, phylum, etc.) should reflect the monophyly of groups. This means that if you are describing a new genus, or family, or class, the number of lineages nested within the new group is largely subjective and the only real criterion is that all the lineages have descended from a common ancestor.
When basing taxonomy on the estimation of phylogenetic trees (which is pretty much how it’s done these days since tree building is how one establishes monophyly), your taxonomies are only going to be as good as the trees you use. Granted, the tree in the Nicholson et al. paper has strong statistical support, but that only really means that it does a good job of describing the data used to construct it in the first place. If down the line there is more or better data, a new tree may have better support, and then new taxonomies will have to be proposed. Since our understanding of taxonomy is dependent on phylogenetic information that is subject to change, and since we can say with certainty that Anolis in the broad sense represents a monphyletic group, AND much of the research out there treats it as such, I think we’re better off just keeping Anolis the way it is. But up to this point, I’m a consumer of systematics and not an authority on this by any means.
The question remains, can a single genus be ~130 million years old? And the answer is absolutely yes. While our genus, Homo, is only just over 2 million years old, Ginkgo is probably about 200 million years old. And they’re both considered genera! My point is that Linnean classification, while useful, really serves a purpose in the sense that someone knows what museum drawer to put these things in. And I think Anolis should be one drawer (with almost 400 species, that’s a big drawer!).
In any case, under the newly proposed taxonomy, the species I study, A. carolinensis, will remain in Anolis. So I have little to lose, other than a divorce from hundreds of other fascinating possibly former congeners.