The distichus group on Hispaniola, including forms suggested for full species status by Glor and Laport. Image from their Figure 1.
In a recently accepted paper in Molecular Phylogenetic and Evolution, Rich Glor and Robert Laport suggest that the stalwart Hispaniolan anoles, A. distichus and A. brevirostris, actually represent complexes of species under the general lineage species concept. This idea is not new, but it’s surprising how long it’s been since it’s gotten serious attention. Before his tragic death in a car accident, Preston Webster made substantial progress working on the brevirostris-group species problem, using allozyme data to study the genetics of Haitian populations in the 1960s and 70s. Webster found evidence for genetic isolation among several brevirostris populations differing in dewlap color (Webster and Burns 1973), but never erected any species. He advocated the idea though, and under the guidance of legendary Caribbean systematist Albert Schwartz, Douglas Arnold erected three additional species from within Anolis brevirostris, naming one after the late Preston Webster (A caudalis, A. marron, and A. websteri; Arnold 1980). He also named erected two additional A. brevirostris subspecies.
In several later papers, Susan Case also used allozymes to study distichus and brevirostris subspecies, but she stopped short of naming any as species. She did, however, note evidence of stable genetic breaks among some distichus subspecies (e.g., Case and Williams 1984).
In the paper at hand, Glor and Laport turned their attentions mainly to the widespread Hispaniolan Anolis distichus, which has 16 subspecies (including some not on the main island of Hispaniola) that often differ remarkably in dewlap coloration. Focusing on the Dominican Republic side of Hispaniola, they found evidence for deep divergence in mtDNA among these subspecies, and argue that they represent distinct evolutionary lineages. The picture isn’t completely clean of course – one of the forms (favillarum) renders another (dominicensis) paraphyletic for this particular marker – but the authors still make a case that these groups represent true evolutionarily distinct units. Certainly some will disagree with Glor and Laport’s decision to elevate these subspecies using the general lineage concept. But species concepts aside, it’s hard to argue with their conclusion that “studies that continue to treat A. distichus (sensu lato) as a single reproductively continuous unit will be problematic.”
Check out the paper! I think this is the tip of the iceberg for distichoid anole systematics. Glor and Laport refrained from tackling the Haitian distichus subspecies and also remained agnostic on the formal status of the three subspecies of A. brevirostris. Rest assured this is just the beginning though…
The latest, from the April 2011 issue of Evolution, highlights a new paper by Steve Poe and company about the relationship between deep evolutionary history and recent naturalization success in anoles. The punch line is that anole species endemic to single-species islands share a suite of traits with anoles that have become naturalized outside of their native ranges. Furthermore, the traits of such ‘solitary anoles’ may be used to predict naturalization more generally within Anolis. It’s an interesting paper and it demonstrates the utility of phylogenetic “tree-thinking” in matters relevant to conservation biology. Poe et al. go one step further though, provocatively suggesting that human-mediated anole invasions simply represent the acceleration of already-present ecological and evolutionary processes, and that humans have changed “the tempo, rather than the essence, of omnipresent natural processes” (p. 1200).
