Anole Annals

We recently posted the lovely guide to Mexican anoles prepared  by Gray et al., which featured photographs of 46 species and attracted a lot of attention. Close on its heels comes a new paper in Zootaxa by Gunther Köhler who examines two little known species, A. cumingii and A. guentherii, each known from a single specimen. To make a not very long story short, Köhler examined the type (and only) specimens of both species and concluded that neither is a valid species: cumingii is sunk within A. sericeus and guentherii into the Jamaican A. grahami. In the latter case, it is much more likely that the type locality of “Mexique” for the 1870’s vintage specimen is incorrect than the alternative, that a population of grahami occurs somewhere in Mexico.

This would seem to be a major setback in Anolis’s inexorable climb to the 400 species plateau (put most recently at 386 in a paper I read). Fear not, though—these species have been so poorly known that they were not included in most species listings, including the Gray et al. poster (except A. forbesi).

Köhler concludes by noting that there are a number of other extremely little-known Mexican species requiring further examination, concluding: “However, there are still several nominal species associated with the anoline herpetofauna of Mexico that are of uncertain status, such as Anolis adleri Smith 1972, A. damulus Cope 1864, A. forbesi Smith and Van Gelder 1955, and A. simmonsi Holman 1964. I agree with Lieb (2001) that, as has been the case with the two species treated in the present paper, some, if not the majority, of these enigmatic taxa will be shown to be synonyms of well-known species.” As mentioned, A. forbesi is illustrated in Gray et al.’s guide, and they note that they intend to sink adleri and simmonsi into other species.

For a number of years, Roger Thorpe and colleagues have been studying patterns of geographic variation in Anolis roquet on the island of Martinique. This species is famous–along with A. marmoratus on Guadeloupe to the north–for the tremendous amount of phenotypic variation that occurs on a relatively large island, so great that Skip Lazell described six subspecies of A. roquet. The photo above illustrates how different looking these populations can be.

Martinique is an unusual island, unique in the Caribbean as far as I’m aware, in that it is an amalgam of several different islands that were distinct for millions of years before being united by a volcanic eruption that poured out lava that connected them. Previous work has shown that there is still a clear genetic signature of this historic isolation, with different lineages occupying their ancient homelands. In addition, Martinique harbors considerable environmental heterogeneity, from sealevel to the 1400 meter peak of  Mount Pelée. Much of the mountainous area is cloaked in rainforest, whereas in the rainshadow of the mountains, the environment is quite dry.

This situation has allowed Thorpe and colleagues to ask: which drives divergence more, historic isolation (i.e., allopatry) or the divergent selection pressures that occur in different environments? To examine this question, they have sampled along transects that either cross the boundaries where two lineages meet or that cross environmental transition zones within a single lineage. These transects are exhibited in the figure above–the white lines are the separation among the lineages, the background color represents the environment, and the red lines are the transects (note that the transects cross the lineage boundary at one end, but those sites were excluded from the analysis). Across these transects, the authors measured genetic and morphological differentiation, the latter by examining body patterning and the color of the dewlap and body, as well as limb dimensions and scalation.

The results reported in their most recent paper show that both isolation and environmental differences can lead to divergence, though more predictably so for the latter.

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The Anolis dewlap is a recurrent topic of discussion on Anole Annals. This is not surprising considering that it is commonly viewed as playing a role in many aspects of social interaction, including species recognition and even sexual selection, although, I am unaware of empirical studies supporting sexual selection in the context of female choice.

A recent post by Ian Wang asked the question, “Does This Dewlap Go With My Signalling Environment?” In order to answer this question I would encourage the readers of Anole Annals to have a discussion of what really is an “anole’s signaling environment.”

The paper by Ng et al. (2012) presents some interesting results, and I would encourage everyone to read this paper. The amount of data presented in this paper is impressive, with the authors combining molecular, dewlap reflectance, and satellite data (i.e., GIS data) to evaluate if there is a relationship between dewlap traits and climatic variables across populations of A. distichus. As the precision of GIS data increases, the ability to explore questions at a finer geographical scale is becoming more common. This paper nicely illustrates this approach. Additionally, A. distichus is a nice system for the study of dewlap variation. In fact, in my opinion, one of Al Schwartz’s (1968) best anole monographs describes all sorts of geographic variation in the distichus complex. This monograph is a must read for all Anole Annals fans, with beautiful plates and a lot of natural history data.

One of the main findings of Ng et al. is that geographic variation in dewlap coloration is correlated with the “habitat types” in which populations are found. Interestingly, habitat type seems to have a stronger signal than geographic or genetic distance between populations. I have to admit that I am biased, but this is music to my ears. However, before we jump into further conclusions, I feel that it is important to take a step back and evaluate the question I posed at the start of this post – namely, what is the “signaling environment”?

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