Geographic Variation In Body Size And Cells In Anolis Carolinensis

Anolis carolinensis from Miami. Photo by J. Losos.

Think quick: how many states does A. carolinensis occur in naturally? And can you name them?

The answer is 11: Florida, George, North and South Carolina, Tennessee, Alabama, Mississippi, Louisiana, Texas, Arkansas and Oklahoma.

This is an enormous geographic range encompassing great variation in environment and climate. Amazingly, almost no research has been conducted on geographic variation in this, our only native species of anole. In fact, it was only recently that good studies of phylogeographic variation in genetics were published. Why more work hasn’t been conducted on green anoles is a good question. My hunch is that scientists view them like squirrels: too common and ordinary to be interesting. This isn’t really fair to this magnificent species: consider how different we would view the beautiful green lizard with a pink dewlap if it occurred in, say, Costa Rica.

But more importantly, there is actually a lot of variation—morphological, ecological, behavioral and otherwise—in this species, but it has not been well-studied, much less well-explained. Into this breach now comes a nice paper by Rachel Goodman and colleagues that examines geographic variation in body and red blood cell size and muscle number across the range of the green anole. They show that both vary quite significantly. For example, the figure illustrates the average body size (measured as snout-vent length, including both males and females) for 19 populations, which varies from 48.4 mm in southeastern Florida to 64.5 in Brownsville, Texas. Surprisingly, variation correlated better with latitude and longitude than it did with a variety of climatic measures. With regard to body size, the lizards are smallest in Florida, and increase in size both westward and northward, but then decline in size further to the north. The explanation for these patterns is not clear, but this study provides a clear example of the interesting variation that exists within this species and awaits explanation.

Here’s the abstract of the paper:

Geographic patterns in body size are often associated with latitude, elevation, or environmental and climatic variables. This study investigated patterns of body size and cell size of the green anole lizard, Anolis carolinen­sis, and potential associations with geography or climatic variables. Lizards were sampled from 19 populations across the native range, and body size, red blood cell size and size and number of muscle cells were mea­sured. Climatic data from local weather stations and latitude and longitude were entered into model selection with Akaike’s information criterion to explain patterns in cell and body sizes. Climatic variables did not drive any major patterns in cell size or body size; rather, latitude and longitude were the best predictors of cell and body size. In general, smaller body and cell sizes in Florida anoles drove geographic patterns in A. carolinensis. Small size in Florida may be attributable to the geological history of the peninsular state or the unique ecologi­cal factors in this area, including a recently introduced congener. In contrast to previous studies, we found that A. carolinensis does not follow Bergmann’s rule when the influence of Florida is excluded. Rather, the opposite pattern of larger lizards in southern populations is evident in the absence of Florida populations, and mirrors the general pattern in squamates. Muscle cell size was negatively related to latitude and red blood cell size showed no latitudinal trend outside of Florida. Different patterns in the sizes of the 2 cell types confirm the importance of examining multiple cell types when studying geographic variation in cell size.

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Jonathan Losos

Professor of Biology and Director of the Living Earth Collaborative at Washington University in Saint Louis. I've spent my entire professional career studying anoles and have discovered that the more I learn about anoles, the more I realize I don't know.

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