EPOW - Ecology Picture of the Week

Puzzle of the Green Anole

Green Anole (Anolis c. carolinensis), Family Polychrotidae (prev. Iguanidae)
Jean Lafitte National Historic Park and Preserve, Louisiana, USA

Explanation:  Here is an ecological puzzle of a very common species.  All of these photos are of green anoles, small arboreal lizards found throughout southeast U.S. (with subspecies also occurring in the Bahamas and Cuba).  

Here's the puzzle.  Why do some green anoles appear green, and others brown?

Some sources suggest that these are color morphs.  Indeed, I observed and photographed both green and brown forms in the same location -- in these photos, this was in Jean Lafitte National Historic Park and Preserve, in the bayou country of coastal Louisiana.  If these are color morphs, then parts of the population will appear different -- in this case, green forms and brown forms.  And if this persists over time, it is referred to as a "balanced polymorphism."  

But ... why?  What could be the advantage of two color forms in the same population?  Would one color provide a greater camouflage advantage over the other, as on green leaves versus brown leaves?  

Take a look a the main photo; both forms are on brown substrates, and the green form seems to stand out far more.  But look at the other photo to the right here, where a green form anole is hiding pretty well among equally green leaves of water pennywort (Hydrocotyle ranunculoides).   So maybe the colors serve a camouflage purpose.

However, some sources suggest that brown-colored anoles signal distress, and that the green forms turn brown under duress or when cold.  Why this would be the case is unclear.  

Moreover, green anoles are sometimes called American chameleons, although they are not true chameleons and their color-altering abilities are rather limited.  

To make matters more complicated, an introduced species called the brown anole (Anolis sagrei) looks a bit like the brown morph of the green anole, and is spreading in Florida and other coastal locations.  But where the green anole can appear brown, the brown anole cannot appear green.

Wait, it gets worse.  Another species called the Cuban green anole (Anolis porcatus) has also been introduced into various locations of southeast U.S., and it appears quite similar to the native green anole, with both green and brown morphs.  

Conservation of native species, such as the green anole, is made more difficult when pretenders and invasive or introduced species come to occupy some of the same locations and appear quite similar!