Author: Jonathan Losos Page 126 of 130

In an unprecedented display of organismal superiority, an anole graces the cover of a major scientific publication for the third time in six months (the others may be seen here and here [editor’s note: see comment]).  The photo advertises an article on environmental niche modelling and biogeographic boundaries in two Hispaniolan anole species, which will be the subject of a forthcoming post. Incidentally, not that anyone’s counting, this makes two cover shots for Richard Glor and one for Luke Mahler.

Guess what these are

Anolis polylepis is a small and very abundant anole that occurs in southwestern Costa Rica. Recently, Köhler and colleagues divided A. polylepis into two species based on the structure of the hemipenis illustrated above. The vast majority of A. polylepis retains the name, but populations of the lizard on the Osa Peninsula, where the famous Corcovado National Park is located (and hence from where many people know A. polylepis) are now to be known as A. osa.

The species may be distinguished by their man parts.  Anolis polylepis, whose hemi-tallywacker is on the top row above, has a bilobed organ, whereas that of A. osa, on the bottom row, is unilobed.  What appears to be a narrow hybrid zone occurs at the base of the Osa Peninsula, where lizards exhibit an intermediate hemipenial morphology.  Köhler et al. examined a number of other morphological characters, including dewlap color, and found that in all other respects, the two taxa could not be distinguished.

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Anolis sagrei. Photo by Melissa Losos.

Anoles are renowned for their adaptation to different habitats. One particularly well-documented and ubiquitous axis of adaptation involves the length of the hindlimbs. Both among and within species, lizards that use broader surfaces have longer legs. The adaptive explanation for this correlation appears to revolve around a locomotion trade-off: on broad surfaces, longer limbs provide greater sprinting ability, whereas on narrow surfaces, shorter legs provide enhanced nimbleness. Anoles, and particularly A. sagrei, are also known for their ability to adapt rapidly to novel conditions (but see caveat below)—experimental populations introduced to different environments differentiate in hindlimb length in ten years.  For these reasons, anoles may be a particularly good organism to examine the extent to which human-caused habitat alterations lead to evolutionary change or, looked at another way, whether a species can adapt to changing conditions in a human-altered world.

In this vein, Erin Marnocha and colleagues studied populations of A. sagrei on four islands in the Bahamas. On each island, she compared two populations, one in natural, forested habitat, the other in disturbed habitats around houses. These habitats differ both because disturbed areas have fewer trees, but also because disturbed areas have more broad surfaces, such as big trees, walls, and fenceposts, as compared to natural forest, which has lots of narrow diameter vegetation. The prediction is straightforward: A. sagrei in disturbed areas should have relatively longer legs. And that is exactly what they found.

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