Author: Jonathan Losos Page 129 of 133

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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I’ve now read the book in which the Toda et al. paper (see previous post) is published. There are several other chapters that discuss the hypothesis that introduced A. carolinensis are responsible for the decline and even extinction of endemic insects on these islands. For example, one chapter notes that dragonflies have decreased greatly and that green anoles can eat two dragonflies a day. Also, note the green anole eating a cicada on the cover! There is also an article that suggests that green anoles may serve as pollinators.

Anole species have been introduced to many places throughout the Caribbean and elsewhere (for example, Florida and Costa Rica), but relatively little research has examined the ecological impact of these invaders.  Anolis carolinensis has been in the Ogasawara Islands of Japan for several decades, where it attains high population densities and has been blamed for local declines and even extinctions of native insects. It also is thought to negatively affect an endemic skink. Toda et al. report efforts to eliminate the green anole from port areas, so as to prevent them from stowing away and invading additional islands, and to reduce their population densities in other areas. They have found the most effective techniques to be putting out glue-traps designed for cockroaches (pictured here), which reduced anole densities by as much as 50% in some areas, and building Teflon-sided fences that anoles cannot climb.  Efforts are continuing to eradicate these anoles and other invasive species on these islands. This paper also briefly reports a nice demographic study of the lizards, finding that some individuals could live longer than four years.

What's that I hear? Photo by Melissa Losos

We think of anoles as visually oriented animals, but they can hear as well. Very little work has investigated their hearing ability, much less how they respond to aural phenomena. In a recent study, Huang et al. reported that anoles alter their behavior depending on what they hear. In particular, they show that A. cristatellus in St. John, U.S. Virgin Islands, appear to display less after hearing the call of a predatory bird, a kestrel, compared to their response to a non-threatening granivore, the bananaquit. They also report that simulated ecotourists playing the sound of a camera shutter clicking lead to a decrease in display rate compared to controls or the faux tourists taking flash photos. They interpret this finding as indicating that the sound of SLR cameras clicking, but not their flashes, are interpreted as a threat by the anoles. These results are interesting, but cry out for more thorough study, especially given that data were collected by approaching lizards, watching them for 1-2 minutes, presenting the stimulus, and then recording behavior for another minute and comparing rates of behavior from before and after. Moreover, differences in behavior among treatments were only detected in the final 15 seconds of the post-stimulus observation period, where no differences were detected in the first 45 seconds. Bottom line: it would be very interesting to investigate the role of hearing in anole behavior, and this study provides an inkling that there may be interesting work to be done.