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.
Category: New Research Page 64 of 66
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.
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.
Owl monkeys in the genus Aotus may be the closest extant relatives of the Greater Antillean primate fauna. Fig. 1 is from Cooke et al.'s recent PNAS paper and summarizes known primate fossils from the Greater Antilles.
Imagine wandering around the Greater Antilles on an anole hunt with monkeys bouncing among the trees above. As it turns out, your imagination wouldn’t need to take you back more than a few hundred years to make this vision a reality. The Jamaican monkey (Xenothrix macgregori) – which was described in 1952 by Ernest Williams (a.k.a. the godfather of Anolis biology) and Karl Koopman (a.k.a. the namesake of the Haitian endemic Anolis koopmani) – may have even survived to see the first European explorers.
A recent PNAS article describes the fifth species of extinct monkey endemic to the Greater Antilles (two are from Cuba, two from Hispaniola, and one from Jamaica; see map above for more details). A precise age for this fossil is unknown, but the available evidence is consistent with the Holocene. In their description of Toussaint’s island monkey (Insulacebus toussaintiana), Cooke et al. contribute new data to the long-standing debate about the origins and evolutionary implications of the West Indian primate fauna. Most students of Greater Antillean monkeys agree that they represented a relictual clade of primates that had long since disappeared from northern South America. Although their precise phylogenetic affinities are still being debated, the West Indian species seem to be most closely related to either the owl monkeys (Aotus) or the titi monkeys (Callicebus). Cooke et al. further suggest that the large size of the Greater Antillean primates relative to mainland relatives may have resulted from the island effect.
Dewlap variation in Anolis apletophallus (formerly, A. limifrons). Photo courtesy Jessica Stapley.
Jessica Stapley writes:
I am a Marie Curie Postdoctoral fellow co-hosted by the University of Sheffield and the Smithsonian Tropical Research Institute (STRI) in Panama. I have just started a new project aimed at identifying loci underlying Anolis dewlap colour pattern.
Understanding the evolution and maintenance of phenotypic variation is a major goal in evolutionary biology. Addressing this goal ultimately requires linking molecular genetic variation to phenotypic variation, but identifying the genes responsible for important traits has been a major challenge in non-model organisms. Recent advances in DNA sequencing technology however, have revolutionized the development of genomic resources and paved the way for major advances in linking phenotype and genotype in non-model organisms.
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.
Julián Velasco and colleagues recently added a new species to the anoles: Anolis anoriensis from the central Andes of Colombia, described in The Herpetological Journal. This species is placed in the aequatorialis group, and appears to be very similar to Anolis eulaemus, another Dactyloa group anole from the central Andes. Anolis anoriensis joins a host of recently described Andean anoles from this clade (e.g., Ayala-Varela and Velasco 2010; Ayala-Varela and Torres-Carvahal 2010 – see New Anole Literature for full citations) and adds to the incredible diversity of anoles in Colombia, which already boasts more recognized species than any other country. Despite these recent descriptions, the relationships of Andean anoles remain extremely poorly known, as does our understanding of the factors responsible for the generation of such diversity.
Anolis anoriensis (top panels) versus Anolis eulaemus (bottom panels), from Velasco et al. 2010
Since Darwin’s time, biologists have believed that evolution occurs at a very slow, glacial scale. A corollary of this belief is that ecologists need not consider evolution as they work out the intricacies of ecosystem functioning—it occurs much too slowly to be a factor in understanding the day-to-day interactions among species and their environment. In recent years, however, it has become apparent that, when natural selection is strong, evolutionary change can occur very quickly. This raises the possibility that ecological interactions can lead to rapid evolutionary change, which could then quickly have ecological effects. For example, several recent studies have shown that fish species will evolve adaptively in response to competitive and predatory interactions, and that these evolutionary changes affect the ecosystem, changing rates of primary production, decomposition and altering the biotic and abiotic composition of the ecosystem. The study of “eco-evolutionary dynamics” is taking off and was recently reviewed by Tom Schoener in Science. In that review, Schoener referred to ongoing research on Anolis sagrei in the Bahamas as an example of how ecological interactions could lead to evolutionary change that would then feedback and alter ecosystem properties (see above).