Author: Jonathan Losos Page 78 of 130

Last year, Nicholson et al. proposed splitting Anolis into eight genera in a paper in Zootaxa.  This idea was extensively debated in AA’s pages (e.g., 1,2,3 and links therein). Now, two papers have been published criticizing the methods and conclusions of Nicholson et al. and suggesting that the generic name Anolis be retained for the entire clade.

In a paper just published two days ago in Zootaxa, Steve Poe argues strongly against Nicholson et al.’s proposal on multiple grounds, primarily on the lack of demonstrated monophyly of most of the proposed genera. Poe concludes at the end of the introduction of the paper: “Nicholson et al. (2012) selectively adopted results of their own flawed, unstable, and conflicting analyses, selectively incorporated pertinent published data and results, and changed names for over 100 species that have never been included in a phylogenetic analysis. The proposed taxonomy is unnecessary and unwarranted according to standard taxonomic practice. It should not be adopted by the scientific or nonacademic communities.” The paper is only five pages long and is readily downloaded.

Meanwhile, within the past month, Castañeda and de Queiroz published a paper in the Bulletin of the Museum of Comparative Zoology on phylogenetic relationships within the Dactyloa clade of anoles (pdf, supplementary material). The paper is a follow-up to their 2011 paper on Dactyloa, adding morphological data to the molecular dataset analyzed previously. We’ll have more on this paper soon, but the pertinent part for today is the “Note added in Proof” appended to the beginning of the paper. The authors explain “Shortly after our paper was accepted, Nicholson and colleagues published a phylogenetic analysis of anoles and a proposal to divide Anolis into eight genera… Here, we comment briefly on their study as it pertains to the phylogeny and taxonomy of the Dactyloa clade,” and then go on to criticize Nicholson et al.’s recognition of genera (in this case, Dactyloa) and species groups that are not monophyletic in their own analyses. Moreover, like Poe, Castañeda and de Queiroz present strong critiques of the Nicholson et al. methodology and analyses, concluding “Because our results are based on larger samples of Dactyloa species (for both molecular and morphological data), as well as larger samples of molecular data (with respect to both numbers of bases and numbers of gene fragments, and including both mitochondrial and nuclear genes), and because many of their taxonomic conclusions that differ from ours are either contradicted by their own results or unsubstantiated, we do not consider any of the differences between our phylogenetic results and taxonomic conclusions compared with those in the study by Nicholson et al. (2012) to warrant changes to our proposed taxonomy. In contrast to Nicholson et al. (2012), we refrain from assigning some species to series and treat some taxonomic assignments as tentative because of contradictory results or poorly supported inferences, and we present justifications for all taxonomic decisions pertaining to species not included in our analyses.”

The Castañeda and de Queiroz critique is only two pages long. Read ’em both and decide for yourself.

Bat eating frog. from http://www.impactlab.com/wp-content/uploads/2008/04/bat-eating-frog.jpg

Micronycteris microtis. Photo from http://www.chiroping.org/images/bats/microtis2.jpg

A question that comes up from time to time is whether bats are among the panoply of species that munch on anoles, particularly in the mainland neotropics. As we all know, some bats are renowned for catching and eating frogs, but will they also sup on our little friends? As far as I’m aware, there are no records in the literature of anolivory in bats, but perhaps a reader can correct me on this point. One can imagine two scenarios: first, bats active at dusk or dawn might nab anoles while still active. Alternatively, second, perhaps bats can use their sonar to locate sleeping anoles on leaves. This latter point has generally been considered unlikely because the acoustic clutter in a thick vegetational matrix has been thought to be make it difficult for bats to identify and locate non-moving objects in the vegetation.

A recent study shows that this is not so. Studying the insectivorous bat Micronycteris microtis from Panama, Geipel et al. have just shown that bats can use echolocation to find and capture non-moving prey, in this case dragonflies. More details are provided in the abstract pasted below. It would seem to follow, then, that bats may, indeed, prey on sleeping anoles, but in a critical oversight, the authors fail to comment on this pressing issue.

Abstract: “Gleaning insectivorous bats that forage by using echolocation within dense forest vegetation face the sensorial challenge of acoustic masking effects. Active perception of silent and motionless prey in acoustically cluttered environments by echolocation alone has thus been regarded impossible. The gleaning insectivorous bat Micronycteris microtis however, forages in dense understory vegetation and preys on insects, including dragonflies, which rest silent and motionless on vegetation. From behavioural experiments, we show that M. microtis uses echolocation as the sole sensorial modality for successful prey perception within a complex acoustic environment. All individuals performed a stereotypical three-dimensional hovering flight in front of prey items, while continuously emitting short, multiharmonic, broadband echolocation calls. We observed a high precision in target localization which suggests that M. microtis perceives a detailed acoustic image of the prey based on shape, surface structure and material. Our experiments provide, to our knowledge, the first evidence that a gleaning bat uses echolocation alone for successful detection, classification and precise localization of silent and motionless prey in acoustic clutter. Overall, we conclude that the three-dimensional hovering flight of M. microtisin combination with a frequent emission of short, high-frequency echolocation calls is the key for active prey perception in acoustically highly cluttered environments.”

Mentally put an anole in there, and you can see we’ve got trouble!

Large prey taken by brown anoles (top two photos) and Swinhoe’s tree lizard (bottom two).

Starting in the 1970s, Caribbean anoles became a model system for studying community ecology, especially interspecific competition. Such studies generally focused only on anole species. Though seemingly chauvinistic, this anolocentrism is reasonable in many localities, where resource competition probably is primarily between anole species (although there was a boisterous debate in the 1980s on the extent to which anoles and insectivorous birds might compete).

However, this is not always the case. In Central and South America, for example, the much greater non-anole saurifauna than on Caribbean islands makes it likely that anoles may experience much greater resource competition with non-anole lizards, as well as other taxa. And the same may be true for anoles introduced to far-flung regions.

Take, for example, the brown anole in Taiwan, which occurs with the native Swinhoe’s tree lizard. Like brown anoles, the agamid is found on the ground and low on tree trunks, and thus might be considered a trunk-ground anole. Being only slightly larger than brown anoles, the tree lizard probably eats much the same food. Gerrut Norval posted a while back on the amazingly large prey that brown anoles and tree lizards eat in Taiwan, and now he and colleagues have published a paper documenting the extensive diet overlap between the species (Gerrut previously provided a post on the background to this study, including some interesting information and photographs on the research methods). Very likely they are strong competitors, although Norval et al. argue that the size discrepancy means that the effect is asymmetric. However, at least in some areas, brown anoles have much higher densities, meaning that their aggregate effect on tree lizards may be just as great as the reverse.

Brown anoles are most dense in hot, open areas, whereas the tree lizards reign supreme in shaded habitats, suggesting that environmental effects mediate the outcome of interspecific interactions between the two species. In addition, this difference indicates that reforestation efforts would be a good conservation move to stem the effect of the brown anole invasion.

Over at The Lizard lab, Martin Whiting discusses a recent paper published in Biological Conservation on the conservation status of reptiles. Basically, a cast of thousands assessed a random sample of 16% of the world’s reptile species, categorizing them into the IUCN’s categories of conservation concern, which range from “least concerned” to “critically endangered” and, of course, “extinct.”

Martin nicely summarizes the paper in his post, but I’ll reprint his conclusion summary paragraph here: “59% of species were Least Concern, 5% were Near Threatened, 15% Threatened (Vulnerable, Endangered or Critically Endangered) and 21% were Data Deficient. To put this another way, one in five species are threatened with extinction and another one in five are data deficient. The paper identifies freshwater habitats, oceanic islands and tropical regions as containing the highest proportion of threatened species. Habitat loss and direct harvesting are two key threats to reptile populations and these are depicted in Figure 3 from the paper” (above).

Of course, from the AA perspective, the question is: what about anoles? The results were, to me at least, surprising. Of the 65 species surveyed, 29.3% were in one the three threatened categories, nearly twice as many as the global average! I would have guessed the opposite–most anoles seem to being doing reasonably well. But, then I rationalized, it must be the mainland anoles, because Caribbean anoles are generally doing fine. Again wrong! 11/28 (39%) Caribbean anoles are in these categories (including the only two “critically endangered species, A. juangundlachi (known from one specimen, if I recall correctly) and A. roosevelti), compared to 8/37 (22%) for mainland species. One non-surprise is that all 10 “data deficient” species are from the mainland; however, even when they are removed, the percentage threatened in the mainland (30%) is still less than in the Caribbean. At least for the Caribbean species, the biggest predictor seems to be range size, as all threatened species either have small distributions or occur on small islands. I am less familiar with some of the mainland species, but think the same may be true for those. I’ll append the list below.

One last note: the paper truly has an extraordinary number of authors who contributed to this massive compilation. One amusing consequence is that the list of authors’ affiliations at the start of the paper is three pages long!

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