Author: Jonathan Losos Page 72 of 129

Some like it hot. Anolis allisoni on Roatan, an inhabitant of open areas, will benefit from increased global temperatures. Photo by J. Losos.

Thanks to HerpDigest, a regular email compendium of herpetological news, here is a press release on a recent paper in Global Change Biology:

A new Dartmouth College study finds human-caused climate change may have little impact on many species of tropical lizards, contradicting a host of recent studies that predict their widespread extinction in a rapidly warming planet.

Most predictions that tropical cold-blooded animals, especially forest lizards, will be hard hit by climate change are based on global-scale measurements of environmental temperatures, which miss much of the fine-scale variation in temperature that individual animals experience on the ground, said the article’s lead author, Michael Logan, a Ph.D. student in ecology and evolutionary biology.

To address this disconnect, the Dartmouth researchers measured environmental temperatures at extremely high resolution and used those measurements to project the effects of climate change on the running abilities of four populations of lizard from the Bay Islands of Honduras. Field tests on the captured lizards, which were released unharmed, were conducted between 2008 and 2012.

Anolis bicaorum, a denizen of closed forest, from Utila, Honduras. Photo by J. Losos.

Previous studies have suggested that open-habitat tropical lizard species are likely to invade forest habitat and drive forest species to extinction, but the Dartmouth research suggests that the open-habitat populations will not invade forest habitat and may actually benefit from predicted warming for many decades. Conversely, one of the forest species studied should experience reduced activity time as a result of warming, while two others are unlikely to experience a significant decline in performance.

The overall results suggest that global-scale predictions generated using low-resolution temperature data may overestimate the vulnerability of many tropical lizards to climate change.

Another photo of A. allisoni, just because they’re so cool. Photo by J. Losos

“Whereas studies conducted to date have made uniformly bleak predictions for the survival of tropical forest lizards around the globe, our data show that four similar species, occurring in the same geographic region, differ markedly in their vulnerabilities to climate warming,” the authors wrote. “Moreover, none appear to be on the brink of extinction. Considering that these populations occur over extremely small geographic ranges, it is possible that many tropical forest lizards, which range over much wider areas, may have even greater opportunity to escape warming.”

An example of open habitat, from the island of Cayo Menor. Photo by Mike Logan.

An example of closed forest, from the island of Roatan. Photo by Mike Logan.

Story Source: The above story is reprinted from materials provided by Dartmouth College, via EurekAlert!, a service of AAAS.

Phylogeny of lizards from Pyron et al.

In a monumental undertaking, Alexander Pyron and colleagues have just produced a molecular phylogeny for 4,161 species of lizards (including snakes), more than 40% of the 9400+ species described to date. The paper, now available online at BMC Evolutionary Biology, is a blockbuster, containing 28 figures, one an overview of the entire phylogeny and the remainder walking through lizard-life one clade at a time.

The analysis is based on sequence data from 12 commonly used and phylogenetically informative molecular markers (seven nuclear genes, five mitochondrial). On average, 12,896 base pairs of sequence data are available per species and, as is necessary in an endeavor such as this, the data set is incomplete, with an average of only 19% of base pair data being available for any given species.

The results are generally very concordant with recent molecular phylogenies, perhaps not surprising given that these data have been used in the most recent studies. The overall picture of lizard phylogeny is little-changed from what we’ve seen in recent molecular phylogenetic publications, but there are a few surprises at lower levels. You’ll have to peruse the paper yourself to check out your favorite group, as there’s way too much in it to go through here.

Of course, what readers of AA really want to know is: what does the phylogeny say about anole relationships? And, in fact, the results are for the most part concordant with previous studies. Perhaps surprising to many readers, the analysis supports the monophyly of the eight clades recognized by Nicholson et al. as separate genera. Well, almost. In contradiction to the paper’s statement, Nicholson et al.’s Anolis is not monophyletic because A. argenteolus is placed as the sister-taxon to the Xiphosurus clade (which contains Chamaeleolis and the ricordii group), rather than occurring with other species placed into the restricted Anolis. This is an odd finding, contradicting both Nicholson et al. and the Alfoldi et al. genome paper analysis, with the implication that the transparent lower eyelids of A. argenteolus and its putative sister taxon A. lucius are not homologous, but I don’t buy it. Other than that, I didn’t find anything too exciting in this phylogeny, though further scrutiny (it’s enormous) may turn up interesting relationships I didn’t notice.

Other than this one exception, however, the Nicholson et al. eight fare well. Nonetheless, the authors of this paper do not follow the Nicholson et al. taxonomic suggestion of subdivision, stating: “since Anolis is monophyletic as previously defined, we retain that definition here…for continuity with the recent literature.”

Laemanctus longipes, a member of the sister group to Anolis. Photo by Petrovan Silviu.

Probably the most interesting finding concerns the closest relative to anoles, a topic of great uncertainty. This analysis strongly confirms that Polychrus is not the sister group to Anolis; rather, Polychrus appears related to the hoplocercids, which means that it’s dewlap must be convergent with the anole flasher. To whom, then, are anoles related? The answer appears to be the basiliscines (Corytophanidae in more modern parlance), the morphologically diverse and fascinating neotropical group containing not only basilisks, but also Corytophanes and the little-known Laemanctus.

Two last points: first, as noted above, there’s lots of missing data. Clearly, this is not the last word and, in particular, the question of the sister taxon to Anolis cries out for further study. Second, as the authors note, this paper will be of inestimable value in conducting comparative studies spanning the entire lizard radiation. To facilitate such, the authors have made available a Newick file containing the phylogeny (if you don’t know what this means, suffice to say that it’s a very helpful move that will make it easy to use this phylogeny in comparative studies).

Now, let’s get out and sequence the other 5000 species and finish the job!

[Editor’s Update, March 18, 2014]: I was mistaken in saying that the Pyron et al. tree found only one inconsistency with the Nicholson et al. genera. In addition to the exception noted above, Nicholson et al. place christophei in their Chamaelinorops clade, but Pyron et al. find it allying with species that Nicholson et al. put in Xiphosurus.