Author: Jonathan Losos Page 67 of 129

The 50th annual conference of the Animal Behavior Society kicks off today in Boulder, Colorado. Anole presentations are few: only two posters, which begs the question, why aren’t more behavioral biologists studying anoles? Certainly, their behavior is easily observed and manipulated. And, indeed, some such work is conducted, but not nearly as much as one might expect given the ubiquity of the animals in the southeastern U.S. and throughout the neotropics. And, moreover, the behavioral work that is done is relatively infrequently published in the behavior literature or, apparently, reported at behavior meetings. Behaviorists, you’re missing the boat!

In any case, the sole anole reporter at ABS is Joe Macedonia, who is presenting two posters. The first is a comparison of the behavior of the odd gray-dewlapped green anoles with more ordinary, red-dewlapped populations, and the second is a study using anole robots to determine the relative importance of dewlap color and behavior in species recognition; this study has recently been published and we should be hearing more about it soon.

A Comparison of Headbob Display Structure in Gray-Dewlapped and Red-Dewlapped Anolis carolinensis

JM Macedonia, LE Cherry, DL Clark

Many species of diurnal lizards engage in motion displays, termed ‘pushups’ or ‘headbobs’. In the diverse genus Anolis, headbob display structure typically exhibits substantial interspecific, and in some cases population-level, variation. The green anole (Anolis carolinensis) exhibits a red-dewlapped (RD) form found throughout the southeastern USA, as well as a gray-dewlapped (GD) form that is restricted to southwest Florida. Prior research has shown that RD A. carolinensis produce headbob displays of three basic types (Type A, B, C) that vary primarily in display unit durations. Based on known genetic and physiological differences between the two dewlap color forms, we hypothesized that GD and RD males also would differ in headbob display temporal structure. We quantified 440 displays from 24 GD and 15 RD males, and found some, though not all, display units to differ significantly in duration between the two populations. Our results therefore indicate that stereotyped display behavior can be added to the list of known traits that differ between the gray-dewlapped and red-dewlapped forms of A. carolinensis.

Color and motion display discrimination in Anolis grahami: evidence from responses to lizard robots

JM Macedonia, DL Clark, DJ Kemp

Anolis lizards exhibit color and motion displays that are thought to mediate species recognition, but direct experimental support is limited. We used lizard robots in two field experiments to test the relative importance of dewlap color (calibrated using a computational visual model) and headbob display structure for species recognition in Anolis grahami on Bermuda. Results from experiment 1 revealed equivalent, significant decrements in responsiveness of 102 adult male subjects to color and motion display manipulations, relative to the conspecific robot control. Findings also suggested that dewlap hue, not brightness, was responsible for reduced subject response to non-control dewlap colors. In experiment 2 we presented 93 different A. grahami males with conspecific or heterospecific (Anolis extremus) robots that performed their own, or the other species’, headbob displays. Results revealed species-specific body/dewlap coloration to be more important than headbob display structure for species recognition. Although more work is needed, our findings support the proposition that interspecific variation in color and motion displays provides important cues for species recogntition in anoles.

Mark Yokoyama’s second edition is now out, and available for download for free. Or, if you want to go old school, hard copies are available for purchase on Amazon.

The 128 page guide covers both the native and introduced fauna of Saint Martin, with more than 500 photographs and considerable treatment of invertebrates as well as vertebrates.

Of course, the most important subject of the book are the anoles, two native and two introduced, each of which gets a page. Mark has published previously on the introduced anoles, A. sagrei and A. cristatellus. Both for the moment are restricted in range–to a resort complex and a cruise ship terminal,  respectively. If they expand their ranges–and I’m betting they will–it will be interesting to see how they interact with the native A. gingivinus, as well as each other.

The image below on A. pogus will give you a feel for the book. Certainly a must-have if you’re going to St. Martin, and a nice-to-have even if you aren’t.

Cophotis ceylanica. Photo by M. Wickramasinghe

It’s got a dewlap, too!

Those upstart Asian agamids are at it again, trying to out-anole anoles. We’ve already marveled at the dewlap of Sitana and its friends, which—I hesitate to say this—makes any anole dewlap look bland by comparison. Now can we all agree that this guy here, Cophotis ceylandica, is a twig anole’s twig anole?

Any way, the photo comes from a new paper that reports an observation of a jungle crow in a Sri Lankan park catching one of these guys, tearing it in half (grutesome!) and then eating it. And then it did it again three more times in the next half hour, two more C. ceylandica and a third, unidentified lizard. This was just one bird in a flock of 37, and guards at the park say they are quite prolific lizard catchers. The authors make the interesting point that jungle crow populations in the park appeared to have grown as a result of all of the garbage, and an incidental victim of this may be lizard populations.

German speakers, we need you again. Can you look at the attached paper and confirm that the two parts are German and English versions of the same text?

In an interesting new paper in the journal Checklist (subtitled, the “journal of “species lists and distribution”), Bienentreu et al. report on 28 new specimens of A. salvini from western Panama.  On its face, the paper is simply a description of many new specimens of a little known species. But lurking within are a variety of fascinating tidbits.

First, A. salvini is a member of the pentaprion clade of twig anole-like mainland species. The authors note that previous work by Köhler subsumed A. vociferans into A. salvini, but no one seems to have noticed—maybe this paper will help.

Second, and perhaps most interesting, the authors note extensive variation in dewlap color within this species, as illustrated in the figure above: e-h are males, and i-l are females.This variation is striking and worthy of further investigation.

Lastly, third, the authors note that the species vocalizes when handled, and even provide a spectrogram. Very few anoles make sounds, a topic which has received very little attention.

Chamaeleolis, the un-anole anole. Does this evolutionary one-off demonstrate that island anole radiations are not convergent? Photo by Veronika Holanova and more on this snail crunching anole in a previous post.

Stephen Jay Gould famously proclaimed that if the tape of life were rewound and played again, a different evolutionary outcome would result. He argued that chances events–a lightning strike, a particular mutation–would send evolution careening down a different path. Gould’s idea has been controversial and provocative, but also untestable beyond the confines of the laboratory (you actually can replay the tape of life with microbes, but that’s another story).

The next closest possibility is to look at closely related species evolving in similar environmental settings. These “natural experiments” are in some ways a test of Gould’s hypothesis–will evolution from a similar starting point, in similar environments, unfold in similar ways? Gould would have said no, but what do the lizards say?

The evolutionary radiations of Anolis lizards on the islands of the Greater Antilles are renowned for their convergence, with the same set of “ecomorphs” (i.e., habitat specialists) evolving repeatedly on each island. The existence of the ecomorphs would seem to indicate that, in fact, evolution is deterministic–put an ancestral anole on a Caribbean island and let it evolve, and you get the same ecomorphs each time. But there’s a catch, two of them, actually. First, not all ecomorphs occur on all four Greater Antillean islands. Grass-bush anoles are missing from Jamaica and trunk anoles from both Jamaica and Puerto Rico. Moreover, second, there are some habitat specialists that are unique to a single island, with no ecomorphological counterpart on the other islands. The leaf-litter dwelling Anolis (Chamaelinorops) barbouri from Hispaniola or the Chamaeleolis clade–snail-crunching chameleon döppelgangers–from Cuba, pictured above. These quite distinctive habitat specialists–and a number of others–are evolutionary one-offs, with no convergent counterparts elsewhere.

So, convergence isn’t complete across the Greater Antilles. And that raises the question of whether the island radiations are actually replicated or not. Sure, there are some particular instances of convergence, but it’s always possible that these are instances embedded in a larger sea of non-convergence. Is island radiation truly deterministic? Are the evolutionary outcomes on the four islands actually more similar than one might expect by chance?

Average distance of species to their nearest neighbor on another island (gray line) is considerably less than would be expected by chance (gray blocks representing the results of many simulation trials; see papers for details on how these simulations were conducted).

A paper just published by Luke Mahler et al. in Science asks exactly that question (disclosure: I’m one of the authors). The paper took two approaches, using data on the morphology of each species (e.g., limb length,  head length,  number of toepad scales). First, the morphological similarity of each species to all others was quantified, based on these measurements. In this way, the morphological distance (in a statistical sense) to the nearest species on another island could be calculated. We then asked whether species had a nearest neighbor on another island that was closer (more similar) than would be expected by chance. The result is clear, and illustrated by the figure above. The average distance to nearest neighbor is much smaller than expected by chance. In other words, species tend to have convergent counterparts on other islands.

The number of convergent shifts to the same adaptive peak is substantially greater than expected by chance.

The second approach used a new method developed by Travis Ingram and Luke Mahler which estimates the underlying macroevolutionary landscape. To make a long story short, based on phylogenetic relationships of species and their morphology, the method identifies the minimum number of adaptive peaks across all islands. Convergent evolution would be indicated by unrelated species evolving to occupy the same peaks. The results indicate that there is far more convergence than expected by chance. This result indicates that the underlying macroevolutionary landscape on the islands is similar on the four islands, thus driving evolutionary diversification to occur in similar ways. The idea of the macroevolutionary landscape traces back to famed paleontologist George Gaylord Simpson, and this study is perhaps the first to explicitly test the idea that similarity in the macroevolutionary landscape is what leads to replicated adaptive radiations.

So, Gould seems to have gotten it wrong–let anoles diversify in similar settings, and the outcome will be very similar. Not identical–perhaps revealing the importance of his so-beloved historical contingencies–but pretty darn  close, much more so than one would expect by chance. Now, in Gould’s defense, there is reason to believe (because he once told a reporter so) that he didn’t mean his tape rewinding metaphor to apply to the minor dabblings of insignificant little lizards; rather,he was concerned about grand patterns, deep in evolutionary time, when evolution was much less constrained and life was still exploring vast horizons and testing its limits.

Regardless, there is one last Gouldian twist. Anoles have been diversifying on these islands for tens of millions of years. So, the fact that the placement of the adaptive peaks is so similar suggests that there is a long-term stability to the macroevolutionary landscape. Such a long term arrangement would lead to lack of evolutionary change. As we all know, evolutionary stasis was another of Gould’s favorite ideas, so it would  seem that SJG went one-for-two with anoles, a .500 average good enough for the all-star team in many leagues.

If you want to more on this paper, there’s a nice article/interview of Luke Mahler by Ed Yong on the Phenomena: Not Exactly Rocket Science website.