Category: New Research Page 44 of 67

Three stereotyped head-bobbing patterns of A. carolinensis. The black area represents the amplitude of the head as it moves up and down. Although amplitude can vary within and among individuals, the cadence remains constant for each of the display types. The hatched area refers to times when the dewlap is displayed. Length and number of dewlap displays and associated headbobs at the end of the display can be quite variable. This figure is a modification from Jenssen et al. (2000) that appeared in Lizards in an Evolutionary Tree.

Anole displays have proven to be as frustrating as they are fascinating. These displays, which are species-specific and typically involve headbobs and/or pushups that may or may not be accompanied by dewlap extensions, are as varied as one might expect within a group as diverse as Anolis. However, despite concerted efforts by an energetic group of researchers aimed at understanding the form, context and meaning of these varied adult male displays, a complete understanding of this complex signal eludes us. The stereotyped displays exhibited by many anole species are of particular interest, and of these, arguably the best-studied are the A, B, and C displays of that lab rat of the anole world, Anolis carolinensis.

In a recent paper, Jenssen and collaborators report a characteristically detailed and rigorous field study on the use of such stereotyped displays in both breeding and postbreeding free-ranging A. carolinensis males. Through painstaking analysis of videotapes of thousands of undirected male displays in nature with no obvious receiver, they show, among other results, that breeding males in “monitor” mode (i.e. lizards that signal while stationary) used mostly C displays, but increased use of A and B displays while moving or “travelling.” Monitoring lizards also exhibited an overall lower display rate than travelling males, and used more and longer volleys of displays. Additionally, about a third of all displays had an extra “shudderbob” tacked on. These patterns held through the postbreeding season. Interestingly, Jenssen et al. note that these undirected displays aimed at no-one in particular are most similar to aggressive signals used by males engaged in contests. The implication is that these undirected displays are in fact directed at an unidentified (or undetected) rival male audience, rather than being for the benefit of any single lady lizards in the area.

The notion of males displaying aggressively just in case any rivals might be present makes sense for a species such as A. carolinensis that defends areas harbouring females, rather than trying to attract them. One wonders if this result would hold for species that place less emphasis on territory defense and that have been rumoured in the past to exhibit signs of female preferences (Anolis valencienni, anyone?).

Annual conferences are a major way for scientists to get their research out to a broad audience and to find out what is new and emerging in different fields. For those of us who study Anolis lizards, there are two annual conferences that are a major draw for our community – the Society for Integrative and Comparative Biology (SICB) meeting in January and the SSE/SSB Evolution meeting in June. There are other conferences, as well, that meet less often, such as the World Congress of Herpetology and the Anolis Symposium, which are also important gatherings for our growing community.

Last year, we were pleased to report that Anolis research was prominently featured throughout the SICB conference in Charleston, South Carolina. In addition to more than a dozen talks and posters, there was also an open forum on the Anolis genome and evo-devo research, in light of the publication of the A. carolinensis genome. The online schedule for SICB 2013 has just been published and a preliminary search using the keyword Anolis returns a list of 18 talks and posters. There is a great diversity of topics explored this year, including phylogenetic frameworks for evolutionary convergence, aggressive behavior, locomotion, thermal ecology, and parasitism, among others.

One of the cool things we did last year was blog live from SICB in Charleston (1, 2, 3). Because the conference was hosted in South Carolina, Marc Tollis shared some pictures of actual anoles at the conference center. We plan to blog live from the conference in San Francisco and provide you with information about all the interesting research being done on anoles. Stay tuned for more!

Phylogenetic comparative methods whiz Liam Revell has developed a new method to visualize character evolution of continuous traits on a phylogeny. The program is cool and worth checking out on his Phytools blog, but the important point is that he illustrates the method by reconstructing size evolution in Greater Antillean anoles.

Variation in the hand morphology of lizards. The drawings to the right of each foot indicate the arrangement of the tendons. Note that in B (anoles and Polychrus) and C (geckos), the tendons are independent, whereas in the others, they fused into tendenous plates in the palm of the hand.

In a paper in Acta Zoologica, Tulli et al. examine the tendons of the hands of a variety of lizards, including a dozen anole species. Their hypothesis is that differences in tendon struct should reflect ecological adaptation: in arboreal species, the tendons running to each finger (digit) should be independent, allowing great flexibility, whereas in more terrestrial lizards, the tendons should be fused, presumably providing great stability during locomotion at the cost of less agility.

The data show great variation in tendon morphology, with much of the variation falling out along phylogenetic lines. Form B in the figure above corresponds to all anoles and Polychrus. The data provide a suggestion that the authors’ hypothesis is correct, but statistical analyses incorporating phylogenetic information–affected by the similarity of closely-related species–fail to confirm the result.

Marıa J. Tulli, Anthony Herrel, Bieke Vanhooydonck and Virginia Abdala (2012). Is phylogeny driving tendon length in lizards? Acta Zoologica, 93, 319-329 DOI: 10.1111/j.1463-6395.2011.00505.x

Brown anole eating a curly tail lizard. Photo by Joseph Wasilewski.

We’ve had a number of posts concerning predation by curly tail lizards on brown anoles, in the Bahamas, Florida, Cuba and elsewhere. Now comes a report from near Miami that the brownies aren’t just sitting back and taking it. Rather, they’re rounding up vigilante posses to track down and consume baby curlies, hitting the predator’s population where it’s vulnerable. Ok, perhaps that’s a stretch, but in a recent note in Herpetological Review, Krysko and Wasilewski publish the first report of Anolis sagrei preying on Leiocephalus carinatus, revealing that the ecological interactions between the two species are more complicated than previously thought: we already knew that curlies prey on brown anoles and that the two species also compete for some of the same insect prey (making this an example of the phenomenon of intra-guild predation),  but this study raises the possibility that the interaction–and its likely ecological and evolutionary consequences–could be substantially more complicated. One might think that because of the massive size advantage of the curly-tails, the effects must mostly be one-way; however, the massive population size differential between the two species means that brown anoles, in theory, could greatly affect curly tail populations as well. Although the effects of curly tails on brown anoles have been studied, the opposite experiment has not been done. Of course, previous work on tiny Bahamian islands indicates that curly tails substantially reduce brown anole populations, but maybe dynamics are different in larger and more complicated ecosystems. Personally, I wouldn’t bet on it, but who knows?

Battling green anoles. Photo from http://dmcleish.com/Maui2009/AnoleFight/DSC_0278.jpg

Both theory and empirical examples from many types of organisms indicate that animals alter their fighting behavior based on the outcome of previous fights. That is, if an animal won its previous fight, it is likely to win its next one, whereas previous losers are likely to keep on losing. In a new paper in Ethology, Garcia et al. examine whether such winner and loser effects occur in the green anole, A. carolinensis.

To create winners and losers independent of their innate fighting ability, the investigators first staged encounters in which one lizard was 40% larger than the other. Because size is a very good predictor of encounter outcome, they used this method to create animals which had won or lost their first encounter. Indeed, most of the larger animals won in these matches. Then, in the second round, they placed individuals of the same size together, one of which had won its previous encounter and the other that had lost.

Results did not support the hypothesis: probability of winning was not affected by previous experience: winners in the first round were no more likely to triumph in the second round than were first round losers. However, there was one interesting finding: losers that had put up a good fight in Round 1 were likely to win Round 2, whereas those who hadn’t continued to lose. Two possible explanations are either: 1) that the feisty losers were intrinsically more aggressive and couldn’t overcome the size disadvantage in Round 1, but when paired against similar-sized animals, were able to use their aggressiveness to overpower their opponent; or, second, that this is an example of a variation of the “loser effect,” only that it is not the outcome of the fight, but the quality of it, that matters. Losers who put up a good fight might still feel emboldened and thus do well in the future, whereas losers that lose badly may continue to lose in the future.
Mark J. Garcia, Laura Paiva, Michelle Lennox, Boopathy Sivaraman, Stephanie C. Wong, & Ryan L. Earley (2012). Assessment Strategies and the Effects of Fighting Experience on Future Contest Performance in the Green Anole (Anolis carolinensis) Ethology, 118, 821-834 DOI: 10.1111/j.1439-0310.2012.02072.x

It’s been a good couple of years for studying lizard smarts. Last year, Manuel Leal demonstrated keen cognitive abilities in Anolis evermanni. More recently a couple of studies Down Under have shown that slippery Aussie skinks have a lot going on upstairs as well. Over at The Lizard Lab, Martin Whiting has just posted a nice review of these studies.

For those who work primarily in the West Indies, it can be difficult to imagine a lizard fauna dominated by anything other than anoles.  However, if you’re interested in learning more about lizard communities that don’t include anoles, no book fits the bill better than L. Lee Grismer’s recent monograph on the Lizards of Peninsular Malaysia, Singapore and their Adjacent Archipelagos.  Grismer takes readers on a tour of Peninsular Malaysia’s impressive lizard diversity, with species-by-species accounts that include morphological diagnoses, notes on coloration in life and among sexes, dot maps, and detailed notes on each species’ natural history.  Grismer is the first to comprehensively review Peninsular Malaysia’s 128 lizard species, and his book represents the “first time the entire distribution of this fauna has been precisely mapped.”  Of course, Grismer’s book is also chalk full of spectacular photographs, including many of Grismer’s trademark photos of animals in their natural habitat.

Map from Malaysian Bat Education Adventure: http://www.ttu-mbea.org/krau-wildlife-reserve/

Sandwiched between Thailand and Myanmar to the north and Indonesia to the south, Peninsular Malaysia is a geographically, historically, and ecological diverse region that includes numerous mountain ranges, offshore archipelagos, and isolated karstic rock outcrops.  The habitats of Peninsular Malaysia range from mangrove forest to lush multi-layered Dipterocarp forest to “post-apocalyptic” oil palm plantation dominated landscapes.  Grismer does a great job familiarizing readers with the region by beginning his monograph with detailed information of the region’s biogeography and environmental diversity.

Most importantly, of course, Peninsula Malaysia is home to 128 lizard species, mostly geckos, skinks, or agamids, but also the occasional dipamid, lacertid, varanid, and leiolepid.    Some 45% of these species are endemics, the vast majority of which are skinks and geckos that are narrowly distributed in montane habitats, isolated karstic rock outcrops, or off-shore archipelagos.  The agamids, however, are likely to attract the immediate attention of anole lovers because this group includes most of the region’s arboreal, diurnal, and often conspicuous, lizards.

Image from http://animals.nationalgeographic.com/animals/reptiles/draco-lizard/

The most diverse agamid radiation in Peninsula Malaysia is Draco, the remarkable genus of gliding lizards that is found throughout much of southeast Asia.

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Variation in the back patterns of Anolis sagrei in the Bahamas. From Calsbeek and Cox (2010).

Last year, we had a series of posts discussing the evolution of dorsal patterns of female anoles, as well as several studies that reported intrapopulation variation in female patterning. Why such variation should exist is a mystery, and studies on both A. humilis in Costa Rica and A. sagrei in the Bahamas failed to find evidence that natural selection was acting on this variation.

Now, Calsbeek and Cox report an experimental study of natural selection on dorsal pattern on small islands in the Bahamas. They introduced anoles with the three patterns shown on the left onto four small islands. Two of the islands had birds and snakes, the other two had neither. One predator-exclusion island was studied in 2008, the other three in 2009. In addition, the authors measured selection in a natural population over the course of four years.

The major result of the study is that not only was survival reduced on islands with predators, but also in the presence–but not absence–of predators, the intermediate diamond-bar pattern had higher survival than the other two patterns. How this intermediate pattern leads to heightened survival is not clear, and the authors propose a few hypotheses for future testing.

R. CALSBEEK & R.M. COX (2012). An experimental test of the role of predators in the maintenance of a genetically based polymorphism Journal of Evolutionary Biology DOI: 10.1111/j.1420-9101.2012.02589.x