Anole Annals

Anolis cristatellus from Puerto Rico. Photo taken by Liam Revell

Anolis lizards are a model system for studies of evolutionary ecology because they are remarkably adaptable creatures. We know from long-term studies conducted by Jonathan Losos, Dave Spiller, Tom Schoener, and others that anoles can rapidly adapt their behavior and morphology over ecological timescales. For example, the presence of a ground-dwelling predator (Leiocephalus carinatus) forged a strong selective gradient in favor of A. sagrei with longer hindlimbs within a single generation. Interestingly, in a follow-up study the long-term effect of this predator is that A. sagrei evolves shorter hindlimbs, as they will tend to perch higher off the ground, where the perch diameter is narrower than near the ground. These studies of rapid morphological evolution puts anoles in the a very exclusive club with the likes of stickleback fishes, Peromyscus beach mice, guppies from Trinidad, Galapagos finches, and few others, as vertebrate systems in which evolutionary change on ecological timescales has been confidently demonstrated.

A notable exception to Anolis ‘evolvability,’ however, is thermal physiology. The thermal physiology of reptiles is generally evolutionarily conserved – taxa separated by millions of years and found in very different thermal environments will often share similar physiological patterns. But recent research has suggested that some physiological metrics may not be as static as previously thought, and that Anolis invasions provide an excellent opportunity to see how labile physiology actually is.

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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.