Author: Martha Muñoz Page 1 of 8

A small sample of anole dewlap diversity. Image from Nicholson et al. (2007).

Dewlaps are pretty dazzling, ranging in size, coloration, and sexual dimorphism substantially among the 400+ species of anole currently recognized. Levi Gray, a doctoral candidate at the University of New Mexico is fascinated by Anolis dewlaps, and has spent many years studying them. One of the classic hypotheses surrounding dewlap evolution in anoles is that its size follows a clinal pattern with environment (Fitch and Hillis 1984). In their formulation, Henry Fitch and David Hillis proposed that, due to a relatively short breeding season, anoles in more seasonal habitats have larger dewlaps than anoles in more aseasonal habitats. This hypothesis makes an explicit connection between the intensity of sexual selection and the size of a conspicuous ornament.

Levi set out to test the Fitch-Hillis hypothesis in 40 species of Mexican anoles distributed across environmental gradients, with some species found in aseaonal cloud forests and rainforests and others found in more seasonally dry habitats. Contrary to the Fitch-Hillis hypothesis, he found no relationship between seasonality and dewlap size in the Mexican anoles. He did detect a few clade effects: for example, a group of closely related western Mexican anoles all have large dewlaps. He then examined the Fitch-Hillis hypothesis within a single widespread species of anole, A. sericeus, to see if the pattern holds up within species, even if it doesn’t hold up among species. Again, he didn’t detect a pattern. Levi suspects that the relatively limited sampling of the original study might have led to a pattern that doesn’t hold up when a broader sampling within and among species is employed. It is possible that seasonality impacts a different aspect of the dewlap, such as coloration, but this remains untested. Levi’s results suggest that the processes impacting dewlap size might be complex, and promises more to come. Stay tuned!

Levi Gray presents his research on dewlap size evolution in Mexican anoles at SICB 2018 in San Francisco.

Postdoctoral scientist, Dr. Shane Campbell-Staton, presents his work on CTmax shifts in Anolis cristatellus at SICB 2017.

Greetings from New Orleans, where SICB 2017 is well underway! Kicking off the conference was Dr. Shane Campbell-Staton, currently a postdoctoral researcher at the University of Illinois, Urbana-Champaign. Shane presented some work he has been doing with Kristin Winchell, a graduate student in Liam Revell’s lab at the University of Massachusetts, Boston. Kristin’s work focuses on how the crested anole, Anolis cristatellus, adjusts its biology to life in urban areas. In previous work, Kristin documented adaptive shifts in limb and toepad morphology in these anoles in urban areas, a shift she correlated with the broader perches urban anoles use.

In this neat follow-up study, Shane and Kristin have documented how perch temperatures in urban Puerto Rican habitats are higher than in natural environments on the island. In response, urban Anolis cristatellus have a higher heat tolerance. Results from a common garden experiment indicate that the urban shifts in heat tolerance are primarily due to plasticity. At the moment, Shane is performing genomic analyses to search for signatures of selection on heat tolerance.

Austin Garner, an undergraduate at the University of Akron.

Anoles, geckos, and some species of skinks have adhesive toepads that allow them to cling to substrates. This adhesive ability is remarkable – anoles, for example, can hang from a glass pane using just one toe. Gecko adhesion is particularly well studied, but most research has focused on how these animals cling to dry surfaces. In their natural habitats, however, geckos often have to contend with wet surfaces.

Austin Garner, an undergraduate at the University of Akron working with Peter Niewiarowski, wanted to know whether geckos could move effectively on wet substrates. He measured sprinting performance in two species of gecko, Gekko gecko and Chondrodactylus bibronii, across a 2-meter vertical racetrack that was misted with water. Average sprint velocity on wet substrates did not differ significantly from the average sprint velocity on dry substrates, indicating that geckos can sprint equally fast on slippery surfaces. The substrate material, however, influenced how often geckos slipped. Geckos slipped more on glass substrates compared to acrylic substrates. Austin hypothesized that this is likely due to the surface chemistry of glass. Glass is a hydrophilic substrate, meaning that water is attracted to its surface more so than the surface of acrylic. Interestingly, the frequency of slipping differed among species. Chondrodactylus bibronii, a species of gecko from an arid habitat, slipped more often than G. gecko, a gecko found in the tropics. Although C. bibronii slipped more on wet substrates, this species did not suffer a decrease in average sprint velocity on wet substrates. This suggests that C. bibronii is somehow compensating for the slipping observed on wet substrates, but Austin is unsure of the mechanism behind this compensation. Overall, his study suggests that geckos can travel on wet substrates up to 2-meter without a reduction in their adhesive ability, and that at least one species of gecko can compensate for any loss of traction caused by the presence of water.

Dr. Jerry Husak presents his poster at SICB 2016

*This post was written by David Delaney, a Ph.D. student in Fred Janzen’s lab at Iowa State University.*

Organisms must balance tradeoffs between performance, growth, immune function, and reproduction in order to maximize fitness. Adults and juveniles experience different life history pressures because juveniles are not reproductively mature, whereas adults should invest in reproduction. Thus, adults and juveniles may balance these life-history traits differently.

Dr. Jerry Husak of the University of St. Thomas presented on a study that he and undergraduate co-author Jordan Roy conducted to examine if adult and juvenile green anoles vary in resource allocation. To do this, 22 lizards were trained on a treadmill whereas 23 lizards were not. Training consisted of running lizards on a small pet treadmill 2 times per week. The incline was increased every two weeks for a period of 9 weeks to increase training intensity.

They found that training reduced the body mass of juveniles, which did not occur for adults. Training increased endurance capacity which also occurred in adults, however adults had a sex effect that juveniles did not. Training did not affect body length in juveniles, whereas it increased adult body length. Training eliminated the sex differences in juvenile immune function which did not occur for adults. Training increased hematocrit and heart ventricle mass which was also found for adults. In addition, juveniles exhibited very high variation in their response to training. Overall this study shows that juvenile green anoles balance these tradeoffs differently than adults, which likely reflects differences in the importance of certain life history traits throughout ontogeny.

Shane Campbell-Staton gives his talk at SICB 2016.

Climate change isn’t just leading to greater average environmental temperatures – it’s also leading to an increase in the frequency and severity of extreme weather events, such as heat waves and hurricanes. Of interest to Shane Campbell-Staton, a post-doctoral researcher in the Cheviron Lab and a recent graduate from the Losos Lab at Harvard, is understanding how the recent polar vortex in North America impacted the native green anole, Anolis carolinensis. The polar vortex of winter 2013/2014 set several records in snow fall and in all-time low temperatures in the south, and also led to severe weather in the midwest and east.

Shane found that, immediately following the polar vortex event, cold tolerance (CTmin) was significantly lower in lizards from southern Texas, as low as in lizards from much higher latitudes. He suggested that this result stems from differential survivorship during the event – lizards in south Texas that were more cold tolerant (i.e., had a lower CTmin) were more likely to survive the winter vortex  than less cold tolerant individuals. He then returned to south Texas a few months later and sampled both the survivors and their offspring and found that the decrease in CTmin persisted, indicating a potential evolutionary shift in cold tolerance. He put the final nail in the coffin by running a common garden experiment, where he demonstrated that, even when reared under common laboratory conditions, offspring exhibited cold tolerance similar to their parents, indicating high heritability in this trait and that the shift observed in nature was evolved rather than due to plasticity.

Shane then examined the response to the weather event at the genetic level by sequencing liver transcriptomes. Transcriptomes quantify patterns of gene expression levels for all genes regulated in a tissue; hence, by examining what genes are differentially expressed following cold stress, we can figure out the molecular underpinnings to cold adaptation and acclimation. He found that gene expression in survivors from the south closely resembled expression patterns in northern lizards, indicating a shared molecular pathway to cold tolerance adaptation in lizards from both habitats. The gene expression modules (or groups of genes) that exhibited a strong statistical association with CTmin variation were overrepresented for genes associated with oxidative phosphorylation. Oxygen consumption, which feeds oxidative phosphorylation, is directly related to CTmin: Animals that are more cold tolerant consume less oxygen during cooling. Hence, the expression differences in oxidative phosphorylation may pinpoint a proximate mechanism for cold tolerance adaptation.

You can learn more about Shane’s work on adaptation following the polar vortex in his recent Harvard Horizons talk.

*The following post was written by Chris Robinson, a Master’s student in Matt Gifford’s lab at the University of Central Arkansas.*

Like at every SICB conference, anoles are well represented among the talks and posters here in Portland and we here at the Anole Annals couldn’t be more thrilled to see the love for one of our favorite genera.

Christopher Anderson, a post-doctoral associate in Thomas Roberts’ lab at Brown University, gave a talk examining how muscle physiology influences whole organism performance in five species of anoles. His group examined two muscles, the M. ambiens pars ventralis (a swing phase muscle of the leg important for locomotion) and the M. abductor mandibulae externus superficialis anterior (a muscle in the jaw used in biting), to see if they differed from each other in how they perform in order to meet their functional demands. The muscle of the leg, which is used in sprinting, is cyclically activated and deactivated as an organism moves, whereas the muscle of the jaw is used more episodically.

Anderson and his colleagues found that the leg muscle builds passive tension at shorter lengths and has a twitch time that is 1.3-2.0 times faster than that of the jaw (to see how twitch time relates to sprint speed, see the post about Noel Parks’ poster). From this, Anderson concluded that these muscles are tuned to meet their physiological demands. Locomotion muscles, which are used frequently, generate a lot of force rapidly and the quickly developing passive tension in these muscles may serve as a form of protection for the muscle during active lengthening.