Anole Annals

While it wasn’t technically a talk about anoles, we’re sure AA readers will want to know the latest work from Alex Gunderson (pictured below), currently a postdoc with Jonathon Stillman at UC Berkeley and SFSU. Yesterday at SICB, Alex described his work on thermal plasticity in five major ectotherm clades (insects, crustaceans, fish, amphibians, and reptiles). Using acclimatization response ratios (ARR) for hundreds of species from these groups, Alex tested the hypothesis that animals in more variable thermal environments would exhibit greater flexibility in thermal acclimation. While he did not find support for that relationship, he did find that habitat type has a strong association with plasticity, as freshwater and marine species have more thermal flexibility than terrestrial species (like our favorite anoles). Next, he extracted the standard deviation of weekly temperatures from the NOAA database, and found that terrestrial animals had more plastic responses to cold tolerance (critical thermal minimum or ‘CTmin’), but not heat tolerance (critical thermal maximum or ‘CTmax’). Additionally, he found and there was no relationship between standard deviation of weekly temperatures and tolerance traits in aquatic species. Thus, terrestrial species had greater plasticity to lower temperatures than higher temperatures. Overall, he found that many types of ectotherms have relatively low capacity for acclimation. This result suggests that plasticity in acclimatization responses will not allow animals to compensate for rising temperatures across the planet, and behavioral responses will instead become more critical.

Alex Gunderson, thermal ecologist. Photo from his website.

Anolis proboscis, showing the male-specific proboscis. Photo by D. Luke Mahler.

A long–time favorite here at Anole Annals, the Ecuadorian Horned Anole (Anolis proboscis) made an appearance at SICB. Diego Quirola and colleagues from Pontificia Universidad Católica del Ecuador described the use of the proboscis during social interactions. They captured male and female anoles and videotaped staged male-male and male-female interactions. From the videos they were able to quantify behavioral patterns of these fascinating lizards. They did some very anole-like behavior, but they definitely have a flair all their own! With such a fascinating, chameleonic appendage one would expect some important functions of the proboscis, and one would not be disappointed. Watching videos that Diego had on display revealed social behavior very reminiscent of chameleons, with males puffing up, curling their tails, and swaying while doing the more typical anole dewlap extensions.

Then there’s the proboscis. This structure, much like the dewlap, is used during both courtship and agonistic interactions. In both contexts, males actually lift the proboscis. Yes, they can move the proboscis up and down, something not seen in chameleons with rostral appendages (no, we don’t know how they do it!). Diego suggests that the proboscis is lifted to either stimulate females or allow the male to bite the nape as other lizards do while copulating. Males also display a behavior called “proboscis flourishing” where the proboscis is prominently displayed while moving the head side to side. During agonistic interactions it may serve as a dominance indicator, though they are still working on those analyses. Proboscis anoles seem to be at the low end of aggression for anoles, but males occasionally fight and lock jaws. During male fights the proboscis likely gets in the way, and it appears to be purposely lifted during these fights. It’s possible that they lift it to keep the rival male from latching onto their snout, or it could be moved so that they can get better bites in. I was very much looking forward to learning more about these anoles, and I was not disappointed. As more work is done on these fascinating anoles we’ll be able to better understand why it has evolved such an interesting, and un-anole-like appendage, as well as the unique behavior that is associated with it.

Anolis carolinensis dewlapping. Photo by Cowenby available on Wikipedia.

On Sunday, Simon Lailvaux of the University of New Orleans gave one of the first anole talks of the SICB meeting, on his work examining the mechanisms underlying seasonal fluctuations in dewlap size. Simon began the talk by describing observations from field and lab studies (Irschick et al. 2006) that revealed that during the summer breeding season, when male anoles extend the dewlap frequently during behavioral displays, male dewlaps are much larger than during the winter nonbreeding season when the dewlap is used rarely. Simon and his lab then conducted a dietary-restriction study to test the hypothesis that this seasonal plasticity is due to resource availability, but found that diet was not associated with dewlap size (Lailvaux et al. 2012).  So, the search for the mechanism underlying this change in dewlap size was on.

Along with several colleagues from Trinity University – Jack Leifer (a materials engineer) and anolologists Bonnie Kircher and Michele Johnson (full disclosure – that’s yours truly), Simon and colleagues then conducted a laboratory experiment to determine whether reduced dewlap size related to less use in the nonbreeding season. To conduct the experiment, the researchers prevented dewlap extension in one set of male green anoles by tying dental floss loosely around their throats, and compared the dewlap size and skin elasticity of those lizards to an unrestrained control group that could dewlap at will. They found that dewlap size in the restrained group continually decreased over time, as compared to unrestrained lizards that, again, exhibited larger dewlaps in the breeding season. Together, these results suggest that use of the dewlap is directly related to its size. Then, the researchers measured the elasticity of dewlap and non-dewlap (belly) skin, and found that the dewlap is more elastic than belly skin, and that both types of skin samples were more elastic in the summer breeding season than in the winter. Because skin is a dynamic tissue whose mechanical properties are altered by sex steroid hormones, Simon suggested that dewlap size plasticity may be the result of seasonal endocrine fluctuations, combined with behavioral use of the structure.

These results suggest so many next steps.  Look for the upcoming manuscript describing this work in more detail!

References

Irschick, D.J., Ramos, M., Buckley, C., Elstrott, J., Carlisle, E.,Lailvaux, S.P., Bloch, N., Herrel, A. and Vanhooydonck, B. 2006. Are morphology -> performance relationships invariant across different seasons? A test with the green anole lizard (Anolis carolinensis). Oikos 114: 49-59.

Lailvaux, S.P., Gilbert, R.L. and Edwards, J.R. 2012. A performance-based cost to honest signaling in male green anole lizards (Anolis carolinensis). Proceedings of the Royal Society of London B: Biological Sciences 279: 2841-2848

Lauren Davis presenting her work on invasion success in lizards.

As our planet becomes increasingly connected and humans facilitate novel species interactions, we must ask why some introduced species are destructive and others relatively harmless. Lauren Davis, a senior in Dr. Michele Johnson’s lab at Trinity University, conducted a study on behaviors, and their neural correlates, that may influence the invasiveness of non-native lizards. She compared the invasive Anolis sagrei to the native Anolis carolinensis, the invasive House Gecko (Hemidactylus turcicus), and the native Texas Banded Gecko (Coleonux brevis). They hypothesized that highly invasive species display more ‘bold’ behaviors (in this case, the number of enclosure boundaries crossed during an experimental period) and have larger and/or denser neurons in associated brain regions than less invasive species. While there are many documented behavioral trials with boldness in Anolis, geckos have received little attention in this regard. Lauren and her fellow researchers found that A. sagrei is indeed bolder than A. carolinensis, but that the two gecko species do not differ in traits associated with the boldness syndrome (Fig. 1).

Figure 1: Invasive Brown Anoles are bolder than native Green Anoles

The researchers also found that neuron size in brain regions known to influence boldness and aggression were opposite than expected values, so the team plans to analyze neuron density in these regions to help explain the observed behaviors. This is one of the first studies comparing behavior and brain morphology to invasion success, and it paves an exciting path towards our understanding of species interactions in our changing world.

Lauren is graduating in May, and hopes to work in conservation or public health before continuing her education in graduate school.

Anolis sagrei mating. Taken from the Cox lab website.

On the first day of SICB 2015 Robert Cox gave an interesting talk about reproductive investment and sexual selection in lizards. At the center of his talk was the striking notion that males and females are different biologically, yet should still be integrated into cohesive theories of sexual selection. According to Dr. Cox, past theory has generated mutually exclusive ideas about the costs of reproduction for each sex. Whereas theories about females have focused on life history and investment in the egg and offspring, theories about males have focused on mating investment. Cox stressed that this is overly simplified and doesn’t reflect biological reality,  as males and females also share many of the same costs of reproduction as well. Issues like growth, survivorship, energy storage, and parasite load are shared between the sexes. Dr. Cox is now trying to test how sex-specific reproductive mechanisms affect these shared reproductive constraints by surgically removing the gonads of each sex. Preliminary analyses show that parasite load appears to be a shared effect among the sexes regardless of the underlying mechanism (testosterone derived from testes versus estrogen derived from the ovaries). Studies directly comparing the underlying mechanisms of sexual dimorphic anatomy, physiology, and behavior are critical for the further development of sexual selection theory and for improving our understanding of anoles. Studies like Dr. Cox’s are an important step in that direction.

Anolis cristatellus in Miami, Florida. Picture by Jason Kolbe.

Humans and wildlife are sharing the same spaces more and more frequently, but there’s still much that we do not know about how animal behavior is altered in urban environments. To address these questions, graduate student Kevin Avilés-Rodriguez (pictured below) and Dr. Jason Kolbe of the University of Rhode Island studied the responses of Anolis cristatellus to simulated predators in urban and natural environments in Puerto Rico. They found that lizards in an urban habitat had shorter flight initiation distances (the distance a simulated predator – in this case, Kevin – could approach before the lizard fled) than in a natural, forested site.  In addition, lizards’ predator-escape behaviors generally corresponded to the sizes of their perches and to their proximity to vegetation, but perch types differed between the urban and natural sites.  Whereas lizards in natural habitats tended to jump into nearby plants to escape, urban lizards tended to avoid capture by squirreling on larger, more isolated perches.  Kevin also reported that lizards perching on cement walls had adjusted their predator responses dramatically, as they generally did not jump or squirrel. In sum, this study suggests that habituation to humans and/or human-shaped habitats have altered the responses of these lizards to potential predators in important ways.

Kevin Aviles, stalking lizards in the field. Photo from Kolbe lab website.

How do lizards move in nature? Note the added emphasis on “in nature.” For many years people have studied the mechanics and patterns of of lizard movement and anoles have played an important role in this research. But today Jerry Husak of the University of St. Thomas in St. Paul reminded us that most of this research has focused on characterizing maximum performance ability, despite the fact that  animals rarely achieve this level of activity in nature. For example, most of the time many lizards are merely scurrying about on the ground and not sprinting at their full ability. Hence, although measuring maximal spring speed in the lab is a common theme, this measurement may not actually reflect what animals do in nature. Dr. Husak also stressed to the audience that animal locomotion is context dependent. Specifically, a lizard’s speed depends on whether it is moving in grass or over rocks, and whether it is foraging or fleeing from a predator. During his enlightening discussion, which included a description of him trying to sprint on a frozen Minnesota sidewalk, Dr. Husak described a series of biotic and abiotic factors that should be incorporated into models of terrestrial lizard movement.  Finally, he concluded by challenging our obsession with maximum sprint speed once again by asking whether running at top speed can lead animals to make to costly mistakes. Based on a set of foraging data, he showed that this may be the case.  Dr. Husak’s talk highlighted the importance of understanding the natural habits of lizard behavior and performance.