Anole Annals

As many of us I’m sure know, many lizard species have the ability to lose their tail in order to escape predators or competitors. However, the tail doesn’t grow back as originally lost! The bone, muscle, and fat is replaced by a cartilaginous rod. Lizard species that use their tail in social communication might suffer a severe cost associated with losing their tail because they might lose their ability to communicate information to predators or members of the same species. Amy Payne, a student with Michele Johnson at Trinity University, recognized this issue and used a cross-species comparison to determine just what factors influence tail breakage.

Amy set out to test the hypotheses that species that use their tail in a social context will have lower rates of tail loss, species that use their tail in a predatory context will have higher rates of tail loss, and that species that primarily store fat in their tail will have lower rates of tail loss. They used curly-tail lizards, earless lizards, house geckos, and crested and green anoles in their work and found that curly tail lizards exhibit the greatest tail loss despite using their tails constantly. Earless lizards exhibited the lowest rates of tail loss and they used their tails quite frequently, and anoles had intermediate rates of tail loss based on social use. Tail use in a predatory context was rare for anoles, but quite common for curly tails (that exhibited a higher rate of tail loss) and earless lizards (that exhibited a lower rate of tail loss). They also found no relationship between tail autotomy and energetic storage in the tail. Their major takeaways are that species that use their tail very frequently in communication can exhibit either large or low rates of tail loss, and that there are a lot of intermediate rates of tail loss perhaps due to the multi-faceted role tails play in the evolution, ecology, and behavior of lizards. They are going to follow up this work using bomb calorimetry to more precisely measure species differences in the energy stored in the tail, and increasing the species sampling to incorporate more species (especially more anoles!)

Anolis RPM muscle cross-section. The darkened area in the middle of the muscle shows white blood cell infiltration, which indicates damaged tissue.

Martin measured the muscle damage of the RPM for 5-10 males in 27 different species of anoles. This estimate was made by calculating the cross sectional area (CSA) of the RPM and the CSA area of muscle damage of each muscle. He then calculated a ratio of muscle damage (damaged CSA / total CSA) for each RPM and then averaged to give each animal a single value. These species were also observed in the field to measure an observed copulation rate (totaling ~1000 hours of observation). He and his collaborators used phylogenetical generalized least squares regressions to test for a correlation between observed copulation rates and the average ratio of muscle damage across these species.

Positive correlation between observed copulation rates and the average ratio of damage of the RPM for 28 species of anole.

They found a significant and strong positive correlation between these estimates, suggesting that examining muscle damage may be an efficient way to estimate behavioral rates. Martin drove home the point that measuring the damage in the RPM of these species took him 2 orders of magnitude less time than estimating copulation rates in the field. This suggests that researchers may be able to more easily estimate behavioral rates of different species, as well as examine individual variation within species. In the future, this group hopes to explore the relationship between muscle damage, copulation rate, and recovery so they can more accurately describe the window of behavior they observe through muscle damage.

The color change from a bright, vibrant green to a dull, muddy brown is one of the most characteristic qualities of the green anole (Anolis carolinensis) (I am aware that some dewlap enthusiasts may take issue with this statement). Given the dramatic differences between the colors, Daisy Horr, a Junior in the Johnson Lab at Trinity University in San Antonio, TX, wondered how social behavior and body temperature may influence body color, and whether these relationships differ between males and females.

First, Daisy observed green anole social behavior in Palmetto State Park, TX, and found that males exhibited green body color more frequently than females, and males that performed more pushup and head bob displays also changed colors more frequently (between green and brown). She also found that females were more often green during social interactions.

Because green anoles are ectothermic, more commonly known as cold-blooded, ambient temperature plays an important role in nearly every aspect of their lives. Therefore, there might be a relationship between body color and thermoregulation. Daisy spent a lot of time searching the Trinity University campus for green anoles, and measured body temperatures, the temperatures of the perch on which she found them, and the distance to the nearest alternative perch (a measure of exposure). While she did not find any association between body color and temperature, she did show that males used warmer substrates than females, and that males were typically more exposed (greater distance to the nearest perch). Additionally, she found that males are generally greener than females throughout the day.

Daisy plans to pursue graduate school after she finishes at Trinity University, and we all hope she continues to contribute to anole research! Graduate advisors, you don’t want to miss out on a fabulous researcher!

(This post’s author’s diploma from Trinity University does not affect his assertion that Trinity graduates are among the best minds in biological research.)

Effects of urbanization pose major challenges to biological systems globally. One example that impacts the thermal environments of urban areas is the urban heat island effect, where urbanization creates an environment that is hotter than nearby natural areas. In Shane Campbell-Staton’s talk “Temperature-mediated shifts in performance and gene expression between populations of the Puerto Rican crested anole in natural and urban habitats” he sought to investigate divergence in thermal physiology and gene expression between urban and natural populations of anoles in Puerto Rico.

In situ, he investigated whether there were differences in urban and natural microhabitats, lizard thermal tolerance between urban and natural populations, and if there were differences in thermal physiology if this was a plastic or genetic response. He found that urban microhabitats were warmer, and that lizards from urban environments maintained function at higher temperatures when compared to their natural environment counterparts. This increase in thermal tolerance is a plastic response in the urban lizards. He then investigated the transcriptomics to investigate if there is evidence for temperature-mediated selection in urban heat islands, and found that selection on ancestral plasticity may play a role in acclimation to urban heat stressors. Future work includes identify genes involved in this accommodation. Amazing things to come!

Leah Elkhoury, an undergraduate student in the Fokidis Lab at Rollins College, investigated whether access to food would increase agonistic behaviors in the notoriously aggressive brown anole. First, to see if fasting would affect brown anole aggression, she tested wild caught brown anoles by feeding control lizards a regular diet and fasting treatment lizards for either 24, 48, or 72 hours. The treated anoles were then size-matched with a control lizard and placed in an enclosure, where their agonistic displays were recorded and analyzed.  The results of that portion of the experiment indicated that fasting does not increase agonistic behavior.

Next, lizards were separated into two groups: one with predictable feeding schedules, and one with a randomized feeding schedule for one month. This lizards then were tested for aggression in a similar way to the first experiment. The anoles were then sacrificed, and their blood was tested for stress steroid, fat mobilization, and fat deposition. Their brains were then collected and regionally divided to in order to measure stress steroid. Interestingly, lizards in the unpredictable feeding group exhibited more dewlap flashes, one of the brown anole’s agonistic behaviors. They also showed an increase in fat deposition and plasma corticosterone (stress steroid).  Though there were no differences in corticosterone between brain regions.

These exciting results show the “choices” brown anoles make about energy allocation under stress, and Leah plans to continue to ask questions about the link between feeding and aggression. We can’t wait to hear about her work in the future!

One of the most challenging things an organism will do throughout its lifetime is balance its energy budget. Energy is used to grow, develop, reproduce, survive, and how animals allocate that energy will forever be a fascinating question to biologists. If you have more energy, then in theory you should be able to be more active and be a “fitter” individual. For most lizards, excess energy can be represented by fat stores, so if individuals tend to store more energy, then they should be less able to put energy into other reproductive or physiological traits. This was the idea tested by Marzieh Rouzbehani of Trinity University, working in the lab of Michele Johnson.

They studied two anole species: crested and bark anoles (Anolis cristatellus and A. distichus) and found that the two species exhibit different energy-physiology relationships. They found crested anoles with larger eggs had more fat stores, and that crested anoles with larger eggs did not exhibit activity tradeoffs. Bark anoles on the other hand exhibited no relationship between egg mass and fat stores, but found a trend where bark anoles with larger egg masses had lower activity levels. In addition for both species, they found no relationship between hematocrit (the volume percentage of red blood cells in blood) and activity levels, and their work emphasizes the complexity that is species-specific physiological dynamics for female anoles. Different anole species are likely to have different physiological traits influence their behavior and activity in different ways. Fascinating stuff!

Anna Thonis, a Master’s Student in the Lister Lab at Rensselaer Polytechnic Institute, used distributional projection models to predict future ranges of anoles in Puerto Rico. There are ten species of anoles in Puerto Rico, and all of them are predicted to be faced with range shifts in the coming years due to climate change, as Puerto Rico may be faced with both warming and drying out in the future.

Thonis used population occupancy data collected by Lister from 1976-2012 as an input for her models. Using climate models and open source software, Thonis projected anole populations for 2050 and 2070. Based on these models, there will be an average reduction of the most suitable of anole habitats of 29.5% by 2050, and 8 of 10 anole species in Puerto Rico face habitat reduction. In 2070, the models predict and increase in habitat reduction, with a 39.6% reduction in the most suitable habitat and 9 of 10 species of anole facing habitat reduction.

Though these models sound dismal for anoles, Thonis hopes that future work with distributional models can help inform conservation decisions as climate change processes. More detailed models may be able to inform decisions on where protected habitats for anoles should be placed.

Sometimes, males and females of the same species differ in traits linked with their ability to survive and reproduce. These differences, called sexual dimorphisms or polymorphisms are quite common in lizards, including anoles! Female brown anoles have a polymorphic back pattern while males are usually of a single pattern. A lot of work has tried to uncover why this back pattern polymorphism exists in nature and what advantages it offers these lizards. Rachana Bhave, a Ph.D. student with Robert Cox at the University of Virginia were interested in determining just how these male and female-like morphs of brown anoles differ in their morphology, behavior, and which traits influence survival.

Using a captive island population in Florida, Bhave et al. captured all of the lizards on the island and measured differences in morphology between the morphs, finding that female-like morphs tend to have higher survival as juveniles but not as adults. These morphs differed in their growth rates but did not experience different selective pressures, indicating perhaps a very complex control regulating the back pattern maintenance in this population. They also found that while female-like morphs tend to display at a higher rate, there weren’t any differences in the morphs probability to attack. They plan to integrate more physiological data such as growth or performance metrics to try and uncover the governing factors responsible for maintaining this back-pattern polymorphism. Awesome stuff to come!

Male-male competition is one of the most widespread phenomena in lizards. Males compete for access to critical food resources, territory space, and female lizards, making a male’s ability to win competitions against other males critical to survive and reproduce. However, how the behavior of a male can vary depending on what social environment he grew up in, the abundance of certain predators or competitors, or the density of other male and female lizards. Therefore, determining what environmental factors influence the behavior of male lizards as they attempt to procure resources necessary to survival and reproduction is a critical question in biology today.

From Virginia Tech, (now a Ph.D. student with Shawn Kuchta at Ohio University) Emily Watts and her collaborators sought to understand what environmental factors influence the behavior of male brown anoles (Anolis sagrei). They used males reared in a common garden from four different populations in the Bahamas to try and determine if genetic or environmental factors influence the aggression differences among males of different populations. Using male-male competition experiments and mirror experiments (where a single male perceives himself as a rival), they tested the hypothesis that males reared in a common garden will not differ in aggressive behavior. They found that aggression varied significantly among populations when using mirror tests, but they found support for their original hypothesis when using male-male competition experiments. This work highlights that aggressive behavior of males is shaped by a multitude of pressures from the environment, to genetics, and ultimately how and where a lizard develops to adulthood. More is to come as they continue to increase the number of their experimental trials with more Anoles!