Anole Annals

Predicting the responses of species to current environmental and climate change is one of the largest duties of current biologists. Ectothermic species (including lizards) are particularly vulnerable because they lack the ability to metabolically generate heat and rely on environmental sources of temperature to maintain their body temperatures. For species that live in the tropics, this task is much harder because tropical environments experience less temperature variation both within and across seasons. Tropical lizards traverse these landscapes to try and maintain optimal and preferred body temperatures, but are all thermal environments equal in the constraints they impose on lizards?

To address this question, Lauren Neel, a student of Mike Angilletta’s at Arizona State University, collected an astounding amount of data from two species of anole: Anolis sagrei from their native range on Great Exuma in the Bahamas, and A. apletophallus in Panama. She collected environmental temperature data using biophysical models, thermal performance data by racing anoles at several different body temperatures and measuring their sprint speed, and preferred body temperatures by placing lizards in a thermal gradient. Despite both lizards living in tropical climates, she found distinct differences between the environments (and anoles!). Anolis sagrei thermoregulated more,  was active for longer periods of time than A. apletophallus, and exhibited warmer preferred temperatures. Neel and colleagues also found that A. sagrei is not likely to suffer a drop in performance capacity as environments warm over time, whereas A. apletophallus is likely to experience a significant reduction in their speed performance which might be a physiological precursor to population collapse and a rise in local extinction events. Great stuff coming from Lauren Neel; stay tuned for more!

Gianni Solis presents her work entitled “Effects of arginine Vasotocin and mesotocin on aggression in male Caribbean anoles.”

Male aggression in Anolis lizards is governed by the circulating sex hormone, testosterone. Two species of anoles, the brown anole (Anolis sagre) and the Caribbean anole (A. cristatellus), both exhibit high aggression. However, A. sagrei has low concentrations of testosterone in comparison to A. cristatellus. This suggests that there may be other underlying mechanisms governing male aggression rather than just testosterone.

Regulation of aggressive behaviors in male Anolis lizards was the focus of Gianni Solis’ poster presentation at the 2019 SICB conference. Solis is an undergraduate sophomore at University of St. Thomas under Dr. Jerry Husak, although one would think she is an established graduate student based on her knowledge and enthusiasm for this project. She predicted that there would be a difference in aggressive behaviors exhibited by A. sagrei and A. cristatellus and these behaviors would be influenced by Arginine Vasotocin (AVT) and Mesotocin (MT).

Solis examined aggressive behaviors towards a mirror in A. sagrei, a low-testosterone species, and A. cristatellus, a high-testosterone species. IP injections of non-steroid hormones AVT and MT were given along with Phosphate Buffered Saline (PBS) as a control. After a 15-minute acclimation period, aggressive behaviors were documented in 20-minute lengths. Latency, total number of bouts, average and total duration, and combination of displays were recorded. Aggression scores were calculated utilizing a PCA and a one-way ANOVA identified statistical significance.

While her results were non-significant, potentially due to small sample size, statistically close values suggest that there may have been an influence of AVT and MT on aggressive behaviors. MT-injected A. sagrei tended to be less aggressive than other treatments and MT-injected A. cristatellus tended to be more aggressive than other treatments. Other mechanisms by which these behavioral differences occur between both species, such as potential estrogenic influences, may also be the target for future studies. Anolis male aggressive responses and underlying processes remain in question, however, we are looking forward to hopefully seeing Solis again with more questions at SICB 2020.

Zachary Morris presents his research entitled “The role of craniofacial growth zones in shaping crocodylian snouts.”

Evolution of the crocodylian skull is driven by developmental changes. While embryos share many similarities, at some point within development they diverge into unique ecomorphs. Prior studies in American alligators (Alligator mississippiensis) showed that the snout is a source for early facial proliferation, wherein later stages lack growth plates that resemble post-hatching anole lizards. Snouts of crocodilians are described as moderate, blunt, and slender. Snout structure is related to dietary and ecological differences; for example, long, slender snouted crocodiles such as the Tomistoma (Tomistoma schlegelii) feed largely on fish. Heterochrony of slender-snouted crocodiles is responsible for continued elongation of the embryonic snout.

Zachary Morris of Harvard University following his great talk at SICB 2019.

To further understand forces behind these developmental changes, Zachary Morris, a current PhD student of Dr. Stephanie Pierce at Harvard University, began by asking the questions “When does this difference (in skulls) become apparent?” and “What are the cellular dynamics of snout elongation?” He presented his work on Saturday at the 2019 SICB conference and shared his experimental approach to answering such questions. To do this, he traveled to Imperial College London to work with Dr. Arkhat Abzhanov.

In answering his initial question, Morris incubated A. mississippiensis, dwarf crocodile (Osteolaemus tetraspis), and T. schlegelii embryos to developmental stages 14 and 17. These time-points were selected based on Ferguson staging. He could then examine snout/head length ratios to determine when skull differences, such as elongation, became apparent. At stage 14, no differences among blunt, moderate, or slender-snouted crocodilians were visible. However, at stage 17, he found that slender elongation began. To investigate his latter question, he followed the same procedure, but was able to calculate cell proliferation rate for tissue regions utilizing injection of EdU in ovo. He found that while elongation patterns such as facial shape were apparent during stage 17, early cell proliferation rate at the same stage was not apparent. His findings suggest that blunt species types (such as O. tetraspis) have decreased cell proliferation along the tip of the snout in comparison to slender species types (such as T. schlegelii).

In the future, Morris hopes to investigate whether cell proliferation at the tip of the snout is maintained in Tomistoma and if there is greater proliferation at lateral edges of facial structures in broader-snouted crocodilians. While these modern-day dinosaurs derived species-specific morphological differences from actual dinosaurs, the evolutionary processes by which these occurred remains the target of Zachary Morris’ interesting and exciting research.

We tend to think of exercise as a human activity–training our bodies in specific way to accomplish tasks, maintain strength and endurance, and live a healthier lifestyle. Wild animals exercise just as often if not more than humans, but the benefits to animal exercise have been somewhat contentious in biology. The responses to organismal exercise are very conserved with respect to evolutionary change and speciation. Those responses include an increase in performance capacity (such as speed or endurance), but often times trades-off with some other physiological trait, such as immunocompetence. With this trade-off looming, one outstanding question remains: does the exercise response enhance reproductive success and survival? Can we call this response “adaptive”?

To test this idea, Jerry Husak from the University of St. Thomas and his co-author, Simon Lailvaux at the University of New Orleans, measured the exercise response in 90 green anoles (Anolis carolinensis). They had 30 control lizards, 30 lizards trained with speed trials, and 30 lizards trained with endurance trials. They found that overall, exercise enhanced performance for all lizards relative to the controls, but training decreased the ability of a lizard to fight off an infection. They found that lizards that had been trained did not exhibit increases in movement rates, and also found that over time, trained lizards exhibited decreased survival relative to the controls! Is exercise actually bad for lizards?! Green anoles were twice as likely to survive when they were not trained, and differences in lizard body condition might be intimately linked with their probability of survival. Husak and Lailvaux are going to continue to test the idea that the exercise response confers some benefit to lizards outside of performance. Stay tuned!

Members of the same species share a common genome, the same set of genes and regulatory networks that build the proteins responsible for phenotypic diversity. However, that means that both of the sexes share a common genome, and that is an issue when males of a species are sensitive to their own environmental stimuli, and when females are required to invest a lot of their energy towards reproduction and rearing offspring. Species are often sexually dimorphic as well, where either the male or the female will be larger than their inter-sex counterpart, and this has to do with what ecological tasks each sex is responsible for. Do you have to defend a territory? You better be big! Do you want to create a lot of high-quality offspring? You better not invest that much energy into your own growth! It’s an interesting question in biology today: what happens genetically when a sexually-dimorphic species develops to adulthood?

To answer this question Albert Chung, a graduate student at Georgia Southern University, and his colleagues Robert Cox and Christian Cox designed an experiment to quantify changes in gene regulation in brown anoles throughout ontogeny and quantify how changes in gene regulation produce sexual dimorphism. They quantified gene expression at four different time points until adulthood across three different tissue types (brain, liver, and muscle) using RNA sequencing (RNAseq). Chung and colleagues found that sex-biased gene expression exhibits age specificity, with different age classes exhibiting different patterns of sexual dimorphism in gene expression. They also found that the number of sex-biased genes increases throughout development, important for a species to be able to develop both a larger sex and a smaller sex. In addition, sex-biased gene expression also varies among the different tissue types, with the liver exhibiting an increase in sex-biased genes throughout development, potentially to increase growth in male brown anoles compared to females! Chung spoke in the Raymond Huey Best Student Paper Award session for the Division of Ecology and Evolution and delivered a fantastic presentation. We look forward to learning more about the development of sexual dimorphism (especially in anoles!) from Albert and his co-authors.

Ectotherms such as lizards often take extreme care when it comes to laying their eggs. Eggs are incredibly sensitive! When female lizards don’t retain their eggs and give live births (we call this viviparous), female lizards will seek out the perfect temperature and moisture conditions for her eggs to develop and hatch. Oftentimes, when researchers use anoles in the laboratory for a variety of experiments, they incubate eggs at the temperature that these eggs experience in their natural environment. However, many studies only use a constant, mean temperature, rather than using a more realistic diel cycle of fluctuating temperatures over time. However, does that matter at all? It’s an important question for a variety of anole biologists that raise eggs to hatching: does the thermal regime of your incubator matter when it comes to offspring phenotype?

Josh Hall, a Ph.D. student at Auburn University under Dan Warner, set out to address just that question! He raised brown anole eggs in one of four distinct thermal treatments: a constant temperature, a repeated sinusoidal (sine wave) fluctuating temperature, a fluctuating temperature parameterized by the mean daily fluctuations these lizards experience in the field, and natural environmental conditions. He did this for both a cool developmental temperature (reflecting eggs developing earlier in the reproductive season) and a warmer developmental temperature (reflecting eggs developing later in the reproductive season). Even Josh didn’t recommend doing so many treatments! However, the amount of work that went into these treatments is impressive.

Hall and Warner found that natural temperature treatments increased the developmental rate of brown anole eggs only at cooler temperatures, and actually decreased the developmental rate at warmer temperatures. They didn’t find any other effects of any treatment on egg phenotypes. They also found that natural temperature treatments increased the endurance of hatchlings compared to the constant temperature treatment  at cooler temperatures. I was really struck by this study: it seems really obvious that eggs would do better in the lab when developed at temperatures that they experience in the field, but an experiment like this is so rarely performed because it requires so much intensive care and work! Can’t wait to hear more about how different developmental conditions affect anoles from Hall and Warner!