Egg Incubation Temperature Does Not Influence Adult Heat Tolerance in the Lizard Anolis sagrei

New literature alert!

In Biological Letters
Gunderson, Fargevieille, and Warner

Abstract

Extreme heat events are becoming more common as a result of anthropogenic global change. Developmental plasticity in physiological thermal limits could help mitigate the consequences of thermal extremes, but data on the effects of early temperature exposure on thermal limits later in life are rare, especially for vertebrate ectotherms. We conducted an experiment that to our knowledge is the first to isolate the effect of egg (i.e. embryonic) thermal conditions on adult heat tolerance in a reptile. Eggs of the lizard Anolis sagrei were incubated under one of three fluctuating thermal regimes that mimicked natural nest environments and differed in mean and maximum temperatures. After emergence, all hatchlings were raised under common garden conditions until reproductive maturity, at which point heat tolerance was measured. Egg mortality was highest in the warmest treatment, and hatchlings from the warmest treatment tended to have greater mortality than those from the cooler treatments. Despite evidence that incubation temperatures were stressful, we found no evidence that incubation treatment influenced adult heat tolerance. Our results are consistent with a low capacity for organisms to increase their physiological heat tolerance via plasticity, and emphasize the importance of behavioural and evolutionary processes as mechanisms of resilience to extreme heat.

Help Identify More Cuban Anoles

A few more photos. 1-3 are from Cienaga de Zapata area and 4 is from a cave near Havana (Parque Escaleras de Jaruco).

 

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In the Eye of the Beholder: How Do Anoles Respond to Human Clothing Color?

Water anole (Anolis aquaticus), Costa Rica

Have you ever wondered how your clothing color affects how many anoles you see and catch on a given day? When we go out herping, a lot of us favor some sort of clothing color scheme – whether it’s conscious or subconscious, scientific or superstitious. Since anoles have such excellent color vision, and since they’re so sensitive to the signaling colors of the individuals they interact with, this makes sense, right?

(a) Water anole dewlap; (b) Orange and blue shirts; and (c) green shirts worn in this study.

Bree Putman (Cal. State San Bernardino), Andrea Fondren (an undergraduate researcher), and I teamed up to determine if there was any truth behind the superstition. In an effort to understand how anthropogenic colors affect the behavior of lizards, we designed a study to test whether researcher shirt color would influence the sighting and capture rates of water anoles (Anolis aquaticus). Male water anoles have large orange dewlaps, which is their most conspicuous sexual signal. Using a modified version of the species confidence hypothesis, we predicted that water anoles would be least fearful of anthropogenic colors that most closely resembled the color of their own sexual signals (orange). To test this, a group of us spent the summer surveying water anole populations wearing three different shirt colors: orange, blue, and green. We carefully allocated shirt colors to research teams and study sites, planning it out in advance so that all shirt colors were worn by all researchers and used at all sites evenly in the study.

Our results, published in Biotropica, may make you rethink your own field shirt color choices. Both our sighting rates and our capture rates of water anoles were significantly higher when wearing orange shirts – matching the color of water anole dewlaps. Lizards likely have sensory biases for colors used in their species-specific displays, and we found that this translates into clear differences in behavioral responses to anthropogenic colors. On some level, I think many of us expected that the green shirts, which camouflaged us beautifully in the forest, would have been the most successful. Not so. Looking more broadly, Bree Putman’s previous study on western fence lizards (Sceloporus occidentalis) helps to solidify the idea that lizards are biased toward anthropogenic colors that they themselves “wear.” Western fence lizards have blue sexual signals and – corresponding nicely to our water anole results – these lizards are less fearful of researchers wearing blue clothing. Taken together, these findings remind us that placing a human perspective on animal perception can sometimes lead to flat out wrong conclusions.

As ecotourism is on the rise, it’s worthwhile to consider how the anthropogenic stimuli that ecotourists bring into a species’ native habitat can affect species behavior and survival. Reducing a species’ exposure to more frightening stimuli (such as unfamiliar colors) can reduce stress and disturbance. Something for the ecotourism community to consider as researchers continue to explore ways to minimize disturbance of natural populations, while promoting sustainable use of natural areas.

As for me, it looks like I’ll be buying quite a few orange shirts this year.

 

SICB 2020: Do Large Brown Anoles Get the Most Mating Opportunities?

Rachana applying fluorescent powder to a wild brown anole

If you’ve ever tried to note how often lizards mate, you’ve likely found yourself staring at an individual for hours at a time, sometimes with little to no movement at all, let alone observing copulations! Further, if you’re unable to catch the animal after your behavioral observations, you may not be able to draw any conclusions about traits that influence how successful an individual is at mating with another.

Rachana Bhave, a fourth year PhD candidate in Bob Cox’s lab at University of Virginia, studies pre- and post-copulatory sexual selection in brown anoles (Anolis sagrei). One of her interests includes estimating mating rates in the wild and, in particular, testing if traits such as body size directly influence these rates. Given the power required to detect selection statistically, using simple behavioral observations can be inefficient. Further, because selection is a measure of covariance between phenotype and fitness, one needs phenotypic values for each individual within her analyses. Thankfully, Rachana was able to come up with a robust technique to estimate mating rates using an island population of brown anoles in Florida: fluorescent powders!

To understand how size affects mating rate in the brown anole, Rachana and colleagues caught 153 adult male lizards in May and 128 adult male lizards in July, weighed them, and then assigned them to one of four fluorescent powder treatments. Each mass quartile was painted with a unique color of fluorescent powder on their cloaca and released to their initial capture location. After two days, all females on the island were captured and their cloaca were examined under UV light to look for the presence and color of fluorescent powder, which would suggest that she mated with a painted male. Using this technique, Rachana found that within two days, 24% of the captured females had mated in May and 48% had mated in July. These rates were shockingly high for such a short time frame!

A) Powdering an adult male brown anole; B) copulating brown anoles; C) powder visible on the cloaca of a female brown anole, evidence of copulation
Images from Rachana’s poster

Further, she found that both larger males and larger females mated significantly more than smaller males and females across the two sampling periods. Interestingly, 2% of females had multiple colors on their cloacas, which suggests they mated multiple times with males from different size classes in the two-day span. Because multiple matings within the same size class would be undetectable, this is likely an underestimation of multiple matings in the wild.

Next, Rachana plans to quantify male reproductive success using genetic parentage analysis to begin to tease apart how pre- and post-copulatory selection influences selection. We are all looking forward to her results next year! Meanwhile, you can take a look at her poster to find out more on her website.

 

SICB 2020: Oviposition Site Choice in the Brown Anole, Anolis sagrei

Abigail Dennis at SICB 2020

Embryonic environment is arguably one of the most influential factors on offspring development and later-life phenotypes. For oviparous species, this critical stage can experience potential fluctuations in moisture, temperature, and oxygen-availability. However, maternal choice in nest-site has the opportunity to buffer embryos from environments that might negatively affect survival or disadvantageous phenotypes. Undergraduate student Abigail Dennis of Trinity University in San Antonio, TX in Dr. Michelle Johnson’s lab, sought to investigate maternal nest-site choice when mothers are given nesting conditions that have been shown to be unfavorable to offspring development. 

To address this, Abigail housed female brown anoles (Anolis sagrei) in groups of 2-3 with 1 males per cage. Within each cage, females were given an option to nest in a heated box or an unheated box (ambient box). The heated nesting box was placed over a thermostat-controlled mat and both boxes were checked for eggs every 2-3 days. When an egg was found, depth and water proportion in surrounding soil were recorded. She predicted that females would avoid the deeper, warmer nesting conditions in the heated box and that nesting depths would be more variable in the ambient box. Thermal readings from the surface and base of the soil were recorded for each box. These temperatures were averaged in the ambient boxes and coupled with depth and temperature models for the heated boxes. Thermal conditions varied from 25.5 to 38 °C, although most nesting sites were found between 26.5 and 31 °C. 

At SICB’s poster session on Monday, Abigail reported that there was no difference between the number of nest sites (N=36) found in heated or ambient boxes. However, females tended to avoid nesting in sites greater than 33 °C and there was a trend suggesting nests in the ambient box were deeper than those in the heated box. Soil moisture readings also did not differ between nest boxes. Abigail speculated that if global change increases surface soil temperatures, females may avoid higher temperatures that would negatively influence offspring development by altering their nest depth. Abigail is writing this work as part of her Senior Thesis and is interested in pursuing graduate work in the evolution of development. 

SICB 2020: Sex-biased Parasitism and the Expression of a Sexual Signal in a Tropical Forest Lizard

Panamanian slender anole (Anolis apletophallus) (Photo Credit: Dr. Christian Cox)

Male sexual signals, and their often-associated distinct phenotypic and behavioral displays, have been hypothesized to have evolved from multiple sources. Two of which include the Good Genes hypothesis, which suggests sexual signals serve as an honest signal to potential mates, and the Immunocompetence Handicap hypothesis, which indicates trade-offs to elaborate signals. However, Dr. Christian Cox, an assistant professor in the Biology Department at Florida International University, thinks of these as a continuum rather than opposing hypotheses. The vibrant dewlaps of Anolis species serve as an excellent model system to address questions related to this continuum. Dr. Cox’s lab has documented sex-biased parasitism, which he discussed on Monday at SICB 2020. 

Dr. Christian Cox

The Panamanian slender anole (Anolis apletophallus) is known to host ectoparasitic trombiculid mites (also known as chigger mites). In this species, males and females are roughly the same size and, as with most anole species, males carry a large, colorful dewlap beneath their chins. Dr. Cox asked whether males and females of this species differ in the attachment site and intensity of mite infestations and whether any other factors (e.g., energetics) might influence infection. Using a combination of field and laboratory studies, Dr. Cox and his colleagues quantified the number of mites, prevalence, and intensity of infestation on individuals. He also measured mass, snout-vent length, and dewlap size. Following this, he collected fat bodies, livers, and gonads to investigate differences in energetics. 

Dr. Cox found that males were more likely to have mites on their dewlap whereas females had more mites in the inguinal and axillary regions. Additionally, large males had more mites than smaller ones and there was a significant correlation between the size of the dewlap and the number of mites. Dr. Cox also found that there was a negative relationship between fat body mass and the total number of mites. In other words, males with a heavier fat body had less mites. In females, there was a positive relationship between gonad size and the number of mites. These findings suggest sex-dependent factors influence ectoparasite load and are indicative of trade-offs to male sexual signals. 

SICB 2020: Arginine Vasotocin Stimulates Chemical Communication and Social Behavior in Anolis carolinensis

Dr. Stephanie Campos presenting her research at SICB 2020

A captive green anole (Anolis carolinensis) (Photo Credit: Dr. Stephanie Campos)

Exocrine signals (e.g., pheromones) and endocrine signals, like those associated with chemosensory organs, stimulate communication among and within species. Dr. Stephanie Campos is especially interested in the endocrine signals of reptiles and highlighted some of her work at SICB 2020. 

Dr. Campos is a postdoctoral research fellow at Georgia State University Center for Behavioral Neuroscience and Neuroscience Institute in Dr. Walt Wilczynski’s lab. She investigated the role of arginine vasotocin (AVT), a modulator of social interaction similar to the mammalian homologue vasopressin, on reptilian chemosensory systems. Previous work in green anoles (Anolis carolinensis) showed that AVT reduces aggressive visual display rates and stimulates females to display more than untreated counterparts.

In this study, Dr. Campos and colleagues tested the role of chemosensory systems in A. carolinensis by injecting resident males with AVT and introducing a male or female intruder. Ten minutes after injecting with AVT or a control solution, an untreated male or female was placed in the tank for thirty minutes. Chemical behavior, including tongue flick, jaw/chin rub, lip smack, lick, fecal/urine deposit, or cloacal rub were recorded.

They found that male intruders displayed more of these chemical behaviors toward individuals treated with AVT than controls. Additionally, males treated with AVT displayed quicker (e.g., tongue-flicking) to female intruders than controls. Dr. Campos speculates that AVT might boost production of odor cues or interior mediated endocrine-mechanisms. This might serve as an indication for multimodal communication in reptiles.

You can learn more about Dr. Campos’ research by following her on Twitter

SICB 2020: Acute Interactions between Green and Brown Anoles

Jordan Bush giving her talk on the interaction between green and brown anoles at SICB 2020

Green and brown anole interacting within Jordan’s enclosures.

As brown anoles (Anolis sagrei) become more and more abundant, many people (trained and citizen scientists alike) are intrigued with exactly how the native green anole (A. carolinensis) will respond. Newspaper articles still report on these interspecific interactions, and some recent research has shown the brown anoles can be quite mean to the native green. Thankfully, it seems that the green anole may simply be moving higher into the canopy and aren’t being merely driven to extinction by the invading brown. However, we do not yet understand the nuances of how green anoles respond when brown anoles first arrive to a new location, and that’s where Jordan Bush, a sixth year PhD student in Dan Simberloff’s lab at the University of Tennessee, Knoxville, comes in.

To understand how green anoles immediately react to the novel presence of brown anoles, Jordan built 5 x 5 x 5m enclosures in which she placed 6 female and 6 male green anoles. These animals then set up territories and became acclimated to their new living space. Jordan quantified baseline behavior and territory sizes (in 3D!!!) for each individual in an enclosure.

Example 3D territories

After 10 days, Jordan introduced brown anoles in these enclosures, either two females and two males or four females and four males to investigate the effects of density, and quantified behavioral and territorial changes in the green anole. Being the careful researcher that she is, she also introduced the same number of green anoles to other enclosures so that she could show that any changes in behavior were not simply due to more animals being present. After 10 days of interacting with the brown anole, Jordan found no change in activity level, home range volume, or perch height, suggesting that, at least within an acute time frame, the green anole can handle its own against the brown anole.

SICB 2020: Impacts of a Novel Environment on a Tropical Anole Species

Dan Nicholson at SICB 2020

Evolution has long thought to be a slow process, taking thousands if not millions of years. Recently, there has been a paradigm shift in how scientists think about evolution. We now know that we can observe evolution on a contemporary timescale, observable to the human eye. Dan Nicholson, a Ph.D. Candidate at Queen Mary University of London in Rob Knell’s lab, is working with Mike Logan and others to observe the effects of habitat change on the evolutionary ecology of Anolis apletophallus.

Dan and his team transplanted anoles from the mainland of Panama to several islands around Barro Colorado Island in July of 2017. Before release, they recorded the anoles’ morphological characteristics, including hindlimb and forelimb length, toe pad size, and head depth, and well as characteristics of their perch location, including height and width. Tracking changes in these characteristics can detect natural selection at work. At SICB 2019, Dan reported the results of the first generation of island anoles.

At SICB 2020, Dan included the trends of the second generation of island anoles. The preliminary results indicate the island anoles have continued to use wider perches than the mainland anoles. However, the majority of the island anole morphological traits now align with the mainland anoles. The exception is that hindlimb length of the island anoles decreased, while the mainland anoles hindlimb length has increased.

Some potential causes of these results, Dan speculates, include genetic drift due to the small population size. The islands started with a robust number of anoles, but over the two years of this study, their numbers have rapidly dwindled. Another possibility is the island anoles are aligning with the mainland anoles morphologically due to gene flow. In the future, Dan wants to further analyze the preliminary results from a population angle, looking at changes in groups of traits instead of individual traits.

You can learn more about Dan’s research by following him on twitter.

SICB 2020: Why Do Anole Heads Fail to Develop Properly When It’s Hot?

Sylvia presenting her work at SICB 2020

Another SICB, another great presentation from Sylvia Nunez from Thom Sanger’s lab investigating how the interaction between heat and oxygen availability affects development in the brown anole (Anolis sagrei). Last year, Sylvia presented a poster showing that above 33°C, embryonic survival was greatly reduced and many embryos developed craniofacial malformations. With some potential nesting sites for anoles now exceeding 40°C, understanding mechanisms leading to decreased survival is critical.

Low oxygen at sublethal temperatures can recapitulate negative effects on craniofacial development at high temperatures.

As a follow up to this study, Sylvia set out to understand exactly how it is that heat and oxygen can interact to lead to craniofacial deformities. She posited several hypotheses and was able to eloquently test each one, including the neural degeneration hypothesis and the oxygen limitation hypothesis. Specifically, Sylvia noted that disruption in sonic hedgehog has been linked to facial development and that oxygen demand can often exceed oxygen supply at high temperatures.

First, Sylvia tested the oxygen limitation hypothesis by examining whether low oxygen coupled with sublethal (elevated) temperature conditions recapitulate the effects of craniofacial malformation under thermal stress. Previous work in the lab induced craniofacial malformation at 36°C; Sylvia showed you could mimic this effect using 33°C with low oxygen, with a greater rate of malformation than in 27°C (the standard control temperature) with atmospheric oxygen, 27°C with low oxygen, or 33°C with atmospheric oxygen. She then tested whether an increase in oxygen can rescue embryonic survival at high temperatures. To do so, she split eggs among two treatment conditions: 27°C with high oxygen and a hot nest site temperature with high oxygen. She found further support for the oxygen limitation hypothesis – when oxygen availability was increased above atmospheric conditions there were no differences in embryonic survival. Wow! Further, there were no craniofacial malformations in the high temperature treatment when oxygen conditions were high.

To follow up on this finding, she examined if oxidative stress could be the link between temperature and craniofacial malformations using superoxide dismutase (SOD), an enzyme that helps turn the superoxide radical (O2) into oxygen (O2) or hydrogen peroxide (H2O2), as a marker for oxidative stress in the telencephalon. Indeed, within mere minutes of a temperature increase, SOD becomes upregulated, suggesting that thermal stress contributes to oxidative stress. But Sylvia didn’t stop there. She then treated some embryos with an SOD inhibitor to show that when SOD is absent craniofacial malformations appear.

Overall, Sylvia has very eloquently shown that increased temperature leads to craniofacial malformations via thermal effects on oxidative stress. I cannot wait to see what she presents next year!

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