The large, colourful dewlap is an obvious defining characteristic of the anole. Understandably, then, there has been a lot of investigation (and speculation) on what the dewlap is used for. Without doubt it’s for social communication, but to communicate what. Historically, the dewlap was thought to be used for species recognition, which remains a reasonable explanation today. But a typical assumption made by many anole researchers and evolutionary ecologists alike is the dewlap, and specifically its size, is effectively an ornament used to attract mates or advertise potential fighting ability among territorial rivals. In other words, the evolution of the dewlap is the product of sexual selection.
If that’s the case, then dewlap size should be linked to some aspect of an individual’s ‘quality’ or physical condition, especially in males who seem to be the ones courting females (not vice versa) or defending territories. This is because a male’s quality or condition can be hard to assess by general appearance alone, unless there is a key feature that provides an honest indicator of that quality. In anoles, this is assumed to be a large dewlap that’s physiologically costly to produce.
One easy way that has been proposed to test for sexual selection in the origin of a morphological structure like the dewlap, is to look how it scales with body size. Structures that are honest indicators of condition will be costly to develop and maintain. Large males are often in better condition than small males because of the underlying factors that result in bigger bodies (e.g., a history of successful foraging, superior growth rate, having ‘good’ genes). This means larger males can invest more in exaggerating the size of the dewlap than smaller males. There would be a clear evolutionary incentive to do so as well, because having a larger dewlap would attract more mates and appear more threatening to male rivals. The outcome of this should be disproportionately larger dewlaps in larger males. This is called positive allometry or hyper-allometry. If dewlap size has a hyper-allometric scaling relationship with body size, then it probably resulted from sexual selection. Or at least that’s the idea. And you can find this out by just measuring a bunch a males.
The dewlap of anoles featured heavily in the original formulation of this idea, with the conclusion being that dewlap size was hyper-allometric and assumed to be the product of sexual selection. Anoles have therefore become a classic example of how sexual selection drives hyper-allometric scaling in ornament size.
Tom Summers
Tom Summers was a graduate student who thought about hyper-allometric scaling a lot. He looked at the scaling relationship of ornaments that he had confirmed experimentally to be the target of sexual selection in fish, and found they were hyper-allometric…sometimes. Tom found natural selection on ornament size can often work in the opposite direction to sexual selection. This is because large ornaments can interfere with locomotion and often be conspicuous targets for predators. When these pressures are high, species tend not to show hyper-allometry in ornaments. Those ornaments were still the product of sexual selection, but their allometric scaling was dampened by opposing natural selection.
Tom turned this attention to the anoles, and found overwhelmingly that dewlap size was not hyper-allometric but hypo-allometric. That is, larger males have disproportionately smaller dewlaps than smaller males. He even looked at another group of lizards that have independently evolved a dewlap, the southeast Asian Draco, and found the same pattern. His results have just been published in the Journal of Evolutionary Biology.
The scaling relationship of the dewlap in both groups varied from one species to another, but never was it hyper-allometric. In the case of the anole dewlap, this variation in dewlap size was predicted by factors important in signal detection (receiver distance and habitat light). This was consistent with the general hypo-allometry of the dewlap as well.
The effectiveness of a visual flag (like the dewlap) in attracting the attention of a receiver (another lizard) is dependent on the gross size of that flag, not how big it is relative to the signaller’s body (i.e., allometric scaling is irrelevant). Beyond a particular threshold size, which is dependent on the visual acuity of the animal in question, there are diminishing returns for detection with increasing size. Even a large increase in dewlap size beyond a certain point wouldn’t really improve signal detection, a phenomenon known as ‘Weber’s Law’. The resulting pattern when comparing dewlap size among males is hypo-allometric scaling. Larger males have generally reached the size threshold for reliable detection, so there’s little point in further elaboration.
It also fits with the extensive amount of work showing that the dewlap is likely to be most important in signal detection, rather than a cue of quality.
So why such a dramatically different finding to earlier investigations of the anole dewlap? All studies prior to Tom’s measured dewlap size by catching the lizard and manually pulling out the dewlap using forceps. Simon Lailvaux has discovered that the skin of the dewlap varies in its elasticity. Larger dewlaps are going to be more stretchy than smaller dewlaps. This means you can probably pull the dewlap out to a larger size in larger males. This would subsequently generate the artifact of hyper-allometric scaling when comparing dewlap size across males of different size.
Tom had measured dewlap size from high-definition videos of free-ranging males fully extending their dewlaps during display. There are various analyses in his paper that confirm this approach provides an accurate measure of dewlap size. His logic at the time was this view of the dewlap would be how lizards actually see and evaluate the size of the dewlap relative to body size. It also meant animals didn’t have to be caught, so the approach was less intrusive for the animal (always a plus). It just happened he avoided the potential problem of over stretching the dewlap if he had caught the animals and manually extended the dewlap by hand.
What does this mean for all that data that has been based on researchers pulling out the dewlap using forceps to measure its size? Honestly, I don’t know. Maybe nothing depending on what the data are being used for. Maybe everything if the data are being used in allometry studies.
This book is published by Chimaira and is supported by a range of international conservation agencies. With 608 pages and around 900 images, it attempts to be a thorough, up-to-date account, of the natural and introduced reptile species in this biodiversity hotspot. The reptiles are a dominant component of the natural terrestrial vertebrate fauna. For example, there are almost three times more native terrestrial reptile species than passerine birds, and unlike the birds these are overwhelmingly endemic to the Lesser Antilles.
There is a lot on anoles-including images of every species and the various within-island ecotypes.
The book is available at NHBS, Chimaira (the publisher), or elsewhere.
On a hot day in July, evolutionary biologist Martha Muñoz is leading four undergraduate students on a scouting expedition in the Smoky Mountains of North Carolina. As they hike up a steep trail, Muñoz turns over rocks and pokes leaf litter to assess where they might find salamanders when they return that night. She quizzes the students about how the weather might affect their chances, then demonstrates how the crunch of leaves underfoot is an easy way to assess an area’s dryness. Too much crunch means the salamanders won’t be out that night.
When one student falls behind, Muñoz hangs back to lend a hand if needed. Aha Anderson has a balance disorder and apologizes for their slowness. “No apologies needed,” Muñoz assures them. Later the crew will stop by Walmart to pick up a walking stick for Anderson. When another student, Jesús Buenrostro, proves squeamish about spiders, centipedes, and even grasshoppers, Muñoz reassures him with a few words in Spanish.
After dark, the group will return with headlamps, thermometers, and humidity sensors—and the goal of collecting 10 gray-cheeked salamanders to add to the growing salamander collection in Muñoz’s lab at Yale University. They’ll document the precise environment in which each one is found.
The southern Appalachians are a diversity hot spot for these creatures, but many of the roughly 30 species of lungless salamanders here look similar. Their environment also seems uniform, at least at first glance—creating a puzzle about how so many species could have evolved. Muñoz suspects subtle differences in behavior or habitat may have driven the salamanders to diversify, and she wants to figure out what they could be.
At 37, Muñoz has already won recognition for her discoveries about underappreciated influences on evolution, some of which buck classical thinking in the field. Her extensive studies with Caribbean lizards called anoles, for example, have provided some of the best empirical evidence that organisms can shape their evolutionary trajectory through their behavior, either speeding up or slowing down the evolution of physiological and morphological traits. She brings perspectives from multiple disciplines to evolutionary questions, says Robert Pringle, an evolutionary ecologist at Princeton University. “Her research is at the nexus of ecology, evolution, and physiology, and she has been in the vanguard of testing whether behavior acts as a drag on evolution or instead accelerates it,” Pringle says.
Muñoz sees a parallel in her own career path. The daughter of Cuban refugees, she knows firsthand the challenges people from underrepresented groups face as they try to get a toehold in academic science. “There is power in knowing that we can take control of our own circumstances, that we can guide our futures,” she says. “And there is even more power in knowing that this is a process that has unfolded for millions of years. It’s not the exception; it’s the norm.”
With that in mind, not only does Muñoz work hard to influence evolutionary thinking, she also strives to make sure others have a chance to make their own impact, no matter their background. “In my home you could often hear, ‘El éxito de uno de nosotros es el éxito de todos’—the success of any of us is a success for all of us,” she explains. “This is how I run my lab.”
MUÑOZ CREDITS her grandmothers and parents for her work ethic and success. After fleeing Cuba in the 1970s, her maternal grandmother scrubbed toilets to keep Muñoz’s mother and aunt housed and fed and later took care of Muñoz so her parents could work. The family eventually moved to a semidetached house in Queens near LaGuardia Airport, where despite regular insults from a racist neighbor, Muñoz found the diverse neighborhood exciting and inspiring. “We were all immigrants, all trying to get ahead,” Muñoz recalls. To help out, Muñoz took a job as a cashier at the local Rite Aid, where she endured threats from angry patients being refused expired prescriptions, met customers who had to choose between food and medicine, and put up with condescending doctors. “There isn’t anything about being a PI [principal investigator] that you can’t learn by being in retail,” she says.
Muñoz fell in love with nature at an early age. She and a friend scaled the chain link fence at a local park, pretending they were climbing trees in the wilderness. “I dragged every adult I could find” to the American Museum of Natural History, the Bronx Zoo, and the New York Botanical Garden, where she could connect to the natural world.
In freshman biology at Boston University, she learned about the rapid diversification of animal species during the Cambrian explosion more than 500 million years ago. It “moved me to tears,” she recalls, and inspired her to study evolutionary biology. She was accepted into a Ph.D. program at Harvard University, which had rejected her undergraduate and midcollege transfer applications. “I was so proud to be able to tell my parents I got into Harvard because then they relaxed—they knew they had done their part,” she says.
At Harvard, she worked with evolutionary biologist Jonathan Losos, whose research on Caribbean anoles has become a classic example of how evolution can follow a predictable path. For decades Losos and his students have studied lizards introduced to new islands, finding that when faced with similar challenges, these newcomers often adapt by evolving similar characteristics.
Muñoz added a twist to this story with field research on anoles in the Dominican Republic, which boasts some of the region’s highest peaks. Tropical lizards there can thrive at 3000 meters’ elevation, where it can be bitter cold. Most researchers had assumed that when a tropical lizard expands to the top of a mountain, its body would change over generations to tolerate the cold. But after comparing different species, Muñoz found little evidence of physiological differences that would confer cold tolerance. Instead, whereas sea-level anoles seek shelter from Sun in moist vegetation, the high-altitude lizards stayed warm by spending their days perched on boulders. They were “behaviorally nimble, exploiting Sun and shade to their advantage to stay optimally warm,” Muñoz explains.
The mountain lizards’ shift in behavior sped up morphological change, Muñoz found. Compared with their peers at low elevations, they had quickly evolved shorter hindlegs and flatter skulls that enabled them to hide from predators in narrow crevices in the rocks where they bask, she and her colleagues reported in 2017. The work showed a single behavior could slow one aspect of evolution, such as physiological changes in heat tolerance, and speed up another, such as the changes in anatomy she’d observed. “Far from being passive vessels at the mercy of their circumstances, organisms can influence evolution directly,” she says.
That idea wasn’t new, but prior to Muñoz few researchers had gone looking for empirical evidence. The influence of behavior on evolution “is an underemphasized problem that has not received nearly enough attention,” says Harry Greene, an emeritus evolutionary biologist at the University of Texas, Austin. With her data, “Muñoz is causing us older folks to think harder.”
After finishing her Ph.D., Muñoz did a postdoc at Duke University, where she explored another underappreciated influence on evolution: biomechanics. Duke integrative biologist Sheila Patek had been figuring out how predatory mantis shrimp evolved such fast, powerful forelimbs for crushing the shells of the snails they eat and snagging prey swimming by, and what influenced their evolutionary trajectories. These invertebrates use what’s called a four-bar linkage, in which components of the forelimb act (mechanically speaking) as four “bars” connected end to end via movable joints to form a closed loop that can resemble a parallelogram. This arrangement abounds in nature and in human-engineered devices, such as locking pliers. Many researchers had assumed each bar had a similar influence on the forces produced and would be equally likely to evolve.
But that’s not what Patek and Muñoz found. By comparing bar lengths in 36 species with known relationships on the mantis shrimp family tree, they showed the shortest bar often changed as a new species evolved. That bias most likely arose because the shortest bar has the most dramatic effect on mechanical output, amplifying force more than any of the other three when it got shorter.
Patek and Muñoz made a similar discovery in certain fish with four-bar linkages in their jaws. This arrangement enables wrasses, cichlids, and sunfish to snap open their mouths extra wide and suck in prey, and the proportions of the bars in these fish vary depending on whether their prey is fast moving or stationary. Fish that chase faster prey have shorter short bars that generate more force and enable them to snap prey faster, the researchers reported in 2018. Much like behavior, biomechanical principles can sculpt the rate, pattern, and direction of evolution, Muñoz says.
In 2020, Muñoz won the Society of Integrative and Comparative Biology’s award for achievements in biomechanics. The following year she won the society’s comparative physiology award, becoming the first researcher to win both. “She is able to integrate diverse concepts in novel and interesting ways, says Raymond Huey, an emeritus ecologist at the University of Washington, Seattle. “Most people focus on ‘A’ or ‘B,’ a few can add A plus B, but Martha can multiply them.”
IN 2019, Muñoz landed her current job at Yale, where ecology and evolutionary biology department chair Thomas Near has been working to recruit faculty from underrepresented groups and provide a welcoming environment. In his interview with Muñoz, Near acknowledged the challenges she’d face if she took the job. “He understood that I would have to battle the diversity dimension as well as the academic dimension,” she says.
These were challenges she knew well, having previously experienced the “imposter syndrome” common among scientists from underrepresented groups, who feel (however unjustly) that they don’t deserve to be where they are. She’d endured slights and insults as well, such as being told she’d have to work hard even though she was a diversity hire. The reality, Muñoz says, is that scientists from underrepresented groups feel tremendous pressure to work even harder than their peers. “We know that we have undue visibility due to our sparse numbers and correspondingly, we have a responsibility to be the best role models possible.”
At Yale, Muñoz signed up to be a resident fellow in one of the colleges, where undergraduates are housed, so she and Vigo, her German shepherd, would be embedded in the community. Seven months after arriving in New Haven, Connecticut, COVID-19 grounded her—and gave her time to write a proposal for the grant that now supports the salamander work.
The dozens of woodland-dwelling Plethodon species in the southern Appalachians posed irresistible evolutionary questions. These salamanders look so much alike, and the environment they live in seems so uniform, that researchers have considered them an example of “nonadaptive” radiation, in which organisms split into multiple species through the accumulation of random mutations and the slow march of geographic isolation, not because they have evolved different traits. Based on her work on lizards, Muñoz suspected there might be more to that story. Perhaps these salamanders have evolved behavioral or physiological differences that make each species distinctive, or perhaps their environment isn’t as uniform as it appears, creating subtle selective pressure to diversify.
Like about two-thirds of the 700 or so species of salamanders, Plethodon species lack lungs, breathing instead through their skin. Lungless salamanders have limited oxygen to fuel their activities and must make sure their skin stays moist enough to absorb as much oxygen from the air as possible. They’ve adapted by hiding and resting during the day, and by having a simplified nervous system to reduce their energy needs. As the evening cools down, they emerge from burrows, leaf litter, or rock crevices to sit, wait, and nab any insects or other prey that wander by. Most salamanders spend their lives within just a few square meters.
In the past few years Muñoz and her colleagues have collected thousands of observations of these animals, carefully recording the temperature and humidity at the exact spot where each salamander was spotted and at many other spots nearby. Already, they have documented diverse “microhabitats” in their study area—at the base of trees, under rhododendron leaves, on rocky ledges, and elsewhere—each with a specific range of temperature and humidity.
In a 2020 study of 26 species led by her postdoc Vincent Farallo, now at the University of Scranton, Muñoz and colleagues found that each prefers a slightly different combination of temperature and humidity. By choosing certain spots, each species is hydro- and thermoregulating, Muñoz says. Overall, the species mostly fall into two groups. One chooses warm, wet surroundings, where the moisture helps their skin absorb oxygen. “If their environment is wet, then they can capitalize on warmer temperatures,” which allows them to be more active, Muñoz explains. A second group can tolerate drier environments—but must opt for shade or other cooler places to keep from dying out.
Muñoz hosts hundreds of salamanders from dozens of species in her lab, where she and colleagues are measuring metabolic rates, water loss rates, preferred temperatures, heat tolerance, cold tolerance, and other traits. They hope to learn whether the animals’ preferences for specific spots, combined with physiological adaptations, may be contributing to the formation of new species.
So far they’ve found that resistance to water loss varies considerably among species, suggesting this physiological trait is evolving rapidly. Species that are less tolerant of water loss prefer wetter environments in the wild, whereas species that are more resistant to desiccation can use drier environments. If salamanders have chosen different microhabitats to suit their different moisture requirements, some populations could be becoming isolated from others, potentially setting the stage for them to become a new species.
AFTER WORKING IN THE LAB all summer, Muñoz’s students are eager to see the salamanders in their native habitat. The first night out is challenging, as the species they’re seeking proves elusive. But by the second night the students know the routine better, and they’ve set their sights on a different species that proves to be more plentiful. Anderson, with the aid of the new walking stick, catches a few to help the group meet its goal. And Buenrostro, who as a youth worked alongside his mom packing fruit, shows no fear as he digs into the dirt. They finish up before midnight, far earlier than expected. “You guys are awesome,” Muñoz says. “In one day, you figured it all out.”
Such encouragement is quintessential Muñoz, says Jessica Coutee, one of the students on the trip. Coutee, an Army veteran, admits she wasn’t sure what to make of Muñoz when they first met. Muñoz was wearing an elegant red dress as she led a group of veterans on a tour of Yale’s natural history museum. But she didn’t hesitate to don a pair of long yellow gloves and plunge her hands into a tub of chemicals to pull out a preserved giant iguana to show the group. “When you look at her, you might think she’s a girly girl, but she’s not,” Coutee says. Coutee, who calls herself Louisiana Creole as she’s a mix of Black, French, and Native American, is part of the first generation in her family to go to college. She, too, has wrestled with imposter syndrome, but not in Muñoz’s lab. “I feel I belong,” she says. “It’s an unbelievable feeling that I just don’t want to let go of.”
Providing a nurturing community for students of all backgrounds is Muñoz’s goal. “The first step into science is the hardest, so I try to make it as easy as possible,” she explains. Meanwhile, she’s still trying to figure some things out for herself. She is thinking about starting a family, but she has yet to receive tenure and still feels pressure to be perfect. “It feels as if I’m barely above water.”
Those closest to Muñoz say she works too hard, and she doesn’t deny it. But she says her work keeps her optimistic. “What nature is teaching us is that—like the lizards and salamanders I study—we are not passive vessels at the whim and mercy of our environments,” she says. “While we cannot extract ourselves from existing in a certain environmental context, I see hope and possibility in our future.”
Which anole species will grace the pages of this year’s calendar? Pictured here is Anolis allisoni. Photograph from Wikimedia Commons.
The Anole Annals Photo Contest: 2022 Edition
Welcome to the Anole Annals Photo Contest! As in previous years, we at Anole Annals want your best anole photographs for our 2023 calendar.
Here’s how it works: anyone who wants to participate can submit their favorite photos. The editors of Anole Annals will choose a set of 30-40 finalists from that initial pool. We’ll then put those photos up for a vote on this blog, and the 12 winning photos will be chosen by readers of Anole Annals, as well as a panel of anole photography experts. The grand prize winning photo will be featured on the front cover of the 2023 Anole Annals calendar, and the second place winner will be featured on the back cover; both photographers will win a free calendar!
The Rules
Submit your photos (as many as you’d like) as email attachments to anoleannalsphotos@gmail.com. To make sure that your submissions arrive, please send an accompanying email without any attachments to confirm that we’ve received them. Photos must be at least 150 dpi and print to a size of 11 x 17 inches. If you are unsure how to resize your images, the simplest thing to do is to submit the raw image files produced by your digital camera (or if you must, a high quality scan of a printed image). If you elect to alter your own images, don’t forget that it’s always better to resize than to resample. Images with watermarks or other digital alterations that extend beyond color correction, sharpening and other basic editing will not be accepted. We are not going to deal with formal copyright law and ask only your permission to use your image for the calendar and related content on Anole Annals (more specifically, by submitting your photos, you are agreeing to allow us to use them in the calendar). We, in turn, agree that your images will never be used without attribution and that we will not profit financially from their use (the small amount of royalties we receive are used to purchase calendars for the winners). Please only submit photos you’ve taken yourself, not from other photographers–by submitting photos, you are declaring that you are the photographer and have the authority to allow the photograph to be used in the calendar if it is chosen.
Please provide a short description of the photo that includes: (1) the species name, (2) the location where the photo was taken, and (3) any other relevant information. Be sure to include your full name in your email as well. Deadline for submission is November 1, 2022.
Good luck, and we look forward to seeing your photos!
The Puerto Rican Crested Anole (Anolis cristatellus)
Hurricanes are powerful storms that shape ecosystems by removing or displacing individuals. Additionally, hurricanes can change habitats due to tree mortality, damage and/or landslides. Ecosystem changes caused by hurricanes can impact species diversity. For example, following Hurricane Hugo, some insects thrived due to higher abundances of new young leaves as the canopy regenerated. On the other hand, canopy openness led to warmer and drier forest conditions which negatively affected other species. While we have several examples of how hurricanes impact species in forest environments, virtually nothing is known about how hurricanes affect urban species..
Hurricane in the city:
Cities can be quite different than non-urban ecosystems resulting in diverging ecological and evolutionary trajectories. Often, green spaces are highly cultivated which directly affects which species are able to exploit city environments. In this study, my co-authors and I evaluated the urban exploiter Anolis cristatellus to contrast population density and species composition in the months following Hurricane Maria.
Relative gust speed in knots of Hurricane Maria in the municipalities of Puerto Rico. Brighter colors show regions that experience the strongest winds. The letters correspond to the location of paired urban and forest sites. Pictures show the sites four months after the storm.
Anole populations after the storm:
Hurricane Maria was a powerful category 5 storm that made landfall in Puerto Rico in 2017 near the southeastern region of the island. As such, eastern locales experienced stronger winds in contrast to more western regions. We began our study four months after the hurricane and visited sites again eleven and sixteen months after the storm. The main takeaway we found was that irrespective of when we visited, forest sites had nearly double the number of lizards as urban sites. Sites in the east had the lowest population numbers at four months after the hurricane and showed nearly a doubling in population size between four and eleven months afterward. We presumed that this is due to higher mortality at these sites since they experience stronger winds associated with the hurricane.
Estimated lizard density per hectare. Forest sites are shown in green and urban sites in blue. Sites in San Juan had the lowest population density four months after the hurricane and showed population growth in the following months.
City humans as ecosystem engineers
An unexpected finding of this study was documenting how new plant growth following the hurricane facilitated the colonization of a bush specialist anole ecomorph at one of our sites. Four months after the hurricane, the forest floor consisted of leaf litter and downed trees and tree branches. However, both eleven and sixteen months afterward, new plants had established exploiting access to light resulting from the open canopies. Access to shrubs and young plants provided the preferred habitat of the grass-bush ecomorph Anolis krugi, a species that was not previously seen within that forest plot. In contrast, urban environments remained relatively unchanged. All of the downed branches and trees were quickly removed. Thus, while forest habitats and the ecosystems they support appear to be altered dramatically by hurricanes, human intervention maintained urban habitats near constant conditions during the extent of our study. Future studies might consider how human intervention in urban habitats affects ecosystems and the species they support.
Anole perching on a tree trunk in Ogasawara. (Photo: Naho Mitani)
The Ogasawara Islands are isolated oceanic islands with a subtropical climate located 1,000 km south of Tokyo. They are very attractive islands with many endemic plants and animals. However, those interested in nature may notice that there are few sounds of insect wings or signs of insects in the forests on Chichijima Island, an inhabited island within the Ogasawara Islands.
I first saw the green anole when I was involved in a project to eliminate introduced feral goats in Ogasawara. Wildlife management and conservation is my specialty. In this field, the problems of overabundant mammals such as deer and invasive introduced species are important issues. Researchers and practitioners who love animals frequently discuss the efficient capture of these animals and the eradication of invasive species at academic conferences.
When I attended conferences on reptiles, there were studies on conservation of reptiles that are affected by habitat destruction or non-native species. However, there were only a few studies that were oriented toward taking action against reptiles that cause damage to ecosystems as invasive species. Therefore, I thought I might have something to contribute, even though I am not a herpetologist.
In our first study of anoles published in 2015, we tested in the laboratory and in the field to see if we could attract them with a bait. If the bait could be seen moving, it could attract anoles up to about 2 m, even if it was in a transparent container. However, non-hungry anoles were not interested at all even if there was a bait in front of them. After this study, we wondered if it would be possible to identify their preferred location as a perching tree and capture them intensively. When we studied preference by tree species, they preferred the screw pine.
In the latest paper, I re-tabulated the data from the tree species preference study by trunk diameter. Anoles avoided tree trunks thinner than 1 cm in diameter, but had no preference by diameter for trunks larger than 2 cm. Except for very thin trunks, this means that trunks of any thickness are used according to their frequency of occurrence.
These behavioral traits may be a disadvantage when trying to capture green anoles and reduce their numbers. They are not attracted to dead, immobile baits; they are not interested in baits unless they are hungry themselves; they prefer the screw pine, but use other trees as well. Conditions for high-frequency use of sites are not clearly limited. Controlling lizard populations may be more difficult than for mammals.
On the Ogasawara Islands, where there are many endemic species, chemicals such as insecticides cannot be used easily. Also, consideration must be given to the bycatch of non-target species. We must improve our measures step by step to break through this difficult challenge.
Or perhaps we need to think differently from the way we capture mammals and insects. I assume that there would not have been many occasions in human history when we would have wished to capture a large number of reptiles in an efficient manner. It would be a great help if researchers in various fields are interested in controlling reptile numbers. In this regard, it is fortunate for those of us involved in anole control in Ogasawara to publish an article on the subject in Anole Annals, which attracts many people interested in lizards.
Green anoles have become a cause for concern in Japan, as the arrival of this invasive species commenced the decline of several range-restricted arthropods. Credit Judy Gallagher, Wikimedia Commons.
While green anoles may be a pleasant sight throughout their native range, they’ve become cause for concern in Japan–just one region of the Pacific where this specieshas invaded and become successfully established. The arrival of these anoles initiated a decline of several endemic arthropods, propelling a handful of subsequent studies on the invasion biology of this species. The most recent contribution to Anolis carolinensis ecology and biology in Japan is from Mitani (2022), who collected and analyzed perch ecology data on the Ogasawara Islands–check it out!
New literature alert!
Selectivity of Perch Diameter by Green Anole (Anolis carolinensis) for Trapping in Ogasawara
In the Ogasawara Islands adhesive traps are the primary means of controlling non-native Anolis carolinensis. If the types of tree trunks most frequently used by this lizard are identified, trapping efficiency can be improved by concentrating traps at such points. To analyze selectivity by trunk diameter, the diameters of 270 tree trunks used by the lizards and 1,024 tree trunks in the study area were measured. The analysis indicated the lizards avoided trunks of 1 cm or less in diameter. On the other hand, trunks with diameters over 2 cm appeared to be used randomly, regardless of diameter size. The diameter class distribution of trees varies by region and by forest. The range of tree trunk diameters commonly used by lizards is thus expected to vary by location. It would be advantageous to develop a capture technique that is effective for trunks and branches of various diameters.
I can’t call myself a herpetologist, let alone an anologist, these days – now I mostly work on freshwater fish in Aotearoa/New Zealand, though I have dabbled in collaborations on native NZ geckos and skinks. Nonetheless, I was pleased to recently publish a paper on Puerto Rican anoles that was a decade in the making.
My one proper field season with anoles was back in 2012 when I was a postdoc with Jonathan Losos. I tried some experimental enclosures that didn’t ultimately work out, and took some pictures that contributed to a macroevolutionary study of dewlap size. In between these projects, I decided to pull together a dataset of several niche dimensions in the anole community around the El Verde Field Station. My undergraduate assistant Tanner and I collected data from 200 anoles of six species (Anolis pulchellus, A. krugi, A. cristatellus, A. gundlachi, A. stratulus, A. evermanni) in three ecomorph classes, with the idea to measure how niches were partitioned among ecomorphs, species, and sexes. We measured the usual perch characteristics and body temperature, and also collected diet samples non-lethally using gastric lavage (stomach flushing).
Nothing much happened for some time, as I had moved on to a second postdoc and then my current job at the University of Otago. A few years ago when Jonathan was clearing out his former lab, I put out a call for interest in the stomach samples that were still sitting in a drawer, and was lucky enough to spark Sean Giery’s interest in a collaboration. Sean, now at Penn State, has plenty of experience counting terrestrial invertebrate samples, and he made quick work of processing the stomach contents.
Now that the data set was complete, I just had to find some time to revisit it. Last summer I had study leave on Rēkohu/Chatham Island, and made use of the down time between fieldwork days to get the analysis done and written up. We used hierarchical analyses to estimate how much of the variation in perch characteristics*, body temperature, prey size, and prey composition was partitioned among ecomorphs, species, and sexes.
*I used perch curvature rather than diameter as the second measure, along with perch height. Curvature is just the reciprocal of the radius, assuming a cylinder, but it allows missing data (anoles perched on walls or the ground, for which a measure of diameter is meaningless) to be included assuming that these have effectively zero curvature. It made sense to me, but I’d be interested to hear if other practitioners find this intuitive or not.
Percentage of variation explained by ecomorph, species, sex, site, individual (far right columns only) and residual variation in each niche dimension
The results aren’t going to blow your mind, and they confirm a lot of what is already understood about Greater Antillean anole communities. As expected based on decades of previous work, variation among ecomorphs explained the largest share of perch height and curvature, and variation among species nested within ecomorphs explained by far the most variation in body temperature. Perhaps the more surprising results were that ecological sex dimorphism explained little of the variation in any niche dimension, and that a large fraction of most dimensions was unexplained.
My feeling is that this approach to measuring multidimensional niche diversity in communities is more interesting than any particular result of this study. An idea I quite like is using this hierarchical approach for a comparative study of different communities. For example, one could ask how the partitioning of variation at each level changes over time as communities assemble, or how it changes across some natural or anthropogenic gradient. There is also room to do analyses that properly incorporate variation among individuals – we did include individual diet variation in a version of the analyses (using multiple items in one stomach as replicates), but the same individuals should be sampled repeatedly over time to see how consistent their foraging patterns really are.
All in all it has been fun thinking about anoles again after a long break. Our paper is available to read for free in the Journal of Zoology.
The large, colourful dewlap is an obvious defining characteristic of the anole. Understandably, then, there has been a lot of investigation (and speculation) on what the dewlap is used for. Without doubt it’s for social communication, but to communicate what. Historically, the dewlap was thought to be used for species recognition, which remains a reasonable explanation today. But a typical assumption made by many anole researchers and evolutionary ecologists alike is the dewlap, and specifically its size, is effectively an ornament used to attract mates or advertise potential fighting ability among territorial rivals. In other words, the evolution of the dewlap is the product of sexual selection.
