S.A.’s Common Critters: Nothing common about the green anole, San Antonio’s most common lizard

The male green anole has a throat fan called a dewlap that’s much larger than the one on females.Photo: Tongho58 /Getty Images

The Marvel comic book character Anole, who is named after the lizard.Photo: Marvel Entertainment

San Antonio audiologist Sarah Baade takes photos of the green anole lizards around her home gardens.Photo: Sarah Baade

San Antonio audiologist Sarah Baade takes photos of the green anole lizards around her home gardens. This is a closeup of one of her Instagram posts.Photo: Sarah Baade

Sarah Baade practically considers anole lizards her personal gardeners. The green little reptiles have a knack for keeping her company at her San Antonio home while she tends to her front yard tomatoes and backyard squash, poking out their slender heads from under her plants to stare at her.

She calls it a mutually beneficial relationship. The anoles eat any pesky bugs, and Baade rewards them with a free drink whenever she waters her gardens.

But there’s something else these simpatico green thumbs share: The joy of silence.

“It’s kind of my peaceful quiet time,” said Baade, who works as an audiologist. “They are my peaceful, quiet companions when I’m gardening.”

Anole lizards, the most common lizards in and around San Antonio, may not make much noise, but they sure make an impression — especially now as we see them more often while we spend more time in and around the house. And take it from another anole fan, one who’s studied them for nearly 20 years, there’s nothing common about this so-called common lizard.

“I think they’re incredibly charismatic,” said Michele Johnson, a biology professor at Trinity University who runs the kid-friendly website, lizardsandfriends.org. “I think that they’re a really interesting lizard because they seem so familiar, and yet there’s still things about them that we haven’t figured out yet.”

Here are some familiar and not so familiar facts about the anole.

Tomato, tomato. Anole, anole. San Antonio is home to the Carolina anole (Anolis carolinensis), sometimes just referred to as the green anole.

Anole is pronounced “ah-NOH-lee”, though Johnson noted most scientists say anole like “ah-NOLE.” She doesn’t think there’s one right way to say the name.

Anoles range beyond the Carolinas. The Carolina anole is native to North America and ranges across the southeastern United States, from around the middle of Texas east and up through the Carolinas. The lizard prefers warm and moist environments with trees, though you’re sure to spot them just about anywhere else there’s foliage, from forests and roadsides to lawns and doorsteps.

It’s easy being green. The Carolina anole also is known as the green anole for its bright, verdant color. The anole can change color into shades of brown, but that doesn’t make it a chameleon. Chameleons are not found in the Americas. Rather, anoles belong to the iguana family of reptiles.

Hey, baby, do you like my camo? Yes, an anole’s ability to change color can help it blend in with its surroundings, which is great for hunting insects and avoiding predators. But most anoles change color as a sign of dominance or sexual attraction, rather than trying to blend in.

“We know for sure it’s not camouflage,” Johnson said. “There’s been several studies.”

Little green men and women. Male and female anoles look almost exactly alike save for two distinguishing features. The female often sports a white dorsal stripe along her back, while the male displays a larger throat fan, or dewlap, that’s bright red and three times the size of the female’s fan.

Long tails, short bodies, short life spans. Anoles range in size from 5 to 8 inches long, and more than half of that is tail. Anoles live only around two to three years in the wild. The lizards are popular pets though, and can live up to seven years in captivity.

Days spent in the trees. Anoles are diurnal, meaning they’re active in the daytime. They’re also arboreal, meaning they live in trees.

They really toe the line. Johnson noted anoles have big toe pads that allow them to cling to surfaces.

They also cut and run. An anole will shed its tail to escape a predator. The twitching limb serves as a distraction for the lizard’s escape. A new tail will grow back, though not as long or as colorful as the original.

A bug’s life for breakfast, lunch and dinner. Anoles eat all sorts of insects, including moths, crickets, ants and spiders.

Keep off the dudes’ turf. Male anoles are extremely territorial and will fight other males to preserve their areas for themselves.

Self-reliant hatchlings. A few weeks after mating, a female anole will lay her first egg, then lay another every other week until she reaches around 10 eggs. The hatchlings then emerge 30 to 45 days later. The babies must fend for themselves without mother or father to care for them.

“I know that they had babies in my front garden because I’ve seen the babies,” Baade said. “It’s cool to see them scurry around.”

The anole is one of the X-Men. The Marvel comic book character Anole is one of the lesser-known mutants to join the heroic X-Men. The openly gay young hero exhibits lizardlike traits and abilities, including green scaly skin and the power to grow back lost limbs.

A first in genome sequencing. As part of scientists’ efforts to better understand the evolution of various animals, the green anole was the first reptile to have its entire genome sequenced. Johnson said the lizard was chosen because it has a small body and a fast reproduction time — and it’s way easier to keep in a lab than, say, a crocodile or snapping turtle.

She noted that sequencing the green anole has since led to a better understanding of such processes as forming eggs and regenerating tails. Take that, GEICO Gecko.

Living High with a Cool-Cold Anole – Part II

By Miguel Angel Mendez Galeano

On August 18, 2020

In All Posts

Illustration of Anolis heterodermus on a Frailejon inflorescence (Espeletia grandiflora). Illustration: Sebastian Perez.

Continuing with my adventure with Phenacosaurus (see Part 1 here), during the process of publishing papers from my thesis about thermoregulation in the high Andean lizard Anolis heterodermus , I realized that I only studied one population of this species, but some populations living above 3000 meters of elevation in the subparamo and paramo tropical andes ecosystems, as well as others that are below 2600 m. Furthermore, Martha and I evaluated only thermoregulation, but other thermal traits remains unknown. Despite not having grants and without have been a postgraduate thesis, I decided to expand my research and study whether thermoregulation, thermal tolerances and thermal sensitivity vary with elevation. I expected to find that at high elevation, lizards would be more active thermoregulators, eurythermal and cold tolerant, as happens in other Anolis lizards like the cristatellus and cybotes species groups.

To investigate these questions, I took new data during 2016 with Martha Calderón at two new localities: Chicaque Natural Park, a cloud forest reserve at 2000-2600 m elevation, and Matarredonda Ecological Park, a subparamo to paramo reserve at 3200-3400 m elevation. This time we invited our colleague and Martha Msc. student Felipe Paternina, who had done his thesis research on thermoregulation and extinction risk by climate change in the high-Andean nocturnal snake Atractus crassicaudatus. We also took data on Gachancipa, a municipality close to Tabio. At the beginning of this year, after the Covid-19 Pandemic, fortunately our second paper was published in the Journal of Thermal Biology.

Chicaque Natural Park (left) and Matarredonda Ecological Park (right)

First of all, we did not find changes in thermal preference range between the three localities. Similarly, cold tolerance (CTmin) and thermal performance breadth were similar along the elevational gradient. Nevertheless, the most exciting discovery was that cold tolerance (CTmin) is very low (4.4°C in Matarredonda) and thermal performance ranges are wide. Surprisingly, CTmin in Chicaque, the lowest altitude, was 6.2°C, even though the potential lowest body temperatures at night could be only 10°C (calculated as operative temperatures with our null-models of Anolis heterodermus). This clue makes us think that maybe cold tolerance is constant due to a niche conservatism: during Pleistocene glaciations, Andean ecosystems were colder than now, and maybe this trait did not evolve when climate became warmer because there is no selective pressure for that. Definitely, Anolis heterodermus is the king mountain of anoles (in fact, it has a co-osified cranial crown).

Vertical thermal gradient to measure thermal preference of Anolis heterodermus. Figure from Méndez-Galeano & Calderón-Espinosa (2017)

Null model of Anolis heterodermus to measure operative temperatures in the field; in this case, the model was placed on a potential perch.

As well as with cold tolerance and thermal preference, critical thermal maximum and thermal sensitivity did not change with elevation; however, thermoregulation does: at both low and high elevations, this species has to face thermal constrains, like a cold and narrow temperature range of the Chicaque cloud forest due to its canopy cover, or the extreme fluctuating temperatures, with tendency to the coolest regimes in our study, in the Matarredonda subparamo. To deal with that, individuals become thermoconformers, contrasting in this mode with the seasonal trends in thermoregulation in Tabio. We attribute this change to the fact that seasonal changes can be behaviorally compensated with active thermoregulation, but elevational changes are more extreme, and the species have to resign to be active at suboptimal temperatures and exist under the cold range of this extreme ecosystem.

Measuring locomotor performance to assess thermal sensitivity on Anolis heterodermus. There is a very slow lizard, which the local people call “The Andean Chameleon.”

Thermoregulatory adjustments also exist at other temporal scales, such as day-by-day. At the highest elevation, subparamo and paramo days could be extremely different from one day to the next; on some days, the sun could burn your face, while on other days, you could not see anything due to the cloud cover. So, we evaluated thermorregulation between these regimes, too, and observed that on cloudy days, Anolis heterodermus remained a thermoconformer, but on sunny days, the thermal quality of the habitat offered some optimal microhabitats, and this species takes advantage by changing from thermoconformity to active thermoregulation on a daily temporal scale. Undoubtedly, this species is a thermo-oportunist, plastic in its thermoregulation, and showing us that general patterns observed at only one scale do not always tell the complete story.

Our findings placed this species closer to the static hypothesis of the evolution of thermal physiology due to behavioral buffering on selection, better known as “The Bogert Effect.” Also, thermoregulation is so dynamic, that Anolis heterodermus can be an active thermoregulator in high thermal quality habitats (or times) and a thermoconformer when the habitat become so cold or so fluctuating that thermoregulation is not feasible.

Other reptiles from the Bogotá Savannah, Eastern Cordillera of Colombia, which could be at extinction risk by climate change and which we study in our research group. From left to right: Anadia bogotensis, Atractus crassicaudatus*, Riama striata, Stenocercus trachycephalus. Photos: *Uber Rozo, Guido Fabian Medina.

Now, after all of this, the cold reign of our highland king is threatened by climate change, the effect of which could be devastating for tropical biota, especially to endemic species. Climate change puts high-elevation reptiles in a vulnerable situation due to a restricted possibility to distributional displacements, taking them to a dead end, upwards, what is called “the mountaintop extinctions.” Now it is our responsibility to, at least, predict the potential extinction risk by climate change of Anolis heterodermus and other co-distributed reptiles with our thermal data in order to prevent the possible loss of our cool-cold anole forever. Stay tuned for the final part of this trilogy of the thermal biology of Anolis heterodermus, our Andean chameleon.

Cites:

Méndez-Galeano, M. A., & Calderón-Espinosa, M. L. (2017). Thermoregulation in the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) at high elevation in the Eastern Cordillera of Colombia. Iheringia. Série Zoologia 107.

Méndez-Galeano, M. A., Paternina-Cruz, R. F., & Calderón-Espinosa, M. L. (2020). The highest kingdom of Anolis: Thermal biology of the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) over an elevational gradient in the Eastern Cordillera of Colombia. Journal of Thermal Biology 89: 102498.

How Well Can Anoles See Each Other’s Dewlaps in Different Environmental Conditions?

By Nick Herrmann

On August 16, 2020

In New Lit Abstracts

A male Anolis sagrei flashing its dewlap

New literature alert!

The interacting effects of total light intensity and chromatic contrast on visual signal visibility in an Anolis lizard

In Animal Behaviour
Fleishman, Wadman, and Maximov

Abstract

The sensory drive hypothesis states that selection acts on signals to make them more detectable in the habitat conditions in which they occur, resulting in signal divergence for species occupying different habitats. For colour signals, visibility depends on the luminance contrast and the chromatic contrast between the signal and the viewing background. Sensory drive has been tested in studies of the colourful dewlaps of anolines occupying different habitats. These studies found that red or orange dewlaps were more visible than yellow or white dewlaps across all habitat types, counter to the predictions of sensory drive that a species’ signal should be more visible in its own habitat than in habitats of other species. However, in these, and other sensory drive studies, chromatic contrast was calculated with a visual perception model that assumed that total light intensity has little or no effect on chromatic contrast perception. We carried out behavioural experiments testing the probability of detection of green, yellow and red stimuli presented against luminance-matched green backgrounds, at low and high light intensity typical of shaded and unshaded habitats. We found that the red stimulus was most detectable in the high light condition, while in low light, yellow and red stimuli were equally detectable. We modelled the stimuli with a receptor noise model that takes total light intensity into account. The model predictions were consistent with the behaviour results. We conclude that there is an important interaction between total light intensity and chromatic contrast in determining the visibility of colour signals, which should be taken into account in visual ecology studies. For animals with small eyes, shade level, which strongly influences total light intensity, may be as important as, or more important than habitat spectral quality in the evolution of signal colour diversity through sensory drive.

Read the full paper here!

#DidYouAnole – Anolis longiceps

By Chelsea Connor

On August 13, 2020

In All Posts

File:Anolis longiceps lizard.jpg - Wikimedia Commons

Photo by USFWS R. Colon

Hope you are all having a great week!

I have searched high and low for this anole and now I’m here to present to you, Anolis longiceps.

This anole is found only on Navassa Island. Navassa is 76 km west of Haiti, has an area of 5.4 km² and is uninhabited (by humans). The introduction of cats and dogs, as well as goats that contribute to the destruction of vegetation, have led to the Navassa Anole being listed as Vulnerable by the IUCN. The island also had faced habitat degradation from mining.

Navassa Anole males can get up to 83 mm (SVL), while the females are at about 76 mm. Some have light spotting which is yellow-ish in their green phase and white in their dark phase.

The name longiceps means “longhead” and refers to the anole’s snout which is described as long and tapering to a point, much like A. maynardi. Its dewlap is orange with white scales.

These pictures appear to be of the holotype (a specimen used to describe and name a new species) from the Smithsonian Institution’s Division of Amphibians and Reptiles at the NMNH.
There don’t seem to be any other pictures I can find of this anole, but if you are aware of any, please let me know!

Anolis Lizards that Colonize Islands without Other Anoles Lose Their Parasites and Thrive: Experimental Study in Panama

By Jonathan Losos

On August 11, 2020

In All Posts

Anolis apletophallus. Photo credit: Dario – https://www.inaturalist.org/photos/31736257

From a press release from the Smithsonian Tropical Research Institute:

When the U.S. flooded Panama’s Chagres River valley in 1910, Gatun Lake held the record as the world’s biggest reservoir. This record was surpassed, but researchers at the Smithsonian Tropical Research Institute (STRI), who are now studying invading lizards on the tiny islands that dot the lake, discovered that islands with native lizards act as another kind of reservoir, harboring the parasites that control invaders. The study, published in the journal Biology Letters, is valuable experimental evidence that biodiversity is better, making ecosystems more resistant to invasion.

As part of another study to find out how many generations it takes for slender anole lizards (Anolis apletophallus) to adapt to climate change, a research team led by Christian Cox, a visiting scientist at STRI from Florida International University, and Mike Logan from the University of Nevada, Reno, transplanted lizards from the tropical forest on the mainland to the islands, which tend to be hotter and drier. Before the transplant, they did a general health check of the lizards that included counting the number of parasites (mites) on their bodies.

When they came back several times during the next two years to see how the lizards were doing in their new habitats, they recounted the number of mites.

“We found that on the islands with no resident species of anole lizard, the slender anole lizards that were transplanted to the islands lost their mites within a single generation, and the mites are still gone several generations later (up until the present),” Cox said. “Indeed, individual founding lizards that had mites during the initial transplant had no mites when they were later recaptured. In contrast, anole lizards that were transplanted to an island with another resident (native) species of anole lizard kept their mites for three generations, and some of the founders on the two-species island never lost their mites.”

“Our study turned out to be a large-scale experimental test of the enemy release hypothesis,” said Logan, who did this work as a three-year STRI/Tupper postdoctoral fellow. “Often, when an invasive animal shows up in a new place, all of its pathogens and parasites are left behind or do not survive, giving it an extra survival advantage in the new place: thus the term enemy release.”

The team also found that the two-species island had lower density and lower biomass per unit area of the invasive lizard species, indicating that the continued presence of the mites may be keeping their populations under control.

“Our study is a clear example of something that conservationists have been trying to communicate to the public for some time,” Logan said. “Diverse native communities sometimes function as ‘enemy reservoirs’ for parasites and diseases the keep down the numbers of invaders.”

Funding for this study was provided by the Smithsonian Institution, Georgia Southern University, the Theodore Roosevelt Memorial Foundation and the American Museum of Natural History.

#DidYouAnole – Anolis maynardi

By Chelsea Connor

On August 6, 2020

In All Posts

Photo by Mike Vallee

Hello there. I’m here to bring a bright spot to your day with a little weird lizard, as you do.

Anolis maynardi, is endemic to Little Cayman in the Cayman Islands and introduced to Cayman Brac, and while it looks like a few of the other anoles in the carolinensis series, this one has a really long nose. It also can have striping (marbling?) along its body.

This one even has checkering!

Like the other anoles, it is capable of a dark phase. I think this is one of the better ones I’ve seen.

Photo by Pat Shipman

Its been noted that they feed on nectar like a few other anoles too. The Little Cayman Green anole has a yellow dewlap and was (hilariously) described as “…apparently stupid…” in The Herpetology of Cayman Islands (1940) by Chapman Grant.

Its elongated snout is described as pincer- or tweezer-like, and possibly aids in catching flying prey.
Like with the other anoles in this group, female Little Cayman Green anoles have smaller, more proportional heads to their bodies.

A study looking at the population of these anoles on Little Cayman and the introduced population on Cayman Brac, found that the Cayman Brac population had a higher bite force. The morphological differences between the two populations may have occurred for a few reasons. Check it out!

The Schwartz-Zug Expedition to Cuba in 1958

By Aryeh Miller

On August 4, 2020

In All Posts

George Zug’s machete from one of his undergraduate collecting expeditions to Cuba (June-August 1958) where he accompanied his mentor, Dr. Albert (Al) Schwartz.

In the summer of 1958, Albright College in southeastern Pennsylvania concluded its spring semester. Upon the end of classes, in early June, herpetologist Al Schwartz and his then undergraduate mentee and student—George R. Zug—began the long drive south from Reading, PA to the Florida Keys. In Key West, Schwartz and Zug (now Curator Emeritus at the Smithsonian Institution’s National Museum of Natural History) boarded a car ferry headed for Havana, Cuba. The two were preparing for an expedition lasting more than two months collecting amphibians and reptiles across the western half of the country.

Cyclura nubila nubila from Cayo Largo, Cuba.

After setting up in Havana, Al and George ferried to Isla de la Juventud (formerly Isla de Piños), Cuba’s largest island outside the mainland, where they spent nearly 20 days on the northern half of the island surveying the local herpetofauna. The southern third of the island was inaccessible by car at the time owing to dense swamp, thus leaving a short flight as the only viable option. Al’s dread for flying made traveling to this southern region unappealing, but George, with convincing argument and promise of plentiful reptiles, successfully persuaded Al to board. The two then rented a boat in order to access a handful of remote islands off the southeastern coast, where they would collect a series of Cyclura nubila nubila, which were subsequently deposited at the American Museum of Natural History, along with many other specimens found. Other notable squamates collected included a new subspecies of Tropidophis, T. melanurus ericksoni (Schwartz and Thomas, 1960), which remains known only from Isla de la Juventud.

Cuban Side-blotched Curlytail (Leiocephalus macropus).

In mid-July, the two returned to mainland Cuba and traveled to a farmer friend’s residence in Santa Clara Province, but were quickly advised to get back into their silver van and return to Havana as a militant outpost was reportedly not far at the time. Their remaining days in Cuba were spent in Pinar del Río Province, which yielded many more new exciting contributions to the herpetofaunal diversity of Cuba, such as Tropidophis melanurus dysodes (Schwartz and Thomas, 1960), three new Leiocephalus subspecies (Zug, 1959), and Eleutherodactylus klinikowskii (Schwartz, 1959).

I thank George R. Zug for discussion of the expedition and the research derived from it.

Schwartz, A. 1959. The status of Eleutherodactylus pinarensis and a new species of the genus from western Cuba. Herpetologica 15: 61–69.

Schwartz, A., and Thomas, R. 1960. Four new snakes (Tropidophis, Dromicus, Alsophis) from the Isla de Pinos and Cuba. Herpetologica 16(2): 73-90.

Zug, G. R. 1959. Three new subspecies of the lizard Leiocephalus macropus Cope from Cuba. Proceedings of the Biological Society of Washington 72: 139–150.

How Do Island Anoles Respond to an Influx of Resources?

By Nick Herrmann

On August 1, 2020

In New Lit Abstracts

New literature alert!

Consumer Responses to Experimental Pulses Subsidies in Isolated versus Connected Habitats

In The American Naturalist
Wright, Yang, Piovia-Scott, Spiller, and Schoener

Abstract

Increases in consumer abundance following a resource pulse can be driven by diet shifts, aggregation, and reproductive responses, with combined responses expected to result in faster response times and larger numerical increases. Previous work in plots on large Bahamian islands has shown that lizards (Anolis sagrei) increased in abundance following pulses of seaweed deposition, which provide additional prey (i.e., seaweed detritivores). Numerical responses were associated with rapid diet shifts and aggregation, followed by increased reproduction. These dynamics are likely different on isolated small islands, where lizards cannot readily immigrate or emigrate. To test this, we manipulated the frequency and magnitude of seaweed resource pulses on whole small islands and in plots within large islands, and we monitored lizard diet and numerical responses over 4 years. We found that seaweed addition caused persistent increases in lizard abundance on small islands regardless of pulse frequency or magnitude. Increased abundance may have occurred because the initial pulse facilitated population establishment, possibly via enhanced overwinter survival. In contrast with a previous experiment, we did not detect numerical responses in plots on large islands, despite lizards consuming more marine resources in subsidized plots. This lack of a numerical response may be due to rapid aggregation followed by disaggregation or to stronger suppression of A. sagrei by their predators on the large islands in this study. Our results highlight the importance of habitat connectivity in governing ecological responses to resource pulses and suggest that disaggregation and changes in survivorship may be underappreciated drivers of pulse-associated dynamics.

Read the full paper here!

#DidYouAnole – Anolis brunneus

By Chelsea Connor

On July 30, 2020

In All Posts

Photo by Thomas Sanger

Hey there! Look at you! Back for more anoles.
You love to see it.

This week we are talking about Anolis brunneus, the Crooked Island anole!

Update from Crooked Island - Anole Annals

Like its name suggests, this anole is from Crooked Island in the Bahamas and can also be found on Acklins Islands.

Photo by S. Blair Hedges

This member of the A. carolinensis series isn’t bright green like the others, and can’t shift to it either. It’s brown and its colour change abilities consist of shifting to a darker brown or grey, some can shift to an olive tone, or they can enhance the prominence of blue on the heads of males.
They do have really nice marbling on their sides as well and the females are less conspicuous than the males.

It does have that pink dewlap consistent with its relatives though.

Photo by S. Blair Hedges

These anoles can get up to 76 mm (SVL) and, like the other members of the carolinensis Series, is a trunk-crown anole.
Like many other anoles, the males also have nuchal crest that they can erect.

Battle of Anolis Brunneus - Anole Annals
This last picture is one taken by Michele Johnson of a fight between two males. She got to see this fight on Crooked Island with Thomas Sanger (and two students) on a trip to research these guys!

Morphology Does Not Distinguish Candidate Species of Anolis distichus

By Tanner Myers

On July 28, 2020

In All Posts, New Research

Photo by Richard Glor

Anolis distichus, the North Caribbean bark anole, is probably best known by readers of Anole Annals for its striking variability in dewlap color among populations. Primarily based on these differences in dewlap color, Albert Schwartz published a monograph with descriptions for 18 subspecies distributed across Hispaniola and the Bahamas (1968). The large number of subspecies and the question of their origin has helped establish Anolis distichus as one of the most intriguing cases for the study of speciation in anoles. Do the subspecies of Anolis distichus represent geographic patterns in dewlap color variation? Or, are the subspecies evolutionarily isolated lineages worthy of species status?

Molecular genetic data have revealed several genetically distinct populations of Anolis distichus that appear to be at varying stages of the speciation process. However, with the exception of A. d. ignigularis and A. d. favillarum, these genetically distinct groups did not align with the subspecies described by Schwartz, corresponding better to geography than patterns of dewlap color variation (Geneva et al. 2015). Most recently, using genome wide markers and multicoalescent species delimitation methods, MacGuigan et al. (2017) identified six candidate species within A. distichus. The authors, however, did not update the taxonomy because the boundaries among the candidate species remained unclear.

To clear up those boundaries, we tested if the candidate species identified by MacGuigan could be distinguished by morphological characters. Because Schwartz considered scale counts along with dewlap and body color pattern in his monograph and was not able to recover any diagnostic differences, we focused on morphometric characters and measured 13 traits from more than 500 animals (available on Dryad). We conducted univariate and multivariate analyses to test if (a) any of the individual characters distinguished candidate species; and (b) if characters considered in aggregate could distinguish the candidate species. Because the candidate species are parapatrically distributed across Hispaniola, locality information has the potential to aid diagnosis. To account for this, we carried out comparisons of all candidate species together and only the pairs of candidate species that potentially come into contact.

Although ANOVAs recovered significant differences in mean character values, visual examination of violin plots showed that none of them were diagnostic for any of the candidate species. Discriminant Function Analysis (DFA) revealed clustering of some of the candidate species, but there was still substantial overlap in multivariate space and candidate species were diagnosed with poor accuracy. DFA did prove to be more accurate when asked to classify individuals only between the pairs of potentially co-occurring candidate species instead of all of the candidate species together. Ultimately, we still rejected the hypothesis that candidate species could be distinguished on the basis of our morphometric dataset due to gaps in our sampling and overall similarity among the candidate species.

Univariate and multivariate results from Myers et al. (2020). (A) Example violin plots for two characters, snout-vent length and head width. (B) Multivariate plots of DFA results.

Because both univariate and multivariate analyses did not recover support for the hypothesis that the candidate species could be distinguished by morphometric characters, we decided to test how many species were supported by the data. We tested alternative species delimitation scenarios with a model fitting approach that uses normal mixture models (Cadena et al. 2018). Normal mixture models consider morphological variation to consist of a mix of different normal distributions and, unlike DFA, does not require individuals to be assigned to different groups a priori. We tested the support for models specifying up to as many as 12 species and compared the support for these generic models to models specifying MacGuigan’s candidate species and Schwartz’s subspecies. The best supported normal mixture model specified two groups; however, the model specified a group containing 489 individuals and another with 24 individuals and followed no clear geographic trend. We scrutinized the principal components used to estimate these models and determined that longitudinal and vertical ear opening diameter were driving this result. We removed them and conducted the normal mixture model analysis with the reduced dataset and recovered a single morphological group.

Is Anolis distichus only one species? Do the candidate species lack distinguishing features? We weren’t comfortable making either conclusion. Our dataset of linear morphometric characters was not capable of distinguishing candidate species, but future datasets featuring other aspects of phenotypic variation e.g., geometric morphometrics, might. Larger, genome-scale datasets with more comprehensive geographic sampling than previous molecular genetic studies will also help address the question of species boundaries in A. distichus. We also discuss some possibilities for why we were unable to recover distinguishing morphological differences, including that local adaptation across Hispaniola’s environmentally heterogeneous landscapes has resulted in morphometric variation that does not align with candidate species boundaries. Ng et al. (2013) found that dewlap color in A. distichus is correlated with local environmental signaling conditions, which would explain why dewlap color does not correspond with putative evolutionary lineages in this group of lizards. Many of the morphometric traits we considered (e.g., limb length) affect ecological performance and may have responded similarly to selective pressures.

We were not able to resolve the confounding taxonomy of Anolis distichus in this paper, but I enjoyed the project and found it to be a very rewarding first publication. I was able to travel to the Dominican Republic to catch lizards twice as an undergraduate for this project and we were able to amass a large and geographically comprehensive dataset. Working on the taxonomy of this confounding group of lizards helped me realize my interest in speciation, which I plan to pursue further in my PhD. A lot of friends and collaborators helped with this project by assisting with fieldwork and providing input on manuscript drafts. And, of course, this work wouldn’t have been possible without my co-authors and mentors, Pietro de Mello and Rich Glor.

References

Cadena, C. D., F. Zapata, and I. Jiménez. 2018. Issues and perspectives in species delimitation using phenotypic data: Atlantean evolution in Darwin’s finches. Syst. Biol. 67:181–194.

Geneva, A. J., J. Hilton, S. Noll, and R. E. Glor. 2015. Multilocus phylogenetic analyses of Hispaniolan and Bahamian trunk anoles (distichus species group). Mol. Phylogenet. Evol. 87:105–117.

MacGuigan, D. J., A. J. Geneva, and R. E. Glor. 2017. A genomic assessment of species boundaries and hybridization in a group of highly polymorphic anoles (distichus species complex). Ecol. Evol. 7:3657–3671.

Myers, T. C., P. L. H. de Mello, and R. E. Glor. 2020. A morphometric assessment of species boundaries in a widespread anole lizard (Squamata: Dactyloidae). Biol. J. Linn. Soc. 130:813-825.

Ng, J., E. L. Landeen, R. M. Logsdon, and R. E. Glor. 2013. Correlation between Anolis lizard dewlap phenotype and environmental variation indicates adaptive divergence of a signal important to sexual selection and species recognition. Evolution 67:573–582.

Schwartz, A. 1968. Geographic variation in Anolis distichus Cope (Lacertilia, Iguanidae) in the Bahama Islands and Hispaniola. Bull. Mus. Comp. Zool. 137:255–309.