Why are there so many types of lizards?

Study sheds light on biodiversity of Anole lizard family trees

Date:  February 23, 2018

Source:  Arizona State University

Summary:

Researchers have sequenced the complete genetic code -- the genome -- of several vertebrate species from Panama. They found that changes in genes involved in the interbrain (the site of the pineal gland and other endocrine glands), for color vision, hormones and the colorful dewlap that males bob to attract females, may contribute to the formation of boundaries between species. Genes regulating limb development also evolved especially quickly.

Continued  

An evolving sticky situation- While many animals try to avoid sticky situations, lizards evolved to seek them out. An evolutionary biologist shows how different groups of lizards -- geckos and anoles -- took two completely different evolutionary paths to developing the beneficial trait of sticky toe pads. – via Herp Digest

Source: Michigan State University, 10/12/17

Travis Hagey, Michigan State University evolutionary biologist, shows how different groups of lizards - geckos and anoles - took two completely different evolutionary paths to developing the beneficial trait of sticky toe pads.

Credit: Luke Mahler

While many animals try to avoid sticky situations, lizards evolved to seek them out.

Travis Hagey, Michigan State University evolutionary biologist, shows how different groups of lizards -- geckos and anoles -- took two completely different evolutionary paths to developing the beneficial trait of sticky toe pads.

In a paper published in the journal Evolution, Hagey showed that anoles seemed to commit to a single type of toe pad, one that generates lots of friction. As a group, they were able to develop sticky toe pads early. Geckos, meanwhile, opted for an evolutionary "drunken stumble," and seemingly didn't commit to a single approach, instead evolving toe pads that generate plenty of friction in some species and others that excel at sticking directly to a surface.

The stumbling theory, formally known as the Brownian motion model, best explains gecko evolution. Different groups of geckos sought various approaches and jumped at adaptive solutions. They achieved the beneficial traits by pursuing different ways, moving forward some eras and backward during others, Hagey said.

Did anoles have but one option? Is there merely one evolutionary path to become the best tree-climbing lizard? Were geckos more laissez faire with evolution?

"We're trying to explain how evolution works and how predictable it is," said Hagey, who's part of MSU's BEACON Center for Evolution in Action. "Good science answers one question while producing more questions. Anoles and geckos are two different large groups of lizards. They live on different continents, and evolutionarily, they're separated by 250 million years of time. So even though they have some of the same traits, you can't assume that they were developed the same way.”

Evolution is a tinkerer, he added. Hagey likens it to a person who lives on a dirt road and decides to build a bicycle.

"But they can use only the parts they can get their hands on and make modifications and repairs until they get a bike they like," Hagey said. "Two different people might build two different bikes that both work well on dirt roads, but the process and steps they went though will probably be different. The same is true for geckos and anoles. They both evolved sticky toes but got there different ways.”

Hagey's research team included scientists from the University of Idaho, Cambridge, the University of London, and Lewis and Clark College.

In a related paper in PLOS ONE, Hagey chose to focus on limb length. Geckos and anoles live on trees and climb vertical surfaces. They have to deal with the same mechanical aspects, but did they take different paths to gain those advantages? Did they evolve traits that emphasized sprint speed over balance or vice versa?

"Studying sticky toe pads and limb length help scientists understand how and why animals are shaped the way they're shaped and the mechanics of their movement," Hagey said. "You'd think there would be only one good way to climb a tree or one good way to swim, but there are many."

For both studies, Hagey traveled to exotic locales in the Dominican Republic, Australia and Thailand. Visiting a breeder in Oklahoma allowed him to observe 15 lizard species from five continents. Overall, his research reviewed 30 species of geckos and 20 species of anoles.

The study showed that geckos generally have shorter legs than anoles. The scientists are unsure why this is the case, but once they factored in the length difference they made an interesting observation.

Lizards living on bushes, regardless of geckos or anoles, have long tails, striped backs and long legs. Those living on small branches in the canopy of a forest tend to be brown, with short tails, long snouts and short legs. These traits were consistent despite being separated by oceans or hemispheres.

"Even though we were able to find some cool similarities, we really don't know why, yet," Hagey said. "Maybe they're all adapting to be the best bush lizards or the best tree-climbing lizards and all heading toward the same evolutionary solutions."

Story Source:

Materials provided by Michigan State University. Note: Content may be edited for style and length.

Journal Reference:

            1          Travis J. Hagey, Josef C. Uyeda, Kristen E. Crandell, Jorn A. Cheney, Kellar Autumn, Luke J. Harmon. Tempo and mode of performance evolution across multiple independent origins of adhesive toe pads in lizards. Evolution, 2017; 71 (10): 2344 DOI: 10.1111/evo.13318

Caribbean Anoles Function as Model Organisms for Evolutionary Dynamics – via Herp Digest

The small lizards (Anoles) adapted to unique niches among dozens of Caribbean isles.

By Amber Dance, The Scientist, January 1, 2017

It’s not easy to snare a lizard. Evolutionary biologist Michele Johnson affixes a noose made of dental floss to a telescopic fishing rod to reach into the bushes and tree canopies where Caribbean anoles live. By the end of the summer field season, her students from Trinity University in San Antonio, Texas, develop a knack for it. “We almost always catch our lizards,” says Johnson.

She doesn’t just collect field measurements and observations; she’s taken 30 different species of anoles back to her lab to analyze their physiology. Anoles have become a favorite model for evolutionary biologists because of their extraordinary diversity—there are more than 400 species in genus Anolis—and because of how they originally populated the Caribbean islands. The relative scarcity of mammals, snakes, or birds on the islands left many niches open for the lizards to occupy.

As anoles—which also inhabit Central and South America—reached individual islands, their populations diversified into island-specific forms that occupy certain niches. For example, each of the four largest islands in the Greater Antilles (Hispaniola, Cuba, Puerto Rico, and Jamaica) hosts one or more species that are green lizards hanging out in the lower canopies of trees, and another group of short-limbed, slow-moving reptiles that perch on twigs. These are two of the six “ecomorphs” that scientists who study Caribbean anole species have defined. To be considered an ecomorph, a set of habitat specialists must exist on more than one island, though the species in each group differ between islands. And yet, other anole species belong to no particular ecomorph class.

Caribbean anoles offer scientists a sort of “natural experiment,” explains Luke Mahler, an evolutionary biologist and herpetologist at the University of Toronto. Each isle, with similar environments, acts as a replicate for how anoles underwent convergent evolution into ecomorphs. As a result, evolutionary studies of anoles have flourished in the past couple of decades—think Darwin’s finches, but scalier.

“They really are a good model system for lots of questions, from very small-scale molecular work all the way up to adaptive radiation,” says Jerry Husak, a physiologist at the University of St. Thomas in St. Paul, Minnesota.

The basic anole ecomorphs go way back in evolutionary history, found Jonathan Losos, an evolutionary ecologist at Harvard University. Emma Sherratt, now at Australian National University in Canberra, got a hold of 20 fossil anoles while a postdoc in Losos’s lab. The fossils dated back 15 million to 20 million years, when the lizards were preserved in amber on the island of Hispaniola. Some were in museums, others in private collections. Using CT scans, the Losos team examined anatomy to confidently assign these fossils to four of today’s ecomorphs; a couple other fossils might be part of a fifth (PNAS, 112:9961-66, 2015). “At least several of the habitat specialist types already existed,” concludes Losos.

Despite the countless hours biologists have spent studying Caribbean anoles, the genus seems to have plenty of surprises still in store. In addition to her ongoing studies of physiology and behavior in diverse anole species, Johnson has recently focused on how her local Texan anole, Anolis carolinensis, determines dominance. A. carolinensis, like many other anole species, adopts a strict mating hierarchy in captivity, with males battling each other for access to prime habitat and to females. In the field, the hierarchy is more complicated—a lizard defending his own territory is more likely to win a fight, she thinks. She figured the biggest males would also be more likely to triumph, either in the lab or the field, and thus achieve larger territory and more females to court.

In order to correlate body characteristics and behaviors with dominance, Johnson’s group set up a sort of lizard fight club, pitting anoles against each other in one-on-one cage matches, with a single perch to battle over. Winners tended to execute more visual displays, performing push-ups and head-bobs and expanding the showy throat skin known as a dewlap. They also chased and bit the losers, who tended to back away and to hide in a corner.

But larger anoles weren’t always the winners in captivity or in the field. “Body size doesn’t predict who wins these fights at all,” says Johnson. Instead, behaviors made a huge difference—the most aggressive lizards won their matches. A longer head also helped, perhaps because it looked to opponents like a serious biting weapon. In the field, animals with a wider head and powerful jaws occupied larger territories with more females present (Anim Behav, 118:65-74, 2016).

Body size still probably matters, Johnson says. She has not yet tested in field studies whether size might help an A. carolinensis male establish his territory or take over a vacated area. And at least in other anole species, bigger males sire more offspring.

Mahler also got a surprise from the anoles when, in 2010, he received an email from Miguel Landestoy, a Dominican naturalist who claimed he’d seen a new species. Mahler was initially skeptical. “Everybody thinks they’ve got a new species,” he says, yet “the Caribbean anoles are the best known anoles, by a long shot.”

Then Mahler opened Landestoy’s pictures. “Holy crap,” he said. “That doesn’t look like anything we’ve seen on Hispaniola.” The critter was huge, by anole standards—about a foot from nose to tail tip. It had short legs, a short tail, and a mottled greenish-gray pattern that suggested it could easily blend into a mossy or lichen-covered branch. “I bought the first cheap flight I could find,” recalls Mahler.

The other thing that struck Mahler about the new species—which he and his colleagues dubbed A. landestoyi—was that it looked similar to anoles found in Cuba. Their clade is called chamaeleonides for their creeping, chameleon-like movements and camouflage prowess. These particular kinds of anoles, scientists had assumed, were unique to Cuba. But here was another species, making its living in many of the same ways, on Hispaniola (Am Nat, 188:357-64, 2016). “This is an example of what might be a seventh ecomorph. . . . Evolution is more predictable than we have yet given it credit for,” says Johnson, who was not involved in the project.

“It’s amazing, in part, that anything new there could be found after all these years,” adds Losos, a coauthor on the study. “The age of discovery is not yet over.”

Look at me! Forest-dwelling anoles 'glow' to attract attention

Date: August 14, 2015

Source: University of Missouri-Columbia

Summary: See and be seen. In the elaborate game of seeking and attracting a mate, male anole lizards have a special trick -- they grab attention by perching on a tree limb, bobbing their heads up and down, and extending a colorful throat fan, called a dewlap. The dramatic 'glowing' effect, according to a new study, increases the efficacy of the male lizard's visual signal, making them stand out better to females.

Continued ...

An Embarrassment of Anoles - via Herp Digest

by Jonathan Losos , 4/11/13 NyTimes Blog-Scientist at Work 

Colonia Tovar, a small town in the mountains above Caracas, was founded by Germans from Baden in the 1850s. In recent years, it has become something of a tourist attraction. 

For the last leg of our lizard expedition, we’ve moved to Colonia Tovar, a quaint German-flavored town in the mountains above Caracas. Mercifully cool, the weather at 7,000 feet is a relief from the brick oven that is Maracaibo. So far, the trip has been reasonably successful. We’ve discovered new aspects of two little-known anole lizard species. We’ve also identified similarities and differences between these species and the habitat specialists that evolved on Caribbean islands. 

The last leg of the trip, however, promised to be the most challenging. Our primary quarry is the tiger anole, Anolis tigrinus. The tiger is another mystery. Living in the middle elevations, it is nearly identical in appearance to the small twig-using specialists in the Caribbean. But whether it actually uses narrow surfaces or behaves like a twig anole is unknown. 

What is known is that twig anoles are extremely difficult to find. They are well camouflaged in various shades of gray and green. Most species are small, move very slowly and often live high in thick tree vegetation. We did have good success in Colombia finding the twig anole-like variable-scaled anole, but they occupy a different habitat in the bushy Andean matorral, or scrubland, where the lizards are lower to the ground and more readily discovered. 

So if the twig anole is hard to find, and the tiger anole looks a lot like the twig anole — well, that tells you something about our prospects. As we set out to search for the tiger, we agree on a bet of unprecedented size — three candy bars — for the first person to find one. Candy bars are surprisingly expensive in Venezuela, but none of us were worried about the large ante. Rather, we all expected a fruitless day of lizardless searching, in recognition of the fact that none of us expected to find any. 

Shortly after arriving at midday, we began our search in the little patch of woods behind our rooms at Cabañas Heidelberg. One side of the property is a grassy hill sloping down to a small stream; on the other side there is a forest. Anthony Herrel of the Museum of Natural History in Paris walked down to the stream to begin searching the woods. Rosario Castañeda, a Colombian biologist, and I used our binoculars to scan the treetops from higher ground. “I’ve got one,” Anthony shouted up the hillside. 

Jonathan Losos A tiger anole on the prowl. 

As with our search for the variable-scaled anole a week and a half ago in Colombia, we had struck gold quickly. But this time the story was different. Our early luck wasn’t dashed by a quickly following drought. Moments later I spotted another tiger anole perched on a vine hanging down from high in the canopy. Out came the two video cameras. Then a third lizard marched into view. 

And that’s how it went all afternoon, one lizard after another. A veritable lizard cameo queue formed as we tried to keep track of the additional tiger anoles. There were as many as four at one point, most spotted by Anthony, waiting for their 30 minutes of fame. 

From watching nature documentaries on television and reading stories about researchers like Jane Goodall, many people have a romantic view of what it’s like to study animal behavior in the field. The reality is that most animals — certainly most reptiles — spend most of their time doing nothing, remaining motionless. The thrill can evaporate quickly, replaced by boredom. And mainland anoles can really bring on this ennui. The variable-scaled and beach anoles are masters of inactivity. But perhaps this is evolution’s end game to avoid drawing the attention of the many predators found in mainland settings. 

Imagine our delight, then, to discover the tiger anole to be an exception. They are a blur of activity: eating, scratching, pooping, posturing, courting and almost constantly on the move. And not only that, but the males were displaying frequently, pumping out their beautiful white and orange dewlaps to intimidate their rivals and impress the lady lizards. A hot afternoon at the lizard revue. 

This activity, however, presented its own challenges to the lizard videographer. It’s like going from tortoises to jack rabbits. We tried to film from a discreet distance, but it was easy to lose track of them as they darted in and out of the vegetation. That lead to a frenetic — indeed, stressful — time trying not to miss valuable data if the lizard did something cool out of frame. Still, I’ll take stress over tedium any day, particularly when it means discovering interesting tidbits of what it’s like to be a tiger anole. 

Jonathan Losos The writer, tracking anoles. 

As expected, the lizards were primarily found on narrow surfaces — twigs, small branches, vines and lianas. Combined with their great anatomical similarity to their Caribbean counterparts, they seemed good candidates for membership in Club Twig Anole. But as the videotaping progressed, the tiger anoles presented us with one further surprise. Anoles that use narrow surfaces — whether Caribbean or mainland — tend to move slowly, often crawling at a snail’s pace, so we expected the same for this species. 

Wrong again. 

These guys could boogie, and they did so frequently and in a very untwiggish manner. These lizards may look like twig anoles and live in twig anole habitats, but they certainly don’t act like twig anoles. What does it mean? At this point, we don’t know, but our mental wheels are spinning just trying to come up with ideas. 

The action continued fast and furious until late in the afternoon, when cool weather and impending dusk called an end to the day’s frolicking. We returned to the room, exhausted but exhilarated. We had expected not to find any lizards and instead had found more than a dozen. We had expected a sparse smattering of drying lizard paint, but had been given a reptilian Renoir, an intimate living composition in vibrant color. What a day — one of the best ever in my three decades of lizarding. 

But as always, questions remain. 

In our observations, we found four males for every female. That may reflect greater activity or choice of more conspicuous perches by the males, but how can we test this idea? We still have some lizard-catching tricks up our sleeves, but they’ll have to wait for another day. For now, it’s off to dinner and to purchase Belgian-born Anthony his three bars of well-deserved dark chocolate. 

Puerto Rican Anoles Are Chilling In Florida – New Research By Jason Kolbe And Colleagues - via Herp Digest

Posted on August 16, 2012 by Martha Munoz

Anoles are remarkably adaptable creatures. You can find anoles in hostile environments, such as the tops of mountains in the Dominican Republic, in near-desert environments, and in places with over-winter freezing. Anoles are also a model system for rapid evolution; in response to strong selective pressure, an equally strong evolutionary response occurs within a few generations. It is perhaps unsurprising, then, that anoles are also one of the most invasive reptiles in the World. Although they are endemic to the tropical and subtropical regions of the New World, today anoles can also be found in such remote places as Guam, Hawaii, Taiwan, and Hong Kong.

One of the major questions surrounding anole invasions is how the organisms will respond to the challenges of a new environment. When anoles invade new environments they inevitably encounter new thermal and hydric conditions – how do these anoles adapt to a different environment? Jason Kolbe has spent many years exploring the ecology and genetics of Anolis invasions, and has focused especially on invasions in Florida (1, 2, 3). The Puerto Rican trunk-ground, A. cristatellus, has been found in Key Biscayne and South Miami since the mid-1970s. Ambient temperature is important for A. cristatellus and other anoles have been documented to acclimate to low temperatures. In this study Jason Kolbe and colleagues addressed two questions: (1) To what extent does the thermal environment change from Puerto Rico to Florida? and (2) Is there a phenotypic response in tolerance to cold?

To address the first question the authors used species distribution modeling (SDM) to model the thermal niche shift from Puerto Rico to Florida experienced by A. cristatellus. They gathered locality data for this species from museum databases and extracted relevant temperature variables (mean annual temperature, maximum temperature, minimum temperature, seasonality, etc.) from the WORLDCLIM data set. They then generated niche models using Maxent, a widely used program that uses the environmental conditions of known localities to predict habitat suitability over large geographic areas. They ran two models – one with the entire Caribbean basin as the background and one with just Puerto Rico as the background.

The discrimination ability of the Caribbean model, which refers to how well it can predict occurrences compared to a random selection of points, was greater than the model using just Puerto Rico as a background. Both models were similar, however, in that they gave low suitability scores to the Florida habitat (Fig. 1 and Fig. 2). In fact, all of Florida received a suitability score of zero from the Caribbean model. A strong thermal niche shift was detected in both runs, but the inability of the models to detect suitable habitat in Florida, despite the presence of A. cristatellus there, suggests that locality data alone do not predict distributions well. There is a growing literature, in fact, arguing that the inclusion of organismal data will improve distribution models (i.e. ‘mechanistic niche modeling’; 1, 2, 3, 4).

To address the second question the authors assessed acclimation response in temperature tolerance in various native and invasive populations of A. cristatellus. The ability to acclimate thermal tolerance to ambient temperature conditions is potentially instrumental in facilitating invasion in a cooler environment in this species, and so the authors hypothesized that invasive populations of A. cristatellus should exhibit more plasticity in their tolerance as compared to native populations. The metric used in this study is CTmin, which refers to the low temperature at which a lizard loses the ability to right itself when flipped onto its back. Because performance is tightly dependent on body temperature in ectotherms such as anoles, the CTmin is a good metric for understanding the thermal limits to performance. In a previous study Kolbe and colleagues found that populations of A. cristatellus in Florida derive from two distinct invasions. These two genetic sources came from different regions of Puerto Rico, permitting a natural replicate of the CTmin acclimation experiment.

To this end, they maintained invasive populations of A. cristatellus (Key Biscayne and South Miami) and their source populations from Puerto Rico (Fajardo and San Juan) in the laboratory under winterizing conditions (22.5◦C) for four weeks. This temperature falls within the typical range of winter temperatures in south Florida, and so it accurately reflects the thermal conditions experienced by the invasive populations. The authors also tested a population of A. sagrei, the invasive brown anole from Cuba, and the native green anole, A. carolinensis.

Surprisingly, the results of the acclimation experiment varied among populations of A. cristatellus (Fig. 5 above). Although they experience similar winter conditions, only the Miami population of A. cristatellus exhibited plasticity in CTmin. The population from Key Biscayne showed no appreciable change in cold tolerance – in fact, it increased between weeks 2 and 4. Neither source population exhibited an acclimation response in CTmin. Both A. sagrei and A. carolinensis showed plasticity in thermal tolerance, and their final mean CTmin was similar to that of the Key Biscayne population.

We know that animals chilled beyond their CTmin lose mobility and can certainly die. In a previous post, I discussed this possibility in Dominican anoles from cool pine forests at high elevation. Thus, seasonal adjustment of CTmin to track environmental conditions is likely adaptive, and so it is puzzling why the Key Biscayne population does not exhibit tolerance plasticity. Although the invasions are equally young, Kolbe notes that the invasion in Miami is more genetically diverse than the Key Biscayne population, which suggests that more additive genetic variation in the Miami population may be involved in the acquisition of thermal acclimation. Moreover, CTmin acclimation is potentially sensitive to many factors, and so the experimental conditions used here may not trigger an acclimation response in the Key Biscayne population. Perhaps a different thermal treatment, such as acute or chronic exposure to progressively lower temperatures, may elicit a response that exposure to mean winter temperatures does not. It is also possible that animals in the Key Biscayne population (but not the Miami population) use retreat behavior to evade thermal conditions that approach the thermal limit, and so acclimation in cold tolerance may not be ecologically relevant in this population.

The contingency in thermal acclimation in different populations of A. cristatellus highlights that understanding invasions requires studying organismal variation at the population level. While it is difficult to project how differences in thermal plasticity will translate into invasion success, these results do show that similar thermal environments do not always yield the same phenotypic outcome, making this paper an informative and enjoyable read.

Jason J. Kolbe, Paul S. VanMiddlesworth, Neil Losin, Nathan Dappen & Jonathan B. Losos (2012). Climatic niche shift predicts thermal trait response in one
but not both introductions of the Puerto Rican lizard
Anolis cristatellus to Miami, Florida, USA Ecology and Evolution DOI: 10.1002/ece3.263

Climbing out of hiding: With lizard's re-emergence, an opportunity for deeper understanding of evolution – via Herp Digest

June 21, 2012 By Peter Reuell

For decades, scientists have puzzled over the small lizard, whose defining feature is a horn on its nose, but have been stymied in their attempts to better understand it because it appeared to be all but extinct — until now.

Two teams of researchers — one from Harvard, the other from the University of New Mexico — working with colleagues in Ecuador, have rediscovered the lizard, alive and well, in the forests of South America. As reported in a pair of papers published in Breviora, the journal of Harvard’s Museum of Comparative Zoology (MCZ), the work has shed new light on the lizard’s behavior, and is raising intriguing questions about evolution.

“There are more than 400 species of anoles, but this species has always been very enigmatic,” said Jonathan Losos ’84, the Monique and Philip Lehner Professor for the Study of Latin America, curator in herpetology, and author of one of the papers. “I and many other people have been enchanted by this lizard, but for us it was almost like a unicorn. Because there are only six specimens worldwide, and it hadn’t been seen in the field since 1966, it was this marvelous animal that we knew very little about. We didn’t even know if the female had a horn.”

Rediscovering a species once thought lost, however, took a bit of luck and some help from Google.

Proof that the proboscis anole still exists in the wild came in 2005, when a group of bird-watching tourists snapped a picture of one as it attempted to cross a road near Mindo, a rural area in central Ecuador. The photo wound up on the Internet, where Losos stumbled onto it while conducting research for his book, “Lizards in an Evolutionary Tree: Ecology and Adaptive Radiation of Anoles” (2009).

Spurred by a handful of similar sightings, Steven Poe ’93, an associate professor at the University of New Mexico and associate of Harvard’s Museum of Comparative Zoology, in 2009 traveled to Mindo. His findings, which suggest the lizard isn’t as elusive as initially believed, describe it as being approximately six inches long, very slender, and typically sleeping on the end of tree branches between 20 and 50 feet high. Poe’s team also resolved the question of whether the female has a horn: it doesn’t, a finding supported by the work of a team of Ecuadorian scientists who captured several specimens and reported on them in a paper in the Ecuadorian journal Avances en Ciencias e Ingeniería in 2010.

But while Poe’s work represented a dramatic leap forward in describing the lizards’ environment, it was largely made up of observations conducted at night. Losos in 2010 launched a second research effort, this time aimed at observing the lizard’s behavior during the day. This turned out to require spotting one at night, then returning just before dawn to watch the lizard as it moved about in the morning.

“What we discovered is that they are extremely well-camouflaged,” Losos said. “They’re usually about 10 to 20 feet off the ground and live on the ends of branches, where there is a lot of vegetation. They also move extremely slowly, so they blend right into the vegetation.

“Having observed them in the wild, it’s easy to understand why no one has found them for more than 40 years,” he added. “It’s because it’s almost impossible to find them if you know what you’re looking for. Ultimately, we ended up finding only two or three during the day.”

Aside from his excitement about the re-emergence of the species, Losos is eager to study the lizards for clues to how evolution works.

“The major focus of my entire career has been how these lizards have evolved in the Caribbean,” Losos said. “Essentially, each island has been its own evolutionary theater, but the end result has been very similar. The same set of habitat specialists has evolved on each island, so on each island you find lizards that live in long grasses that have long tails, and you find lizards that live in trees that have large toe pads.”

While anoles are also common in Central and South America, research suggests those mainland populations evolved along different lines. What makes the proboscis anole unusual, Losos said, is that, aside from its horn, it almost perfectly mimics a species of Caribbean lizard, the twig anole.

“Our goal was first to capture specimens to see if that impression was correct and second to ask whether the ecology and behavior is like the twig anole,” Losos said. “These lizards have the same habitat, they move the same way, and, unlike most mainland anoles, they have adapted in the same way as the Caribbean species. They are dead ringers for twig anoles, with one very obvious difference.”

The purpose of that difference — the horn — remains a mystery, though researchers have gathered some tantalizing clues.

Given that females do not have a horn, Losos speculates that it likely plays a role in attracting mates, possibly by making the lizard appear larger. While not unusual in lizards, horns are typically bony structures used in fighting. In the case of the proboscis anole, however, researchers were surprised to find that the horn is not rigid, and that the lizard can actually move it.

“That the horn can move is stunning to people who study lizard morphology,” Losos said.

While Losos and Poe’s research has answered a number of nagging questions, it also raises new ones about why such widely scattered animals seem to have followed the same evolutionary pathways.

“It is interesting that on the mainland the evolutionary outcomes are very different,” Losos said. “The question is why do we see such repeated similarity on the islands but not on the mainland? Our working hypothesis is that the reason things are different has to do with greater number and variety of predators on the mainland compared to the islands. Among the Caribbean species, it is the slow-moving twig anoles that are most concerned about predators, so it might not be so surprising that lizards in the same habitat on the mainland have adapted along the same lines.”

Funding for the research was provided by the David M. Fite Fund.

Provided by Harvard University 

This story is published courtesy of the Harvard Gazette, Harvard University's official newspaper. For additional university news, visit Harvard.edu.