Professor of Biology and Director of the Living Earth Collaborative at Washington University in Saint Louis. I've spent my entire professional career studying anoles and have discovered that the more I learn about anoles, the more I realize I don't know.
Pre-Pleistocene fossils of Anolis lizards from the mainland of the Americas are exceedingly rare: only two specimens referred to a single species have been described previously. Here we report on a third specimen, preserved (as are the other two) in Miocene amber from Chiapas, Mexico, and consisting primarily of the anterior vertebrae of the caudal sequence. Despite the fragmentary nature of the fossil, it preserves key osteological characters that permit confident referral to the Anolis clade and further suggest placement within the Dactyloa subclade in a clade of three extant species within the Anolis aequatorialis series. The Chiapan provenance of the fossil indicates that the geographic distribution of the Dactyloa clade (and possibly that of the A. aequatorialis series) extended considerably farther north during the Miocene. Although the new fossil represents a different part of the body than the two fossils representing the fossil species Anolis electrum, its inferred phylogenetic relationships are the same as one of the several possible phyloge
The key sentence: “As a newly minted urologist in 1988 I saw male patients with challenging sexual problems. I was curious about testosterone (T) therapy (TTh) due to my prior research restoring sexual behavior in the castrated male lizard, Anolis carolinensis, with intracranial T pellets.” Read the two-page paper here.
Two Cuban brown anoles, Anolis sagrei (Credit: Day’s Edge Productions).
By way of Georgia Tech:
Georgia Tech-led study captures two lizard species adapting in response to competition. The study provides some of the clearest evidence to date of evolution in action.
In South Florida, two Caribbean lizard species met for the first time. What followed provided some of the clearest evidence to date of evolution in action.
Lead author James Stroud, anassistant professor in the School of Biological Sciences, was studying Cuban brown anoles (Anolis sagrei) in South Florida when the Puerto Rican crested anole (Anolis cristatellus), suddenly appeared in the region.
Published in Nature Communications, the study documents what happens as the two Anolis lizards adapted in response to the new competitor, while helping to resolve a longstanding challenge in evolutionary biology — directly observing the role of natural selection in character displacement: how similar animals adapt in response to competition.
“Most of what we know about how animals change in response to this process comes from studying patterns that evolved long ago,” Stroud says. “This was a rare opportunity where we could watch evolution as it happened.”
Competition from coexistence
While these two small, brown lizards diverged evolutionarily between 40-60 million years ago and evolved on completely separate Caribbean islands, the two species are nearly identical, and fill similar ecological niches.
So, when the Puerto Rican crested anole suddenly appeared in Cuban brown anole habitat at Fairchild Tropical Botanic Garden in 2018, the two were competing for similar habitats and food sources.
“When two similar species compete for the same resources, like food and territory, they often evolve differences that allow them to coexist,” Stroud says. But, while scientists have found many examples of similar species developing different traits to ease this overlap, “scientists have rarely been able to observe this process as it unfolds in nature.”
Stroud’s team had already been studying Cuban brown anoles at the Fairchild Tropical Botanic Gardens in Miami, Florida, two years prior to when the crested anoles invaded. The team was able to quickly pivot to observe how the invasion changed both species, analyzing the lizards’ changing diets, measuring if the lizards were moving through foliage or on the forest floor, and recording the different species’ locations relative to each other. For over a thousand lizards, they also measured perch height — the distance from the ground that the lizard is perching — a primary marker of how Anolis lizards divvy up habitat.
“We not only observed how these lizards changed their habitat use and behavior when they encountered each other,” says Stroud, “but we also documented the natural selection pressures driving their physical evolution in real-time.”
Human-made habitats and natural experiments
The research team found that when these lizard species occur together, they divide up their habitat in predictable ways — the Cuban brown anole shifted to spend more time on the ground, and evolved longer legs to run faster in this habitat, while the slightly larger Puerto Rican crested anole lived in vegetation above the ground.
“We found that brown anoles with longer legs had higher survival after crested anoles showed up,” says Stroud. “This matches perfectly with the physical differences we see in populations where these species have been living together for many generations.”
Stroud adds that while the research provides some of the strongest observations of evolution in action to date, it also demonstrates how human activities can create natural experiments that help us understand fundamental evolutionary processes — both species of Anolis lizard in the study were originally non-native to South Florida.
“As species increasingly come into contact due to human-mediated introductions and climate change, these studies may be important for predicting how communities will respond,” he says. “By studying these non-native lizards who are meeting each other for the first time in their existence, we had a unique opportunity to see the actual process unfold and connect it to the patterns we observe in nature.”
A nearly-extinct Caribbean reptile is showing signs of a comeback following years of conservation efforts. The population of the Sombrero ground lizard (Pholidoscelis corvinus) has increased from less than 100 individuals in 2018, to over 1,600 in 2024. The huge population jump is detailed in a survey released on December 18.
Sombrero ground lizards are a small reptile that primarily eats the eggs of ground-nesting birds, corn, and other plants. It is endemic to Sombrero, the northernmost island of the Lesser Antilles and roughly 34 miles off the coast of Anguilla. This tiny Caribbean island ranks in the top three of the world’s 36 biodiversity hotspots, with several species that are only found on this 94 acre island. The colorful Sombrero Island bee, a to-be-named pygmy gecko, and the Sombrero Island wind scorpion, and numerous others all call this place home. The island also supports large seabird colonies and is designated as an Important Bird Area.
“The Critically Endangered Sombrero ground lizard is an endemic species, which means it’s found only on Sombrero Island and nowhere else in the world,” Farah Mukhida, a natural resources manager and Executive Director at Anguilla National Trust tells Popular Science. “It’s a beautiful little reptile with its black-blue scales.”
A study from 1999 estimated there were only between 396 and 461 individuals left. Sombrero Island was also once on the verge of environmental collapse. Mineral mining, a population of invasive mice, deforestation, and severe hurricanes had all taken their toll.
“That it’s managed to survive decades of phosphate mining, invasive species, and now climate change with longer periods of drought, higher temperatures, and even stronger hurricanes and storm surges that sweep over the island is absolutely astounding and shows just how resilient this lizard is,” says Mukhida.
Major conservation efforts beginning in 2021 have focused on removing the invasive mice and planting more native species on the island. Experts from the Anguilla National Trust, Fauna & Flora, and Re:wild have worked to help the Sombrero ground lizard and its island habitat recover. The lizards are showing huge signs of improvement, with their population increasing roughly 16 times in six years.
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“We were absolutely ecstatic when we analysed the results of our population surveys and found this enormous increase in their numbers,” says Mukhida.
The island itself has been declared pest-free and is much more green. Native plants including the sea bean, seagrape, and prickly pear are already showing healthy new growth. The conservationists are also expressing some cautious optimism for the future.
“This is a remarkable turnaround for this cheeky and charismatic lizard but while we celebrate this recovery, we recognise that there is much more to be done to secure their future and that of other Caribbean wildlife,” Jenny Daltry, Caribbean Alliance Director, Fauna & Flora and Re:wild, said in a statement. “The combined impacts of biodiversity loss and climate breakdown are being felt with greater intensity every year in the Caribbean and around the world. Indeed, we are still busy helping our partners in Jamaica and St Vincent and the Grenadines to recover from the devastation wreaked by Hurricane Beryl earlier this year.”
Efforts will continue to preserve this biodiversity hotspot in the face of a changing landscape. One of the factors helping this recovery is the island’s distance from the mainland and fairly low number of visitors. The team plans constant vigilance to make sure they can respond quickly if more invasive rodents arrive. The continued re-wilding here will also require constant upkeep for the island’s flora, including building soil reserves and sowing additional seeds.
“These restoration interventions have cascading effects: they attract insects which help pollinate plants, they attract birds that drop seeds, they provide food and shelter for lizards that also serve as seed dispersers, pollinators, and nutrient transporters,” says Mukhida. “We’re committed to Sombrero’s recovery, sharing lessons learned, and building on successes.”
The lizard wars of South Florida help reveal how evolution works
Evolutionary biologist James Stroud holds a crested anole caught by his mini lasso on an island at Fairchild Tropical Botanic Gardens in Coral Gables. Scientists are studying how the brown anole from Cuba and the crested anole from Puerto Rico compete with one another and drive each species to adapt and find slightly different niches in the ecosystem. (Joe Cavaretta/South Florida Sun Sentinel)
CORAL GABLES — Fairchild Tropical Botanic Garden may look serene at first glance, but beneath the resplendent orchids and majestic banyans, two invasive lizards are waging a turf war.
The war started a few years ago when Cuban brown anoles, who have called South Florida home for about 100 years, came face to face for the first time with a new rival: crested anoles from Puerto Rico.
As the two species, which look almost identical and occupy the same ecological niche, faced off, biologists were able to document who was winning, and more importantly, how quickly the losers were adapting to survive on new turf.
A new study reveals that the losing species is adapting at a rapid pace, changing their behavior, but also their bodies. This fast adaptation is altering what we know about how evolution works.
Nearly identical invaders
Brown and crested anoles are almost identical — lanky, 4 to 8 inches long, splotchy brown and skittish (lots of animals eat them). But the cresteds are slightly bigger, and the males grow a crest on their tails.
Both lizards evolved on separate Caribbean islands to perch on tree trunks where they can scan the forest floor dart into leaf little to snag meals such as spiders and roaches.
But they’ve never had to compete against each other. “They’re convergently evolved,” said Georgia Tech evolutionary biologist James Stroud, who led the team of researchers on the study.
“They evolved completely independently. … Their last common ancestor is probably around 60 million years ago. To put that in perspective, humans and chimps, their last common ancestor was 13 to 16 million years ago. So the lizards are deeply deeply diverged.”
Stroud said that in 2018, crested anoles showed up at Fairchild Tropical Botanic Garden, where he’d already been studying survival rates and evolutionary adaptation of the brown anoles.
A crested anole looks out from a container in the lizard lab at Fairchild Tropical Botanic Gardens in Coral Gables, Thursday, Nov. 21, 2024. The lizard will be released in the exact spot where it was captured, and researchers will later study the species’ survival rate and how that correlates with physical traits such as long legs or large toe pads. (Joe Cavaretta/South Florida Sun Sentinel)
The arrival provided Stroud and his team the opportunity to study, in real time, how quickly species can adapt under pressure.
They used a fishing pole with a tiny lasso on the end to catch every lizard on an island at Fairchild the size of a football field. They then measured their physical traits, tagged them with ID numbers, released them exactly where they caught them, and spent months observing them. They then recaptured the survivors several months later.
“What we saw was when they came into contact, the cresteds, which are a little bit bigger, can dominate behaviorally, so they pushed the browns to the ground,” said Stroud. In other words, the crested anoles won the turf war, and the browns moved to a more dangerous place with a lousy view.
The territory change showed behavioral elasticity, but Stroud was also interested in physical adaptation. His team found that over time, brown anoles with longer legs had higher survival rates after the crested anoles showed up.
Researchers also tested the finding at other lizard hot spots around South Florida. They discovered that wherever brown and crested anoles had to compete for territory, the browns became more land-based, and those with longer legs lived longer. If there were no crested anoles present, long legs did not correlate with better survival.
James Stroud, of Georgia Tech, speaks with research assistants in the lizard lab at Fairchild Tropical Botanic Gardens in Coral Gables. (Joe Cavaretta/South Florida Sun Sentinel)
“Before the cresteds arrived, when the browns were not living on the ground much, leg length didn’t really matter to survival,” Stroud said. “But as soon as the crested anoles arrived, brown anoles with relatively longer legs survived better. … Now that brown anoles have shifted where they’re living — suddenly there’s an adaptive benefit to having longer legs.”
Stroud suspects that the longer legs helped the browns run faster to escape predators such as herons, egrets, mocking birds and larger invasive brown basilisk lizards from Central America.
From that survival rate, he and other evolutionary biologists can gain a clearer understanding of how natural selection, and thus evolution, is operating in the world.
“This is called microevolutionary dynamics,” Stroud said. Over the past 40 or 50 years, evolutionary biologists have begun to realize that evolution might actually happen quickly enough to record in something as short as a 10-year field study. “We never thought it was possible,” Stroud said.
This bucks against one of main tenants of Charles Darwin’s theory of evolution, that evolution happens very, very slowly over time.
Darwin’s notion of slow evolution made sense at the time, Stroud said. Some fossil records don’t change at all for 50 million years. “Slow gradual change through the fossil records was the evidence Darwin used to think that evolution moved at a really, really slow pace,” Stroud said.
But Stroud’s lizards in this study, as well as previous ones, show rapid changes almost constantly. Anoles live short, fast lives. Males rarely survive longer than a year, and females sometimes eke out two years of life. And they’re constantly laying eggs.
Their generations compile quickly compared to humans and other large mammals. “We think these sorts of evolutionary dynamics play out in all organisms, it just changes relative to the organism’s life history,” Stroud said.
A tagged anole is seen under fluorescent light in the lizard lab at Fairchild Tropical Botanic Gardens in Coral Gables. (Joe Cavaretta/South Florida Sun Sentinel)
If brown anoles at Fairchild evolve to have longer legs, that doesn’t mean they’ll change the species globally. These blips in traits can fade. But if the pressure is right, if natural selection is strong and widespread, “it can lead to rapid evolutionary change,” Stroud said.
The Lizard Olympics
Stroud isn’t done with South Florida’s invasive lizards. He’s currently conducting a study that he’s dubbed the “Lizard Olympics.”
This past spring, he and the team tested the hundreds of lizards they’ve caught on the island for various physical skills. They tested their speed on a race track; they tested their bite strength with a highly sensitive bite meter; and they tested their grip strength by placing them on leaves and bark surfaces and pulling them off.
They then tagged them and let them go on the island, and will later recapture them to see if those skills correlate to better survival for different species.
Stroud said they’ve already inferred longer legs mean faster speed and thus better survival for brown anoles, but now they’re testing it directly.
He anticipates that each species will have different skill-survival correlations: running speed might be irrelevant to the tree-dwelling green anoles, but grip strength might be important, while brown anoles might need more speed.
The toe pads of an anole in a lizard lab at Fairchild Tropical Botanic Gardens in Coral Gables. Researchers have found that native green anoles have evolved larger toe pads over decades as a result of competition with brown anoles. (Joe Cavaretta/South Florida Sun Sentinel)
The lizards are being put to the test, but so are the researchers. “My students are hating me, because we just finished processing 2.5 thousand slo-mo videos of lizards running.”
Quick localized evolution, and what it means for the bigger picture of a species, is something Stroud and his peers are trying to understand — how these micro events fit into the macro story of a species.
“We now know that evolution can happen on really rapid evolutionary time scales, but what does that mean for the creation of new species?”
South Florida, with its menagerie of invasive species, gives them a unique opportunity to cast a bit more light on the mystery.
Hard to imagine a more important service than this! Miami resident Julie Katz provides the details: “When I walked out of my condo building one night this past spring to walk my dog I encountered a first – a small lizard feasting on a roach.”
