For sheer breadth of freakish anatomical features, the chameleon has few rivals. A tongue far longer than its body, shooting out to snatch insects in a fraction of a second. Telescopic-vision eyes that swivel independently in domed turrets. Feet with toes fused into mitten-like pincers. Horns sprouting from brow and snout. Knobbly nasal ornaments. A skin flap circling the neck like a lace ruff on an Elizabethan noble.
Of all its corporeal quirks, the chameleon is most defined by one, noted as far back as Aristotle: color-changing skin. It’s a popular myth that chameleons take on the color of what they touch. Though some color changes do help them blend into their surroundings, the skin’s changing hue is in fact a physiological reaction that’s mostly for communication. It’s the lizard using colorful language, expressing itself about things that affect it: courtship, competition, environmental stress.
At least that’s the belief today. “Even though chameleons have attracted attention for centuries, there’s still a lot of mystery surrounding them,” says Christopher Anderson, a biology postdoctoral associate at Brown University and a chameleon expert. “We’re still piecing together how their mechanisms actually work,” from the explosive projection of the tongue to the physics of the varying skin colors. (Learn more about chameleons at a website Anderson runs.)
“Even though chameleons have attracted attention for centuries, there’s still a lot of mystery surrounding them.”
Christopher Anderson | biology postdoctoral associate at Brown University
Scientists recently have made important discoveries about chameleon physiology by watching the lizards in captivity. Their future in the wild, meanwhile, is far from certain.
When the International Union for Conservation of Nature (IUCN) released a new Red List assessment of chameleons last November, it ranked at least half the species as threatened or near threatened. Anderson is a member of the IUCN Chameleon Specialist Group, as is biologist Krystal Tolley, a National Geographic grantee whose expeditions in southern Africa have documented new chameleon species and vanishing habitats. (Read Tolley’s blog posts from her expeditions.)
In Afrikaans, says Tolley, chameleons have two common names. One is verkleurmannetjies, which means “colorful little men.” The other, trapsuutjies, translates as “treading carefully.” That refers to the lizards’ odd, slow gait—but also could be read as a plea to conserve the curious species and their home terrain.
How Chameleons Change Color
About 40 percent of the 200-plus known chameleon species are found on the island of Madagascar. Most of the rest live on the African continent. Thanks to DNA testing, some chameleons that look nearly identical have been found to be genetically distinct. More than 20 percent of the known species have been identified in just the past 15 years.
Given their many odd traits, chameleons “have always intrigued naturalists,” Anderson says. Because the lizards often died on the journey from Madagascar and the African continent to Western laboratories, early herpetologists could only guess at how live chameleons worked. That yielded theories that seem laughable now, he says: “It was once thought that the chameleon tongue projected because it inflated with air or filled with blood, like erectile tissue.”
“It was once thought that the chameleon tongue projected because it inflated with air or filled with blood, like erectile tissue.”
Anderson studies chameleon feeding in intricate detail. Using a camera that captures 3,000 frames a second, he turned 0.56 seconds of a chameleon eating a cricket into a 28-second instructional video on projection mechanics. (See videos of chameleon tongue projections.)
Stored in the lizard’s throat pouch is a tongue bone surrounded by sheaths of elastic, collagenous tissue inside a tubular accelerator muscle. When the chameleon spies an insect, it protrudes its tongue from its mouth, and the muscle contracts, squeezing the sheaths, which shoot out as if spring-loaded. The tongue tip is shaped so that it acts like a wet suction cup, grabbing the prey. The tongue recoils; dinner is served.
Scientists have more to learn about tongue projection, Anderson says. His research suggests that in some chameleons, it may go even farther and faster than previously thought.
The understanding of chameleon coloration also has changed over time—and dramatically earlier this year, when Michel Milinkovitch’s research was published. Scientists had long thought that chameleons changed color when skin cell pigments spread out along veinlike cell extensions. Milinkovitch, an evolutionary geneticist and biophysicist, says that theory didn’t wash, because there are many green chameleons but no green pigments in their skin cells.
So Milinkovitch and his University of Geneva colleagues began “doing physics and biology together,” he says. Beneath a layer of pigmentary skin cells, they found another layer of skin cells containing nanoscale crystals arranged in a triangular lattice.
By exposing samples of chameleon skin to pressure and chemicals, the researchers discovered that these crystals can be “tuned” to alter the spacing between them. That in turn affects the color of light that the lattice of crystals reflects. As the distance between the crystals increases, the reflected colors shift from blue to green to yellow to orange to red—a kaleidoscopic display that’s common among some panther chameleons as they progress from relaxed to agitated or amorous. (See a video Milinkovitch’s team made of a panther chameleon color change.)
New Ways to Hide
At age seven, Nick Henn got his first chameleon. Twenty years later the hobbyist and breeder keeps as many as 200 of them in the basement of his business in Reading, Pennsylvania.
Rows of wire-mesh cages contain plants for climbing and sandy floors where females can lay eggs. Lights and misters simulate the lizards’ native climes. Arranging the cages is as tricky as seating warring factions at a United Nations summit. To keep the animals from riling each other, Henn places females where they can’t see males, and males where they can’t see females—or rival males.
Ember, a young male panther chameleon, is a so-called red bar, a variety that’s native to the Ambilobe district in northern Madagascar. His torso has red and green zebra stripes plus an aqua blue racing stripe along each side. When Henn opens Ember’s cage and prods him to climb onto a long stick, he “gets grumpy,” which Henn knows because the chameleon’s red bars get a little brighter.
Henn carries Ember on the stick around a corner to the cage inhabited by Bolt, an adult male blue-bar panther chameleon and the largest lizard in Henn’s collection. When Henn opens the door, and Bolt sees Ember, the response is immediate. By the time Bolt has advanced a few inches, his green bands have turned vivid yellow, and his eye sockets, throat, and spiked spine have changed from green to red orange. Ember becomes redder—but as shows go, Bolt’s is far more flamboyant. For good measure, as Bolt crawls nearer, his mouth gapes wide, displaying bright yellow gums.
“I keep envisioning the little chameleons clinging to their branches as that forest is getting chopped.”
Krystal Tolley | biologist and National Geographic grantee
Henn retreats and puts Ember back in his cage. Had he not, he says, Bolt might have tried to ram or bite Ember, whose skin almost certainly would have changed to brown—the color of crying uncle. (A 2014 study concluded that chameleons developed this fade-to-drab submissive ability because their “slow-moving lifestyle severely restricts their ability to rapidly and safely flee from dominant individuals.”)
Though all chameleons change color, some species don’t change dramatically enough to cow observers. However, almost all chameleons do have another technique for physical intimidation: They can make themselves look larger. They narrow the width and increase the height of their bodies by unfolding their jointed, V-shaped ribs to elevate their spine. They also can look more massive by coiling their tails tightly and using their tongue apparatus to expand their throats. Turning this profile to its nemesis, the lizard looks significantly bulkier.
In the cages where Henn keeps female chameleons, one named Katy Perry—salmon pink because she’s ready to mate—is next door to one named Peanut, pink with dark bars because she has already mated and is gravid, carrying eggs. If Katy were approached by a male that impressed her with his courtship colors and bobbing, swaying dance, she might submit to being mounted. If the same male approached Peanut, she would become intensely darker with bright spots and open her maw menacingly at him. If he persisted, she’d hiss or try to bite him.
Both male and female chameleons are polygamous. Most species are egg layers, but some deliver live young in clear, cocoon-like sacs. Chameleons do no parenting, so the young are on their own as soon as they’re born or hatched.
To avoid the birds and snakes that hunt them, chameleons have evolved novel ways to hide. Most species are arboreal; when they narrow their bodies, they’re slender enough to hide on the opposite side of a branch. If ground dwelling chameleons see a predator, Tolley says, some “play leaf,” contorting their bodies to look like crumpled leaves on the forest floor.
Chameleons can hide from some threats but not from the slash-and-burn agriculture destroying their habitats. The IUCN lists nine species as critically endangered, 37 as endangered, 20 as vulnerable, and 35 as near threatened.
Identifying New Species
Tolley and her team have identified 11 new chameleon species since 2006, in South Africa, Mozambique, Tanzania, and the Democratic Republic of the Congo. The Massachusetts-born professor has studied the lizards in Africa since 2001 and works for the South African National Biodiversity Institute in Cape Town.
When a genetics study confirms that a chameleon is a new species, “it feels like you’re not just writing some random scientific paper that nobody will read,” Tolley says. “You’re accomplishing something—this is going to be forever.”
In the next breath she notes that “at the same time as thinking, ‘Wow, this is so cool,’ it was awful. I keep envisioning the little chameleons clinging to their branches as that forest is getting chopped.”
Describing it, her voice breaks. “I could not help thinking, I wish we’d never found them,” she says. “Because if this doesn’t stop, they’ll soon be extinct.”