In Praise of Lizards
Biologist Michael Denton commented here the other day on the mysteries surrounding the origin of lizard scales, as well as bird feathers and mammal hairs, research that began with the discovery of a mutant “naked” bearded dragon, born without scales. Their scales, however, only scratch the surface of what makes lizards fascinating.
For most of us, or at least boys who enjoy the challenge of trying to pick them up without getting bitten, interest in lizards tails off after age eight or so.
As adults, if you live in that kind of climate, we’re more likely to stamp at them to get them out of the garage. Their lives seem dull and rather repetitive; sit motionless, run; sit motionless, run.
They deserve more respect. They outlived the dinosaurs, after all. They’ve earned a constellation in the sky (Lacerta). Here are some other facts about lizards.
First, the basics. Lizards are squamate (scaly) reptiles. There are about six thousand known species. They can be found on every continent except Antarctica. Unlike the dinosaurs, whose legs were underneath the body, lizards have legs that splay out to the side. They have tails, shed their skins, and are cold-blooded. Most eat insects, but some eat fruit. A few are venomous, like the Gila monster, but most are harmless to humans.
The largest is the Komodo dragon of Indonesia, which has been known to stalk, attack, and kill people. A new one-meter-long monitor lizard was reported on Papua New Guinea, Science Daily reports.
Fortunately, the lizards most of us come across are much smaller; many of us have held a horned lizard in the palm of the hand to marvel at its spiny skin.
Some lizards, like geckos, iguanas, and bearded dragons, make good pets. See Live Science for a gallery of “gorgeous bearded dragons.” Gorgeous indeed.
The diversity of lizards is really astounding. Some are drab, but others are spectacularly colored. Some are superb runners (the basilisk runs so fast, it can run across water).
There are legless lizards that are not snakes, and some with tails much longer than their bodies (see one from Asia via National Geographic).
“Worm lizards” burrow underground with tiny legs and can’t swim, but live on five continents (University of Bristol).
On the Galápagos Islands, marine iguanas can swim down thirty feet foraging for food, while the land iguanas roam the rocky slopes of volcanoes in severe heat. Scientists are still trying to understand how lizards keep their cool, Phys.org says; “Working out how much of a lizard’s behavior is related to controlling its body temperature has been a goal of scientists for a long time.”
The anoles of the Caribbean take on many colors, and inhabit many different habitats. Scientists at TGen, the Translational Genomics Research Institute in Phoenix, studied anoles recently to learn how they regenerate their tails. That would be a good thing to know. Maybe what science learns could someday help accident victims regenerate body parts. (See? There’s something a lizard can do that you can’t.) Would you have guessed that the secret involves micro-RNAs that can mold tails like a potter with clay?
“This work highlights the importance of tiny RNA molecules in the tissue regeneration process, and showed for the first time an asymmetric microRNA distribution in different portions of the regenerating lizard tails,” said Dr. Marco Mangone, a co-author and Assistant Professor with ASU’s School of Life Sciences and Biodesign Institute. “It seems like microRNAs may play an active role in this process, and are potentially able to shape the regenerating lizard tail like playdough.” [Emphasis added.]
Two lizard types deserve special attention: first, the gecko. Most of us only know geckos from car insurance commercials.
Some two hundred species are known. Their claim to fame (for some species) is being able to walk up any kind of surface, smooth or rough, without falling.
They can scamper up glass and run across the ceiling. Only in recent years was their secret revealed: microscopic hairs, called spatulae, on their foot pads and toes adhere to the atoms on a surface through van der Waals forces.
That’s where protons in the atoms on one surface attract electrons on the other. This atomic attraction is very weak, but the spatulae are so numerous that the collective force is enough to hold the gecko up against gravity, no matter what the surface.
Since no glue is involved, the gecko can simply peel its foot off and step again. It’s a neat trick, and some inventors have made it work on experimental “gecko robots” (New Scientist). It’s hard to scale up to human size, but DARPA succeeded in making gloves and footpads that allowed a 218-lb man walk up a pane of glass. But the human models aren’t self-cleaning like gecko toes are (see Nature Communications about that feature).
Gecko skin, too, is self-cleaning, as noted here last year. Two new species of gecko were found recently in New Guinea, Phys.org reports, both unusually large and colorful.
Another lizard to admire is the chameleon. Chameleons earn several design awards. For one thing, they can move their eyes independently.
For another, they can rapidly change color for camouflage, mating display, or as a warning. Third, they have prehensile tails that allow them to hang from branches.
Finally, they have one of the fastest tongues in the animal kingdom. If you have watched slow motion video of a chameleon catching an insect, you were undoubtedly amazed at the reach of these living catapults, sometimes extending twice the animal’s body length.
In April, mathematicians at Oxford proposed a model for the dynamics of the chameleon tongue, says Phys.org. Notice the interrelated requirements for it to work:
What sets it apart is its speed — a chameleon can push its tongue out at a target at speeds up to 100 kilometers per hour. But how it does so, has not been well understood.
In this new effort, the researchers have found that in order to reach such incredible speeds so quickly, the chameleon relies on three main parts: the sticky pad that is situated on the end of its tongue which adheres to prey, coils of acceleration muscles and retractor muscles that pull prey back in before they have a chance to escape.
They also note that both types of muscles coil around a tiny bone in the mouth — the hyoid. In order for a chameleon to catch prey, all of its systems must work in near perfect unison.
The article has slow-motion videos of a chameleon catching a cricket. Not mentioned are other requirements: eyes to focus on the prey, ability to aim the tongue accurately, brain power to operate the equipment, and systems to keep the tongue in working order for the next catch.
Speaking of the sticky pad, that secret was just revealed by scientists in Belgium and France. Phys.org says that the secret is sticky mucus, a thousand times more viscous than human saliva. It’s able to cling to the insect in spite of the high speed contact and recoil. That’s all fine, but how does the chameleon release its prey in the mouth? And how can the lizard keep from biting its tongue? “We can only hypothesize” about those matters, said one researcher on the team.
“Despite their nonchalant appearance, chameleons are formidable predators,” researchers from Paris and Brussels say via EurekAlert.
Chameleons are fascinating creatures with amazing characteristics. Their feet have opposable toes, giving them a tongs-like appearance, to firmly grip branches. Their eyes move independently of each other to provide 360 degree vision. Their skin changes colour via the active tuning of a lattice of nanocrystals contained in some cells. But their most outstanding characteristic is probably their ballistic tongue, allowing the capture of distant preys.
Thus equipped, a chameleon can sit motionless on a branch, watching everything, till an insect comes within reach. It’s all over in a split second, even if the prey is 30 percent of the chameleon’s own weight. Faced with a catapult coming at 1500 m/sec2, the prey doesn’t stand a chance.
Chameleons even seem to have some emotions and cognitive abilities, like cats.
When a male chameleon sees itself in a mirror, it will turn red as if facing a rival.
National Geographic tells some amusing facts about chameleon color-change behavior. The mechanism behind it, however, is no joke.
“Scientists had thought pigment-containing cells at the skin’s surface control the changes. Instead, a lattice of nanocrystals within another skin cell layer alters to reflect light differently.” That was only figured out last year.
Oh, and by the way. We hate to bust a myth, but the popular YouTube video at the top of the page, with a chameleon changing colors to match a line of colored sunglasses (click on the image to see it), was a Ray-Ban advertising gimmick, according to Snopes. Chameleons usually turn red, orange, yellow, or green. Sorry. It’s still pretty remarkable what they do.
