by Becky Crew
In 2008, Wade C. Sherbrooke, director of the Southwestern Research Station at the American Museum of Natural History in New York and Kurt Schwenk, professor of ecology and evolutionary biology at the University of Connecticut, published the results of an examination of some road-killed Texas horned lizards in the Journal of Experimental Zoology. The pair opened the lizards’ stomachs to find that they were packed with dozens of poisonous Pogonomyrmex ants. Sherbrooke and Schwenk discovered that mucus-secreting papillae, which are the little fleshy projections that line the back end of the horned lizard’s tongue and the pharynx, are the key to their survival against the venomous ants. The papillae squeeze and bind the ants in mucus strands as they are swallowed—and never chewed—and once they reach the esophagus, the ants are met with specialized mucus-secreting skin folds that ensure they are incapacitated all the way down to the stomach.
In mid-2010, Sherbrooke revisited his Texas horned lizard research with biologist William Cooper of Indiana University-Purdue University to test if a hypothesis known as “escape theory” applies to a species so good at camouflaging itself. Escape theory predicts that once an animal has detected a predator nearby, it will not flee immediately, but wait and monitor the predator’s approach, weighing up the risk of getting caught versus the cost of fleeing from its current location where food foraging and mating opportunities may exist. If an animal does decide to flee, its level of fitness will determine the initial distance left between it and its predator—a space known as “flight initiation distance.” The fitter the prey, the shorter the distance left between it and the predator before the prey takes off. What the researchers found when observing the Texas horned lizard was that the individuals who were alone when spotted by a predator had an average flight initiation distance almost twice as long as those who were in the company of other lizards and interacting socially with them. They were reluctant to flee so quickly when potential mates were present, and are thus living proof of escape theory.
“Hi Spanish Ribbed Newt, how’s this Thursday sound? I’ll bring Scrabble. x”
Will Rib You to Death
SPANISH RIBBED NEWT
(Pleurodeles waltl)
IN 1879, GERMAN ZOOLOGIST and comparative anatomist Franz von Leydig noticed some very odd behavior in a rather unassuming species of newt. When provoked, the Spanish ribbed newt’s ribs will burst out of its skin to produce twin rows of poison-tipped spears, perfect for fending off anything that was considering taking a bite out of it. But it would take 130 years before scientists had the technology to explain just how an animal can wield its own skeleton as a weapon.
Also known as the Iberian ribbed newt, the water-loving Spanish ribbed newt grows to 12 inches long and is endemic to Morocco and the central and Iberian Peninsula, which runs through Spain, Portugal, and Andorra. It has a flat head and a slender tail measuring half the length of its body and a row of rust-colored tubercules, or warts, that run down each side where the ribs protrude.
In a 2009 paper published by the Journal of Zoology, zoologist Egon Heiss of the University of Vienna in Austria and colleagues reported what they saw using a combination of photographic and X-ray imaging and computed tomography (CT) scans. They discovered that when agitated, this newt is able to swing its long ribs forward by up to 65 degrees while keeping the rest of its body still. This causes its ribs to end up at a perpendicular (90 degree) angle to the spine, piercing through the skin on the side of its torso. The Spanish ribbed newt manages this grisly party trick because of its peculiar anatomy. Each of its hollow, spear-shaped ribs is attached to its corresponding vertebra by a flexible two-headed joint that allows it to be swung forward independently of the rest of the body.
Being mostly small and soft, amphibians have had to evolve many different kinds of defense mechanisms in order to survive, and one of the most common of these is secreting venom through the pores on their skin. The Spanish ribbed newt combines its defense mechanisms by secreting a noxious, milky substance onto its skin when threatened, which coats the exposed rib points to inflict a series of painful, stinging jabs. What particularly surprised Heiss was that the species appears to be immune to the pain of repeatedly piercing its bones through its skin, observing that “the skin in the penetration areas lacks permanent pores through which the ribs could be projected.”
A powerful immune system seems to protect the newt’s wounds from becoming infected while its skin works at regenerating itself through a process called cell dedifferentiation. Cell differentiation sees a stem cell develop into a more specialized type of cell, such as a bone or blood cell, whereas dedifferentiation means a specialized cell will revert to its primitive form, often for the purpose of regeneration. In the newt’s case, the cells around the puncture wounds dedifferentiate, multiplying rapidly and differentiating again to create new skin cells. This process also applies to limbs and other organs, which newts are known to be able to regenerate multiple times over.
What a couple of dinner guests Texas Horned Lizard and Spanish Ribbed Newt would make.
Mr. and Mrs. Bullfrog will be in their kitchen before they arrive and Mrs. Bullfrog will be like, “I don’t know why you invited them, I only just had the carpet steam-cleaned after the last time …”
“They reimbursed you for it though.”
“That’s not the point. It’s a hassle, and I bet there are still blood molecules in the fibers.”
“Blood molecules. Jesus.”
The pair will arrive, looking typically nervous, and they’ll all sit down in the living room with a bottle of wine while Spanish Ribbed Newt silently measures the distance between himself and every object in the room that could fall on him. Or that he could fall into. And he’ll decide to crouch in the corner on the floor because that will give him the biggest head start should the couch or the grandfather clock decide to charge at him or something. Texas Horned Lizard will look embarrassed about it, but she’ll be the one carrying industrial-strength carpet cleaner in her handbag.
She’ll tell the Bullfrogs about her promotion at work and Mr. Bullfrog will be all, “This calls for champagne!” and Texas Horned Lizard and Spanish Ribbed Newt will simultaneously say “No champagne” exactly like how two people say it in a sitcom when they’re hiding a hilarious secret.
“Since when?”
“We were at a restaurant last week and someone unexpectedly popped a champagne cork behind us and we practically shat ourselves. I got blood all over the tablecloth and Spanish Ribbed Newt put a waiter in the hospital. It was very embarrassing.”
“He was standing too close and got a rib in his thigh,” Spanish Ribbed Newt will mutter to the carpet.
Mrs. Bullfrog will show everyone into the dining room. “Spanish Ribbed Newt, you’re over there next to Mr. Bullfrog, and Texas Horned Lizard, you’re on this side with me.” Dinner will begin pretty smoothly, except for one minor hiccup when Mrs. Bullfrog will startle everyone by accidentally dropping her knife on her plate with a loud clang, and Texas Horned Lizard will nervously joke about her carpet cleaner.
But Spanish Ribbed Newt will be looking down at his exposed ribs under the tablecloth with a silent and intense expression of horror. “Shit. Oh shit. Oh shit. Ohhh shit. Erm, Mr Bullfrog …” But then he’ll think better of it, put his skeleton back in, and pour himself another glass of wine.
“So I was like, ‘Hey, Johnson in accounts, Alex Perry called, he wants his botox back—’ Ughhh.”
“What, honey?”
“I suddenly feel terrible. Oh god …”
Spanish Ribbed Newt will quickly drag Texas Horned Lizard to the door, all like, “Keep moving, I’ll explain on the way!” while Mr. Bullfog’s moans get louder and more gurgly. Then he’ll remove his waistcoat. “Hey, what are these hole—”
Thud.
Playing Dead Pros
VIRGINIA OPOSSUM
(Didelphis virginiana)
THE SWEET LITTLE VIRGINIA opossum not only has a well-stocked bag of tricks to get itself out of a
sticky situation, it’s also forcing venomous snakes to up their game.
The opossum is one of the most primitive living ancestors of marsupials and has remained morphologically unchanged for the past 60 million years, despite dramatic habitat changes. The only marsupial in North America, it made its way from South America during what scientists consider to be one of the most significant geologic events in the last 60 million years. A volcanic strip of land known as the Isthmus of Panama rose up out of the ocean as two of the Earth’s plates slowly collided 15 million years ago, and gradually the Central American Seaway that separated North and South America was filled in completely 3 million years ago. Not only did this rearrangement of the Earth’s terrestrial regions have a significant impact on its climate and environment, it also profoundly changed the biodiversity of the Americas.
Known as the Great American Interchange, this period saw the ancestors of South American animals such as the armadillo, sloth, porcupine, anteater, and opossum migrate to North America, and the ancestors of bears, cats, pigs, dogs, and horses journey in the opposite direction. Much later, the Virginia opossum, which was native to the eastern United States, was introduced to the West during the Great Depression in the early twentieth century as a source of food.
Looking just like a sneakier version of Mickey Mouse, the Virginia opossum has a long snout that tapers to a pastel pink nose, dark, beady eyes framed by a snow-white face, and black, rounded ears. They share their habitat with the huge population of cats and dogs in the United States, so can only survive with the help of the many defenses that render them undesirable to predators. When threatened, they will stand their ground, open their mouths wide, and expose an array of pointy teeth. If this gaping leer doesn’t ward off the predator and the opossum can’t escape the situation by fleeing, it will suddenly, and very convincingly, play dead.
Named after the Greek word for “putting to death,” thanatosis describes the process of an animal, insect, bird, or reptile going into a comatose state in the face of danger, which can often work in its favor, because limp, immobile prey is nowhere near as fun to play with as struggling, terrified prey. The Virginia opossum will fall to its side with its body flexed, mouth agape, and heart rate, respiratory rate, and body temperature rapidly decreasing. And to make things just a little bit more authentic, the thanatosis is accompanied by excessive drooling, urination, and the excretion of droppings and greenish, foul-smelling anal fluid. Sometimes the males will even have an erection. Chances are that the predator will assume the opossum is extremely sick or dead, and its instincts will tell it to keep away for the sake of its own health.
There have even been suggestions that the Virginia opossum somehow remains conscious during thanatosis. “Several authors have raised the question of consciousness during paralysis in animals. Our opossums appeared aware of their assailant during paralysis,” Geir Wing Gabrielsen, a senior research scientist in zoo physiology from the Institute of Medical Biology University of Tromsø in Norway wrote in his 1985 paper published by Acta Physiologica Scandinavica. “We observed a delay in recovery as long as the dog was present or the opossum was touched by man. During paralysis in ducks, the birds similarly appeared alert and aware of escape opportunities. They also seemed to distinguish between approaches by foxes and humans.”
More recently, scientists have investigated another of the Virginia opossum’s talents—its invulnerability to snake venom. The Virginia opossum is known to eat rattlesnakes, copperhead pit viper snakes, and some species of tropical pit vipers called lanceheads. These snakes all wield a powerful type of venom made up of dozens of toxic compounds that can cause massive internal hemorrhaging. Publishing in PLoS ONE in 2011, researchers from the American Museum of Natural History in New York suggested that the opossum’s resistance to viper venom is driving the substance’s rapid evolution. They discovered this by sequencing several opossum genes, including one that had been discovered in a previous study to code for a vital blood-clotting protein called the von Willebrand factor (vWF), which many snake-venom toxins target. Once they started to analyze the data, the researchers found that vWF was an outlier, evolving far more quickly than predicted, forcing the viper venom toxins to keep up by evolving just as quickly.
“Most herpetologists interpret this as evidence that venom in snakes evolves because of interactions with their prey, but if that were true, you would see equally rapid evolution in toxin-targeted molecules of prey species, which has not yet been seen,” said one of the researchers, Robert Voss, curator in the Department of Mammalogy at the American Museum of Natural History. “What we’ve found is that a venom-targeted protein is evolving rapidly in mammals that eat snakes. So it looks like the snake venom is evolving according to its dual roles—feeding and defense—and the snake-eating Virginia opossum is the force driving it.”
Well now, there’s a genius way of getting out of any situation ever, huh, Virginia Opossum? I bet you’re one of those guys who take a million sick days off work just because you can, while the rest of us have to sweat over our overly elaborate lies because we’re cursed with terrific immune systems.
But this kind of attitude can backfire on you, Virginia Opossum. Seriously. You’ll arrive at the office after another one of your “sick days” and realize you missed cake from Badger’s birthday, and everyone will be like, “Oh man, you missed some really good cake yesterday.” And then one of the interns will pipe up and say that actually, this is kind of embarrassing, but it’s her birthday today, and everyone will be like, “More cake!” And you’ll be ‘Oh my god, cake!’ at the same time, but then one of your coworkers—the me-equivalent who knows you’re full of shit—will be all, “Do you really think it’s a good idea to have cake so soon after you fainted and shat all over the carpet? Something is clearly not right with your bowels, Virginia Opossum, and cake is certainly not going to help.”
So then it will be cake time and everyone will have to stop what they’re doing and stand around the cake table, so awkwardly, Virginia Opossum, making small talk about how good the cake is for however long it takes before someone—most likely the me-equivalent—decides to sit back down because their work isn’t going to do itself. And imagine how much more awkward that situation would be for you, Virginia Opossum, because you won’t even have a piece of cake to stare down into and compare its deliciousness level to that of last week’s or yesterday’s cake.
But I guess of course you can always get out of the situation in the same way you get out of every situation and lapse into a pungent coma, but just know that the me-equivalent will be licking the ends of all your pens and farting on your keyboard before you’re even halfway home.
Underwater Mousedeer
WATER CHEVROTAIN
(Hyemoschus aquaticus)
“Seriously, Chevrotain, get out of the water. There’s no one here.”
“No, no, I’m fine where I am. It’s cool. We can play like this. Someone roll for me.”
“You landed on Pall Mall. Do you want it?”
“Want what?”
“PALL MALL.”
“Pall what? Oh, right. No, I’ll leave it.”
“WHAT?’”
“NO THANKS, I’LL LEAVE IT.”
“CAN’T HEAR Y—”
“I DON’T. WANT. IT.”
“I’m having the worst time.”
“WHAT?”
ALSO KNOWN AS A mousedeer, the chevrotain is a nimble, cat-sized mammal with a round, stocky body perched on delicate legs and hooves. It couldn’t look less suited to a life underwater, but its peculiar habit of submerging itself when threatened mirrors the evolutionary transition from terrestrial mammals to primitive whales.
Around 50 million years ago, the chevrotains split from the rest of the ruminants, which are a large group of herbivores including giraffes, cattle, antelopes, and goats that regurgitate their semi-digested food and chew it as cud. They evolved differently—most ruminants have four-chambered stomachs whereas chevrotains have three-ch
ambered stomachs—and separated into their own family called Tragulidae. There are now ten species of chevrotain in the world, found in Africa and Asia, and the water chevrotain (Hyemoschus aquaticus), also known as the fanged deer, is the largest and most primitive.
Until recently, it was assumed that chevrotains, like the deer they look so much like, were unequivocally land mammals, but a couple of chance sightings changed everything. In 2008, a group of researchers led by ecologist Erik Meijaard from the Nature Conservancy in Indonesia carried out a biodiversity survey in the Central Kalimantan Province of Borneo. They passed a greater Malay chevrotain (Tragulus napu) swimming in one of the forest streams. When it spotted the researchers, the startled chevrotain dove underwater and stayed submerged for an entire hour, briefly coming up for oxygen five or six times. Even more remarkable than its ability to stay underwater for multiple five-minute stretches, the particular chevrotain was able to do it while pregnant. The researchers confirmed what the Borneo locals had been saying for years—that the strange little chevrotains tend to head straight for the nearest creek or river to escape their dogs.
That same year, Meijaard and colleagues investigated a single chevrotain in Sri Lanka that submerged itself in a pond to escape a brown mongoose, describing its swimming behavior in Mammalian Biology:
