Sandfish lizards jostle back and forth, bending their bodies into a slithery S-curve to swim through the sands of the Sahara. Like scorpions and several other native desert species, they long ago mastered the difficult art of moving through the myriad grains of a sandy expanse to escape predators or the blistering African sun. And now physicists are close to cracking their secrets.
Daniel Goldman’s team has been trying to figure out just how the sandfish lizards do it for years now; in 2009 they built a robot to simulate the creature’s slithering motion. This time, for a study in the Journal of the Royal Society Interface, the scientists tried to model the physics of an animal knocking around so many grains of sand and see how the lizards burrow with such efficiency.
The team found sine-wave-like movement allows the lizard, and their robot, to push forward in sand, but creating computer models for the experiments proved problematic. Simulating all of the tiny sand grains required a lot of money to purchase time on powerful computers. So, the team performed the same experiments using 3-millimeter-wide glass beads instead of sand. “We wanted something easy to simulate that had some predictive power. We got lucky, because it turned out [the lizard and robot] swim beautifully in the same way through larger glass beads,” Goldman said. [Wired]
Ask a group of snake researchers whether our modern snakes evolved from land-loving or ocean-loving lizards, and you’re likely to start a heated argument. But the days of snake-origin squabbles may be coming to a close–researchers have created the first 3-D images of snake fossils and have discovered that their legs are more akin to the legs of land-dwelling lizards than they are to the ocean-dwelling kind.
The researchers studied a 95-million-year-old fossilized snake called Eupodophis descouensi that was found in present-day Lebanon. Published in the Journal of Vertebrate Paleontology, the scientists used a novel 3-D imaging technique called synchrotron-radiation computed laminography:
“Synchrotrons are enormous machines and allow us to see microscopic details in fossils invisible to any other techniques without damage to these invaluable specimens,” said co-author Paul Tafforeau from the European Synchrotron Radiation Facility. [Discovery News]
While the temperature effects of climate change are expected to be less dramatic in the equatorial regions, the cold-blooded tropical animals that live there may be in for a dramatic shock.
A study published this week in Nature focused on these cold-blooded animals–including insects, amphibians, and lizards–whose body temperatures are not constant, but instead rise and fall with the temperature of their environment. The researchers found that these creatures show great increases in their metabolism from slight changes in temperature; the metabolic increases were on the order of twice that of warm-blooded animals.
“The assumption has been that effects on organisms will be biggest in the place where the temperature has changed the most,” [first author Michael] Dillon said. “The underlying assumption is that … no matter where you start, a change means the same thing. But with physiology, that’s rarely the case.” [Scientific American].
This means that though climate change will be more extreme in toward the Earth’s poles, the cold-blooded animals that live near the equator (where changes should be milder) may react more strongly to the changes.
Whither the lizards?
That’s what biologist Barry Sinervo has been asking lately. In a study published on Friday in Science, Sinvero’s team raised the alarm about lizards around the world, saying that at the very least 6 percent of lizard species will go extinct by 2050, and as many as 20 percent could disappear forever by 2080.
Sinervo and his colleagues make this claim based in part on surveys they did in Mexico.
Sinervo and his team surveyed 48 species of spiny lizards at 200 sites on the Yucatan peninsula in Mexico that had been studied in detail from 1975 to 1995 and found that 12 percent of that population had already become extinct by 2009.
The lizards lived in well-protected areas like national parks, so it wasn’t habitat destruction that caused the population decline, Sinervo said. Instead, it was a tale of rising temperatures disrupting lizard lives [San Francisco Chronicle].
Sure, creatures that reproduce asexually get to avoid some of the hangups that come with sex, but the strategy brings its own problems. First and foremost, how do you prevent genetic deterioration without the fresh infusion of new genes that results from the mixing of male and female DNA? For the all-female whiptail lizard, the solution is to hedge its bets.
In a study forthcoming in Nature, researcher Peter Baumann found that each whiptail lizard egg cells contains twice the number of chromosomes you’d expect. In the fertilized egg cell of a sexually reproducing lizard species, you’d expect to see much what you see in humans—23 chromosomes from the father and 23 from the mother combining into 46. (Most human cells contain 46 chromosomes, but egg and sperm cells contain only 23, so that they can combine to give an offspring a compete, but genetically new, set of chromosomes.)
But the whiptail eggs instead begin with two identical copies of each of their mother’s chromosomes, for a total of 92. Those chromosomes then pair with their identical duplicates, and after two cell divisions, a mature egg with 46 chromosomes is produced. Since crossing-over during the cell divisions occurs only between pairs of identical chromosomes, the lizard that develops from the unfertilized egg is identical to its mother [The New York Times].
When a gecko is desperately trying to escape from a predator, it has a creepy trick: It detaches its tail and leaves it wriggling on the ground to distract the hunter, while the rest of the lizard scampers off. Now, with high-speed video researchers have studied what happens to the left-behind tail, and they found that it flips and flops acrobatically, and changes direction and speed depending on what it bumps into. Researchers (and lizard-watching kids) already knew that the severed tail continues to move, but this study in the journal Biology Letters is the first to determine that the tail can independently respond to its environment.
Says lead researcher Anthony Russell: “The tail is buying the animal that shed it some time to get away.” … If the tail simply moved rhythmically back and forth, predators would quickly recognize a pattern and realize they’d been duped. Unpredictable tail movements keep predators occupied longer, and in some cases, they may even allow the tail itself to escape [Wired.com]. Russell notes that the leopard geckos he studied store fat in their tails, and suggests that if the tail can flop far enough away from the predator the gecko could return later to eat its own tail.
The sandfish lizard appears to “swim” like a fish through sand, but how exactly the animal does it has long puzzled biophysicists. Now, a study published in Science reveals that the four-legged creature really does swim through sand like it would in water by retracting its legs and undulating its body.
To examine the lizard’s movement, researchers had to peek underground. They did this using X-ray imaging, and found that once the lizard, or skink, has dived beneath the sand, it doesn’t paddle. “When started above the surface, the animals dive into the sand within half a second. Once below the surface, they no longer use their limbs for propulsion — instead, they move forward by propagating a traveling wave down their bodies like a snake,” said study leader Daniel Goldman [LiveScience]. This movement was surprising because previous magnetic resonance imaging studies seemed to suggest that the lizards pushed themselves along using their legs.
The first researchers who spotted Australian dragon lizards trotting along on their hind legs were amused, perplexed, and amazed. When the critters took off over the dusty plain in a high-speed dash, they lifted their front legs and ran bipedally, looking a bit like tiny dinosaurs.
Those early researchers assumed that the trick must give the lizards an advantage in speed or endurance, but they didn’t do the lizard races to prove it. They also wondered if the lizards were gradually evolving into entirely bipedal animals. Now, a new study in the Journal of Experimental Biology [subscription required] declares that the maneuver does not help the lizards put on extra speed after all, and actually decreases endurance. In a surprising twist, researchers called the lizards’ upright stance just an “evolutionary accident.”