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].
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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.
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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.
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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.”
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