Category: Mammals

Why porcupine quills slide in with ease but come out with difficulty

By Ed Yong | December 11, 2012 8:00 am

A shorter version of this story appears at Nature News.

In August of this year, Allison Noles rushed her bulldog Bella Mae to the vet. The dog’s face looked like a pincushion, with some 500 spines protruding from her face, paws and body. The internet is littered with such pictures, of Bella Mae and other unfortunate dogs. To find them, just search for “porcupine quills”.

North American porcupines have around 30,000 quills on their backs. While it’s a myth that the quills can be shot out, they can certainly be rammed into the face of a would-be predator. Each one is tipped with microscopic backwards-facing barbs, which supposedly make it harder to pull the quills out once they’re stuck in. That explains why punctured pooches need trips to the vet to denude their faces.

But that’s not all the barbs do. Woo Kyung Cho from Harvard Medical School and Massachusetts Institute of Technology has found that the barbs also make it easier for the quills to impale flesh in the first place. “This is the only system with this dual functionality, where a single feature—the barbs—both reduces penetration force and increases pull-out force,” says Jeffrey Karp, who led the study.

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For 150 years, no one had ever seen a full spade-toothed whale. Then two wash up on a beach.

By Ed Yong | November 5, 2012 12:00 pm

For almost 150 years, no one had seen a spade-toothed whale. That’s not to say that the animal had gone extinct – no one had ever seen one alive. The first clue to its existence came in 1872, when Scottish geologist James Hector described an unusual jaw that had been collected from New Zealand’s Pitt Island a year earlier. Two more partial skulls would follow: another from New Zealand’s White Island in 1950 and the other from Chile’s Robinson Crusoe Island in 1986. But still, no one had seen the animal in the flesh.

Then, in December 2010, two of them washed up on Opape Beach in New Zealand.

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Leopard seals suck

By Ed Yong | November 1, 2012 12:00 pm

“It is an awe-inspiring experience to be faced with a 3-metre-long, 500 kilogram predator, the size of a racehorse, as it launches itself out of the water and slides on its belly for a couple of seconds, coming to a halt barely a metre away from where I stood, without any barrier between me and it.”

That was how Erich Fitzgerald met Sabine the leopard seal.

Leopard seals are like the lions of the Antarctic. They are huge, powerful predators, known for their brutal killing strategy. They bite penguins and seal pups with their big canines, and thrash them onto the surface of the water to flay and dismember their prey.

But Fitzgerald, David Hocking and Alistair Evans have shown that these predators can take smaller prey in a very different way. They suck krill and small fish into their mouths and sieve them in the manner of whales, by passing their mouthfuls of water through tightly interlocking teeth. It’s astonishing behaviour that allows them to dine from the top and bottom of the food chain. As Fitzgerald told me: “This is equivalent to a lion hunting down zebras, but also regularly feasting on ants or termites.

I’ve written about the story for Nature News. Head over there for the full details.

Q: Why don’t apes have bigger brains? A: They can’t eat enough to afford them

By Ed Yong | October 23, 2012 9:00 am

As animals get bigger, so do their brains. But the human brain is seven times bigger than that of other similarly sized animals. Our close relative, the chimpanzee, has a brain that’s just twice as big as expected for its size. And the gorilla, which can grow to be three times bigger than us, has a smaller brain than we do.

Many scientists ask why our brains have become so big. But Karina Fonseca-Azevedo and Suzana Herculano-Houzel from the Federal University of Rio de Janeiro have turned that question on its head—they want to know why other apes haven’t evolved bigger brains. (Yes, humans are apes; for this piece, I am using “apes” to mean “apes other than us”).

Their argument is simple: brains demand exceptional amounts of energy. Each gram of brain uses up more energy than each gram of body. And bigger brains, which have more neurons, consume more fuel. On their typical diets of raw foods, great apes can’t afford to fuel more neurons than they already have. To do so, they would need to spend an implausible amount of time on foraging and feeding. An ape can’t evolve a brain as big as a human’s, while still eating like an ape. Their energy budget simply wouldn’t balance.

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NOC, the white whale that tried to sound like a human

By Ed Yong | October 22, 2012 12:00 pm

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Listen to this recording. It sounds like a drunkard playing a kazoo, but it’s actually the call of a beluga (a white whale) called NOC. Belugas don’t normally sound like that; instead, NOC’s handlers think that his bizarre sounds were an attempt at mimicking the sounds of human speech.

The idea isn’t far-fetched. Belugas are so vocal that they’re often called “sea canaries”. William Schevill and Barbara Lawrence – the first scientists to study beluga sounds in the wild – wrote that the calls would occasionally “suggest a crowd of children shouting in the distance”. Ever since, there have been many anecdotes that these animals could mimic human voices, including claims that Lagosi, a male beluga at Vancouver Aquarium, could speak his own name. But until now, no one had done the key experiment. No one had recorded a beluga doing its alleged human impression, and analysed the call’s acoustic features.

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Spiny mice defend themselves with self-flaying skin and fast healing factors

By Ed Yong | September 26, 2012 1:00 pm

When Marvel Comics created a short superhero who could heal horrific injuries, perhaps instead of “Wolverine”, they should have named him “African spiny mouse”. These tiny rodents can jettison strips of skin from their own hides when captured by predators, and heal those same wounds with extraordinary speed.

Healing powers are common in the animal world. Salamanders and starfish can regrow lost limbs, while some flatworms can regenerate their bodies from a single cell. But mammals lag behind – while some species can grow back a lost tail, when most of us lose our body parts, we do so permanently. The spiny mice are an exception.

Biologists have noted that these rodents have very weak skin, which seems to slough off easily when they are handled. Led by these anecdotal reports, Ashley Seifert from the University of Florida has studied the skin-shedding ability in greater depth, focusing on two species: Kemp’s spiny mouse (Acomys kempi); and Percival’s spiny mouse (Acomys percivali).

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One way to skin a cat – same genes behind blotches of tabbies and king cheetahs

By Ed Yong | September 20, 2012 2:00 pm

The cheetah’s spots look like the work of a skilled artist, who has delicately dabbed dots of ink upon the animal’s coat. By contrast, the king cheetah – a rare breed from southern Africa – looks like the same artist had a bad day and knocked the whole ink pot over. With thick stripes running down its back, and disorderly blotches over the rest of its body, the king cheetah looks so unusual that it was originally considered a separate species. Its true nature as a mutant breed was finally confirmed in 1981 when two captive spotted females each gave birth to a king.

Two teams of scientists, led by Greg Barsh from the HudsonAlpha Institute for Biotechnology and Stanford University, and Stephen O’Brien from the Frederick National Laboratory for Cancer Research have discovered the gene behind the king cheetah’s ink-stains. And it’s the same gene that turns a mackerel-striped tabby cat into a blotched “classic” one.

Back in 2010, Eduardo Eizirik, one of O’Brien’s team, found a small region of DNA that seemed to control the different markings in mackerel and blotched tabbies. But, we only have a rough draft of the cat genome, they couldn’t identify any specific genes within the area. The study caught the attention of Barsh, who had long been interested in understanding how cats get their patterns, from tiger stripes to leopard rosettes. The two teams started working together.

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Why do killer whales go through menopause?

By Ed Yong | September 13, 2012 2:00 pm

Here’s yet another reason why humans are weird: menopause. During our 40s, women permanently lose the ability to have children, but continue to live for decades. In doing this, we are virtually alone in the animal kingdom. From a cold evolutionary point of view, why would an animal continue to live past the point when it could pass on its genes to the next generation? Or put it another way: why don’t we keep on making babies till we die? Why does our reproductive lifespan cut out early?

One of the most popular explanations, first proposed in the 1966, involves helpful grandmothers. Even if older women are infertile, they can still ensure that their genes cascade through future generations by caring for their children, and helping to raise their grandchildren.* There’s evidence to support this “grandmother hypothesis” in humans: It seems that mothers can indeed boost their number of grandchildren by stepping out of the reproductive rat-race as soon as their daughters join it, becoming helpers rather than competitors.

Now, Emma Foster from the University of Exeter has found similar evidence among one of the only other animals that shows menopause: the killer whale.

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Same gene linked to bigger brains of dolphins and primates

By Ed Yong | September 11, 2012 7:00 pm

Every whale and dolphin evolved from a deer-like animal with slender, hoofed legs, which lived between 53 and 56 million years ago. Over time, these ancestral creatures became more streamlined, and their tails widened into flukes. They lost their hind limbs, and their front ones became paddles. And they became smarter. Today, whales and dolphins – collectively known as cetaceans – are among the most intelligent of mammals, with smarts that rival our own primate relatives.

Now, Shixia Xu from Nanjing Normal University has found that a gene called ASPM seems to have played an important role in the evolution of cetacean brains. The gene shows clear signatures of adaptive change at two points in history, when the brains of some cetaceans ballooned in size. But ASPM has also been linked to the evolution of bigger brains in another branch of the mammal family tree – ours. It went through similar bursts of accelerated evolution in the great apes, and especially in our own ancestors after they split away from chimpanzees.

It seems that both primates and cetaceans—the intellectual heavyweights of the animal world—could owe our bulging brains to changes in the same gene. “It’s a significant result,” says Michael McGowen, who studies the genetic evolution of whales at Wayne State University. “The work on ASPM shows clear evidence of adaptive evolution, and adds to the growing evidence of convergence between primates and cetaceans from a molecular perspective.”

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One gait-keeper gene allows horses to move in unusual ways

By Ed Yong | August 29, 2012 1:00 pm

Icelandic horses can move in an odd way. All horses have three natural gaits: the standard walk; the two-beat trot, where diagonally opposite pairs of legs hit the ground together; and the four-beat gallop, where the four feet hit the ground in turn.  To those, Icelandic horses add the tölt. It has four beats, like the gallop, but a tölting horse always has at least one foot on the ground, while a galloping one is essentially flying for part of its stride. This constant contact makes for a smoother ride. It also looks… weird, like watching a horse power-walk straight into the uncanny valley.

The tölt is just one of several special ambling gaits that some horses can pull off, but others cannot. These abilities can be heritable, to about the same extent that height is in humans. Indeed, some horses like the Tennessee Walking horse have been bred to specialise in certain gaits.

Now, a team of Swedish, Icelandic and American scientists has shown that these special moves require a single change in a gene called DMRT3. It creates a protein used in neurons of a horse’s spine, those which coordinate the movements of its limbs. It’s a gait-keeper.

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