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Giant Whales Have Super-Stretchy Nerves

“Hey, look at this,” said Bob Shadwick. He and his team were working on the dissected remains of a fin whale, the second largest animal on the planet, when they noticed a white cord-like structure lying against a slab of muscle. Shadwick picked it up and jokingly stretched it. “It was like a bungee cord,” recalls A. Wayne Vogl who was part of the group. It extended to more than twice its original length before recoiling back.

The team initially thought it was a blood vessel, but they soon realised that it wasn’t hollow. They looked closer and noticed that it had a yellowish central core, surrounded by a thick white coating. “It was then that we realized it must be a nerve, unlike anything we had seen before,” says Vogl.

On one hand, that made no sense. In mammals, nerves have a little slack in them but if you extend them by 10 percent, they’ll stop carrying electrical signals properly. Extend them by 30 percent and they’ll snap. Stretch injuries are the most common type of nerve injuries in people, and can lead to shooting pains, loss of sensation, and paralysis. Simply put: nerves don’t stretch.

On the other hand, the fin whale’s stretchy nerve made perfect sense. This is an animal whose entire existence is built upon extreme feats of stretchiness.

A fin whale nerve being stretched. Credit: Vogt et al, 2015.
A fin whale nerve being stretched. Credit: Vogt et al, 2015.

The giant rorqual whales—fins, blues, humpbacks, minkes, and their kin—feed on tiny crustaceans called krill, which they swallow by the millions using a unique technique called lunge-feeding. A rorqual will accelerate towards a swarm of krill at high speed and suddenly open its gargantuan mouth to a right angle. The two bones of the lower jaw swing outwards, widening the mouth; the tongue inverts, creating even more room. The whole mouth balloons outwards, increasing in circumference by around 162 percent and engulfing an astonishing amount of krill and water. A blue whale can swallow around half a million calories in a single mouthful.

Long pleats in the whale’s mouth allow it to expand without tearing skin or muscle. But what about nerves? Large nerves course through the lower jaw, connecting to the tongue and blubber. Those have to stretch and, as Vogl and Shadwick showed, they do.


The strategy, Vogt writes, is “simple yet elegant”. Each nerve contains bundles of fibres, called fascicles, which sit at its core and are highly folded. The fascicles are surrounded by a thick wall made of two proteins: sturdy collage and stretchy elastin. When a whale lunges, the fascicles and collagen fibres unfold, while the elastin fibres stretch. Once the collagen fibres unfold fully, they become taut, stopping the nerve from stretching any further (and potentially breaking). As the whale closes its mouth after a lunge, the elastin fibres pull the nerve back into its original shape.

And that’s it. The nerve fibres themselves don’t actually stretch. It’s more that they unfold. But that still makes them special. Other nerves that reside in the neck and ribcage of a fin whale don’t have this property, and are barely more extensible than those in your face. Those in the whale’s face, by becoming stretchier, allowed it to evolve its extraordinary style of feeding and its record-breaking size. Without stretchy nerves, fin and blue whales would never have become the giants that they are.

This unexpected discovery highlights how little we know about the giant whales, which have captivated our imaginations for millennia. Just a few years ago, the same team behind this new study discovered that rorquals have a volleyball-sized sense organ at the tips of their lower jaws—and no one had ever seen it before. There are undoubtedly surprises still to come. “One of the big mysteries yet to solve is how these animals actually swallow the food they concentrate after a lunge,” says Vogl. “We still don’t know this.”

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Why Killer Whales Go Through Menopause But Elephants Don’t

Last summer, I met Granny. I was on a whale-watching boat that had sailed south from Vancouver Island, in search of a famous and well-studied group of killer whales (orcas). Two hours after we set off, we started seeing black fins scything through the unusually calm and glassy water. We saw a dozen individuals in all, and our guide identified them by the shape of their fins and the white saddle patches on their backs. Granny, for example, has a distinctive half-moon notch in her dorsal fin.

Seeing her, I felt an intense and solemn respect. She is the oldest member of the group, perhaps the oldest orca on the planet. Her true age is unknown, but a commonly quoted estimate puts her at 103, which would make her a year older than the Titanic, and far more durable. Imagine all that she has seen in that time: the generations of her children and grandchildren; the countless pursuits of fleeing salmon; the increasingly noisy presence of fishermen, scientists and gawking tourists. Decades of knowledge and wisdom live in her brain. Ad that knowledge might explain one of the most unusual features of killer whale biology—their menopause.

Animals almost always continue to reproduce until they die. There are just three exceptions that we know of: humans, short-finned pilot whales, and killer whales. In all three species, females lose the ability to have children, but continue living for decades after. That’s menopause. Female killer whales go through in their 30s or 40s. Why? Why sacrifice so many future chances to pass on your genes to the next generation?

One of the most compelling explanations is called the grandmother hypothesis. Proposed in 1966, it suggests that older females forgo the option to bear more children so they can support their existing ones. By helping their children and grandchildren to survive and thrive, they still ensure that their genes cascade down the generations.

In 2012, Darren Croft at the University of Exeter found evidence to support this hypothesis. His collaborator Ken Balcomb had been studying the resident killer whales of the Pacific Northwest since the 1970s; his astonishingly thorough census had captured the lives, deaths, and family ties of hundreds of these whales.

By ploughing through the data, student Emma Foster showed that if a male orca’s mother died before his thirtieth birthday, he was three times more likely to die the next year. If she passed away after he turned thirty, he was eight times more likely to subsequently snuff it. And if mum had gone through menopause, his odds of dying went up by fourteen times. The data were clear: mothers help their sons well into adulthood, and older mums are especially helpful.

“But that left a big unanswered question,” says Croft. “Old females are keeping their offspring alive, but how? What is it that they’re doing to confer the survival benefit?”

One reasonable guess involves salmon. Salmon makes up 97 percent of the diet of these particular orcas, and salmon are unpredictable. “They’re not distributed equally in space,” says Croft. “There are hotspots that differ with season, year, tide.” So just like human fishermen, the orcas need to know when and where to go to catch their fish. Do they stay at sea or swim inland? Do they go up their inlet or that one? The oldest females might be better at making these decisions, thanks to their accumulated experience.

To test this idea, the team turned to video footage of the southern residents, which Balcomb’s team had captured between 2001 to 2009. Postdoc Lauren Brent analysed over 750 hours of video to work out which whales were swimming together, and who was following whom. She also collected data from nearby fisheries to work out how big the salmon stocks were at different times.

She found that adult females are more likely to lead a group than adult males, and older post-menopasual females (who make up a fifth of the pod) were more likely to lead than younger ones. This bias was especially obvious in seasons when salmon stocks were low. And, as Foster found, there was a sex bias—males were more likely to follow their mother than females were.

These simple trends support the idea that the post-menopausal orcas are “repositories of ecological knowledge”. They lead the others to food, and their skills are especially important at times when food is scarce. And in doing so, they help their young to survive, which offsets the costs of forgoing any further reproduction. “That doesn’t tell us why they stop reproducing,” says Croft. “You could share information while still being reproductive. Why did they stop? That’s the next question.”

The same principles apply to human menopause, too. Some scientists have suggested that human menopause is merely a side effect of our longer lifespans, brought about by medicine and sanitation. But that can’t be right. Among many hunter-gatherers, like the Ache of Paraguay or the Hadza of Tanzania, around half of women survive to 45, and continue living into their late 60s. Like killer whales, they live long after the stop reproducing. And like killer whales, the longer they live, the more they know. In 2001, anthropologist Jared Diamond wrote:

“Old people are the repositories of knowledge in preliterate societies. In my field studies of New Guinea birds, I start work in a new area by gathering the oldest hunters and quizzing them… When the hunters are stumped by my asking about some especially rare bird, they answer: “We don’t know, let’s ask the old man (or woman).” We go into another hut, where we find a blind and toothless old person who can describe a rare bird last seen 50 years ago. Some of that stored information is essential to the survival of the whole village, whose members include most living relatives of the old person. The information encompasses wisdom about how to survive dangers — such as droughts, crop failures, cyclones and raids — that occur at long intervals but that could kill the whole tribe if it did not know how to react.”

Why, then, don’t elephants go through menopause? They are also long-lived animals that stay in family groups, and the old females—the matriarchs—are vital. They are better at recognising friendly faces and they know the best anti-lion moves. They provide their herds with the same benefits that orcas like Granny bestow upon their pods.

But resident killer whales differ from elephants in one critical respect: their sons and daughters stay in the groups where they were born. This means that as a female grows older, her pod becomes increasingly full of her own children and grandchildren. Over time, she becomes increasingly related to her neighbours, and she shares more and more of her genes with her neighbours. This creates a powerful impetus to shift her efforts away from having more children, and towards helping her existing descendants.

That impetus doesn’t exist in elephants because their sons eventually leave their birth group to find new ones. Females become less related to their group-mates over time or, at least, no more related. A matriarch’s best bet, then, is to carry on reproducing until she dies.

And humans? Many anthropologists believed that we started off with female-biased dispersal—that is, daughters would leave to join new groups. “When she joins, she has zero relatedness to the rest of the group,” explains Croft. “But as she ages, she has offspring and her local relatedness increases.” Then again, other animals like hamadryas baboons and the Seychelles warbler also have female-biased dispersal and don’t go through menopause. “So, it’s not just about the dispersal patterns but also the role that old females can play in the group,” says Croft.

In killer whales, the old females might also be better at catching salmon, which they then share with their kin. Perhaps they understand the hierarchies and structures of other groups, and mediate fights between their sons and rivals. These ideas are harder to test. “We have so little information on them,” says Croft. “We see them at the surface and we know so little about their lives.”

Reference: Brent, Franks, Foster, Balcomb, Cant & Croft. 2015. Ecological Knowledge, Leadership, and the Evolution of Menopause in Killer Whales. Current Biology http://dx.doi.org/10.1016/j.cub.2015.01.037

More on menopause:

Why do killer whales go through menopause?

Did conflict between old and young women drive origin of menopause?

The heavy cost of having children

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Electric Eels Can Remotely Control Their Prey’s Muscles

A fish swims in the Amazon, amid murky water and overgrown vegetation. It is concealed, but it’s not safe. Suddenly, two rapid bursts of electricity course through the water, activating the neurons that control the fish’s muscles. It twitches, giving away its position, and dooming itself. Now, it gets zapped by a continuous volley of electric pulses. All its muscles contract and its body stiffens. It can’t escape; it can’t even move. Its attacker—an electric eel—moves in for the kill.

The electric eel can (in)famously create its own electricity. More than four-fifths of its two-metre-long body consists of special battery-like cells, which can collectively deliver a jolt of up to 600 volts. But the way the eel uses that ability is even more shocking. Kenneth Catania from Vanderbilt University has found that this astonishing predator can use its electricity like a remote control, activating its prey’s muscles from afar. It effectively has a button that says “Reveal Yourself” and another that says “Freeze”.

“This is one of the most amazing things I’ve encountered in studying animals, and I’ve seen a lot of unusual things” says Catania. He’s not exaggerating. This is a man who showed that crocodile faces are more sensitive than our fingertips, that tentacled snakes can persuade prey to swim into their mouths, and that star-nosed moles blow bubbles to smell underwater. Guy knows amazing and unusual.

The eel tops them all, not least because its hunting tactics seems unbeatable. It should work on any prey with nerves and muscles, which is most of them.

“I don’t see any defence against it,” says Catania.

Electric eel. Credit: Ken Catania.
Electric eel. Credit: Ken Catania.

Although scientists have studied the electric eel’s anatomy and even sequenced its genome, hardly anyone had looked at how it hunts. “The sense, and I had the same reaction, was that they zap their prey with electricity and eat it; what more is there to know?” says Catania. As it happens: a lot!

Once Catania got his (rubber-gloved) hands on some eels, he realised that they are surprisingly fast. “I thought they might lazily shock their prey and then deal with it afterwards, but they combine the shock with a really rapid strike,” he says. He filmed them with a high-speed camera and noticed something remarkable. When the eels approached their prey, they released an intense volley of high-voltage pulses—around 400 a second. These pulses completely freeze the prey, and that’s when the eel lunges. If the fish isn’t paralysed, the strike would miss. “At that point, I was hooked,” says Catania. “I just had to know more.”

To work out what the pulses were doing, Catania presented eels with zombie prey—lobotomised and anaesthetised fish that were hooked up to a device for measuring forces. An agar barrier prevented the eel from reaching the morsels but allowed its discharges to pass. This macabre set-up confirmed that the eels’ high-voltage pulses force the fish’s muscles to involuntarily contract.

Credit: Catania, 2014. Science
Credit: Catania, 2014. Science

The pulses could either act on the muscles themselves, or on the neurons that control them. To distinguish between these possibilities, Catania injected the fish with curare, a poison that blocks the junctions connecting nerves and muscles. These individuals were immune to the eels’ shocks—a clear sign that the pulses act on the neurons, rather than directly on the muscles.

“That’s pretty much how a taser works,” says Catania. Indeed, getting shot with a taser is probably the closest anyone might come to being on the receiving end of an electric eel. Failing that, “the next most common experience might be to accidentally touch an electric fence at a horse or cattle farm”.

Catania also found that the eels precede their lengthy volleys with a quick pair of pulses. Doublets like these are known to trigger disproportionately strong muscle contractions. The eel, it seems, produces exactly the right kinds of discharge to freeze its prey as efficiently as possible.

But it also produces doublets when there’s no prey in sight. Since the 1970s, scientists have known that hungry eels will prowl around their cages, giving off electric doublets as they explore. And in Catania’s experiments, the eels often released a doublet, and then tried to break through the agar barrier and snatch the fish. That was a big clue: Catania wondered if they might be using the pulses to find their prey in the first place.

“Transport yourself to the Amazon and imagine these nocturnal animals hunting for diverse prey, which are hidden in a complex environment,” he says. So, they release doublets. Any fish or crab that gets hit would twitch and give itself away.

Catania tested this idea by placing the zombie fish in a thin plastic bag to isolate them from any electric pulses. When the eels released their doublets, the fish didn’t react, and the eels never attacked. When Catania deliberately jostled the fish to mimic a twitch, the eels struck. They are extraordinarily sensitive to ripples in the water, and the slightest movement sets them off. And they’re so fast that they can hit the source of the twitch within 20 thousandths of a second. “If you saw this in real-time, you wouldn’t even know that the doublet had elicited a movement in the fish because it would happen so fast,” says Catania.

Many fish can produce weak electric fields, including the elephantfishes of Africa and the knifefish of South America. But only a few can produce strong potentially lethal fields. These include the electric eel (which is actually a knifefish and not an eel at all), the electric catfishes, and the torpedo ray. The eel is the most powerful of these shockers, but Catania suspects that the others might use the same hunting technique. “I wish I had some in the lab,” he says.

Reference: Catania, 2014. The shocking predatory strike of the electric eel. Science http://dx.doi.org/10.1126/science.1260807

PS: Yes, this really is a single-author paper, published in Science in 2014. That’s arguably as shocking as the eel.

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Fruit Bats Have Sonar Too (But It’s Not Very Good)

One in every five species of mammal is a bat. This incredibly successful group splits into two major camps. The so-called microbats include vampires, horseshoes and some 1,000 other species, all of which use sonar to navigate through the dark. They make high-pitched clicks and they use the rebounding echoes to map the world, just like a submarine.

The other group—the megabats or fruit bats—has fewer than 200 species. They tend to be bigger and, with one exception, they don’t use echolocation. They have neither the specialised body parts needed to produce the necessary clicks, nor the genetic signatures that are common to sonar users. Instead, they rely on their large eyes to see at night.

Or, at least, that’s what everyone thought.

Arjan Boonman from Tel Aviv University has put a spanner in this long-held idea, by showing that three species of fruit bats all use a form of echolocation. They have sonar. Okay, it’s crap and inefficient sonar, but sonar nonetheless. Weirder still, the bats produce it with their wings.

There were hints of this before. In the 1980s, Edwin Gould found that the cave nectar bat of southeast Asia makes clicking noises as it flies. Gould thought that it was slapping its wings together with every beat, but couldn’t work out whether the clicks had a purpose. Boonman wanted to find out more.

Together with Sara Bumrungsri and Yossi Yovel, he studied the cave nectar bat, as well as the lesser short-nosed fruit bat and the long-tongued fruit bat. He found that as the animals flew in a pitch-black tunnel, they all made audible clicks. The clicks aren’t accidents of flight. The team showed that the bats can adjust the rate of these sounds, and they click more furiously when flying in the dark than in dim light. Perhaps they actually use these noises to find their way around.

To test this idea, the team released the bats into a room containing a dozen inch-thick hanging cables. This kind of obstacle course is a classic of bat research, and echolocating species can easily weave their way around the cables. The fruit bats could not. Despite their clicks, they crashed often.

But the team didn’t give up. They trained a dozen cave nectar and short-nosed bats to discriminate between two big metre-wide boards: a harder one that’s great at reflecting echoes, and a cloth-covered one that absorbs more sound. Visually, the boards were similar; acoustically, worlds apart. And the bats could tell. They quickly learned to land on the right target and did so 7 times out of 10.

They weren’t exactly graceful about it, though. As the team wrote, “Despite the target being very large, our bats mostly required several attempts in order to land, often crashing into the target in an uncontrolled manner.” Unlike microbats, some of which can snatch spiders from their webs without getting entangled, these big species can barely gauge the distance of a whopping big board. Their sonar is rather unsophisticated, which explains why this behaviour has never been discovered before. People were trying to get the bats to do tasks that were well outside their limited abilities.

Boonman’s team also found that the fruit bats make their sonar clicks in a weird way. Microbats use their voice boxes, in the same way that you might speak or sing. The Egyptian fruit bat—until now, the only megabat known to use sonar—has a different technique: it clicks with its tongue. But Boonman’s three fruit bats shut their mouths when they fly. They click nonetheless, and sealing their mouths with tape does nothing to stop them.

Instead, they seem to use their wings. The clicks are perfectly synchronised with their wingbeats, and can be stopped by weighing one wing down with tape. The bats could be slapping their wings together as Gould suggested, or slapping their wings against some other body part, or even clicking bones within the wings as you or I might crack our knuckles.

“There’s obviously something unusual going on because it doesn’t seem to be linked to the wingbeat frequency,” says Gareth Jones from the University of Bristol. That is, the bats don’t seemto flap any differently in bright light or pitch blackness. “If it was a simple wing-slapping thing, there should be a 1:1 relationship between wingbeats and clicks, but there isn’t. Something odd’s going on there.”

“The discovery changes the discussion of how bats may have evolved sophisticated echolocation,” says Aaron Corcoran from Wake Forest University. “The results are too preliminary to answer that difficult question, but they will make bat biologists rethink the possibilities.”

Bat researchers are divided over how many times echolocation evolved. Some think that it evolved once in the common ancestor of all bats, and was then lost in the fruit bats. Others suggest that it evolved twice in different lineages of microbats, and fruit bats never had it. In both scenarios, the Egyptian fruit bat evolved its tongue-clicking technique independently. And the wing-clicks of the other fruit bats might represent yet another origin. “It’s a major discovery in echolocation research,” says Marc Holderied from the University of Bristol. “It’s a third independent evolution of echolocation, which is truly exciting.”

The wing-clicks might even give clues about how the superior sonar of other bats first evolved. You don’t need any special adaptations to use a crude form of echolocation. Even blind humans can do it with enough training. Some people have suggested that the bats initially used echolocation to avoid large obstacles like cave walls, before they honed the technique for finer navigation.

To be clear, fruit bat sonar isn’t a direct predecessor of microbat sonar. Think of it more as a historical painting—a reconstruction of a possible past. As Boonman writes, “We believe that fruit bats are behavioral fossils, presenting an ancient sensory behavior that (even if recently evolved) allows a rare glimpse at the evolution of a sensory system.”

Reference: Boonman, Bumrungsri & Yovel. 2014. Nonecholocating Fruit Bats Produce Biosonar Clicks with Their Wings. Current Biology http://dx.doi.org/10.1016/j.cub.2014.10.077

More on bats and echolocation:

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Whales Aren’t Keen on Being Flayed Alive By Gulls

The southern right whale is a huge fortress of animal—50 feet and 60 tons of muscle and blubber. At its size, this giant should have nothing to fear from ocean predators, except possibly for killer whales. But in the waters around Argentina, southern rights have been so badly tormented by an unusual threat that they have been forced to take stealthy precautions.

Their nemesis is the kelp gull.

Kelp gulls, like most of their kind, are opportunists. They’ll pluck fish from the sea, and scraps from landfill sites. And those near Peninsula Valdes in Argentina have started stripping flesh from the backs of whales.

Thousands of southern rights gather in those waters to breed between June and December. As they come up for air, the gulls land on their backs and tear off chunks of skin and blubber, leaving 20-centimetre long wounds. As many as eight birds can target one unfortunate whale.

As I reported two years ago, scientists first documented these attacks in 1972. They were rare then, but have been getting steadily worse. By 2008, some 77 percent of the whales were swimming around with gull-inflicted gashes. Partly, that’s because gull populations have soared thanks to the food provided by human fisheries and dumps. They may also be learning the behaviour from each other.

“Nowadays, gull attacks are so widespread in waters surrounding Península Valdés that it seems that there is no place without this interaction,” writes Ana Fazio from CONICET, an Argentinian institution.

The wounds might riddle the whales with skin infections, especially if the gulls are sticking their faces in rubbish heaps beforehand. They might also be distractions. Fazio found that the whales spend a quarter of their daylight hours trying to avoid the gulls, which might exhaust them, while depriving them of feeding opportunities. The calves suffer most: some 80 percent of the gulls’ attacks are aimed at mother-calf pairs.

Local government authorities have recently decided to take action, prompted in large part by pressure from visitors and tour operators. They have kick-started a management programme to protect the whales, including everything from killing the attacking birds, to closing landfills and reducing the waste that sustains the large gull populations.

Meanwhile, the whales have started taking matters in their own flippers. Clearly, they’re not keen on being flayed alive by gulls. They react by flinching strongly, arching their bodies so their heads and tails come up while their backs submerge. Scientists have described this posture as the “galleon position” or “crocodiling”.

Then, in 2008, they started doing something new.

Usually, when they come up for a breath, they do so in a leisurely way, lying parallel against the water surface with much of their backs exposed. But in 2009, Fazio’s team saw that a few of the whales would instead rise at a 45 degree angle so that only their heads were exposed, and only up to their blowhole. Their breaths were shorter and stronger than usual, and they quickly submerged again.

This technique, which the team called “oblique breathing”, exposes as little flesh as possible to the marauding gulls. It’s especially common at a site called El Doradillo, where the gull attacks are especially common. In 2010, 3 percent of the whales in El Doradillo were using oblique breathing. By 2013, 70 percent were doing it, and the behaviour had spread to neighbouring tracts of water. And most recently, the whales have started doing it even when they aren’t attacked, possibly as a preventive measure or to teach the trick to their calves.

It looks like the whales have won this round, but Fazio notes that oblique breathing isn’t an easy technique. These animals are naturally buoyant at the sea surface, so it takes energy to keep their backs and tails underwater. The technique may be especially taxing for the calves and this, combined with the actual attacks, may explain why the calves of Peninsula Valdes are dying in higher numbers than expected.

Reference: Fazio, Belen-Arguelles & Bertellotti. 2014. Change in southern right whale breathing behavior in response to gull attacks. Marine Biology http://dx.doi.org/10.1007/s00227-014-2576-6

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Pregnant Snake Prepares For Motherhood By Eating Toxic Toads

Some expectant mothers prepare for the arrival of their babies by reading books of parenting tips, painting nurseries, and buying a pram. The tiger keelback snake takes a different approach. When females get pregnant, they slither into the forest to eat as many poisonous toads as they can find.

The tiger keelback is a beautiful orange, olive, and black creature found in Japan. It defends itself with two glands on its neck, which contain poisons called bufadienolides. These irritate the airways and harm the hearts of any would-be predator. But the snake doesn’t make these poisons itself. Instead, it gets them from the toads it eats. It is immune to these poisons and shunts them into its own glands, defending itself with the pilfered defences of its own prey.

Deborah Hutchinson from Old Dominion University, Virginia discovered the tiger keelback’s thievery back in 2008. She showed that baby keelbacks that are raised in captivity are born without poisons, but quickly build up a supply if they can eat some toads. A wild-born snake doesn’t have this problem. Its mother laces her eggs and yolks with her own stolen poisons, arming her babies with chemical defences even before they hatch.

To do that, pregnant females need to find toads. After all, they’re eating poison for two.

Yosuke Kojima and Akira Mori from Kyoto University tracked the movements of 24 tiger keelbacks and found that females noticeably change their behaviour when they get pregnant.

These snakes live in a diverse area that includes forests, grasslands, riverbanks, and rice fields, all of which are teeming with amphibians. For the most part, the snakes stick to grasslands, where their favoured prey—two non-toxic species of frog—can be found in huge numbers. These frogs account for 89 percent of their food. By contrast, the Japanese common toad—the only local species that makes bufadienolides—is rarer, makes up just 1 percent of the snakes’ diet, and lives only in the forests.

Japanese common toad. Credit: Yasunori Koide
Japanese common toad. Credit: Yasunori Koide

But in early summer, while males are still sticking to grass, pregnant females spend a third of their time in the forests. There, they are unusually active and they hunt a lot of toads, which Kojima and Mori confirmed by checking their stomach contents.

The duo also placed several snakes in a Y-shaped maze. One arm was smeared with wet paper that had been rubbed on a toxic toad, and the other was daubed with the essence of a non-toxic frog. The male snakes always headed towards the path that smelled of poison-free prey. The females usually did the same but the pregnant ones flipped their preferences and went after Eau de Toad instead.

All of this strongly suggests that the pregnant snakes deliberately seek out poisonous prey. That’s not a trivial thing to do. The toads are much rarer than the snakes’ usual prey, so it costs more energy to find them. But the effort is presumably worth it.

When baby tiger keelbacks hatch in late summer, their jaws are too small to swallow toads. They have no way of building up their own bufadienolides until the next spring, when smaller, younger toads appear. By then, a predator could easily have killed them. But their mothers, by going the extra mile to stock up on toxins, provide them with defences to see them through this vulnerable window. These snakes practice a kind of toxic nepotism: the females that amass the greatest chemical wealth can give their children the greatest start in life.

Reference: Kojima & Mori. 2014. Active foraging for toxic prey during gestation in a snake with maternal provisioning of sequestered chemical defences. Proceedings of the Royal Society B. http://dx.doi.org/10.1098/rspb.2014.2137

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Cheetahs Prosper: New Study Debunks More Old Myths

The cheetah’s life is reputedly balanced on an energetic cliff. Yes, it’s the fastest land animal, capable of going from 0 to 60 miles per hour in a few seconds. But, according to countless nature documentaries, its high-speed chases leave it exhausted and overheated. If it fails to catch a meal, it’s in bad shape to try again. And even if it’s successful, it is easily and frequently driven away from its own kills by more powerful predators like lions or hyenas. The price of super-speed is a teetering existence, spent scrabbling for food and energy.

Except, very little of that is true.

The cheetah’s true biology is clouded in myth, in speculations that have been passed down through so many wildlife programs that people mistake them for fact. Some of these apocrypha pan out. Their record-breaking top speed was based on a single measurement taken in the 1960s, but a recent study that outfitted wild cheetahs with sophisticated tracking collars confirmed that they really are as fast as claimed. Other factoids have been debunked: they don’t, for example, overheat while hunting.

Now, Mike Scantlebury from Queen’s University Belfast has deflated a few other cheetah myths. By tracking several wild individuals, he showed that cheetahs spend most of their energy walking around in search of prey. The actual high-speed chases are over so fast that they’re mere blips on the animals’ energy accounts. Scantlebury also found that cheetahs only lose about 1 in 10 kills to thieving lions and hyenas, and they can easily compensate for the loss with an extra hour of hunting.

“They’re fairly robust, much more so than we thought they were,” says Scantlebury. “Left to their own devices, they’re pretty good at surviving.”

Over two-week periods, his team followed 14 cheetahs in Botswana’s Kgalagadi Transfrontier Park, and five living freely in South Africa’s Karongwe Game Reserve. They noted whether the animals with lying, walking, sitting, or chasing. They also measured how much energy the cheetahs were burning by injecting them with a form of water that contained slightly heavier versions of the usual hydrogen and oxygen atoms. By looking for the same atoms in the cheetah’s faeces, the team could work out how quickly they passed through the animals’ bodies, and thus how much energy the cheetahs were using.

“We thought that they would have a high energy expenditure just to survive. If you have a supreme engine, just maintaining it would be costly,” says Scantlebury. They were wrong. In fact, the cheetahs were burning as much energy as you’d predict for an animal of their size. They have big hearts, lungs and liver, and their muscles can generate an extreme amount of power when they sprint. But most of the time, their energy costs are low.

Even their famous hunts don’t tip the scales. The team found that the cheetahs spent roughly the same amount of energy on days with chases as on days without them.  That’s because each chase, while intense, lasts for an average of 38 seconds, and cheetahs rarely sprint more than once a day; on average, a cheetah sprints for just 45 seconds each day! By contrast, they spend several hours just walking around in search of prey to sprint after, and these treks sap the largest proportion of their energy. Finding something to sprint after is more costly than the actual sprints.

If cheetahs lose their kills to another predator, they can usually find more potential prey nearby. They can try to catch another one within the hour, without having to do a long searching walk. In fact, the team calculated that cheetahs could lose half of their kills to lions or hyenas, and still break even energetically. As it is, they only lose a tenth. “I think they just don’t bother hunting if there’s lots of other predators around,” says Scantlebury.

For comparison, African wild dogs, which have the highest success rates of all the African predators, suffer more greatly if their food is stolen. These animals wear down their prey through long, dogged chases that can last for several hours. Unlike cheetahs, they burn a tremendous amount of energy during their actual hunts. Losing a meal matters greatly to them.

These results have important implications for protecting the 10,000 or fewer cheetahs left in the wild. “Anything that makes them travel further will increase their energy expenditure,” says Scantlebury. A fence or human settlement that forces them to walk long distances in search of prey might turn them into the energetic paupers that we have mistakenly mythologised them as.

Reference: Scantlebury, Mills, Wilson, Wilson, Mills, Durant, Bennett, Bradford, Marks & Speakman. 2014. Flexible energetics of cheetah hunting strategies provide resistance against kleptoparasitism. Science http://dx.doi.org/10.1126/science.1256424

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The Venomous Cocktail in a Fisherman’s Bait

Anglers often use bloodworms as bait, and aquarists use them as fish food. These small squirming creatures are named for their red bodily fluids which are visible through their translucent skin. They seem innocuous enough—at least, until they extrude their huge, terrifying proboscis, tipped with four, black fangs. Each one is lined with copper minerals, and connected to a venom gland. They are, in fact, venomous fish bait.

A bloodworm’s bite feels a bit like a bee or wasp sting. The venom can stop the heart of the small crustaceans that these creatures eat, but it’s not strong enough to harm a human. It can, however, occasionally trigger a severe allergic reaction, much like a bee sting.

Now, Björn von Reumont and Lahcen Campbell from the Natural History Museum in London have catalogued the full array of venom-making genes that are active in the bloodworm’s venom gland. They found a ridiculous amount of diversity. One species—Glycera dibranchata—makes 32 different types of toxin, which is “in the ballpark for snake venoms”, according to Ronald Jenner who co-led the study.

Venom research is booming, and for good reason. These substances, and the creatures that inject them, instil a morbid fascination. They’re great case studies for how evolution shapes molecules. And they’ve often been sources of new drugs. Using new sequencing technologies, scientists have teased apart the killer cocktails injected by familiar groups like snakes and spiders, and also less obviously venomous ones like vampire bats, Komodo dragons, shrews, echidnas, and one group of weird cave crustaceans.

But there are still many venomous animals left to analyse. Jenner was looking to study some of these neglected creatures, and settled on the bloodworms.

The word “bloodworm” is also used to describe the maggots of some groups of midges, a couple of species of parasitic nematodes, and the fictional ones that cause vampirism in The Strain. This post isn’t about any of those. The bloodworms that Jenner’s team looked at are annelids, members of a large group of segmented worms that also includes earthworms and lugworms. Two groups of annelids are venomous: the leeches, whose toxins stop blood from clotting, and the bloodworms, which use their venom to overpower their prey.

Some scientists have looked at bloodworm venom before, but only in a piecemeal way. Von Reumont and Campbell did something more comprehensive. When genes are switched on, the information encoded within their DNA is transcribed into another molecule called RNA. These transcripts are then used to build proteins, like those found in venom. The team identified all the RNA transcripts that are produced in the venom glands of three bloodworm species.

They found plenty. Many of them belonged to 30 known groups. Some produce proteins that kill nerve cells, punch holes in cell membranes, or trigger intense pain. But a dozen of these toxin types are a mystery—they don’t match anything we know, and may be unique to bloodworms.

The team also compared the bloodworm transcripts to those form other animal groups, and found some that are shared across many venomous lineages. Some resemble toxins in bees that trigger severe allergic reactions in a minority of people, which may explain why some folks go to hospital with severe inflammation after being bitten by bloodworms. One toxin has only ever been found in discovered in scorpionfish, platypuses and echidnas. And until now, one toxin was thought to be unique to sea anemones, while another was supposedly an invention of predatory snails. Now, we know that bloodworms wield the same chemical weapons.

These similarities between bloodworm venom and those of very distantly related animals exemplify the single most important theme in venom evolution: convergence. Different groups of venomous animals have independently transformed the same kinds of proteins into the same kinds of venom. You’ll see the same toxins in shrews and Gila monsters, or in snakes and cone snails. “Venom toxin evolution is rampantly convergent,” says Jenner.

Why? That’s one of the big questions in the field, says Jenner, and there are probably several answers. Venom proteins have to work in the bodies and bloodstreams of other animals, so they have to be very stable. As such, they tend to be rich in components that form strong bridges between one another, so the proteins don’t lose their shape after leaving their owner’s fang or sting.

Jenner also notes that small genetic changes can radically change the way some proteins work. Maybe some groups of proteins are “poised to be weaponised”. In other words, it only takes a few small changes to change them into toxins, so they more readily evolve that way when the need arises.

Finally, there are only so many ways to kill another animal, and many venoms end up hitting the same targets. Fellow Phenomena blogger Carl Zimmer explains this well in his post on the origin of venom:

“For example, cone snails, scorpions, and anemones have all evolved venoms that attack channels on neurons that pump out potassium. Snakes and bees have evolved the ability to block platelets from clumping together, a crucial step in blood clotting. These results show that there are a limited number of ways to kill your victim quickly. No matter what genes you borrow for the evolution of venom, they will end up very similar to other venoms.”

Ironically, venom—a weapon for destroying animal bodies—is also a wonderful testament to the similarities that bind us together.

Reference: Von Reumont, Campbell, Richter, Hering, Syke, Hetman, Jenner & Bleidorn. 2014. A polychaete’s powerful punch: venom gland transcriptomics of Glycera reveals a complex cocktail of toxin homologs.

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When Your Prey’s in a Hole and You Don’t Have a Pole, Use a Moray

Redouan Bshary is best known for studying cleaner wrasse—tiny underwater hygienists that pick parasites from much larger fish, like the roving coral grouper. In 2006, Bshary decided to follow one of the groupers to see whether it sought the services of several cleaners in a row. Instead, he saw something wholly unexpected. The groupers repeatedly swam up to giant moray eels and made a vigorous head-shaking signal. It was a call to arms—a signal that meant “Hunt with me”.

The eels respond by swimming off with the groupers. They can slink through crevices and flush out hidden prey, while the groupers are lethal in open water. When they hunt together, little fish have nowhere to flee.

Working with Bshary, Alexander Vail from the University of Cambridge found that the groupers also use a different signal—a  headstand—to tell the morays where hidden fish can be found. It’s the equivalent of a human pointing a finger—a gesture that says, “The prey’s in here.” These sorts of referential gestures had only been seen in intelligent animals like humans, apes, ravens, dolphins, and dogs. Their use was often taken as a sign of intelligence. The fact that fish—a group hardly known for their smarts—can use similar signals was surprising.

Vail and Bshary made their discoveries by observing fish in the wild. Now, they’ve brought a closely related species—the coral trout*—into their lab, and tested its partnership with morays through experiments. And they’ve found that the fish’s behaviour is even more sophisticated than we thought. It doesn’t just recruit its partner willy-nilly—it can decide when and with whom to collaborate. It recruits morays when the situation demands it, and it picks the more effective of two possible partners. And it performs just as well as chimpanzees did, when confronted with a similar task in an earlier study.

In 2006, Alicia Melis from the Max Planck Institute for Evolutionary Anthropology presented chimps with an out-of-reach food platform connected to some rope. If chimps could pull the platform closer on their own, they generally did. If they needed a partner, they were more likely to recruit one. And if there was more than one partner available, they chose the most effective one. Melis published the results in a straightforwardly titled paper: “Chimpanzees Recruit the Best Collaborators”.

Vail and his colleagues tried to duplicate the gist of that experiment with coral trout. They placed eight captive trout in tanks with a fake moray eel—a life-size plastic cut-out, nestled in a rocky crevice. They also added a similar cut-out of a small prey fish, which either sat out in the open (where the grouper could snatch it) or hidden under a rock (where a moray was necessary). Right from the first day of testing, the trout tried to recruit the moray far more often when the prey was hidden than when it was exposed.

But not all morays are equal. In the wild, the team saw that some eels are consistently more willing to team up with groupers and trout, while others are reticent collaborators. They simulated this by presenting their captive trout with two morays—one that would launch forwards at the right signal, and one that refused to leave its crevice. On day one of testing, the trout had six chances to recruit a partner, and they went after both eels equally. On day two, they went for the cooperative eel five times out of six.

Vail’s experiment featured the same number of subjects and trials as Melis’s study, and his trout performed as well as her chimps. Of course, there are important differences between the two set-ups. “The trout just had to do something very natural for them, something they’ve practiced for their whole lives,” says Vail. “But the rope-pulling thing was relatively novel for the chimps. It was fairly removed from something they normally do.” However, he adds that the chimps “received quite extensive training in each aspect of their task”, before being exposed to the whole experiment. By contrast, he gave his trout no such training.

“The findings are very exciting. Their results suggest that the fish’s behavior is highly adaptive, and I am not surprised to see similarities in how [chimps and trout] cooperate or choose partners,” says Joshua Plotnik, who has studied cooperation in elephants. “However, as the authors rightly point out, similarities in behavior do not necessarily suggest similarities in intelligence. The authors note that much of the fish’s behavior could be due to learning mechanisms, which do not necessarily require the flexibility of more complex cognition.”

In other words, this doesn’t mean that trout are as intelligent as chimps. They almost certainly don’t show the same wide ranging of sophisticated behaviours. But they can behave in complex ways in the situations that benefit them. They have specific smarts driven by ecological needs, rather than all-round smarts driven by big brains. They remind us, again, that complex behaviour doesn’t necessarily imply complex minds.

Still, this experiment, together with the earlier observations in the wild, suggests that the fish are going beyond simple algorithms like “IF want prey, THEN find moray”. They seem to understand the eel’s role, they recruit it in the right circumstances, and they can direct it to the right place. “It’s always going to be hard to get inside the mind of an animal, but my hunch is that the groupers have an idea of what’s going on,” says Vail. “It shows some of the hallmarks of intentional communication that apes have.”

The study adds to the evidence that fish can be smarter than we thought. We know that several species hunt in teams. Lionfish work together to corral prey with their expansive fins, and have a “Let’s hunt” signal for recruiting their peers. Some electric fish flush out their prey with formation attacks, which they coordinate through electric pulses. And the yellow saddle goatfish hunts in packs where individuals assume specific roles—some chase, others block, not unlike a team of lions, wolves or chimps.

Fish also seems to be particularly good at hunting with other species. The roving coral grouper will also partner with the humphead wrasse, the coral trout will form hunting parties with octopuses, and goatfish sometimes team up with banded sea kraits (a type of sea snake).

And recently, a European team found that three captive cod learned to manipulate a feeding device with a tag attached to their fins, after accidentally getting the tag entangled in the device. It was “one of the very few observed examples of innovation and tool use in fish.”

In fact, Vail suggests that you could view the cooperative hunts of coral trout and morays as a kind of social tool use. “A chimp can get a stick and probe honey out of a hole,” he says. “A grouper has no hands and can’t pick up a stick. But it can use intentional communication to manipulate the behaviour of a different species with the attribute it needs.” In other words: When your prey’s in a hole, and you don’t have a pole, use a moray…

Reference: Vail, Manica & Bshary. 2014. Fish choose appropriately when and with whom to collaborate. Current Biology http://dx.doi.org/10.1016/j.cub.2014.07.033

* Common names are letting us down here. The roving coral grouper and the coral trout are both part of the genus Plectropomus. The coral trout is not closely related to the freshwater trout that you might eat.

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Little Giant Whales Take 100 Gulps an Hour

The blue whale can swallow half a million calories in a single mouthful. When it spots its prey—shrimp-like creatures called krill—it lunges forward, accelerating rapidly and opening its jaws to an almost right angle. Its mouth expands, its tongue inverts, and it engulfs around 110 tonnes of water—about the same mass as another small blue whale. Over the next minute, it pushes the water through sieve-like plates, filters out the krill, and swallows. Then, having reloaded its face, it’s ready for another attack.

This sequence, known as lunge-feeding, is the signature move of the rorquals—the family of giant whales to which the blue belongs. It allows these animals to grow to huge sizes by feasting on huge volumes of miniscule prey.

But lunge-feeding didn’t evolve among titans. The fossil record tells us that the technique first arose in species in the size class of the modern minke whales—the smallest of the rorquals at a mere (!!) 5 metres long. To understand how and why lunge-feeding evolved, we need to understand how the minkes do it.

That should be easy, since minkes are the most common whales in the Antarctic. But they are also among the most elusive. Large rorquals like the blues will spend a reasonable amount of time at the surface recharging their lungs, allowing scientists to easily stick tags and recorders to them. But with minkes, “you see them for a breath or two and then they’re gone,” says Jeremy Goldbogen, a whale researcher at Stanford University. “You have a second to get it in the right spot.” No one had been able to tag one, and not for lack of trying.

That changed in February 2013. While trying to study humpbacks in Antarctica, a team led by Ari Friedlander at the Oregon State University found big groups of minkes, up to 40-strong, feeding around large floes of ice. They seemed to be socialising, and they were certainly relaxed enough for the team to sneak up in an inflatable boat. Friedlander sat on a pulpit at the front, carrying a long carbon-fibre pole with a suction-cup tag at the end. He waited, and eventually, one of the whales surfaced at just the right spot for him to stick the tag on. It was a first.

Minke whales in the Southern Ocean. Credit: Ari Friedlander.
Minke whales in the Southern Ocean. Credit: Ari Friedlander.

For 18 hours, the tag stayed on and recorded pressure, temperature and acceleration. A few days later, the team managed to tag a second animal, for a further 8 hours of data.

And what data! During that time, the two animals managed 2,831 lunges over 649 dives. While they were feeding, they lunged around 100 times every hour. That’s just over half a minute to accelerate a five ton body through water, swallow the equivalent of a king-size bed, filter out all the food within it, and be ready to go again. And again. And again.

The team also found that the minkes did something that other rorquals don’t: they made long, shallow dives under large floes of floating ice to feed on the swarms of krill beneath. No other predator can exploit this resource so efficiently. Blue, fin and humpback whales are too big, and they feed in more open, ice-free waters. Penguins and seals can dive under the ice, but they’re limited to picking off one prey at a time. The minke, by combining manoeuvrability with lunge-feeding, can consume the food beneath the ice in bulk.

Their feeding strategy is similar in kind to that of a blue whale, but very different in degree. Since they’re smaller, they can’t engulf as much water, but they also expend less energy on lunging. For a blue, lunging is a massively draining affair that pays off only because it guarantees the world’s most calorific mouthfuls. For a minke, lunging costs barely more energy than steady swimming. So while blues make a few gigantic gulps, minkes can take small gulps at a much faster rate.  And that provides a clue about how lunge-feeding evolved.

Goldbogen thinks that the strategy helped early small rorquals to eat more efficiently, by swallowing large amounts of prey at once. That allowed some of them to become truly enormous, by using the same behaviour to consume vast quantities of prey in the open ocean. Others, like the minke, kept to a small size to exploit patchier swarms that their giant cousins couldn’t reach. “As body size evolved to bigger size classes, you got this niche partitioning,” says Goldbogen. “That’s our leading hypothesis.”

The study is a small victory for the team, not least because “Japan is still whaling minkes in the Antarctic,” says Goldbogen. “They claim it’s for scientific purposes but I don’t think anyone was fooled by that claim. Here we show that you can study whales without killing them.  That was obvious before but providing some published accounts is important too.”

There’s more to come. The team has just developed a new class of tag that has cameras as well as the usual sensors. They’ve deployed it on five humpbacks and two blues, and they’re about to try it on some minkes in the coming months. “It’s pretty much a full flight recorder on top of a whale,” says Goldbogen. “We’ve been having a lot of fun.”

Reference: Friedlander, Goldbogen, Nowacek, Read, Johnston & Gales. 2014. Feeding rates and under-ice foraging strategies of the smallest lunge filter feeder, the Antarctic minke whale (Balaenoptera bonaerensis). Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.106682

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Lionfish Have a “Let’s Hunt Together” Signal

A lionfish is a swimming paradox. It is painted in fierce hues of orange and white but it has an almost melancholy expression. It has fearsome venomous spines sticking out of its back, but elegant fan-shaped fins protruding from its side. And although it floats with an indolent air, it is actually an active and skilled predator—one that hunts in teams using surprisingly sophisticated tactics.

Oona Lönnstedt has spent hundreds of hours watching lionfish, both in the wild and in her lab at James Cook University. During night dives, Lönnstedt often saw teams of two to four lionfish positioning themselves around schools of smaller fish and using their fan-like pectoral fins to corral their prey “like fishermen with their nets”. The hunters then take turns to dart into the school of prey, picking them off one at a time.

That’s how the hunts end. But Lönnstedt was more interested in how they start.

She noticed that they always begin when one lionfish swims up to another, points downwards, flares its pectoral fins, and quickly undulates its tail. After a few seconds of this, it slowly waves one pectoral fin, then the other. The partner almost always responds by undulating its own fins, and the pair moves off in search of victims.

Despite her extensive fieldwork, Lönnstedt only ever saw lionfish make this display before they started hunting together. It looked like a message with a clear meaning: “Let’s hunt.”

Lönnstedt tested her interpretation in an experiment. She would place one zebra lionfish (Dendrochirus zebra) in a maze-like tank. Six tasty cardinalfish sat behind a transparent barrier at one end of the tank. A second lionfish was hidden from view by some opaque dividers at the other end.

After Lönnstedt added the cardinalfish, the first lionfish spent more time next to the prey compartment. But it also repeatedly left these tempting morsels, and swam to the other end of the maze to hang out in front of the second lionfish. Once there, it often made the distinctive fin displays.

These fin displays only happened when the tank contained both prey and another predator to recruit. The second predator didn’t have to be a lionfish of the same species—there are at least a dozen—as long as it was a lionfish. If the potential partner was a grouper, the first lionfish wasn’t interested.

Once the partners were united, Lönnstedt removed the partitions and let them do their thing. Working as a team, the duo captured almost twice as many fish than each of them would normally manage alone.

“There has been anecdotal evidence of cooperative hunting in lionfish since the late 1980s,” says Lönnstedt. “Ours is the first study that empirically demonstrates that it occurs. These are highly complex animals with advanced social behaviours, and they are ridiculously good at catching prey.”

“I find the paper amazing,” says Redouan Bshary from the University of Neuchâtel, who studies fish behaviour. “Fish social behaviour is much more complex than previously assumed. Moving away from a stimulus of major interest—prey—in order to actively recruit a partner that is initially out of sight suggests planning and awareness of objects that [they can’t see].”

Last year, Bshary showed that coral groupers use special gestures to recruit giant moray eels. The two fish hunt cooperatively, with the sinuous moray chasing prey that hides in cracks and crevices and the fast grouper catching any that flee into open water.

But in these pursuits, the two partners are merely hunting next to each other and relying on their complementary abilities. The lionfish are doing something more impressive: they’re working together to corral their prey and taking turns to go in for the kill.

Now, Lönnstedt wants to find out more about how they coordinate their movements. Why does the fish that initiated the hunt always go first? And why do they take turns—is it a cooperative strategy, or does each fish simply need time to recover from its assault? And finally, does the flared fin display that launches the hunt actually convey any information? Is it just a “Come hunt with me” signal, or does it convey information about the location of food, like the famous waggle dance of bees?

PS: Lionfish are known for their painful venom, which Lönnstedt has experienced first-hand. “It’s excruciatingly painful,” she says. She now wears special gloves to stop the spines from piercing through and if that fails, hot water can dull the pain a bit. “If you’re out somewhere on a boat, it’s always good to bring a thermos of boiling water as an extra precaution.”

Reference: Lönnstedt, Ferrari and Chivers. 2014. Lionfish predators use flared fin displays to initiate cooperative hunting. Biology Letters http://dx.doi.org/10.1098/rsbl.2014.0281

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Sailfish Use Inescapable Face- Swords to Wound, Then Kill

Meet the sailfish—a predator that combines teamwork, ninja-like stealth, record-breaking speed, chameleonic colour changes, and a weapon that looks like a sword, works like a sword, and is mounted on its face.

It is surely one of the most spectacular hunters in the ocean. Thanks to a new study by Jens Krause, we now have a much better idea of its technique, and how it uses that distinctive pointed snout.

Sailfish typically grow to around 3 metres in length and are among the fastest of fish, reaching speeds of up to 68 miles per hour (110 kilometres per hour). Like their relatives, the swordfishes and marlins, their upper jaws end in a sharp, protruding bill. Many people assumed that the bills are used to attack prey, but others have claimed that they are too fragile; instead, they might help the fish to swim faster by cutting down on drag.

Krause became captivated by sailfish after watching a sequence in the classic 2001 documentary Blue Planet, in which a hundred-strong team take out a school of smaller fish. He wanted to see these hunts for himself and in 2011, he got his wish. “I took a trip organised by Shark Diver magazine,” he says. “They claimed it was possible to observe these animals. It was, and next year, I gathered a group of scientists to film them seriously.”

By using frigate birds and pelicans as spotters, the team found several groups of hunting sailfish. They jumped in the water, and captured several hours of high-speed and high-definition video. “It’s quite scary,” says Krause. “They do come very close to you, but they’re very accurate and careful, so they never made any contact with the divers.”

The bill isn’t a piercing weapon; it’s a slashing one. Krause’s team saw that a sailfish would swim up, insert its bill within the sardines, and flick it sideways to hit one or more targets. The sardines are none the wiser. The high-speed videos revealed that fish close to the bill don’t react any differently than the ones far away. The bill, which is so obvious to us, is actually a stealth weapon! It’s so thin that it’s hard to see and barely disturbs the surrounding water, allowing the sailfish to thrust it into the sardine school without being detected.

Now, the sardines are in serious trouble. When a sailfish flicks its bill, it either gives a gentle tap that stuns an individual fish, or a violent slash that hits several at once. During a slash, the tip of the bill can cover 6 metres and turn through 575 degrees in a single second. That’s much faster than a sardine can swim, and the bill’s acceleration (among the highest of any aquatic back-boned animal) outmatches the sardine’s reflexes. It’s hard to detect and impossible to avoid.

Krause thinks that the sailfish combine these tactics in a brutal way. They start by chasing schools of fish using their legendary speed, and they erect their eponymous sails to corral their prey. Gradually, they split large schools into smaller ones.

Then, they start slashing to inflict heavy wounds. “They don’t just attack a school and remove individuals, like dolphins or sharks would,” says Krause. “They rough these fish up for many hours. They keep them pinned, go in, and hit multiple individuals over and over again. In smaller schools, virtually every fish has been injured many times. They’re slow and exhausted. That’s when the sailfish start with the tapping. The tapping is targeted harvesting of individuals that have already been roughed up,” he adds.

The sailfish also work in teams. “We’ve seen up to 40 sailfish surrounding just 50 to 100 sardines, although maybe they started with 1,000,” says Krause. They always took turns to attack, presumably to avoid injuring each other with their sharp bills. No one knows how they coordinate their movements, but it might have something to do with their ability to change their colours. When they attack, they switch from silvery to almost black, and their flanks blaze with orange spots and electric blue bars. Perhaps these are signals to other fish, which say, “I’m up now; stand back.”

Krause’s study clearly shows that the sailfish uses its bill for hunting. “There has always been anecdotal information about bill use in feeding, but as far as I know this is the first systematic investigation. Recreational fishermen that fish for marlins and sailfish often use artificial lures or natural baits towed on the surface behind the boat,” says Richard Brill from the Virginia Institute of Marine Science. “I personally have seen blue and white marlin strike lures with their bills immediately before they grab it in their mouths.”

Brill adds that fishermen often catch billfishes whose bills are broken or missing, but that still seem healthy. There is no way of knowing whether most fish with such injuries starve and die, but these catches tell us that at least some individuals can survive without their bills.

Krause thinks that their phenomenal speed might help. He’d sometimes see a lone sardine breaking off from the school and trying to flee. When that happened, the sailfish simply chased it down through sheer speed, and swallowed it. This might explain why fishermen have sometimes found whole, uninjured fish in the bellies of billfish.

Reference: Domenici, Wilson, Kurvers, Marras, Herbert-Read, Steffensen, Krause, Viblanc, Couillaud & Krause. 2014. How sailfish use their bills to capture schooling prey. Proc Roy Soc B. http://dx.doi.org/10.1098/rspb.2014.0444


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Spider Hides From Spider Among Spider-Eating Ants

Most spiders only eject silk from glands in their rear ends but Scytodes—the spitting spider—is an exception. It can also shoot silk from its mouthpart. It does so with great force, and it impregnates these strands with venom to create a sticky gum that both poisons and traps its victims. It’s the closest natural equivalent to Spider-Man’s web-shooters.

If the prospect of a spider with a long-range weapon freaks you out, you are not alone. Even other spiders are wary of Scytodes.

In the Philippines, the spitting spider will readily attack jumping spiders and its web is often littered with arachnid carcasses. Ximena Nelson and Robert Jackson from the University of Canterbury have shown that it often targets a black-and-lemon species called Phintella piatensis. Scytodes will build its nest directly over a Phintella nest and ensnare the jumping spider as it enters and leaves its home. Sometimes, it even taps on the nest with its legs, perhaps to check if anyone’s home.

But Phintella is not entirely defenceless. Nelson and Jackson also found that it protects itself by nesting in the company of the weaver ant Oecophylla smaragdina.

When the duo placed leaves with Phintella nests in a chamber, and wafted in the smell of weaver ants, they found that Scytodes avoided building its own web overhead. And Phintella, in turn, was more likely to build nests on leaves where the ants could be seen or smelled.

Weaver ant kills Phintella. Credit: Robert Jackson
Weaver ant kills Phintella. Credit: Robert Jackson

The reason is simple: the ants are voracious predators and spiders are on their menu. They’re so aggressive that farmers often deliberately use them to protect mango crops from pests. Even Scytodes’ trademark weapon is of little use: its spit will immobilise a couple of weaver ants, but it can’t pin down an entire group. When Nelson and Jackson housed a Scytodes with weaver ants, it was almost always killed.

Phintella, however, isn’t bothered by the weavers. It fashions a silken cocoon like most jumping spiders do, but it uses an especially tough and dense weave that the ants cannot tear open. It also builds doors! It has hinged silken flaps at either end of its nest which seal it away when it’s inside the nest, and which the ants rarely try to open. The ants do sometimes capture Phintella, as the image above shows, but this is relatively rare.

So, its ant-proof home allows Phintella to surreptitiously recruit the weavers as protectors, without succumbing to them itself. It’s like a person who seeks safety by walking into the most dangerous part of town in a Kevlar suit.

There are many cases where ants act as bodyguards for other species, including aphids, acacia trees, and some butterflies, in exchange for food and nutrients. But the relationship between Phintella and the weavers isn’t a mutualism, where both partners benefit. The ants don’t seem to get anything from Phintella’s presence. They don’t suffer either, so it’s not parasitism. Instead, Phintella is more of a commensal—a creature that benefits by living alongside another, without offering any advantages in return.

It’s also not the only jumping spider to have a connection with ants. Some eat them. Others mimic them to a spectacular degree. One mimics ants to avoid being eaten by spiders so that it itself can eat spiders. And Phintella, which neither looks like an ant nor eats them, lives alongside ants and avoids being eaten by them so it can also avoid being eaten by another type of spider, which ants can eat. Ain’t nature grand?

Reference: Nelson & Jackson. 2014. Timid spider uses odor and visual cues to actively select protected nesting sites near ants. Behav Ecol Sociobiol. http://dx.doi.org/10.1007/s00265-014-1690-2

More on Nelson and Jackson’s work:

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Meet The Predator That Becomes Blind When It Runs After Prey

The tiger beetle can run so fast that it blinds itself.

There are 2,600 species of these long-legged predatory insects, and the fastest can sprint at up to 5 miles per hour, covering 120 of its body lengths in a single second. For comparison, Usain Bolt covers just 5 body lengths per second. To match the beetle, he’d have to run at 480 miles per hour.

Tiger beetles use this incredible speed to run down both prey and mates. But as they sprint, their environment becomes a blur because their eyes simply can’t gather enough light to form an image. They have extremely sharp vision for insects, but when they’re running, the world smears into a featureless smudge. To compensate, the beetle has to stop to spot its prey again, before resuming the chase.

It seems like a bad evolutionary joke: a hunter that loses sight of its prey whenever it runs.

But tiger beetles don’t mind because… well… they are really, really fast. They can afford to stop in the middle of a chase because they are so ridiculously quick when they’re in motion. It’s like the aforementioned Bolt pausing at the 50-metre mark for a drink, and still winning.

Hairy-necked tiger beetle. Credit: Daniel Zurek.
Hairy-necked tiger beetle. Credit: Daniel Zurek.

Cole Gilbert at Cornell University discovered the tiger beetles’ staccato hunting style in 1998. Now, together with Daniel Zurek, he has worked out how they cope with another problem: obstacles.

At high speed, it’s hard enough to avoid incoming obstacles. But try doing it when your eyes can’t make out anything, much less small pebbles or sticks. A running tiger beetle is permanently in “collision mode”, says Zurek. “It’s like when I’m driving a car really fast and not wearing my glasses. When something hops in the road, I can’t stop in time.”

He discovered how they cope by watching an American species—the hairy-necked tiger beetle, Cicindela hirticollis. When it runs, it always keeps its antennae in the same fixed position: straight ahead, angled at a V, and held slightly above the ground. The antennae can move, but they never do while the beetle’s in motion.

The antennae are obstacle-detectors. If they hit an obstacle, their flexible tips bend back before springing forwards again. The beetle moves too fast to change course, but it can tip its body slightly upwards so that it skitters over the obstacle rather than running headlong into it. It’s like a blind person holding two white canes (and wearing rocket skates).

“Because of their shape, the antennae can slip over the edge of an obstacle, which tells the beetles that there’s a top they can run over,” says Zurek. He saw how effective this is by filming tiger beetles running down a long track with a piece of wood in the middle. If their antennae were intact, they cleared the obstacle most of the time, even when Zurek painted over their eyes. But if he cut the antennae off, the beetles frequently face-planted into the wood.

This solution is not only effective, but cheap. The beetles could potentially deal with motion blur by evolving more sensitive eyes, but it takes a huge amount of energy to pay for an eye with good temporal resolution. They would also have to analyse that information, and their small brains probably don’t have the processing power. Fortunately, they don’t need anything that over-engineered.  Their antennae provide them with all the collision-detection they need.

Zurek thinks that human engineers should take note. One of the first autonomous robots—Shakey—found its way around with some “bump detectors”. If they hit an obstacle, they bent, and Shakey would back up.

But modern robots rely on cameras. NASA’s Curiosity rover, for example, is currently trundling over Mars with the help of eight hazard avoidance cameras, or Hazcams. “As humans, we tend to think first and foremost from a visual standpoint,” he says. “Many really sophisticated robots rely on an array of cameras that analyse on the fly, which is very computationally intensive.” The tiger beetle’s solution would be simpler, and might help robots to move much faster than Curiosity’s leisurely pace.

PS: How does one catch an insect that moves so quickly? With great difficulty at first, but Zurek says, “It’s pretty fun once you get the hang of it,” he says. “You have to fool them by coming up behind them really slowly and then lowering yourself. I get them around 60 percent of the time.”

Reference: Zurek & Gilbert. 2014. Static antennae act as locomotory guides that compensate for visual motion blur in a diurnal, keen-eyed predator. Proceedings of the Royal Society B http://dx.doi.org/10.1098/rspb.2013.3072

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Toxic Halitosis Protects Tobacco-Eating Caterpillar

Way before people started inhaling nicotine in cigarette smoke, plants were using the chemical to defend themselves from animals.  Nicotine is a poison, and an exceptionally deadly one. It targets proteins that tell our muscles to fire when they receive signals from our nerves. At high enough doses of nicotine, these proteins force muscles to constantly contract, leading to paralysis and death. And since the same proteins are found in every animal with muscles, nicotine can kill cows and caterpillars alike.

The tobacco hornworm is an exception. As a caterpillar, this moth specialises in eating tobacco leaves, because it can cope with doses of nicotine that would kill other species. It gets rid of most of the poison in its waste but, adding insult to injury, it also co-opts a small fraction for its own protection.

Pavan Kumar and colleagues from the Max Planck Institute for Chemical Ecology in Germany have shown that it exhales the poison through pores in its skin, creating a toxic miasma that deters hungry spiders. They call it a “defensive halitosis”.

In 2010, Kumar’s  team, led by Ian Baldwin, raised tobacco hornworm caterpillars on genetically modified tobacco that doesn’t make much nicotine. They found that a gene called CYP6B46 was less active than usual in the guts of these insects, suggesting that it’s usually involved in resisting the effects of nicotine.

To test this idea, the team engineered tobacco plants that could deactivate the gene in any caterpillars that fed upon them, and planted them at a private ranch in Utah’s Great Basin Desert. They waited, and watched.

Soon, they noticed that hornworm caterpillars were more likely to die during the night if they ate the modified plants. A few nocturnal surveys revealed the cause of their deaths—wolf spiders. These powerful, fast-running hunters usually pose no threat to hornworms that eat nicotine-rich meals. However, they readily killed any caterpillars that ate the modified tobacco and had inactivated CYP6B46 genes. Why?

The answer seemed obvious at first. CYP6B46 is part of a large family of metabolic genes, which animals frequently use to detoxify the chemicals in the plants they eat. The team assumed that CYP6B46 was neutralising nicotine by breaking it down into safer substances. But, to their surprise, they couldn’t find any traces of these by-products in the caterpillars’ bodies or faeces.

Instead, they showed that CYP6B46 redirects a tiny amount of nicotine from the caterpillars’ guts to their haemolymph—the liquid that fills their bodies and acts as their bloodstream. From there, the caterpillars can vent the nicotine into the outside world by opening their spiracles—small breathing holes in their flanks, which allow air to enter and leave their bodies.

The caterpillars send just 0.65 percent of the nicotine they eat into their haemolymph. But even this tiny amount is enough to quadruple the concentration of nicotine in the air around them, creating an effective anti-spider spray.

When a wolf spider attacks, it first inspects its prey with chemically sensitive appendages. Here’s what happens when it approaches a caterpillar with a nicotine cloud.

And here’s what happens when it approaches a caterpillar with an inactivated CYP6B46 gene. The caterpillar can’t shunt nicotine from its gut to its haemolymph and can’t exhale the poison into the surrounding air. It pays the price for it.

The hornworm’s nicotine cloud probably works against other predators too. In earlier studies, when caterpillars are reared on tobacco, ants are less likely to attack them. Parasitic wasp larvae are also less likely to survive inside the caterpillars’ bodies, presumably because they are directly poisoned by the nicotine in their haemolymph. But the defence isn’t fool-proof. Kumar’s team showed that two predators—big-eyed bugs and antlions—will kill hornworms despite their halitosis. No one knows why.

Chemical theft is fairly common in the animal world, and many caterpillars store defensive poisons from the plants they eat. For example, the eastern tent caterpillar munches on plants that are loaded with hydrogen cyanide, which it then vomits onto marauding ants. But nicotine is too deadly to store. Instead, the tobacco hornworm has evolved a way of getting rid of it, which also doubles as a potent defence.

Reference: Kumar, Sagar, Pandit, Steppuhn & Baldwin. 2013. Natural history-driven, plant-mediated RNAi-based study reveals CYP6B46’s role in a nicotine-mediated antipredator herbivore defense. PNAS http://www.pnas.org/cgi/doi/10.1073/pnas.1314848111