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With Sonar-Reflecting Leaves, Plant Lures Bats to Poo in it

Imagine a bat flying through the jungle of Borneo. It calls out to find a place to spend the night. And a plant calls back.

The plant in question is Nepenthes hemsleyana—a flesh-eating plant that’s terrible at eating flesh. It’s a pitcher plant and like all its kin, its leaves are shaped like upright vases. They’re meant to be traps. Insects should investigate them, tumble off the slippery rim, and drown in the pool of liquid within the pitcher. The pitcher then releases digestive enzymes to break down the corpses and absorb their nitrogen—a resource that’s in short supply in the swampy soils where these plants grow.

But N.hemsleyana has very big pitchers that are oddly short of fluid and that don’t release any obvious insect attractants. And when Ulmar Grafe from the University of Brunei Darussalam looked inside them, he saw seven times fewer insects than in other pitchers.

Instead, he found small bats.

Grafe enlisted the help of Caroline and Michael Schöner from the University of Greifswald, a wife-and-husband team who had worked on bats. Together, they repeatedly found the same species—Hardwicke’s woolly bat—roosting inside the plants, and nowhere else. In some cases, youngsters snuggled next to their parents.

The plant had adapted to accommodate these tenants: that’s why their pitchers are roomier than average, and have little fluid. And the bats repay them with faeces. Bat poo—guano—is rich in nitrogen, and the team found that this provides the pitcher with a third of its supply. The carnivorous plant has largely abandoned its insect-killing ways and now makes a living as a bat landlord.

This was all published in 2011. Since then, the Schöners and Grafe have discovered another extraordinary side to the relationship between the bat and the pitcher. “It started when we were searching for the plants in the forest,” says Michael Schöner. “We had a lot of difficulty. The vegetation is dense and the pitchers are green.”

This problem should be even worse for the woolly bats. They navigate by echolocation: they make high-pitched squeaks and visualise the world in the reflecting echoes. “Inside these forests, you get a reflection from everything, every single plant and leaf that’s there,” says Schöner. To make matters worse, the bats must distinguish N.hemsleyana from a closely related, similarly shaped, and far more common species, that’s unsuitable for roosting. How do they do it?

In South America, there are flowers with a similar problem: they are pollinated by bats, and must somehow attract these animals amid the clutter of the rainforest. They do it by turning their flowers into sonar dishes, which specifically reflect the calls of echolocating bats. The Schöners wondered if their pitcher plant had also evolved acoustic cat’s eyes.

They contacted Ralph Simon from the University of Erlangen-Nürnberg, who showed up with a robotic bat head.

It has a central loudspeaker and two microphones that look like a bat’s ears. He used it to “ensonify” the pitchers with ultrasonic calls from various directions, and measure the strength of the echoes.

The team found that the back wall of N.hemsleyana—the bit that connects its lid to its main chamber—is unusually wide, elongated, and curved. It’s like a parabolic dish. It strongly reflects incoming ultrasound in the direction it came from, and over a large area. Other pitcher plants that live in the same habitat don’t have this structure. Instead, their back walls reflect incoming calls off to the sides. So, as the woolly bats pepper the forest with high-pitched squeaks, the echoes from N.hemsleyana should stand out like a beacon.

Is this what actually happens? To find out, the team modified the pitchers’ reflectors. They enlarged them by building up the sides with tape, reduced them by trimming the sides with scissors, and cut them off entirely (while propping the lids up with toothpicks). Then, they hid the modified plants among some shrubbery, and placed them in a tent with some bats.

The bats took much less time to approach the pitchers with enlarged or unmodified reflectors than those with trimmed or amputated ones. And when given a choice, they mostly entered pitchers with natural, unaltered reflectors. They seem to be attracted to strong echoes but when they get close, they make a more considered decision about whether they have found the right species.

The team also found that the woolly bats produce the highest-pitched calls ever recorded from a bat. They don’t need such high frequencies to hunt their prey and, indeed, other insect-eating bats are nowhere near that high-pitched. Instead, the team believes that the calls are particularly well suited to detecting targets in cluttered environments. Between these squeaks and the plant’s reflectors, both partners can find each other in the unlikeliest of circumstances. The bat gets a home, and the plant gets its faecal reward.

Reference: Schöner, Schöner, Simon, Grafe, Puechmaille, Ji & Kerth. 2015. Bats Are Acoustically Attracted to Mutualistic Carnivorous Plants. Current Biology http://dx.doi.org/10.1016/j.cub.2015.05.054

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Why Do Luna Moths Have Such Absurdly Long Tails?

You don’t need a field guide to recognise a luna moth. This large insect, found throughout the eastern half of North America, is unmistakeable. It has a fuzzy white body, red legs, feathery yellow antennae, and huge lime-green wings that can stretch up to 4.5 inches across. And at the end of its hindwings are a pair of long, streaming tails that can double the moth’s length.

In 1903, an entomologist named Archibald Weeks suggested that the tails direct predators away from the moth’s body. “Again and again may predator bat or bird, in an effort to capture a moth or butterfly, successively tear away sections of the tails, of which a sacrifice can be readily afforded, without disabling it or retarding its flight,” he wrote.

He was roughly right. More than a century on, Jesse Barber from Boise State University has shown that the luna moth’s tails are the equivalent of eyespots on fish and butterflies. These distinctive markings are typically found on dispensable body parts like tails and outer wings. They serve to draw a predator’s attention away from more vulnerable regions; better to lose a tail than a head.

Eyespots are visual defences, and bats—the main nemeses of moths—are not visual hunters. They find their prey with sonar—they make high-pitched squeaks and visualise the world using the rebounding echoes. To divert a bat, you need something that makes distracting echoes.

That, according to Barber, is what the luna moth’s tails do. They are “auditory deflectors”. Bat distractors.

Luna moth close-up. By Oliver Dodd. CC-BY-2.0
Luna moth close-up. By Oliver Dodd. CC-BY-2.0

Barber pitted luna moths against bats in a dark room, and filmed their encounters with infrared cameras. Under normal circumstances, the bats only managed to snag 35 percent of the moths. But if Barber cut off the insects’ tails beforehand, the bats caught 81 percent of them. That’s not because they become worse fliers—in fact, the tails don’t seem to affect their aerial abilities at all.

When bats aim their sonar at insects, they analyse the rebounding echoes for the distinctive signatures of beating wings. But the luna moths tails, which spin behind them as they fly, also produce echoes that resemble wingbeats. To the bat, they either sound like a very conspicuous part of their target, or like a different target entirely. As a result, they fumble their attacks.

When bats attack, they usually use their wings and tail to scoop an insect towards their faces, so they can deliver a killing bite to their victim’s body. But when bats attack luna moths, they aim about half their attacks at the tails. That’s a mistake—only 4 percent of those attacks succeed. Sometimes, the bat misses the moth entirely (see above). Other times, it bites off a tail while the moth escapes—down one inessential body part, and still alive (see below).

The tails also make the luna moths bigger, which might make them harder for the bats to handle and dispatch. But when Barber pitted bats against the polyphemus moth—an even bigger species that lacks tails—he saw that the predators killed 66 percent of their targets. The luna moths, despite being smaller, were harder to catch. “Clearly, tails provide an anti-bat advantage beyond increased size alone,” Barber wrote.

It’s possible that female moths also judge the health and quality of a male by looking at the size of his tails. But this doesn’t fit with the moths’ behaviour. Female moths spend most of their time hiding in protected nests and drawing males to them by releasing pheromones. They also mate with the first males they find, so there’s no evidence that they’re choosy—much less that they choose on the basis of tail length.

Luna moths belong to a group of large moths called the saturniids—a group that contains members like Copiopteryx and Eudaimonia, with even more extreme tails. By comparing the tail lengths of 113 saturniid species, Barber showed that these moths have evolved long tails on at least four separate occasions. He now wants to know if these other species are also good at foiling bats.

Reference: Barber, Leavell, Keener, Breinhoff, Chadwell, McClure, Hill & Kawahara. 2015. Moth tails divert bat attack: Evolution of acoustic deflection. PNAS http://dx.doi.org/10.1073/pnas.1421926112

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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

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Bats Jam Each Other’s Sonar

A bat is hunting a moth. As it flies, it makes a series of high-pitched squeaks and listens for echoes rebounding off the insect. It gets closer, and now it makes a much faster series of calls—the feeding buzz—that help it to pinpoint exactly where the moth is. It swoops in for the kill… and fumbles. At the last moment, another set of sounds comes out of nowhere, confusing it and sending it off course.

It has just been jammed by another bat.

Bats live in a world of acoustic warfare. Their sonar, or echolocation, allows them to hunt in total darkness, but it also makes them vulnerable. In 2009, Aaron Corcoran and William Conner from Wake Forest University showed that tiger moths can unleash their own ultrasonic clicks to jam the sonar of approaching bats. The clicks overlap with the echoes of the bats’ own calls, muddying up their ability to gauge their distance from their prey. They know roughly where the moths are, but they can’t coordinate a precise strike. This defence is so effective that even if the moths are tethered to a stump, the bats still miss them on four out of five fly-bys.

Clicking moths aren’t a bat’s only problem. Many of them must contend with the sounds of their neighbours too. The Mexican free-tailed bat roosts in groups of up to 1.5 million individuals, and forms such big swarms that they sometimes show up on radar. This supremely social species uses at least 15 different calls to coordinate with its neighbours and defend its own patch of food. But Corcoran and Conner have discovered a new type of call, with a more antagonistic bent.

It’s called the sinFM. The bats rapidly raise and lower the pitch of their call more than a dozen times over, in bursts or “syllables” that last just a tenth of a second. The bats only ever did this when one of their peers was using its feeding buzz, and was about to snag an insect. And when these hunting bats heard the sinFM, they usually flubbed their strikes, missing their targets between 77 and 85 percent of the time.

It’s possible that the sinFM call could be a bat’s version of shouting, “GET AWAY, THAT’S MINE!” But that seems unlikely. While watching wild bats, Corcoran and Conner noticed that animals that are diverted by a sinFM call will double back to try and grab their prey again, rather than simply flying off. They missed their attacks not because they were deferring to a peer, but because their sonar had let them down.

Corcoran and Conner suspected that the bats use their sinFM calls to actively jam the sonar of their competitors. To test this hypothesis, they set up an experiment. They attached a thin line to a street light, and dangled a moth from it. Whenever a bat approached this bait, they played a recording of a sinFM call from a nearby speaker.

The team recording bat calls in the wild. Credit: Aaron Corcoran.
The team recording bat calls in the wild. Credit: Aaron Corcoran.

Normally, bats capture the dangling moths around 70 percent of the time, and neither a loud tone nor burst of noise put them off. But a sinFM call slashed their success rate to below 20 percent. Even though the moths were hanging in place, the bats couldn’t hit them.

And critically, the sinFM only worked if it overlapped with the bats’ feeding buzz. If the team played it just before an attack, it had no effect. Clearly, this call isn’t an off-putting shout. It really does seem to be a way for bats to jam each other. It isn’t meant to overwhelm a target’s senses like, say, a bright light shone into another person’s eyes. It’s more subtle than that. I imagine it to be more like saddling an opponent with a set of goggles that makes their world fuzzier.

If Corcoran and Conner are right, they’ve discovered the first example of a non-human animal that competes with a rival by disrupting its senses.

Reference: Corcoran & Conner. 2014. Bats jamming bats: Food competition through sonar interference. http://dx.doi.org/10.1126/science.1259512

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The Females of the Madagascar Sucker-Footed Bat are Missing

For the last six years, Paul Racey has been trying to find a female eastern sucker-footed bat. He has failed. The bats only live in Madagascar and since 2007, Racey’s team have tramped through the country’s eastern forests with nets, bags, and devices that detect the bats’ sonar. They’ve captured 298 individuals, some many times over. But every single one of them was male.

Where are the females? Why are they so ridiculously hard to find? And why do they segregate themselves from the males? No one knows. After so much fruitless searching, Racey doesn’t even have a good hypothesis.

All he knows is that the females must exist. For a start, a Smithsonian team once collected a female sucker-footed bat around 30 years ago, and it’s still housed in their collection. Also, Racey keeps on finding young males every year. “You can hold their wings up to the light and see bits of cartilage round their joints, which haven’t ossified fully,” he says. So, the bats must be reproducing. “There have to be females. It’s just that we can’t find them, and it’s very embarrassing.”

To put this in perspective, Racey has spent his entire career studying bats and has worked in Madagascar for 20 years. He’s vice-president of the UK-based Bat Conservation Trust, and has received a lifetime achievement award from them. He has published more than 200 papers on bats and edited textbooks about them. He even has a bat species–Racey’s pipistrelle–named after him. This is not a man who is accustomed to being unable to find a bat.

“I set out to do a study on the ecology and social organisation of [the eastern sucker-footed] bat and I’ve only done half of it,” he says. “I’m not used to that sort of failure.”

Eastern Madagascar sucker-footed bat. Credit: Paul Racey
Eastern Madagascar sucker-footed bat. Credit: Paul Racey

The sucker-footed bat (Myzopoda aurita) lives only in Madagascar and was discovered in 1878. For the longest time, people thought that it was the only representative of its family, with no close relatives anywhere in the world. Then, in 2007, Steve Goodman found another one next door. This western sucker-footed bat (Myzopoda schliemanni) lives in the island’s dry western forests while its previously known cousin inhabits the humid eastern forests. The western one poses no mystery—both sexes huddle together in the leaves of the Bismarckia palm. It’s the eastern males that lead an unprecedentedly monastic lifestyle.

Why should the females live apart from the males? “I have no credible hypothesis,” says Racey. The closest example is another bat called Daubenton’s bat. In some northern English valleys, males are found at higher altitudes and females are found lower down, although the gulf between them isn’t absolute. It also exists only in the breeding season, possibly because pregnant females struggle to cope with the harsher high-altitude environment. But this explanation can’t possibly apply to the sucker-footed bats, which live in a low valley.

The males, at least, aren’t hard to find. They roost in the Ravenala tree, or “traveller’s palm”, whose giant leaves spread out like a fan. The start as rolled-up tubes and gradually unfurl over several days, creating a hollow cavity that’s perfect for the bats. Racey once found 53 of them in a single leaf.

Over six years, he and his research assistant Mahefatiana Ralisata have tried to capture these bats by suspending huge nets between trees, and by sending climbers to the top of Ravenala plants with large cloth bags.

They mostly operated out of a coffee research station in south-eastern Madagascar, but they also carried out exhaustive searches of two neighbouring valleys. Young bats can’t fly very far since their arm bones haven’t fully hardened, so if they’re found at a specific site, their mothers are unlikely to be far away. But—aaargh!—where are they? Racey and Ralisata made 833 captures in total. They’d find the same bats again and again, but never any females. They even went back to the village where the Smithsonian found their female. Nada.

It hasn’t been a total loss. The team has learned more about the natural history of the bats. For example, they seem to be completely free of external parasites like ticks or fleas. “That’s easy to explain,” says Racey. “The roosts are spotless.” By huddling inside a rolled-up leaf, the bats protect themselves from parasites. They also stick exclusively to Ravenala. Banana leaves, while also shiny, green and coiled, never contain any bats. “I’m guessing that bananas grow too low and get hammered by rats,” says Racey. “If a rat found a bat, it’d eat it.”

The team have also shown that the bats are poorly named. They stick to leaves with tiny discs on their wrists and ankles, which were thought to act like suckers. But true suckers are held to surfaces because the air pressure outside them is greater than the pressure within their rims. That’s not how the bat’s discs work. Instead, Racey found that they secrete a sweat-like liquid that holds them against a leaf “like a licked piece of paper stuck to a window”. So, the sucker-footed bat isn’t sucker-footed. (The traveller’s palm isn’t a palm, either. Oh, you wacky biologists.)

Meanwhile, the whereabouts of the females are still a mystery. Racey suspects that they live in two very different populations—perhaps one in the high mountains and another near the coast. This would explain why the juveniles arrive in two waves every year, even though every other bat of the same size only has one annual breeding season.

We’re unlikely to find these female enclaves until our technology improves. “If I had a wish, it would be for a satellite tag that’s small enough to go on a 10 gram bat,” he says. Then, the task would be easy. You could just open a laptop and follow the males to wherever their mates are.

Suitably small trackers are probably years off and when they do arrive, someone else will have to use them. Racey is done. He’s had two grants from the National Geographic Society to fund his search, and is not planning on applying for more. “I’m 69,” he says. “We’ve done what we can, but we’ve been pissing in the wind.”

His one consolation is that he has left behind a legacy of scientists in his wake. During his stay in Madagascar, he helped to set up a non-governmental organisation called Madagasikara Voakajy,  dedicated to protecting the country’s wildlife, and training local biologists to do their own unassisted research. “It’s working,” he says. The organisation now has a female Malagasy director and Ralisata (Racey’s assistant) got her PhD on the back of the sucker-footed quest.

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Holy Virus Treasure Trove, Batman!

Think about the type of animal that would make an ideal host for a virus. It would gather in large dense groups, making it easier for the virus to jump into fresh hosts. It should have a relatively long lifespan, so any single individual has many chances of becoming infected. It would certainly travel over long distances to spread the infection far and wide. Humans certainly fit the bill. So do bats.

At least one in every five mammal species is a bat. These diverse fliers—all 1,200 species of them—are reservoirs for an equally diverse group of viruses, including many deadly celebrities that can jump into humans. Bats carry rabies. They harbour SARS and other coronaviruses. They’ve got Nipah virus and Hendra virus, mumps, Marburg, and possibly Ebola.

Now, a team of virus-hunters led by Ian Lipkin from Columbia University has found that bats are also treasure troves for two little-known viral groups—hepaciviruses and pegiviruses. There’s no evidence that these new bat viruses could infect humans, but they could help to explain the origins of others that can.

The most famous hepacivirus is the hepatitis C virus (HCV), which causes liver disease, cirrhosis and liver cancer. It is transmitted through sex and shared blood and is found in around 3 percent of people around the world. HCV was discovered more than 20 years ago but we still don’t know where it came from. The same goes for its relatives, which can infect chimps, monkeys, dogs and horses.

The pegiviruses are even more mysterious. These species, with unremarkable names like GBV-A, GBV-C and GBV-D, have only been identified within the last decade. One of the most recent discoveries—TDAV—may cause a mysterious liver disease in horses that has puzzled vets for a century. When I reported on TDAV in March, one of my sources hinted that “studies on new pegiviruses may be published in the future”. He was right. Just last week, Lipkin’s team announced another new pegivirus from horses.

Now, they’ve shown that these known viruses are just twigs of a lush family tree, one that has been sprouting new trunks and branches in other animals for a very long time.

For a start, they identified seven new hepaciviruses and pegiviruses in wild rodents such as deer mice. That’s important for scientists studying hepatitis C virus. Animal viruses have a long history of helping us understand our own infections. Scientists have used SIV, which infects chimps and monkeys, to study HIV. The cowpox virus led to a vaccine for smallpox. But HCV has no good animal counterpart, and it doesn’t infect rats or mice.

Until now, chimps were the only animals that could be infected with HCV in experiments, and such research is ethically contentious, expensive, and being phased out. Lipkin hopes that his newly discovered rodent hepaciviruses could finally provide an analogue of HCV that can be easily studied in the lab, perhaps leading to new vaccines or treatments.

“In the rodents, our focus was on finding any hepacivirus that was really similar [to HCV],” says Lipkin. By contrast, the goal with the bats was to explore far and wide. “What we did with the bats was more like astronomy,” he says.

Phenix-Lan Quan led the work, which involved searching for new hepaciviruses and pegiviruses in 1,673 blood samples collected by other scientists working in 7 tropical countries. The samples came from 57 species of bats and yielded 83 viruses—including 3 new hepaciviruses and 19 new pegiviruses. These new viruses included some that are so dissimilar from the ones we knew about that their proteins share only a quarter of their amino acids. “It dramatically changes our whole view of these viruses,” says Lipkin. “There’s such extraordinary diversity among them.”

Between them, the two groups of viruses infected nearly five percent of the individual bats in the study (to no obvious ill effect), including those from 20 species and three continents. The similarities between them showed bizarre patterns that could only be explained by a long history of species-hopping and long-distance travel. For example, many of the pegiviruses in Bangladeshi bats were more closely related to those in African bats than they were to each other.

“It takes a long time to generate that sort of diversity,” says Lipkin. “And in humans, there’s very little diversity.” The implication is that these viruses have been diversifying in bats for much of their evolutionary history, and only recently made the jump into humans. Our experience with other bat diseases suggests how these jumps might have happened. Maybe, as with Nipah virus, people became infected by eating food contaminated by bat faeces or meat from infected livestock. Perhaps, as was possibly the case for SARS, the viruses passed from bats to us via animals in crowded Chinese “wet markets”.

These stories are possible, but we still don’t know if bats were the original source of hepaciviruses and pegiviruses (even if the team’s results are furtively pointing a finger in that direction and coughing slightly). We’ll only get clearer answers through studies in other animal groups and, indeed, of more bats from Asia and other continents.

Meanwhile, Quan says, “It is important to understand that there’s no evidence that these viruses are transmitted directly to humans. “She is concerned that people will take her study to mean that bats are threats to public health, and points out that they play important roles as pollinators and insect predators. “Their ecological benefits far outbalance their potential for disease transmission.”

When bats have donated diseases to humans, it’s often because their habitats have been disturbed, either by changing climates or our own encroaching activities. The key to preventing these spillovers, says Quan, is “to gain a better understanding of the ecology of bats and the range of infectious agents that are associated with them”. That could drive active monitoring programmes and to set up efforts to conserve the animal’s natural habitat.

Update: A late-arriving opinion from Linfa Wang, a virologist at Duke-NUS: he believes that in terms of using these new viruses to guide animal research into possible treatments, “there is still a long way to go and the significance of the current discoveries remains to be seen.” But the studies are highly important in showing that bats are reservoirs for these diverse and ancient viruses. Others including Wang have seen similar patterns for other virus families, but never these ones.

Reference Quan, Firth, Conte, Williams, Zambranan-Torrelio, Anthony, Ellison, Gilbert, Kuzmin, Niezgoda, Osinubi, Recuenco, Markotter, Breiman, Kalemba, Malekani, Lindblade, Rostal, Ojeda-Flores, Suzan, Davis, Blau, Ogunkoya, Alvarez Castillo, Moran, Ngam, Akaibe, Agwanda, Briese, Eptein, Daszak, Rupprecht, Holmes & Lipkin. 2013. Bats are a major natural reservoir for hepaciviruses and pegiviruses. PNAS http://dx.doi.org/10.1073/pnas.1303037110

Kapoor, Simmonds, Scheel, Hjelle, Cullen, Burbelo, Chauhan, Duraisamy, Leon, Jain, Vandegrift, Calisher, Rice & Lipkin. 2013. Identification of Rodent Homologs of Hepatitis C Virus and Pegiviruses. mBio http://dx.doi.org/10.1128/mBio.00216-13

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You’ve Seen Fruit Bat Fellatio. Now: Fruit Bat Cunnilingus

Oral sex in fruit bats is clearly a hot area of research. In just four years, the number of papers on this topic has doubled from, er, one to two.

It started in 2009, with a study that described regular fellatio among the short-nosed fruit bat. It earned its authors an  Ignobel Prize in 2010. Here’s what I wrote about it at the time:

The short-nosed fruit bat’s (Cynopterus sphinx) sexual antics have only just been recorded by Min Tan of China’s Guangdong Entomological Institute (who are either branching out, or are confused about entomology). Tan captured 60 wild bats from a nearby park, housed them in pairs of the opposite sex and voyeuristically filmed their liaisons using a night-time camera. Twenty of the bats got busy, and their exploits were all caught on video.

Male bats create tents by biting leaves until they fall into shape. These provide shelter and double as harems, each housing several females who the male mates with. Fruit bat sex goes like this: the female approaches and sniffs the male, and both partners start to lick one another. The male makes approaches with his thumbs (like the Fonz) and mounts the female (like the Fonz). Sex itself is the typical rhythmic thrusting that we’re used to, and afterwards, the male licks his own penis for several seconds.

But Tan also found that female bat will often bend down to lick the shaft of her mate’s penis during sex itself. This behaviour happened on 70% of the videos, making it the only known example of regular fellatio in a non-human animal. It also prolonged the sexual encounter – males never withdrew their penises when they were being licked and, on average, the behaviour bought the couple an extra 100 seconds of sex over and above the usual 2 minutes. The licking itself only lasted for 20 seconds on average, so each second of it buys six extra seconds of penetration.

And here’s a video (The music! Why??!)

Now, to balance things off, a new paper describes cunnilingus among another fruit bat species—the Indian flying fox.

In the summers of 2010 and 2011, Jayabalan Maruthupandian and Ganapathy Marimuthu clocked 1,170 hours watching a colony of flying foxes near a south Indian village. They saw the bats mate 57 times, most of which involved a brief amount of penetration bracketed by longer bouts of cunnilingus. The male would fluff up his penis and sidle over to a nearby female. He craned his neck over and licked her vagina for up to a minute, mounted her for around 15 seconds, and returned to 2.5 minutes of cunnilingus.

The actual sex isn’t exactly lengthy, but as in the short-nosed fruit bat, the flying foxes prolong their liaisons with oral sex. The males bought themselves an extra 2 seconds of penetration if they spent an extra 15 seconds of cunnilingus beforehand.

And obviously, there’s a video. No music on this one.

So, why perform oral sex? That may sound like a silly question, but remember that oral sex is incredibly rare in the animal kingdom. We obviously do it, and there are anecdotal reports for bonobos (of course), orang utans and ring-tailed lemurs. But it seems that, aside from humans, fruit bats seem to be the only species that regularly practice either fellatio or cunnilingus as an actual part of sex.

So: why? There’s the obvious explanation: it makes both partners more aroused, and the extra saliva keeps everything nice and lubricated.

For the short-nosed fruit bat, Tan proposed a long list of alternatives. By prolonging sex, a fellating female could keep her partners away from competitors, disinfect her partner’s penis, or pick up chemical traces that tell her if her mate is a good match.

In the case of the Indian flying fox, Maruthupandian and Marimuthu suggest that a male could remove the sperm of past partners by licking a female’s vagina. That doesn’t explain why he would continue after having mated himself, but Maruthupandian and Marimuthu did find that he spends less time on oral sex after penetration if he spent more time on it before. This might give him the best odds of removing a competitor’s sperm but not his own. Although, as they write, “Observation at close-range is needed to find out whether the male’s tongue enters the vagina or not.”

Sure, guys. You do that.

It’s possible, probable even, that many other bats practice oral sex. A quarter of all mammals are bats, but scientists have only watched wild sex in 10 of the 1,100 or so species.  The flying foxes aside, most of these creatures roost in inaccessible nooks and crannies, and often in darkness. That makes it hard for voyeuristic scientists to get a view of their sex lives. They’re getting there, though.

Reference: Maruthupandian and Marimuthu. 2013. Cunnilingus Apparently Increases Duration of Copulation in the Indian Flying Fox, Pteropus giganteus. PLoS ONE http://dx.doi.org/10.1371/journal.pone.0059743


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Noisy sex means death for flies if bats are listening

Some folks just can’t help being loud in bed, but noisy liaisons can lead to a swift death… at least for a housefly. In a German cowshed, Natterer’s bats eavesdrop on mating flies, homing in on their distinctive sexual buzzes.

Based on some old papers, Stefan Greif form the Max Planck Institute for Ornithology knew that Natterer’s bats shelter in cowsheds and sometimes feed on the flies within. What he didn’t know was how the bats catch insects that they shouldn’t be able to find. They hunt with sonar, releasing high-pitched squeaks and visualising the world in the returning echoes. Normally, the echoes rebounding from the flies would be masked by those bouncing off the rough, textured surface of the shed’s ceiling. The flies should be invisible.

And they mostly are. Greif filmed thousands of flies walking on the shed’s ceiling, and not a single one of them was ever targeted by a bat. That changed as soon as they started having sex. Greif found that a quarter of mating flies are attacked by bats. Just over half of the attacks were successful and in almost all of these, the bat swallowed both partners.


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How vampire bats tuned their thermometers to evolve a heat-seeking face

Mythology imbues the vampire bat with supernatural powers, but its real abilities are no less extraordinary. Aside from its surprising gallop and its anti-clotting saliva, the bat also has a heat-seeking face. From 20 centimetres away, it can sense the infrared radiation given off by its warm-blooded prey. It uses this ability to find hotspots where blood flows closest to the skin, and can be easily liberated by a bite. Now, Elena Gracheva and Julio Cordero-Morales from the University of California, San Francisco have discovered the gene behind this ability.

Among the back-boned vertebrates, there are only four groups that can sense infrared radiation. Vampire bats are one, and the other three are all snakes – boas, pythons, and pit vipers like rattlesnakes. Last year, Gracheva and Cordero-Morales showed that the serpents’ sixth-sense depends on a gene called TRPA1, the same one that tells us about the pungent smells of mustard or wasabi. Boas, pythons and vipers have independently repurposed this irritant detector into a thermometer.

Vampire bats evolved their ability in a similar way, but they have tweaked a different protein called TRPV1 that was already sensitive to heat. Like TRPA1, TRPV1 also alerts animals to harmful substances. It reacts to capsaicin, the chemical that makes chillies hot and allyl isothiocyanate, the pungent compound that gives mustard and wasabi their kick. In humans, it also responds to any temperature over 43 degrees Celsius. The vampire has simply tuned it to respond to lower temperatures, such as those of mammal blood.


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Vine lures bats with leaves that act as sonar dishes

Pollination is the process whereby plants turn animals into sex toys. With nutritious nectar, striking flowers (and the odd bit of deceit), they lure in animal carriers that can transport their pollen to another flower. These partnerships have painted the world in a resplendent palette of flowery hues. But pollination can create other feasts for the senses that are oblivious to us visually focused humans.

The Cuban rainforest vine Marcgravia evenia is pollinated by bats, which find their way around with sonar rather than sight. They make high-pitched clicks and time the returning echoes to “see” the world in rebounding sound. And M.evenia exploits that super-sense with a leaf that doubles as a sonar dish. It reflects the bats’ calls into strong, distinctive echoes, creating a sonic beacon that stands out among the general clatter of the forest.


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Tiny wing hairs allow bats to pull off hair-raising manoeuvres

The wings of bats provide them with support and lift as they fly. But they are also giant sensors that tell bats about the flow of air around their bodies, helping them to execute sharp manoeuvres without crashing.

The wings’ ability to monitor airflow depends on tiny hairs that cover their surfaces. The hairs were discovered almost a century ago. Scientists suggested that they are sense organs that allow bats to fly in complete darkness. That idea fell out of favour in the 1940s when Donald Griffin and Robert Galambos showed that bats navigate by listening for the echoes of their own calls. The discovery of bat sonar solved the mystery of their night-time aerobatics, and the wing hairs fell into obscurity.

But John Zook at Ohio University had not forgotten about them. He has shown that the pre-sonar theories were partly correct. The hairs complement a bat’s echolocation and turn it into a better flier, allowing the animal to “feel” its way through the sky.


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As bats hibernate through the winter, so does rabies

Every year, in mid-September, big brown bats throughout Colorado head for their favourite roosts, where they will spent the winter in hibernation. But some of the bats won’t sleep alone – they are carrying the rabies virus, and it will also hibernate through the winter in its slumbering host.

The rabies virus is a killer. Infections are almost always fatal, and around 55,000 people around the world succumb to the virus every year. Dogs are the leading carriers, but in North America, vaccination programmes have effectively eliminated dog rabies. Bats are another story – they are far more difficult to vaccinate and they have overtaken man’s best friend as the leading cause of American rabies.

Now, Dylan B. George from Colorado State University has shown that the rabies virus, by hibernating alongside the big brown bats, gets a free pass to the next generation.


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Flesh-eating plant doubles as bat-cave

The world’s worst flesh-eating plant lives in the jungles of Borneo. It’s called elongata and it’s one of several strains of Raffles’ pitcher plant. Like its relatives, it has distinctive pitcher-shaped leaves that can lure insects into a watery grave. But unlike other strains, elongata is strangely incompetent at catching insects. Instead, it lures bats into its pitchers, and lives off their poo.


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How bats find water and why metal confuses them


A bat, flying through the night sky, is thirsty. As it flies, it sends out high-pitched squeaks and listens for the returning echoes. It hears a telltale pattern. It hears no echoes form up ahead and the only ones that reflect back at it are coming from straight below. That only happens when the bat flies over a flat, smooth surface like the top of a lake or pond. The bat dives, opens its mouth to take a sip of refreshing water… and gets a mouthful of metal.

In nature, bodies of water are the only large, smooth surfaces around. Waves of sound that hit the surface of still water would generally bounce away, except for those aimed straight downwards. Stefan Greif and Björn Siemers from the Max Planck Institute for Ornithology have found that bats are instinctively tuned to find water using this unique feature (and yes, the institute does mostly, but not exclusively, bird research).


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Ninja bat whispers to sneak up on moths

Batman's logo became much more detailed over the yearsBatman’s logo became a lot more detailed over the years…

The night sky is the setting for an arms race that has been going on for millions of years: a conflict between bats and moths. Many bats can find their prey by giving off high-pitched squeaks and listening out for the echoes that return. This ability – echolocation – allows them to hunt night-flying insects like moths, which they skilfully pluck out of the air. But moths have developed countermeasures; some have evolved ears that allow them to hear the calls of a hunting bat and take evasive action. And bats, in turn, have adapted to overcome this defence.

Holger Goerlitz from the University of Bristol has found that the barbastelle bat is a stealth killer that specialises in eating moths with ears. Its echolocation calls are 10 to 100 times quieter than those of other moth-hunting bats and these whispers allow it to sneak up on its prey. It’s the latest move in an ongoing evolutionary dogfight and for now, the barbastelle has the upper wing.