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Falling Leaf, Flying Dragon

In the canopy of a Malaysian rainforest, a little lizard scuttles to the end of a branch and launches itself into the air. It doesn’t, however, fall to its doom. Instead, it extends two flaps of skin from its flanks, supported by unusually long ribs. The flaps look and work like wings, allowing this lizard—the aptly named flying dragon—to glide to safety. They are so adept in the air that they almost never come to the ground. Why bother, when they can travel for 20 to 30 metres between treetops, without losing much altitude?

There are 42 species of flying dragons, or Draco as they are formally known, and they all glide on extended flaps of skin or patagia. But Danielle Klomp from the University of New South Wales thinks that there’s more to the patagia than gliding. They are also beautifully coloured and Klomp has shown that, in at least one species, these hues match those of falling leaves from the local area. This, she says, is no coincidence. She thinks that the lizards have evolved to mimic falling leaves, to avoid the attention of birds.

“The locals we would chat to would often describe the lizards as looking like falling leaves,” she says. “We spent a lot of time walking around the forest trying to find them, and we often confused a gliding lizard for a falling leaf out of the corner of our eyes.” She would also find fallen leaves on the floors of many different rainforests that looked like the patagia of the dragons that lived in the area. This called for a more systematic study.

Klomp focused one species—Draco cornutus—which lives in Borneo and comes in at least two varieties. The individuals that dwell in coastal mangrove forests have rusty red patagia, and the dominant trees there jettison similarly coloured leaves. Elsewhere, in the lowland forests, the lizards’ patagia are a dark greenish-brown, and so are the falling leaves of the local trees.

Patagia of Draco cornutus from coastal mangrove forests (top) and lowland forests (below)
Patagia of Draco cornutus from coastal mangrove forests (top) and lowland forests (below)

The resemblance is striking to human eyes. To quantify it, Klomp collected both dragons and leaves from the two forests, and analysed the light reflecting from all of them. She showed that the contrast in colour was smallest when she paired the dragons with falling leaves from their own habitat, and higher when she compared them to standing leaves, or falling leaves from a different area.

Flying dragons glide around four times an hour and although they excel at it, they aren’t more manoeuvrable than birds. With plenty of hungry beaks around, it behoves them to have some way of avoiding attention. Mimicking falling leaves is one possible solution and not a far-fetched one, either. Some birds might do the same. The black fairy hummingbird, for example, does a weird gliding flight whenever it leaves its nest. It opens its wings and tail so that its body is horizontal to the ground, and it spins on its way down, recovering just a couple of metres before crashing. The movement looks a lot like a falling leaf.

Other scientists have suggested that the flying dragons use their brightly coloured patagia as billboards for signalling to mates. But Klomp’s team have filmed many of these lizards in the wild, and their 30 hours of footage rarely shows the animals using their wings in displays.

But absence of evidence isn’t evidence of absence, and Jim McGuire at the University of California in Berkeley, who has studied these lizards extensively, has often seen the males displaying with their patagia (here’s some video). They’ll sometimes open just the wing that’s closest to the female.

Other lines of evidence support the idea that the dragons communicate with their patagia. In most species, males have more vividly coloured wings than females, even though both sexes would presumably benefit from mimicking leaves. The colours are almost always species-specific too, and different species with distinct colours often live in the same area amid the same trees.

“There’s no doubt in my mind that patagial colours play an important role in species recognition,” says McGuire. “If it’s possible to evolve a colour pattern that would at once be conspicuous to [other Draco individuals] and simultaneously cryptic to predators, this would be a win-win. However, it’s also possible that Draco could be mimicking something other than leaves, like unpalatable [stick insects] or butterflies. And, of course, Draco may not be mimicking anything at all.”

To support her hypothesis, Klomp needs more data. So far, she has only compared wings and leaves in two populations of Draco from one species. Anecdotally, she has seen that several other species resemble like their local leaves but “this needs to be done properly,” she says. She also wants to test her prediction that species that live in more open habitats, or in places with a single dominant tree species, might benefit more from mimicking leaves.

Reference: Klomp, Stuart-Fox, Das & Ord. 2014. Marked colour divergence in the gliding membranes of a tropical lizard mirrors population differences in the colour of falling leaves. Biology Letters http://dx.doi.org/10.1098/rsbl.2014.0776


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The Bird That Cries Wolf Changes Its Lies

In Aesop’s fable The Boy Who Cried Wolf, the titular boy repeatedly lies to nearby villagers by shouting that a wolf is attacking his flock. When a wolf actually attacks, the villagers ignore the boy’s now-genuine cries. The moral, as parents tell their children, is: Don’t lie. But it could equally be: If you’re going to lie, mix it up a little. Maybe, cry bear now and then.

In southern Africa, there’s a bird that epitomises this lesson: the fork-tailed drongo. “They’re demonic little birds—black with forked tails, red eyes and a hooked beak,” says Tom Flower from the University of Cape Town. They’re also accomplished impressionists. They make at least 51 different alarm calls, and only six of these are their own. The rest are cover versions of the alarm calls of other species.

While working with meerkats in the Kalahari Desert, Flower noticed that the drongos would often scare them away from food by mimicking the alarms of other species—including, possibly, the meerkats themselves—even though no predators were around. He started following them, tracking a wild group of 64 drongos through the baking days and freezing nights of the Kalahari. So far, he has clocked more than 850 hours of observations.

He eventually found that the birds spend a quarter of their time following other animals like meerkats and pied babblers. They act as sentries, warning their neighbours about approaching predators with genuine alarm calls. But they’re also thieves. As Flower saw, the drongos sometimes sound a false alarm when one of its companions finds food. The meerkats and babblers flee from the non-existent predator, and the drongos swoop in to snatch the morsels. These thefts account for a quarter of their daily calories.

The drongos are very specific. They tend to mimic the calls of the species that they’re targeting, and for good reason. When Flower played different alarms to pied babblers, he found that they react more strongly to their own alarms than to those of the drongo itself.

This strategy clearly works, but why does it keep on working? Why don’t the meerkats and babblers get wise to the false alarms, in the manner of Aesop’s villagers? Well, actually, they do. Through his playback experiments, Flower showed that babblers react less strongly if they hear a second false alarm 20 minutes after the first one, and even less strongly if they hear a third. But if he swapped the third alarm to a different one, the babblers reset their reactions and become watchful and attentive again.

That’s exactly what the drongos do. They often try to steal food from the same individual and on three-quarters of these repeated attempts, they swap their alarms. They’re also more likely to swap if their first attempt fails; when they do, they’re more likely to succeed on the next go.

This might explain why the drongos can mimic so many calls—their varied repertoire helps them to keep on deceiving their targets. They’re actually quite similar to infections like HIV, influenza and malarial parasites, which can all change the proteins on their surfaces to fool the immune systems of their hosts.

“It’s not clear yet how strategic the drongos are in terms of what sounds they produce and when,” says Laura Kelley from the University of Cambridge, who studies vocal mimicry in birds. Flower showed that they change alarms after an unsuccessful theft attempt, but what do they switch to? Do they pick another species that shares the same predators as the pied babbler? Do they mimic birds that are especially reliable as alarm callers? Or do they choose another impression at random? “We might expect that every target species does not pay attention to all alarm calls equally – some will be more ecologically relevant than others,” says Kelley.

And what does this say about the drongo’s intelligence? Some scientists have suggested that tactical mimicry implies that the mimic understands something about the mental states of its targets—an ability known as theory of mind. But Nathan Emery from Queen Mary University of London, who studies animal intelligence, says that simple rules can produce the same behaviour. If a babbler with food is present, produce a drongo alarm call; if babbler leaves, take food; if babbler stays, produce babbler alarm call; and so on. It’s a “win-stay, lose-shift” strategy.

Flower himself says “I don’t think drongos intentionally manipulate the minds of other animals, which is how a human might accomplish the same behaviour.” There’s probably a simpler explanation. “Basically, they just keep doing what has previously got them food and if nothing work, then perhaps experiment a bit or generalise from previous experience with other species?”

That’s still impressive, though. “What the drongos are doing is not trivial,” says Emery. They’re flexibly using alarm calls, a behaviour that evolved in one context, to influence behaviour in a different context—food-stealing.

Flower wants to understand exactly how the drongos pull off their flexible deception. “This could show that apparently complex behaviour can arise from simple mechanisms,” he says. “It would also illustrate that when animals do something that we only thought humans could do, it doesn’t mean that they have similar cognitive ability to humans.”

PS: Do the drongos use false alarms to steal food from each other? “Yes, they do,” says Flower. “Whether they are less gullible than other species is unclear, and whether some individuals are more or less likely to be fooled is also unknown.”

Reference: Flower, Gribble & Ridley. 2014. Deception by Flexible Alarm Mimicry in an African Bird. Science http://dx.doi.org/10.1126/science.1249723

Related: African Bird Shouts False Alarms to Deceive and Steal, Study Shows

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The Most Versatile Impressionist In the Forest

Ernesto Gianoli wasn’t the first person to work out his frustrations with a walk in the woods, but the motivation behind that walk—and its results—were certainly unusual.

Gianoli studies the plants of Chile’s temperate rainforests. When he goes out into the field, he usually works to a tight schedule, involving dawn-to-dusk sampling and measuring. “One day, I felt that while being engaged in these work plans, we were missing the joy of the quiet observation of nature,” he says. “I told my students that I would dedicate some hours to walk slowly across the forest, just observing. And then it happened.”

Gianoli noticed that the leaves on one particular shrub seemed to be growing from two very different stems—one much thinner than the other. He eventually realised that the thin stems actually belonged to a Boquila vine, whose leaves were exactly the same as the shrub’s. He walked on and found Boquila entwined around many different trees; in most cases, its leaves matched those of its host. It looked like a mimic, and one with many guises.

“It was astonishing,” he says. “I was familiar with the vine but I had not noticed this feature before. I walked back to the hut where the rest of my team was waiting, and told my undergraduate student Fernando Carrasco-Urra, ‘Do you want to be famous? I’ve got the idea for your thesis.’ Of course, they mocked me.”

But as Carrasco-Urra and Gianoli collected more data, the scepticism faded. Boquila’s leaves are extraordinarily diverse. The biggest ones can be 10 times bigger than the smallest, and they can vary from very light to very dark. In around three-quarters of cases, they’re similar to the closest leaf from another tree, matching it in size, area, length of stalk, angle, and colour. Boquila’s leaves can even grow a spiny tip when, and only when, it climbs onto a shrub with spine-tipped leaves.

“There are some leaf features that are too hard to copy, such as serrated leaf margins,” says Gianoli. “It is common to see cases where Boquila “did her best”, and attained some resemblance, but did not really meet the goal.”

The same vine can even mimic several trees! If it crosses from one plant to another, its leaves change accordingly.

“Even orchids, the world’s best known plant mimics, just mimic one specific model, or just share the general appearance of several similar flowers,” says Anne Gaskett from the University of Auckland. “This vine seems to mimic many specific models, depending on its host—something we’ve previously only seen in animals.”

Environmental factors like light aren’t behind these similarities. After all, Carrasco-Urra and Gianoli found very different Boquila leaves in areas with very similar light levels. They also showed that the unusual leaves only turn up when there are other plants to mimic. A Boquila vine climbing up a bare tree trunk looks exactly the same as one that’s crawling along the forest floor. It only changes when there’s a leaf around to mimic.

Why? Carrasco-Urra and Gianoli suspect that the disguises protect Boquila from hungry mouths. By climbing, the vine can already avoid plant-eaters on the ground, but the duo showed that it bears even fewer signs of damage if it climbs on a host tree rather than a leafless support. Does it just become less conspicuous, or does it gain an advantage by mimicking distasteful hosts? No one knows yet.

It’s also unclear how the vine mimics other trees, let alone so many. Australian mistletoes can mimic the trees they grow upon, but they are parasites that tap directly into their hosts. By contrast, Boquila can match hosts without any contact.

Carrasco-Urra and Gianoli suggest that they might be picking up on airborne chemicals released by other trees. We know that chemicals like these can act as alarms, which tell plants that their neighbours are in danger and to raise their own defences. Perhaps Boquila taps into these danger signals to work out which disguise to adopt.

Alternatively, the vine might be using genes from its host. There are many cases where genes have moved horizontally from one plant species to another, sometimes via a parasite or microbe. This idea is speculative and unlikely, but it is strange that Boquila takes on the guise of the nearest leaf, even if that leaf doesn’t belong to the tree that the vine has actually climbed.

Carrasco-Urra and Gianoli are now trying to solve these mysteries by testing Boquila’s abilities in experiments. They’re moving the vine from one host to another and exposing it to the smells of different hosts, to see if it changes accordingly. They also want to sequence the DNA of the vine and its hosts to see if any genes could be hopping across.

“The naturalist view should come first and the scientific approach should follow,” says Gianoli. Observation, then understanding. It’s the approach that Charles Darwin, the quintessential naturalist, used to develop his theory of natural selection. It’s the approach that Gianoli wanted to return to when he went for his walk.

Reference: Gianoli & Carrasco-Urra. 2014. Leaf Mimicry in a Climbing Plant Protects against Herbivory. Current Biology. http://dx.doi.org/10.1016/j.cub.2014.03.010

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The Supergene That Paints a Liar

The females of the common mormon butterfly are masters of disguise. Some of them look like the black-and-white males, but others embellish their wings with white brushstrokes and red curlicues to mimic distantly related swallowtail butterflies that are toxic. By copying them, the delectable female mormons fool predators into thinking that they are similarly distasteful.

The picture below shows how varied these disguises can be. The right halves are all different butterfly species, and the left halves are all common mormon females.

The left halves are all females of the common mormon butterfly (Papilio polytes). The right halves are either common mormon males (top) or different species of swallowtails (bottom). Adapted from Kunte et al, 2014.
The left halves are all females of the common mormon butterfly (Papilio polytes). The right halves are either common mormon males (top) or different species of swallowtails (bottom). Adapted from Kunte et al, 2014.

British scientists Sir Cyril Clarke and Philip Sheppard studied these butterflies in the 1960s and, through cross-breeding experiments, showed that the insects never mix and match their patterns. You don’t get intermediate butterflies with red streaks from one pattern and white blotches from another. Instead, each pattern is inherited as one.

The duo reasoned that the patterns were controlled by a “supergene”—a cluster of genes that each control different parts of the wings, but are inherited as a single block. Imagine a row of switches that control the appliances in your house, but are taped together so that flipping one flips them all.

The supergene concept has been very influential and scientists have identified many such clusters in plants, snails, and other butterflies. But until now, no one had found the common mormon supergene. Krushnamegh Kunte from the Tata Institute of Fundamental Research in India finally did it and his results are a complete surprise—one that both confirms and refutes Clarke and Sheppard’s hypothesis.

Kunte, together with Marcus Kronforst at the University of Chicago, compared non-mimetic females that resemble males, or mimetic ones that look like the common rose swallowtail. They searched for parts of the butterfly’s genome that were linked to the mimetic patterns, and eventually homed in on a small region containing five genes. Four were similar in all the females, regardless of their patterns.

The fifth gene, known as doublesex, was another story.

Kunte and Kronforst found over 1,000 mutations separating the versions of the gene (alleles) in the mimetic and non-mimetic females. This astonishing variety was all the more surprising since doublesex has a reputation for consistency. It’s much the same in flies, beetles, ants, and every other insect group. And yet, in the common mormon—and only between the mimetic and non-mimetic females—this typically conservative gene was a hotbed of evolution.

The butterflies don’t switch their wing patterns by inheriting different versions of a cluster of genes, as Clarke and Sheppard suggested, but by inheriting different versions of doublesex. The supergene is not a collective, but a single gene. There isn’t a row of switches all taped together; there’s just one switch that controls everything.

The varying patterns of the common mormon butterfly (Papilio polytes). Credit: Wei Zhang
The varying patterns of the common mormon butterfly (Papilio polytes). Credit: Wei Zhang

The doublesex discovery is doubly surprising because this gene already has a well-defined role: it sends developing butterflies down either a male or female path. It’s like finding that the light in your bedroom also starts your car.

Kunte now wonders if scientists have been typecasting doublesex as a sexual differentiation gene, when it could potentially do much more.  “Throughout the animal kingdom, you see tremendously different males and females,” he said. Maybe this particular gene family, involved in sex determination throughout the animal kingdom, is also involved in making deer antlers or peacock tails.”

It’s still not clear how doublesex alleles produce the patterns on the butterfly’s wings. With a thousand mutations to look at, the team understandably had some trouble matching these to specific wing elements. Still, they found some hints about how the gene does its thing.

When genes are activated, the instructions encoded in their DNA are first converted into a related molecule called RNA. These RNA transcripts are then used to build proteins. Kunte and Kronforst found that doublesex RNA is sliced and rejoined into four distinct ‘isoforms’, like different paths through the same choose-your-own-adventure book. One of these isoforms is found in males, and the other three are found in females.

You might think that each of the three female isoforms corresponds to a different pattern, and that’s what Kunte and Kronforst first suspected too. They were wrong. Every female has all three forms, regardless of their pattern. Instead, it’s the way these isoforms are used that matters. The mimetic females make more of them than the non-mimetic ones, especially in their wings and especially in parts that produce white markings.

So, the same gene gets processed in different ways and switched on at different strengths in different parts of the butterfly’s wing to produce a variety of patterns.

But that doesn’t explain why the patterns are so stable. Whenever a new generation is born, different versions of the same gene line up and shuffle their DNA, creating new combinations. In the common mormon, the doublesex mutations that produce one mimetic pattern should eventually shuffle with those that produce another, producing new blends. Clearly, that doesn’t happen.

Kunte and Kronforst found out why: the mimetic version of doublesex is inverted relative to the non-mimetic one, so it sits in a different orientation in the genome. This inversion stops the two versions from lining up properly and prevents them from shuffling, ensuring that the gene’s thousand-plus mutations are all inherited together.

And that is, more or less, what Clarke and Sheppard thought!

They envisioned many elements acting in concert to produce the right copycat wings, and passing to the next generation as a single block. They were right except for one detail: those elements don’t have to be individual genes. They can be different parts of the same gene. As Mark Scriber from Michigan State University told me, it’s amazing that Cyril Clarke basically got the right answer 60 years ago, without any powerful genetic tools that today’s scientists can use.

Matthieu Joron from the CNRS was also impressed. He has found supergenes in a different group of butterflies—the long-winged Heliconius species. These are more in line with Clarke and Sheppard’s ideas: clusters of individual genes, locked together by a genomic inversion. Both lineages of butterflies—the longwings and the mormons—have evolved mimicry in a similar way.

That’s perhaps surprising, since the two lineages use mimicry for very different reasons. The mormons are Batesian mimics—they deceive predators into thinking that they are toxic by resembling species that genuinely are. But the longwings are Mullerian mimics—they are all actually toxic and they reinforce their warning colours by resembling each other, so that a predators which learns to avoid one species also knows to avoid them all.

The Batesian mormons are liars that mooch off the warning signals of their better-defended peers. The Mullerian longwings are honest communicators that find safety in their shared warnings. And yet, both groups have evolved their lookalike patterns in much the same way.

Note: This is an expanded version of a news story in The Scientist.

Reference: Kunte, Zhang, Tenger-Trolander, Palmer, Martin, Reed, Mullen & Kronforst. 2014. doublesex is a mimicry supergene. Nature http://dx.doi.org/10.1038/nature13112

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Fossil Insect Hid By Carrying a Basket of Trash

If you travelled back to Spain, during the Cretaceous period, you might see an insect so bizarre that you’d think you were hallucinating. That’s certainly what Ricardo Pérez-de la Fuente thought when he found the creature entombed in amber in 2008.

The fossilised insect of the larva of a lacewing. Around 1,200 species of lacewings still exist, and their larvae are voracious predators of aphids and other small bugs. They also attach bits of garbage to tangled bristles jutting from their backs, including plant fibres, bits of bark and leaf, algae and moss, snail shells, and even the corpses of their victims. Dressed as walking trash, the larvae camouflage themselves from predators like wasps or cannibalistic lacewings. And even if they are found, the coats of detritus act as physical shields.

We now know that this strategy is an ancient one, because the lacewing in De la Fuente’s amber nugget—which is 110 million years old—also used it. It’s barely a centimetre long, and has the same long legs, sickle-shaped jaws, and trash-carrying structures of modern lacewing larvae. But it took camouflage to even more elaborate extremes. Rather than simple bristles, it had a few dozen extremely long tubes, longer even than the larva’s own body. Each one has smaller trumpet-shaped fibres branching off from it, forming a large basket for carrying trash.

De la Fuente called it Hallucinochrysa diogenesi, a name that is both evocative and cheekily descriptive. The first part comes from the Latin “hallucinatus” and references “the bizarreness of the insect”. The second comes from Diogenes the Greek philosopher, whose name is associated with a disorder where people compulsively hoard trash.


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The world’s shiniest living thing is an African fruit that looks like a pointillist bauble

In the forests of central Africa, there’s a plant that looks like it’s growing its own Christmas decorations. Shiny baubles sprout from between its leaves, shimmering in a vibrant metallic blue. Look closer, and other colours emerge – pinpricks of red, orange, green and violet. It looks as if Seurat, or some other pointillist painter, had turned their hand to sculpture.

But these spheres, of course, are no man-made creations. They’re fruit. They are the shiniest fruits in the world. Actually, they are the shiniest living materials in the world, full-stop.

They belong to a plant called Pollia condensata, a tropical metre-tall herb that sprouts its shiny berry-like fruits in clusters up to 40-strong. These little orbs are iridescent – they use special layers of cells, arranged just so, to reflect colours with extraordinary intensity. This trick relies on the microscopic physical structures of the cells, rather than on any chemical pigments. Indeed, the fruits have no blue pigment at all.

In the animal kingdom, such tricks are commonplace – you can see them at work on the wings of a butterfly, the shells of jewel beetles, or the feathers of pigeons, starlings, birds or paradise and even some dinosaurs. But in the plant world, pigments dominate and structural colours were thought to be non-existent are much rarer.


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Robots in disguise: soft-bodied walking machine can camouflage itself

None of our machines can do what a cuttlefish or octopus can do with its skin: change its pattern, colour, and texture to perfectly blend into its surroundings, in matter of milliseconds. Take a look at this classic video of an octopus revealing itself.

But Stephen Morin from Harvard University has been trying to duplicate this natural quick-change ability with a soft-bodied, colour-changing robot. For the moment, it comes nowhere near its natural counterparts – its camouflage is far from perfect, it is permanently tethered to cumbersome wires, and its changing colours have to be controlled by an operator. But it’s certainly a cool (and squishy) step in the right direction.

The camo-bot is an upgraded version of a soft-bodied machine that strode out of George Whitesides’ laboratory at Harvard University last year. That white, translucent machine ambled about on four legs, swapping hard motors and hydraulics for inflatable pockets of air. Now, Morin has fitted the robot’s back with a sheet of silicone containing a network of tiny tubes, each less than half a millimetre wide. By pumping coloured liquids through these “microfluidic” channels, he can change the robot’s colour in about 30 seconds.


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Cuttlefish woos female and dupes male with split-personality skin

Imagine trying to talk to two people at the same time. I don’t mean just talking to one and then the other – I mean simultaneously saying different things to both of them. And in one of those conversations, you’re pretending to be someone of the opposite sex. That’s exactly the exchange that Culum Brown from Macquarie University has witnessed off the east coast of Australia.

The speakers were mourning cuttlefish – relatives of octopus and squid, and masters of camouflage. By rapidly expanding and contracting sacs of pigment in their skin, cuttlefish can turn their entire bodies into living video displays. Colours appear and vanish. Mesmeric waves cascade across their flanks. They can even produce different patterns on the two halves of their bodies.

Brown saw a male cuttlefish swimming between a female and a rival male, and displaying different messages to both of them. On his left half, the one the female could see, he flashed zebra-stripe courtship colours to advertise his interest. But on his right half, facing the rival male, he flashed the mottled colours of a female. As far as the competitor was concerned, he was swimming next to two females, oblivious to the act of cross-dressing/seduction going on right next to him. The cheater, meanwhile, prospers.


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Fish mimics octopus that mimics fish

Many animals defend themselves by mimicking something distasteful, like a wasp or a venomous snake. But the mimic octopus can don a multitude of disguises. It becomes a sea-snake by pushing six arms down a hole and waving the other two around in a sinuous wriggle. It turns into a flatfish by folding its arms back into a leaf shape and undulating them up and down. Its repertoire of venomous animals potentially includes lionfish, sea anemones, jellyfish, and more. It is one of the most dynamic mimics in the animal kingdom.

And now, the mimic has been mimicked.

Last July, while diving in Indonesian waters, Godehard Kopp saw a black-marble jawfish hanging around a mimic octopus. The little fish perfectly matched the octopus in both colour and pattern, blending in among the brown and white stripes of its arms.


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Octopuses and squids can switch camouflage mode to stay invisible in the twilight zone

There are two ways of becoming invisible: you can either be transparent so all light passes through your body, or you can blend in by taking on the colours of your surroundings. A truly incredible animal would be able to do both, switching between the two at a whim. And that’s exactly what some squids and octopuses can do.

Sarah Zylinski and Sonke Johnsen from Duke University found that two cephalopods – the octopus Japetella heathi and the squid Onychoteuthis banksii – can switch their camouflage strategy depending on how bright their environment is. When sunlight streams from above, they choose the see-through option. When their world darkens, they go for darker colours that blend in.


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Cross-dressing raptors avoid violence

Male and female marsh harriers should be easy to tell apart: the males have grey wing-tips and tails, while the females are mostly brown with distinctive creamy heads. The males also tend to be around 30 percent smaller. But looks can be deceptive. In western France, many of the “female” harriers are actually cross-dressing males that permanently wear the plumage of the opposite sex. Audrey Sternalski has found that this unusual costume allows them to lead more peaceful lives.

Forty percent of male marsh harriers don female costumes, and they start wearing them from their second year of life. Their feathers have the same colours, and they’re smaller in size. Only their irises give them away – they are pale, rather than the ochre-brown of females or the yellow-white of males.

To test the effect of these colours, Sternalski created model harriers and placed them in the territories of real ones. He found that males attacked the male decoys twice as often as either the female or female-like ones. So, by looking like females, male harriers become the beneficiaries of a “non-aggression pact”. They can get access to resources and mates without incurring the wrath of other males. Indeed, Sternalski found that typical males were forced to nest twice as far from another male as the female-like males did.

Sternalski also found that the female-like males almost never attacked male decoys. Instead, they were more likely to attack other females (or female-like males), just as true females are. Not only did they look like females, they behaved like them too.

This raises several questions – are the female-like males simply doing a superficial impersonation, or are they “female” at a deeper physiological level? To find answers, Sternalski now plans to study the genetic basis of the harrier’s female mimicry.

The marsh harrier is one of only two birds whose males permanently don the colours of females. The other – the ostentatious ruff – also uses its disguise to avoid aggressive assaults. They sneak into the territories of more dominant males and surreptitiously mate with the resident females. Such strategies are fairly common in the animal kingdom – they’re found in ants, wasps, fish, and more. In most cases, the deceptive males get some sneaky sex, or avoid attacks from rivals.

But that’s not necessarily the case. In 1985, scientists discovered that some male red-sided garter snakes release a female pheromone that attracts big clusters of up to 17 amorous suitors. By luring these males to him, the female mimic more easily mates with an actual female. The goal seems obvious: distract other males. But the same group later showed that the female-mimics might simply benefit by drawing heat from the writhing balls of other duped males.

Reference: Sternalski, Mougeot & Bretagnolle. 2011. Adaptive significance of permanent female mimicry in a bird of prey. Biology Letters http://dx.doi.org/10.1098/rsbl.2011.0914

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Orchid flowers fool flat-footed flies by faking fungus-infected foliage

The lady’s slipper orchid (Cypripedium fargesii) does not look well. Its red and yellow flowers are nestled among two large leaves, both covered in unsightly black splotches. These look like the signs of a fungal infection, but they’re not. This orchid is deceptive, not diseased. It produces the black spots itself and in doing so, it lures in flat-footed flies that feed on fungus. The flies, duped by the orchid’s false spots, pick up pollen and spread it to another flower. By appearing infected, the orchid reproduces.


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The bird that cries hawk: fork-tailed drongos rob meerkats with false alarms


Late last year, I wrote about a bird called the rocket-tailed drongo and, in response to a comment, I noted the following:

“Drongos are notorious thieves and mimics. In South Africa, I spent a morning with a meerkat researcher, following live meerkats. He said that he had anecdotal evidence that the fork-tailed drongo would sometimes mimic the predator alarm calls of meerkats while they were foraging and then swoop down to nick their unearthed morsels.”

Well that evidence is no longer anecdotal. In a new study published today, Tom Flower from the University of Cambridge has indeed found that fork-trailed drongos can deceive meerkats into scurrying for cover by making false alarm calls. It’s the bird that cries hawk.


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The strumming assassin that hunts spiders on their own webs


For most insects, walking onto a spider’s web and disturbing the sticky threads would be a very bad idea. The distinctive vibrations of wriggling prey only serve to draw the spider closer and inevitably ends in the insect getting bitten, wrapped in silk and digested.  But this story doesn’t always unfold in the spider’s favour. Some vibrations aren’t made by helpless prey, but by an assassin lurking on the web.

The assassin bug (Stenolemus bituberus) is a spider-hunter. Sometimes, it simply sneaks up to spiders on their own webs before striking, plunging its dagger-like mouthparts into its prey. But it also has a subtler technique. Sitting on the web, it plucks the silken threads with its legs, mimicking the frequency of weakly struggling prey. These deceptive vibes are an irresistible draw to the spider, who rush towards their own demise. The bug effectively has a way of ordering for delivery when it doesn’t want to go out for a meal.


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Evolutionary arms race turns ants into babysitters for Alcon blue butterflies


This is an old article, reposted from the original WordPress incarnation of Not Exactly Rocket Science. I’m travelling around at the moment so the next few weeks will have some classic pieces and a few new ones I prepared earlier.

In the meadows of Europe, colonies of industrious team-workers are being manipulated by a master slacker. The layabout in question is the Alcon blue butterfly (Maculinea alcon) a large and beautiful summer visitor. Its victims are two species of red ants, Myrmica rubra and Myrmica ruginodis.

The Alcon blue is a ‘brood parasite’ – the insect world’s equivalent of the cuckoo. David Nash and European colleagues found that its caterpillars are coated in chemicals that smell very similar to those used by the two species it uses as hosts. To ants, these chemicals are badges of identity and the caterpillars smell so familiar that the ants adopt them and raise them as their own. The more exacting the caterpillar’s chemicals, the higher its chances of being adopted.

The alien larvae are bad news for the colony, for the ants fawn over them at the expense of their own young, which risk starvation. If a small nest takes in even a few caterpillars, it has more than a 50% chance of having no brood of its own. That puts pressure on the ants to fight back and Nash realised that the two species provide a marvellous case study for studying evolutionary arms races.