From so simple a beginning

Evolution and Biodiversity

Category: mimicry (Page 2 of 2)

Double deceit

14 September 2017 /

Female cuckoo chuckle call is embarrassing for songbirds

female cuckoo vocally mimics a hawk

By first laying her egg secretively and then giving a loud chuckle call while leaving, a female cuckoo doesn’t seem to behave in a consistent way. But her call adds to her trickery, as Jennie York and Nicholas Davis show.

A female common cuckoo that lays an egg in the nest of a songbird, for instance a reed warbler, behaves as secretly as she can, because if the intended foster parents detect her presence, they will chase her away; and if she has laid her egg already, the parents will either try to eject it or leave their clutch to start a new one somewhere else. With a cuckoo young in the nest, their own young cannot survive. So, a cuckoo visits the nest and quickly dumps her egg when the owners are away, mostly within a minute.

Vigilant

But while she tries to be unseen when laying, she gives a conspicuous chuckle call when flying away afterwards – quite different from the ‘cuck-oo’ call of the male. This seems paradoxical, as the songbirds may notice her presence after all. Why is she seeking their attention now? Jennie York en Nick Davis answer this question.

They reasoned that a calling female cuckoo may be mimicking the call of a sparrowhawk, to which it is quite similar. If the parents hear that sound, they are concerned about their safety. They become vigilant and scan the surroundings to detect the predator, and their attention is diverted away from their clutch. If they perceive a foreign egg in the clutch, they respond in the same way as when they have seen a female cuckoo on their nest: they try to eject the foreign egg or leave the clutch. But when worrying about their own safety, they will pay less attention to their clutch and may overlook a foreign egg.

Less attention

York and Davis could demonstrate that this idea is right. A few meters from reed warblers’ nests, they placed speakers and play backed the call of a male cuckoo, the call of a female cuckoo, the call of an Eurasian sparrowhawk, or the call of an Eurasian collared dove, a harmless bird; they recorded the songbirds’ responses. The results are clear: the sound of a male cuckoo or a dove elicited no response, while the call of a sparrowhawk provoked vigilance – as did the call of a female cuckoo. So, it appears that indeed a female cuckoo vocally mimics a sparrowhawk. Also great tits and blue tits, which are not exploited by cuckoos as foster parents for their young, get alarmed by the female cuckoo’s chuckle.

After such a frightening experience, reed warblers pay less attention to their clutch, as further experiments revealed. When the researchers exposed the reed warblers to the calls again, put a foreign egg in the nests and checked the nests afterwards to see whether this egg was accepted or rejected, they discovered that parents that had been exposed to the call of a sparrowhawk or a female cuckoo were less likely to notice the foreign egg than birds that had heard a male cuckoo or a collared dove.

So, a chuckling female cuckoo deceits the foster parents twice, first by secretly laying her egg and then by vocally mimicking a sparrowhawk, tricking the victims into defending themselves instead of their clutch, while in fact the clutch is in danger.

Willy van Strien

Photo: Trebol-a (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Source:
York, J.E. & N.B. Davies, 2017. Female cuckoo calls misdirect host defences towards the wrong enemy. Nature Ecology & Evolution, online September 4. Doi: 10.1038/s41559-017-0279-3

Floral dress

7 September 2017 /

Pollinators are deceived by flower mimicking crab spider

Epidacus heterogaster sucessfully mimics a flower

The spider Epicadus heterogaster is coloured strikingly like a flower, and bees are lured by the colour to become prey, as Camila Vieira and colleagues show. Its masquerade is completed by a conspicuous abdomen, mimicking a flower’s shape.

The crab spider Epicadus heterogaster, which lives in Brazil, always seems to be dressed in a carnival costume that makes it look like a flower: it has a white, yellow or purple body colour and conspicuous abdominal protuberances. By mimicking a flower, it attracts insects that use to visit flowers to collect nectar, meanwhile pollinating the flowers. All it has to do next, is extend its legs and grab the victims – and the pollinators become prey.

Now, Camila Vieira and colleagues present proof that the crab spider’s colour attracts pollinators.

Sunscreen

Like many flowers, Epicadus heterogaster has an ultraviolet component in its body colour. We cannot see that colour, but insects do and some insects prefer it. The spider’s colour stands out clearly against the green leaves on which she awaits her visitors.

In order to demonstrate that the spiders’ colour indeed lures insects, the researchers treated anesthetized females with sunscreen that blocks ultraviolet light. When they applied the sunscreen on a female’s back, passing pollinators no longer saw an ultraviolet colour and didn’t approach the spider; in contrast, they avoided it. But when the sunscreen was applied not on the dorsal side, but on the ventral side of a spider, it remained attractive to pollinators. Its flowerlike appearance undoubtedly  contributes to the deceit.

Inconspicuous

Juvenile female spiders are coloured like adults, also mimicking a flower, but they exploit their disguise in another manner. They’re not sitting on a leaf to attract pollinators, as they are too small to be of any interest to them anyway, and by being conspicuous, they would attract predators. Instead, youngsters are observed mostly on flowers, where they are perfectly camouflaged.

Willy van Strien

Photo: Alex Popovkin (Wikimedia Commons, Creative Commons CC BY 2.0)

Epicadus heterogaster on YouTube

Source:
Vieira, C., E.N. Ramires, J. Vasconcellos-Neto, R.J. Poppi & G.Q. Romero, 2017. Crab spider lures prey in flowerless neighborhoods. Scientific Reports 7: 9188. Doi: 10.1038/s41598-017-09456-y

Successful imitation

21 August 2017 /

Jumping spider cheats predators by walking like an ant

Jumping spider Myrmarachne formicaria imitates the walk of an ant

The jumping spider Myrmarachne formicaria successfully imitates the walk of ants, misleading larger spiders that hunt for critters. Predators often refrain from attacking the jumping spider, as much as they are reluctant to attack ants, as Paul Shamble and colleagues observed.

The jumping spider Myrmarachne formicaria, only a few millimetres long, resembles an ant; it is, for instance, pretty thin. This resemblance is functional. Many predators, especially larger spiders and wasps, will readily grasp a small spider, but mostly refrain from attacking an ant, as this prey may bite, spray acid or sting to defend itself and is often assisted by nest-mates. By mimicking an ant, a small spider may protect itself against predators.

Not trivial

But a spider that aims to be mistaken for an ant not only has to look like an ant, but it also has to move like an ant.

That is not trivial, Paul Shamble and colleagues point out. Spiders walk on eight legs and ants on six, and the legs are driven differently. Spiders walk along a pretty straight line, while the path of ants is looped – unless they follow an odour track laid down by their nest-mates; in that case they walk a highly regular zig-zag route along the trail. Jumping spiders, to which Myrmarachne formicaria belongs, hunt while walking; they typically stalk their prey carefully, making long pauses. Ants, on the contrary, move on continuously. When jumping spiders approach a prey, they leap towards it from a distance; ants don’t jump.

A jumping spider thus has to modify its movements significantly to mimic the behaviour of an ant. Is Myrmarachne formicaria able to do that?

Using three high-speed cameras, the researchers filmed Myrmarachne formicaria, non-mimecic jumping spiders and ants walking across a glass surface and analysed their gaits. The analysis revealed that Myrmarachne formicaria imitates the walk of an ant very well. The spider walks on eight legs like other spiders do, but it moves its legs in an ant-like manner. It imitates the zig-zag behaviour of an ant that follows an odour trail. It does make pauses, but only very short ones. When stationary, it raises its forelegs, pretending to be an ant with a pair of antennae and three pairs of legs. The researchers never observed it leaping.

Animations

Finally, based on the video recordings, Shamble produced animations of an ant, a non-mimic jumping spider and Myrmarachne formicaria, presented these animations to a large predatory spider and observed its response. The predator was attracted to all of these targets, but not to the same extent. It attacked a jumping spider target more often than an ant target, and, importantly, it was not more likely to attack an ant mimic than an ant.

So, Myrmarachne formicaria cheats large spiders by imitating the appearance as well as the behaviour of an ant, protecting itself from these predators. It would be interesting to know whether predators with better visual capacities, like shrews, birds, lizards or toads, are also misled by this mimicry.

Willy van Strien

Photo: Jeff Burcher (via Flickr. Creative Commons CC BY-NC-ND 2.0)

Source:
Shamble, P.S., R.R. Hoy, I. Cohen & T. Beatus2, 2017. Walking like an ant: a quantitative and experimental approach to understanding locomotor mimicry in the jumping spider Myrmarachne formicaria. Proc. R. Soc. B 284: 20170308. Doi: 10.1098/rspb.2017.0308

Biting prey

12 April 2017 /

Fish with venomous fangs have many imitators

Fangblenny Petroscirtes breviceps mimics a venomous species

Meiacanthus fish species are armed with venomous fangs that deter predators. Many nonvenomous fish species protect themselves from being attacked by mimicking the aposematic colours and the behaviour of Meiacanthus species. A large research team unravelled the evolution of the venomous fish.

A predator fish expecting to easily ingest a small Meiacanthus fish will prove to be wrong. This prey is armed with sharp teeth that inject venom into its enemy. Disoriented, the predator will release its victim – and will not go after the same fish anymore.

Meiacanthus species are the only fish with venomous fangs. They belong to the group of the saber-toothed blennies or fangblennies (Nemophini), which all have a pair of enlarged, hollow canines in the lower jaw. Nicholas Casewell, together with a large research team, has shown that these fangs must have originated in the common ancestor of these blennies. But only species of the genus Meiacanthus developed venomous fangs. They possess venom glands at the base of the fangs and grooves on the fangs to deliver the venom into the wound.

According to the researchers, the venom does not cause pain upon injection, but it reduces the blood pressure in the predator, which becomes weakened and disoriented so that the prey can escape unharmed from its mouth. Blood pressure reduction appears to be such a bad experience that the predator fish will never try to ingest a Meiacanthus again. The venom was found to contain three compounds that had never been found in fish before.

Protection

Some non-venomous fangblennies, as well as many fish species from other groups, profit from the aversion that predators have to Meiacanthus species by looking the same and behaving the same. While not mounting a defence against predators themselves, they are still protected from attacks thanks to this mimicry.

What do non-venomous fangblennies use their fangs for? To eat, probably. This holds at least for all Plagiotremus species, which feed on dermal tissue, scales, mucus, and fins of larger fish. If they look like Meiacanthus species, they can easily approach their victims, which are reluctant to attack.

Willy van Strien

Photo:
Petroscirtes breviceps, with nonvenomous fangs in the lower jaw. ©Alex Ribeiro
CT-scan of the venomous species Meiacanthus grammistes. ©Anthony Romilio (University of Queensland, Australia)

Source:
Casewell, N.R., J.C. Visser, K. Baumann, J. Dobson, H. Han, S. Kuruppu, M. Morgan, A. Romilio, V. Weisbecker, S.A. Ali, J. Debono, I. Koludarov, I.Que, G.C. Bird, G.M. Cooke, A. Nouwens, W.C. Hodgson, S.C. Wagstaff, K.L. Cheney, I. Vetter, L. van der Weerd, M.K. Richardson & B.G. Fry, 2017. The evolution of fangs, venom, and mimicry systems in blenny fishes. Current Biology, March 30 online. Doi: 10.1016/j.cub.2017.02.067

Tiny scarecrow

6 March 2017 /

Red-winged blackbird flinches from whistling caterpillar

red-winged blackbird s scared by whistling caterpillar

It is funny when the tiny caterpillar of the walnut sphinx Amorpha juglandis suddenly emits a high-pitched noise. Thus sound scares birds, as Amanda Dookie and colleagues witnessed, so that they will refrain from picking the caterpillar. Why are birds startled by this whistling caterpillar?

caterpillars od walnut sphinx can make whistling soundsNormally birds are not afraid of a caterpillar, but caterpillars of the moth Amorpha juglandis can scare them, Amanda Dookie and colleagues report, by starting to scream when they are touched – a most peculiar behaviour.

A few years ago, Veronica Bura investigated how the caterpillars produce their high pitched sound. Their respiratory system consists of a network of tubes with on each side a row of openings, the spiracles. When screaming, Bura assessed, walnut sphinx caterpillars contract the front end of their bodies, close all spiracles except the rear pair and expulse the air forcefully through these openings, producing a whistling sound. The posterior spiracles are enlarged compared to the others, which probably is an adaptation for sound production. Often the caterpillars also thrash their heads to defend themselves while whistling, and Dookie wanted to know if the whistle sound in itself is enough to frighten birds, and how great the startling effect is.

Startle response

To find out, she exposed a number of male red-winged blackbirds to playbacks of caterpillar whistles that had been recorded before. Just like the walnut sphinx, red-winged blackbirds are to be found throughout North America. The experimental birds were housed in individual cages and provided mealworms on a small platform for four days before the tests started. Then the platform was equipped with a sensor and a speaker, and as soon as a bird touched the dish during a test, the whistling sound was played back.

That had a huge effect: the sound evoked a startle response in all birds. Most flew away, hopped backwards or clapped their wings. After a while they tried again to pick a mealworm and then they heard the whistle sound again. The birds got habituated a bit and the startle response decreased over time, but when they were exposed to the sound after two days of rest, they were as frightened as they had been the first time.

Danger

Can the caterpillars protect themselves from hungry birds by whistling? Probably so. In the wild, the birds scurry around and when they are scared by a noisy caterpillar, they will abandon that prey and move on in search of another.

But why are birds scared by a whistling caterpillar that is not dangerous or venomous, as far as is known? The birds may associate the short, high-pitched sound with danger, the researchers propose, because the sound is similar to the alarm call that many birds emit when they are threatened. A fright response to such alarm call is hard-wired in birds, and this seems to be exploited by the caterpillars when they mimic the call.

Willy van Strien

Photos:
Large: red-winged blackbird Agelaius phoeniceus. Janet Beasly (Wikimedia Commons, Creative Commons CC BY-SA 2.0)
Small: caterpillar of walnut sphinx, Amorpha juglandis. © Jayne Yack

Sources:
Dookie, A.L., C.A. Young, G. Lamothe, L.A. Schoenle & J.E. Yack, 2017. Why do caterpillars whistle at birds? Insect defence sounds startle avian predators. Behavioural Processes, 138: 58-66. Doi: 10.1016/j.beproc.2017.02.002
Bura, V.L., V.G. Rohwer, P.R. Martin & J.E. Yack, 2011. Whistling in caterpillars (Amorpha juglandis, Bombycoidea): sound-producing mechanism and function. The Journal of Experimental Biology 214: 30-37. Doi:10.1242/jeb.046805

The trick of a snake

8 February 2017 /

Puff adder sticks out its tongue to lure a frog

puff adder extends its tongue to lure a frog

A South African frog that perceives and approaches a tasty worm may be deceived. The worm may turn out to be the tongue of a snake, as Xavier Glaudas and Graham Alexander write, and if it is, the frog is in trouble.

The venomous puff adder (Bitis arietans), which lives in South Africa, hunts its prey by lying in ambush. Mostly nocturnal, camouflaged and hidden in the vegetation, it waits unobtrusively until a victim comes close, and then it strikes. But the striking range is only ten centimetres, so a prey often will stay out of reach.

Luring prey

But the snake uses a trick, Xavier Glaudas and Graham Alexander noticed when they reviewed  a large amount of video recordings they had made of puff adders in ambush in the field. A puff adder often lures a prey by extending and moving the black tongue, the two points spread. The tongue then looks like a squirming worm and apparently, a frog is easily deceived. It hops closer to inspect the snack, and as soon as it comes within striking range, the snake will try to seize it. The frog that thought to find a meal is eaten himself.

Is the puff adder really mimicking a worm by extending the tongue to lure prey? According to the researchers, it does. The snake only extends its tongue if there is a frog or a toad close by, they argue; it doesn’t upon perceiving the presence of other prey, such as a mouse that doesn’t eat worms. Also, snakes use their tongues to sample odours, but chemosensory tongue flicks only take half a second while ‘lingual luring’ bouts take much more time.

The puff adders also wave their tails, and according to Glauda and Alexander that behaviour is also performed to lure prey. But they don’t have any recordings to show this, because their camera had been focussed on the heads of the animals.

Willy van Strien

Photo: Joachim S. Müller (via Flickr, Creative Commons CC BY-NC-SA 2.0

Xavier Glaudas explains his research

Source:
Glaudas, X. & G. J. Alexander, 2017. A lure at both ends: aggressive visual mimicry signals and prey-specific luring behaviour in an ambush-foraging snake. Behavioral Ecology and Sociobiology 71:2. Doi: 10.1007/s00265-016-2244-6

An uninvited guest

27 October 2016 /

Frog breeds safely and undisturbed among leafcutter ants

Lithodytes lineatus breeds among leafcutter ants

Leafcutter ants ignore the frog Lithodytes lineatus when it breeds in their nests. They simply do not notice him, André Lima Barros and colleagues show, because the frog is chemically camouflaged.

Ants behave aggressively against intruders in their nests, but the South American Leptodactylid frog Lithodytes lineatus isn’t molested. In fact, he is at home in the huge colonies of leafcutter ants. Years ago, Andreas Schlüter reported that he had heard frog males calling from the interior of a leafcutter ant nest to attract females. Upon inspection of a nest, he found an adult frog within and numerous tadpoles swimming in a little pool. Obviously, the frogs breed in leafcutter nests.

Odours

It is clear why they willingly live there. Adult frogs, eggs and larvae are safe from predators, for the ants prevent these from entering the nest. Moreover, the nest has an agreeable humid microclimate.

But the question is why the ants, eager to evict all intruders from their nests, do tolerate these animals.

Now, André de Lima Barros and colleagues show that the frogs are chemically camouflaged. In their skin, they synthesize compounds which apparently imitate the odours with which the ants communicate. Since the ants rely on odour perception, the frogs go unnoticed: a good example of mimicry.

Not a burden

The researchers placed frogs of different species close to a nest entrance. When the experimental frog was a Lithodytes lineatus, the ants never attacked, but when it belonged to another species – either a species that is closely related to Lithodytes lineatus or a species that looks exactly the same as this frog – the ants became aggressive and bit the unwanted guest, that tried to escape quickly.

Next, the biologists prepared an extract from the skin of Lithodytes lineatus and coated a frog with it that normally would be chased away by the ants. Impregnated with skin extract of Lithodytes lineatus, the frog elicited no response.

So, Lithodytes lineatus can enter a leafcutter nest unharmed thanks to chemical camouflage. The uninvited guest is not a burden to the ants whatsoever, as he doesn’t touch the ants nor their brood. As he eats all sorts of other critters, such as assassin bugs and crickets, he may help the ants to keep the nest free of such enemies, in return for a safe place to breed.

Willy van Strien

Photo: Lithodytes lineatus, outside ant nest. Andrew Kay (via Flickr, Creative Commons CC BY-NC-SA 2.0)

Sources:
De Lima Barros, A., J. L. López-Lozano & A. P. Lima, 2016. The frog Lithodytes lineatus (Anura: Leptodactylidae) uses chemical recognition to live in colonies of leaf-cutting ants of the genus Atta (Hymenoptera: Formicidae). Behavioral Ecology and Sociobiolology, October 20 online. Doi: 10.1007 / s00265-016-2223-y
Schlüter, A., P. & K. Löttker Mebert, 2009. Use of an active nest of the leaf cutter ant Atta cephalotes (Hymenoptera: Formicidae) as a breeding site of Lithodytes lineatus (Anura: Leptodactylidae). Herpetology Notes 2: 101-105.

Fly trap

24 October 2016 /

Parachute flower smells like a tasty bee in distress

ceropegia-sandersonii-alzheimer1

Flowers of the African parachute plant are deceivers, as Annemarie Heiduk and colleagues show. The flowers mimic the smell of honeybees that are caught in the jaws of a spider. Their volatiles attract flies that feed on the fluids that such unhappy bees excrete. These flies pollinate the flowers.

Many plants have their flowers pollinated by insects. The insects take up pollen from one flower they visit and leave some of it on the pistil of the next flower, that can then grow seeds. And in return, most plants offer their pollinators nectar as a reward.

Clumps of pollen

But not all plants are honest plants. Some lure their pollinators with false promises of a reward.

A sophisticated deceptive plant is the African parachute plant Ceropegia sandersonii, a climbing herb from southern Africa, as Annemarie Heiduk and colleagues reveal.
Its pollinators are Desmometopa-flies. They visit the flowers and disperse the pollen, but not voluntarily. The flower is a trap where they go into. Downward pointing hairs on the flower wall make it impossible for them to get out. Clumps of pollen (pollinaria) within the flower dislodge and stick to their mouthparts.

Only the next day, when the flower withers, the flies are able to escape, packed with pollen. In the flower that they enter next, they will deposit the pollinaria unwittingly on the right place.

The question arises: how is it that the flies can be tricked time and again? Now, Heiduk answered that question: the flower smells like their food.

Volatiles

The flies, especially the females, need protein and they derive it from honeybees. They can’t overpower a honeybee by themselves, as they are much smaller. But when a spider has caught one, they come and feed on the fluids that leak from the dying bee. They find such a bee as they detect compounds that are released from its mandible glands and sting glands when it tries to defend itself by biting or stabbing. Also, they detect the pheromones that the bee releases to alert conspecifics.

Heiduk analysed the blend of volatiles dispersed by the flowers of the parachute plant, and found that many components are identical to the compounds that are released by bees in agony. This blend of volatiles is unique among flowering plants, and clearly adapted to lure the flies. Upon detection, they approach the flower, expecting to find a helpless bee. They find nothing of the kind, however, but are imprisoned for a time and meanwhile serve the plant. For free.

Willy van Strien

Photograph: Ceropegia sandersonii. Alzheimer1 (via Flickr. Creative Commons BY-NC-SA 2.0)

Nasty video: a honeybee is hold by a spider and licked by Desmometopa-flies

Source:
Heiduk, A., I. Brake, M. von Tschirnhaus, M. Göhl, A. Jürgens, S.D. Johnson, U. Meve & S. Dötterl, 2016. Ceropegia sandersonii mimics attacked honeybees to attract kleptoparasitic bees for pollination. Current Biology, online October 6. Doi: 10.1016/j.cub.2016.07.085

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