Successful as bird dropping

Crab spider imitates fresh bird’s poo

bird-dung crab spider mimics bird's poo

It looks like bird dropping, it smells like bird dropping. But it is the bird-dung crab spider Phrynarachne ceylonica, waiting until an unsuspecting fly comes close, as Long Yu and colleagues show.

Crab spiders get their meals by sitting motionless and waiting for a prey to come within range. Then they may strike suddenly. It helps if they don’t look like a spider while they sit-and-wait, but are disguised. The bird-dung crab spider Phrynarachne ceylonica, for example, successfully mimics a moist bird’s dropping, Long Yu and colleagues write.

The spider not only looks like bird poo, but it also smells like it. It was already known to mislead its predators, such as larger jumping spiders, which simply don’t recognize it.

The spiders occurs in Sri Lanka, China, Japan, and Taiwan.

Leaf miner flies

Now this masquerade proves doubly useful. The sneaky spider attracts tasty insects, mainly leaf miner flies (agromyzids), as Yu notes after observing several juvenile and female crab spiders in the field. The larvae of these flies feed on plant tissue, but adults have a different diet, and to them, fresh bird droppings are a favourite source of nutrients.

Yu painted several spiders entirely white or black, and these painted spiders did not attract the flies.

As he shows, the bird-dung crab spider Phrynarachne ceylonica has the same colours as fresh bird droppings to the eyes of insects. Spinning some threads, the spider mimics a dehydrated edge. And it works out well: insects land right next to the spider. The spider attracts prey at a lower rate than a real bird’s dropping, but that isn’t much of a problem if it is satiated after only one meal.

Unfortunately, the researchers do not report whether the crab spiders do indeed capture and consume the leaf miner flies.

Willy van Strien

Photo: LiCheng Shih (Wikimedia Commons, Creative Commons CC BY 2.0)

Another crab spider mimics a flower

Source:
Yu, L., X. Xu, Z. Zhang, C.J. Painting, X. Yang & D. Li, 2021. Masquerading predators deceive prey by aggressively mimicking bird droppings in a crab spider. Current Zoology, online July 24. Doi: 10.1093/cz/zoab060

False alarm

Superb lyrebird male tries to prolong a female’s visit

a male superb lyrebirds show is also used to manipulate females

A male superb lyrebird can deceive a female into believing that danger is imminent, Anastasia Dalziell and colleagues think. This increases the chance that she will stay for a while and copulation ensues.

Superb lyrebirds are masters of imitating all possible sounds, and males make clever use of that talent. When a female pays a visit, a male imitates the sound of a flock of alarmed songbirds, creating the illusion that a predator is nearby, Anastasia Dalziell and colleagues write. Then she might stay a little longer than she really wanted.

The superb lyrebird (Menura novaehollandiae), one of the largest passerine species, lives in the forests of South East Australia. Males and females do not form breeding pairs; each bird lives in its own territory. Females have one young per year, which they raise on their own.

Just watching

During the breeding season, males make themselves as attractive as possible. They construct mounds in their territory, where they sing their songs. Sometimes they sing a special song accompanied by a dance according to fixed rules, as Dalziell described earlier, throwing their decorative tail feathers over their body and head.

The purpose of a male’s show, of course, is to attract females and get them to copulate, because every mating can result in a young that he sires. Females visit several males before making their choice. As a result, a female may come to watch a displaying male, but refrain from mating with him in the end.

That is not what he intended.

Illusion of danger

When she is about to leave without copulating, he adds a new element to his song, which is remarkably similar to the sound of a flock of aroused songbirds.

Small songbirds get aroused when they detect a predator, such as a snake, large lizard, roosting owl, or perched hawk. They utter alarm calls to recruit others and harass the enemy together. The researchers show how accurately a male lyrebird mimics such mobbing flock of multiple simultaneously calling birds. Even the noise of beating wings is incorporated into his song. It is so accurate, that small songbirds are misled and approach to join.

The predators that arouse the small birds are dangerous for lyrebirds too. Therefore, the researchers hypothesize, the song creates the illusion that danger is imminent; the female is inclined to stay, and there is a chance that a copulation will happen.

Deception

A male superb lyrebird also utters this cacophony during mating. This job is not done in a few seconds, as it is other birds. Only after havng sat on her for more than half a minute, does he transfer his sperm. From the moment he mounts her until the end, he mimics the sound of a mobbing flock to prevent her from leaving too soon. During mating, he beats his wings in front of him, obscuring her view. She is unable then to assess whether it is safe to go, the authors suggest.

In conclusion, the superb lyrebird male uses his song not only to advertise his good health and condition, as is usual, but also to get a female to stay by giving a false signal of danger. That is deception.

Whether a female will stay longer because of the false alarm, the researchers don’t know. To find out, they would have to do experiments, which would be difficult for this species.

Willy van Strien

Photo: Courting male, covered with his tail. Kim Edol (via Flickr, CC BY-NC-ND 2.0)

Anastasia Dalziell about her research on YouTube

Sources:
Dalziell, A.H., A.C. Maisey, R.D. Magrath & J.A. Welbergen, 2021. Male lyrebirds create a complex acoustic illusion of a mobbing flock during courtship and copulation. Current Biology, online February 25. Doi: 10.1016/j.cub.2021.02.003
Dalziell, A.H., R. A. Peters, A. Cockburn, A.D. Dorland, A.C. Maisey & R.D. Magrath, 2013. Dance choreography is coordinated with song repertoire in a complex avian display. Current Biology 23, 17 juni online. Doi: 10.1016/j.cub.2013.05.018

Is it an ant?

Jumping spider exchanges jumping proficiency for safety

Myrmarachne jumping spiders resemble ants

To escape from predators, some jumping spider species mimic the appearance of an ant. A smart move, but it may constrain jumping abilities, Yoshiaki Hashimoto and colleagues supposed.

Everyone can tell the difference between a spider and an ant. A spider’s body has two parts: a cephalothorax and an abdomen, which is usually round. It has eight legs. An ant, on the other hand, is slender. Head and thorax are separated, while the abdomen is connected to the thorax by a narrow pedicel. It has six legs and two antennae.

But you can be mistaken, because some jumping spiders, Myrmarachne species, convincingly mimic the appearance of a spider. This is at the expense of their jumping skills, Yoshiaki Hashimoto and colleagues show.

It will certainly be beneficial for these little spiders to look like an ant. Predators refrain from taking an ant, because this prey may bite or sting, spray formic acid or have an army of colleagues nearby. They also avoid spiders that look like an ant.

Complete picture

The jumping spiders imitate ants in several ways. Females of Myrmarachne plataleoides, for example, resemble the green weaver ant (Oecophylla smaragdina) very closely. They are the same size and colour. The shape is also similar, thanks to a constriction behind the head and an elongated pedicel between a slender thorax and a thin, long abdomen with an anterior constriction. Two black spots on the side of the head imitate the large eyes of ants; the eight real eyes at the front are hardly visible. And to complete the picture, these spiders often slightly lift the first pair of legs; it seems as if they have six legs and a two antennae, just like ants.

But Hashimoto wondered: are jumping spiders that mimic ants really jumping spiders? In other words, isn’t the disguise at the expense of their jumping abilities?

Jumping spiders don’t construct a web, but they hunt on the ground and jump to their prey. To jump, they stretch their legs. This not done with muscle power, but with power generated by liquid pressure: the spiders pump hemolymph, their variant of blood, from the abdomen into the cephalothorax, to which the legs are attached, and by compressing the cephalothorax, they raise the pressure, extending the legs. For ant mimics this is difficult, because they have to force the liquid through the thin stalk between the abdomen and the cephalothorax. And as the cephalothorax is thin, they cannot create high pressure. Hence the question.

Giant leap

The researchers took seven Myrmarachne species from tropical Southeast Asia and compared their shape with that of other jumping spider species. Myrmarachne-spiders were indeed more elongated and slenderer. Some ant mimics, including Myrmarachne plataleoides, were very slender because they mimic a very thin ant.

In a lab test, non-mimetic jumping spiders jumped a distance nearly three times their body length. The ant mimics didn’t perform as well. The very slender types only jumped two-thirds of their body length, the thicker ones went a bit further. So, ant-mimicking jumping spiders have indeed sacrificed their jumping ability in exchange for safety. That makes hunting more difficult, because they cannot jump on prey from a distance. Tests show that their prey capture success rate is lower than that of other jumping spiders.

There is some evidence, the researchers write, that the most slender ant mimics switched to a mainly plant-based diet. That would be a giant leap – albeit figuratively.

Willy van Strien

Photo: Jumping spider Myrmarachne plataleoides, female. Renjusplace (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Hashimoto, Y., T. Endo, T.Yamasaki, F.Hyodo & T. Itioka, 2020. Constraints on the jumping and prey‑capture abilities of ant‑mimicking spiders (Salticidae, Salticinae, Myrmarachne). Scientific Reports 10: 18279. Doi: 10.1038/s41598-020-75010-y

Resemblance is striking

Parasitic Vidua nestlings trick host parents with near-perfect mimicry

Vidua nestlings mimic the young of their host parents

In order not to stand out in the nest in which they grow up clandestinely, Vidua nestlings mimic the young of the host parents. They perform very well, Gabriel Jamie and colleagues report. But some slight discrepancies exist.

African whydahs and indigobirds, Vidua species, are brood parasites like the cuckoo. They lay their eggs in the nest of other bird species, in this case grassfinches, and have the host parents raise their young. Vidua finches are unable to provide parental care. But these brood parasites do much less harm to the host families than a cuckoo, because young Viduas don’t eject other nestlings from the nest. The host parents take care for their own offspring, but have some extra, foreign young.

The foreign nestlings should not stand out, otherwise the tricked parents will notice the deception. It was already known that Vidua young resemble their host parents’ young. With special computer software, Gabriel Jamie and colleagues now show how successful the mimicry is.

Ornamented mouths

pin-tailed whydah is brood parasiteThe Vidua genus contains nineteen species. In the breeding period, the males are real beauties, while the females are inconspicuous and difficult to recognize. Jamie took a closer look at three species: pin-tailed whydah (Vidua macroura), broad-tailed paradise whydah (Vidua obtusa) and purple indigobird (Vidua purpurascens). They are host-specific, each Vidua species has a single host species. Jamie compared the Vidua nestlings to that of their respective host parents and of a number of other grassfinch species.

Young grassfinches (Estrildidae) have ornamental mouth markings that become fully visible when they open their beaks; this ornamentation in unusual among birds. Each grassfinch species has its characteristic pattern, colour and structure.

Nestlings of the breeding parasites accurately mimic those characteristic markings, is the conclusion of the research. An analysis with pattern recognition software shows that the pattern is similar to that of their host parent species. The colours match well too. Vidua nestlings also cleverly imitate the begging calls and postures of their foster siblings.

Imprinting

Previous research, by Michael Sorenson, had shown that the nineteen species of whydahs and indigobirds are much younger than their hosts in an evolutionary sense. The idea is that their common ancestor switched to a brood parasitic lifestyle with a grassfinch as host parent.

Speciation could then occur quickly. Whenever a Vidua female happens to lay eggs in the nest of another host, a separate group associated to that new host arises, because Vidua nestlings imprint on the song of their host father. Each grassfinch species has its own characteristic song. When grown up, Vidua males will mimic the song of their host, and females are attracted to this song. Also, females select a nest of the host species they were raised by to lay their eggs in. The group turns into a new species.

The nestlings then become more and more similar to the nestlings of the new host through an evolutionary adaptation process. Because the more a Vidua nestling resembles the young of its host parents, the more likely they are to accept it and care for it, increasing its survival chance.

Exaggerated

And as a matter of fact, the resemblance between foreign and own young in a parasitized grassfinch’s nest turned out to be striking. But it is not entirely perfect. Small but consistent differences exist. Perhaps the foreign nestlings are (yet) unable to fully mimic their nest mates. And apparently, they are doing well enough: the host parents accept them.

But there may be another explanation for the discrepancies, the researchers write. Nestlings of pin-tailed whydah, for example, have spots in the beak that are slightly larger than those of their foster parents’ young, common waxbill (Estrilda astrild), and their begging calls are slightly extended. Unlike a waxbill nestling, they wave a wing under their open mouth while begging.

So, these Vidua nestlings are slightly exaggerating their host’s begging signals. And perhaps the host parents favour them as a consequence. An intriguing thought.

Willy van Strien

Photos:
Large: pin-tailed whydah nestling, the outside of the mouth markings visible. ©Gabriel A. Jamie
Small: pin-tailed whydah, breeding male. Alan Manson (Wikimedia Commons, Creative Commons CC BY-SA 2.0)

Sources:
Jamie, G.A., S.M. Van Belleghem, B.G. Hogan, S. Hamama, C. Moya, J. Troscianko, M.C. Stoddard, R.M. Kilner & C.N. Spottiswoode, 2020. Multimodal mimicry of hosts in a radiation of parasitic finches. Evolution, online July 21. Doi: 10.1111/evo.14057
Sorenson, M.D., K.M. Sefc & R.B. Payne, 2003. Speciation by host switch in brood parasitic indigobirds. Nature 424: 928-931. Doi: 10.1038/nature01863

Hoverflies entrapped

Orchid deceives pollinators, but still offers a reward

Cypripedium subtropicum imitates an aphid colony covered with honeydew

The orchid Cypripedium subtropicum lures hoverflies by mimicking an aphid colony covered with honeydew. The hoverflies fall into a trap and while struggling out, they pollinate the flower, as Hong Jiang and colleagues write.

Pollination normally follows the principle ‘give a little, take a little’. Pollinators, such as bees, butterflies and flies, drink nectar from flowers, and through their visits they transfer pollen from one flower to another. A delicacy in exchange for pollen transport.

However, not all plants play a fair game. Some orchids, for instance, mimic a female wasp to attract male wasps. The males fruitlessly attempt to mate and while moving, they pick up or deposit pollen. Such deceptive flowers lure insects with false promises and make use of their services without paying a reward. On the contrary: a deceived male is just wasting its time.

Now, Hong Jiang and colleagues describe another form of deceit in  Cypripedium subtropicum, an orchid species that grows in mountain forests in southwest China, Tibet and north Vietnam and that is pollinated by hoverflies. It promises its visitors not a mate, but food. Peculiarly, cheated insects do receive a reward from the plant – albeit an unusual one.

Aphid colony

The flowers of Cypripedium subtropicum are dark brown and have an enlarged labellum that has the shape of a pouch and is speckled with white hair tufts. In the eyes of hoverflies, the researchers think, the whole looks like an aphid colony covered with honeydew. And that’s what hoverflies are fond of. Honeydew is a sweet and sticky substance secreted by aphids because the sap they suck from plants contains an excess of sugars. Experiments showed that hoverflies don’t land on orchids that have their white hair tufts removed.

But the imitation goes further. The flowers also smell like an aphid colony: they emit an odour similar to that of alarm pheromones that aphids use to warn each other when danger is imminent.
And to finish it off, the white hair tufts are nutritious and contain a high amount of sugar – just like honeydew. Cypripedium subtropicum mimics the colour, smell and taste of an aphid colony.

Narrow way out

But when hoverflies enjoy the sweet food, it becomes clear that the orchid uses a trick to be pollinated. The labellum has an opening between the white hair tufts. At some moment while eating, a hoverfly will fall into the hole. Crawling back through the opening is impossible because of the curved margin. The animal is trapped.

The only way out is a narrow cleft at the top of the back of the pouch, through which the hoverfly can scramble out. It will first pass the flower’s pistil and then the stamens. When it squeezes along the stamens, a smear of pollen will attach on its back. And if it is trapped again during the next flower visit and tries to escape, it will deposit that pollen on the pistil. Subsequently, it picks up a new dose of pollen.

Cypripedium subtropicum forces hoverflies to pollinate it by trapping them, but at least they get an edible reward in return. The promise is not entirely false in this case.

Willy van Strien

Photo: ©Hong Jiang

Source:
Jiang, H., J-J. Kong, H-C. Chen, Z-Y. Xiang, W-P. Zhang, Z-D. Han, P-C. Liao & Y-i Lee, 2020. Cypripedium subtropicum (Orchidaceae) employs aphid colony mimicry to attract hoverfly (Syrphidae) pollinators. New Phytologist, online April 26. Doi: 10.1111/nph.16623

Protected and aggressive mimics

Young false cleanerfish relies on disguise to bite other fishes

False cleanerfish resembles bluestreak cleaner wrasse

It is beneficial to look like cleanerfish, Misaki Fujisawa and colleagues show. By mimicking cleanerfish, false cleanerfish prevent attack by predatory fish. Also, they can approach other fishes and take a bite – but only small individuals show such behaviour.

The bluestreak cleaner wrasse, Labroides dimidiatus, lives on coral reefs where it offers cleaning services: the cleanerfish removes blood sucking parasites from the skin of other fishes. There is also a pretender, the false cleanerfish Aspidontus taeniatus. It has the same appearance as the cleaner wrasse, but it does not clean other fishes.

Misaki Fujisawa and colleagues wondered why it resembles the bluestreak cleaner wrasse. The disguise, or mimicry, helps to escape from predatory fish, which don’t consume useful cleaner fish and don’t detect the deceit. So there is a protective function. But maybe the mimicry has a second benefit. False cleaners may be able to approach fishes undisturbed in order to attack them. In that case, the disguise would also enable aggressive behaviour.

To find out, the researchers observed the behaviour of the false cleaners in the coral reefs around Sesoko Island in Japan.

Biting fins

The false cleanerfish mainly feeds on benthic animals; it bites off pieces of the tentacles of tubeworms or soft parts of the boring clam. In addition, it bites the fins of other fishes and steals eggs from the nests of damselfish (Pomacentridae).

The resemblance to the bluestreak cleaner wrasse is profitable for fin biting, as it gives the false cleaner a chance to approach unsuspecting victims, even if it behaves a little differently. Whereas a cleaner wrasse invites clients for a cleaning service by performing a zigzag dance, a false cleaner does not: it usually approaches its victims from behind, makes a sudden dart and bites off a piece of the caudal fin. So, the disguise indeed seems to have a second function, next to the protection that it offers the false cleaners against predatory fish.

Less dangerous

But only small individuals rely on their disguise to aggressively approach other fishes, as Fujisawa shows. As the false cleaners grow bigger, they continue feeding on benthic animals, but in addition to exploiting this main food source, they gradually switch from fin biting to egg predation. To raid nests, they often form small groups, and then the mimicry loses its effect, as cleanerfish always operate solitary or with their mate.

The false cleaners have good reason to change feeding tactics, as fish eggs are more nutritious than pieces of fin. But for small false cleaners it is difficult and risky to raid nests, because the eggs are guarded by damselfish parents, which will attack each enemy fiercely and without hesitation. Large false cleaners can elude attacks by swimming fast, but for small fish this is too dangerous. Biting fins is more feasible to them – thanks to their innocent appearance.

Willy van Strien

Photo: Two adult cleaners (middle and right) and an adult mimic (left) at Sesoko Island, Okinawa, Japan. ©Misaki Fujisawa

Sources:
Fujisawa, M., Y. Sakai & T. Kuwamura, 2018. Aggressive mimicry of the cleaner wrasse by Aspidontus taeniatus functions mainly for small blennies. Ethology, 19 april online. Doi: 10.1111/eth.12743
Cheney, K.L., A.S.Grutter & R. Bshary, 2014. Geographical variation in the benefits obtained by a coral reef fish mimic. Animal Behaviour 88: 85-90. Doi: 10.1016/j.anbehav.2013.11.006
Kuwamura, T., 1983. Reexamination on the aggressive mimicry of the cleaner wrasse Labroides dimidiatus by the blenny Aspidontus taeniatus (Pisces; Perciformes). Journal of Ethology 1: 22-33. Doi: 10.1007/BF02347828

Unrewarded services

Orchid utilizes fungi and fruit flies without paying

Drosophila fly on flower of the deceptive orchid Gastrodia pubilabiata

The orchid Gastrodia pubilabiata lives at the expense of other species. It steals sugars from fungi, which also attract fruit flies that provide pollination service, as Kenji Suetsugu shows, without receiving any reward in return.

While most plants produce sugars from carbon dioxide using energy from sunlight in a process called photosynthesis, the orchid Gastrodia pubilabiata leaves the job to others. The small and inconspicuous plant, which grows in Japan and Taiwan, does not have green leaves, as it lacks chloroplasts, the cell organelles that conduct photosynthesis. With its roots, it steals sugars from the underground hyphae of a number of mushroom forming fungi species; the fungi obtained these sugars from dead organic material. The fungi get nothing in return.

And while most plants produce nectar as a food resource for insects (or other animals) that pollinate the flowers in return, this orchid doesn’t. To be pollinated, it exploits fruit flies (Drosophila species) without rewarding them.

Deceived

The flies need fermenting fruit or decaying mushrooms to lay their eggs in, and their larvae will consume that stuff. Apparently, the brown-coloured flowers of Gastrodia pubilabiata smell like fermenting and decaying substrates, as the flies are deceived into laying their eggs on the flowers. Consequently, the larvae will find no suitable food and die. But the orchid has been served. While visiting a flower, the flies pick up pollinia, masses of pollen grains, which they deliver to the next flower they visit, thereby pollinating that flower.

Service

The orchid thus takes nutrients from mushrooms and is pollinated by fruit flies, and neither of these partners receives any reward for its services. Both are victims of a parasitic and deceptive plant.

Now Kenji Suetsugu shows that mushroom-forming fungi still provide another service. Old mushrooms attract fruit flies that have to lay their eggs, and upon arrival, they will also visit the orchid flowers that mimic fermenting and decaying material. Suetsugu conducted experiments in which he removed decaying Mycena mushrooms from the orchids’ proximity or added extra specimens; Mycena species are the main victims of theft by the plant. He found that the more decaying mushrooms are around, the more pollen is removed from and delivered to orchid flowers by flies that are misled, and the more seeds are produced.

So, the fungi not only function as food providers, but also as magnets that attract pollinators – without reward.

Willy van Strien

Photo: Gastrodia pubilabiata, flower and fruit fly bearing pollinia. © Kenji Suetsugu

Source:
Suetsugu, K., 2018. Achlorophyllous orchid can utilize fungi not only for nutritional demands but also pollinator attraction. Ecology, online March 25. Doi: 10.1002/ecy.2170

Deceit, abuse and benefits

Complex relationships between arum, blowflies and lizard

Dead-horse arum flower is attractive to lizard

With its smell of rotting carrion, the dead-horse arum Helicodiceros muscivorus is irresistible to blowflies and a lizard. The blowflies will be abused, the lizard benefits. Ana Pérez-Cembranos and colleagues unraveled these complex relationships.

On islands in the Mediterranean Sea, a plant occurs with a very bad smell, the dead-horse arum, Helicodiceros muscivorus. Its odour contains chemical components that are also emitted by a decomposing dead animal. It irresistible to a female blowfly searching for carcasses to lay her eggs on to make sure that the carnivorous larvae will have food. The dead-horse arum takes advantage of that behaviour.

The plants release their odour on the first day of blooming. Blowflies that perceive the smell cannot ignore it. Upon approaching the source, they find a pink or red curved bract, the spathe, with the hairy end of the spadix (inflorescence), which produces the smell. When they land, the spadix turns out to be warm. To blowflies, the imitation is perfect: this is rotting carrion. Guided by the heat, they crawl into the tube that is formed by the base of the spathe around the lower part of the spadix, which bears female and male florets.

Trapped

Once inside, the blowflies don’t find what they need, which is decaying meat. But if they want to leave, they cannot. Spikes on the spadix keep the door closed. The blowflies are trapped.

Unintentionally, they provide a service to the arum during their imprisonment in the floral chamber. The female flowers at the bottom of the spadix are blooming this first day, and blowflies that had been misled by the arum before, now deliver the pollen that they picked up on that occasion. The plant has its female flowers pollinated.

The next day, the female flowers have faded and the male flowers are mature. The stench and the heat disappear, the spikes wilt and the blowflies escape, and while passing the male flowers, they are loaded with pollen. And here is the second benefit to the plant: the blowflies take the pollen with them to female flowers elsewhere – if at least they find another foul smelling arum on their way and are again misled into visiting it.

So, the blowflies are coerced to pollinate the dead-horse arum without receiving any reward such as nectar. On the contrary: they lose time that they should have spent on searching for genuine carcasses.

Basking

Now Ana Pérez-Cembranos and colleagues show that the Balearic lizard Podarcis lilfordi is also misled by the arum’s odour. The animal is omnivorous and sometimes forages on carcasses, which are also attractive as a heat source; lizards are cold-blooded and when the weather is cool, they may use a rotting carcass as a perching site for basking. In addition, they capture the blowflies that arrive at the cadaver in search for a site for oviposition.

The lizards respond to the smell of the dead-horse arum as they do to the smell of a carcass and will approach the source. If that turns out to be a dead-hors arum instead of a dead animal body, they will not find a meat meal, but they do find a basking place and blowflies, which they take from the spathe or grab from the tube. The lizards thus take away a number of pollinators, but, according to the researchers, enough are left to ensure pollination.

Fruits

So, the lizard isn’t an enemy of the arum. And after the flowering period, when fruits are ripe, a mutualism even develops between both. The lizards consume the fruits and disperse the seeds in their faeces; passage through the lizard’s intestine increases the probability of germination. On Aire Island, a the small island off the southeastern coast of Menorca, where the research was done, the dead-horse arum is a newcomer. It is estimated to have grown there for only about fifty years. In that period, it spread rapidly over the island and nowadays it locally occurs in great densities. That is because of the lizard, which has learned to eat the fruits and now is the main disperser of the seeds, the researchers think.

Willy van Strien

Photo: Balearic lizard on the spathe of the dead-horse arum © Ana Pérez-Cembranos

Sources:
Pérez-Cembranos, A., V. Pérez-Mellado & W.E. Cooper, 2018. Balearic lizards use chemical cues from a complex deceptive mimicry to capture attracted pollinators. Ethology  124: 260-268. Doi: 10.1111/eth.12728
Angioy, A-M.,  M. C. Stensmyr, I. Urru, M. Puliafito, I. Collu & B. S. Hansson, 2004. Function of the heater: the dead horse arum revisited. Proceedings of the Royal Society London B 271: S13-S15. Doi: 10.1098/rsbl.2003.0111
Stensmyr, M.C., I. Urru, I. Collu. M. Celander. B.S. Hansson & A-M. Angioy, 2002. Rotting smell of dead-horse arum florets. Nature 420: 625-626. Doi: 10.1038/420625a

Double deceit

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

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