Mode of transport

Ants select best carrier material for collecting fluid food

Ant Aphaenogaster subterranea uses tools to collect fluid food

The ant Aphaenogaster subterranea uses absorbent material to carry fluid food back to its nest. It selects the most easily portable material, or it takes material that is discovered first, as Gábor Lörinczi and colleagues observed.

Ants of many species possess a greatly distensible crop and a highly modified proventriculus, in which they transport large volumes of liquid food back home for their nest mates. But other species, among which Aphaenogaster subterranea, don’t possess such internal carrier sac. Still, they are able to collect fluid food. They drop debris in such food source, and grasp the food-soaked material with their mandibles to take it with them. Their choice of carrier material is flexible, Gábor Lörinczi and colleagues write.

Aphaenogaster subterranea occurs in forests in Central and Southern Europe. It lives in colonies, mostly in a nest in the soil, under a stone. Specialised workers collect fluid food for the colony: fruit pulp and body fluids of dead arthropods.

Aphaenogaster is flexible in its choice of toolsLörinczi held a number of nests in plastic boxes the laboratory and conducted experiments in which the nests were connected to a foraging arena via a plastic tube. In the foraging arena, he offered a drop of honey diluted in water or honey enriched with sugars as a liquid food source on a plastic disc; or he offered pure water as a control. Around the disc, he placed different piles of carrier material: small soil grains (1 millimetre in diameter), large soil grains (2 millimetre in diameter), pieces of pine needles (5 millimetre in length), pieces of plant leaves (5 millimetre in length) and pieces of sponge (5 millimetre in length). He then observed the foraging behaviour of the ants.

Flexible

If all piles of ‘carrier bags’ were close to the food bait (at a distance of 4 centimetres), the ants selected mainly small soil grains to transport to and drop into the food. These grains are most easily transportable.  If all piles were at greater distance  (12 centimetres), the ants were less selective. And if one type of material was close to the food bait while the other types were not, they used that material relatively more often. So, the choice of carrier material is not fixed. The ants prefer small soil grains, but if something else is discovered sooner or more readily accessible, they will use that, maximizing their efficiency.

Leave fragments were used only infrequently, even if it could be found close to the food bait. This material is difficult to handle.

Ants that retrieved food-soaked material from the food bait, mainly picked up small soil grains. From honey, they also collected many pieces of sponge. As the authors suggest, these may be easy to pick up because of their buoyancy. They also observed that after a while, the ants started to tear the pieces of sponge into smaller fragments before using them.

Into water, objects were dropped infrequently, and no objects were retrieved from it.

So, workers of Aphaenogaster subterranea show flexibility in foraging tool use, and they even modify some material, which is unique among insects as far as is known.

Willy van Strien

Photos:
Large: Aphaenogaster subterranea. Christophe Quintin (via Flickr, cropped; Creative Commons CC BY-NC 2.0)
Small: The ants covered a drop of food with absorbent material. ©Gábor Lörinczi

Sources:
Lőrinczi, G., G. Módra, O. Juhász & I. Maák, 2018. Which tools to use? Choice optimization in the tool-using ant, Aphaenogaster subterranea. Behavioral Ecology, online August 1. Doi: 10.1093/beheco/ary110
Maák, I., G. Lőrinczi, P. Le Quinquis, G. Módra, D. Bovet, J. Call & P. d’Ettore, 2017. Tool selection during foraging in two species of funnel ants. Animal Behaviour 123: 207-216. Doi: 10.1016/j.anbehav.2016.11.005

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Gruesome boost

Damaged cicadas spread fungal spores via sexual behaviour

Magicicada species are manipulated by the fungus Massospora

Massospora fungi produce substances that we know as recreational drugs, Greg Boyce and colleagues write. By doing so, they manipulate the behaviour of cicadas in which they proliferate. The insects face a horrible fate.

The fungus Massospora cicadina infects periodical cicadas of the genus Magicicada and manipulates the behaviour of infested insects in such a way that they will transmit the fungal spores to conspecifics. Horribly enough, they do so by sexual activities, while their rear part has already been largely destroyed and turned into a fungal mass. Greg Boyce and colleagues try to find out how the fungus exerts its dismal influence.

Magicicada species, which live in the east of North America, are almost never to be seen. They spend most of their life underground as nymphs, the immature form. Only once in many years – some species take thirteen years, other species take seventeen years – mature nymphs emerge from the soil, synchronously and massively per species and per area. They moult into mature cicadas that live only for four to six weeks. In this period, they mate and the females lay their eggs on tree branches. Young nymphs fall down and disappear in the soil.

This unusual life cycle makes it very difficult for natural enemies such as birds to specialize on adult cicadas, because they would not be able to find prey for many years while occasionally, once in thirteen or seventeen years, there is an overwhelming amount.

But the fungus Massospora cicadina can deal with the life cycle of these cicadas.

Copulation attempts

Fungal spores rest in the soil until nymphs emerge and then infect them. After moult, the fungus proliferates in the abdomen of adult insects. Eventually, their rear part, genitals included, falls off and a fungal spore mass becomes visible.

The heavily damaged cicadas try to mate, even more vigorously than normal. Of course, this is useless to them, but the fungus benefits: during the copulation attempts, the unfortunate cicadas transmit spores to conspecifics.

In these insects, the fungus forms a second infection stage. Because now time runs out for the adult cicadas, a third infection is not feasible. Therefore, instead of infective spores, the fungus produces resting spores, which fall down and wait in the soil until the next generation of cicadas appears.

Bisexual males

Earlier this year, John Cooley and colleagues described deviant behaviour in males with a first stage infection. Normally, males sing in chorus to lure females. When a female shows interest in a male, she makes a flicking wing movement that is tuned to his song. He then utters more complex song, she answers with a tightly timed wing-flick, and a ‘duet’ is created while the two approach each other.

First stage infected males try to acquire a female mate in the normal way. But they also respond to the song of other males with female-like wing-flicks. As a result, not only females, but also males are attracted – and become infected. The fungal infection spreads extra fast.

It is striking that only males with a first stage infection assume a female role besides a male role. Males with a second stage infection, which does not produce infective spores, don’t exhibit wing-flicks.

Stimulating drug

Now, Greg Boyce shows how the fungus manages to affect the behaviour of the cicadas. Among the substances that it produces in the cicadas’ abdomen is cathinone. This is known as the active substance in khat, which is released when chewing leaves of the Khat plant, Catha edulis. It is surprising that a plant and a fungus share this substance. Cathinone is closely related to amphetamine, or speed, a stimulating drug, and just like the drug, it interferes with the communication between nerve cells. Apparently, this results in abnormal behaviour in male cicadas.

In a first stage infection, in which the cicadas transmit the fungus spores to conspecifics, the fungus produces more of this stimulating substance than in a second stage infection, which shows how accurately it manipulates its host.

Another Massospora fungal species, which infects cicadas with an annual cycle (Platypedia species), also manipulates the sexual behaviour of its victims, Boyce and colleagues discovered. It produces psilocybin, a hallucinogenic substance known from certain mushrooms, most importantly Psilocybe species. Again a remarkable finding, as the fungus is not closely related to these mushroom species.

Willy van Strien

Photo: Magicicada septendecim. Judy Gallagher( Wikimedia Commons, Creative Commons CC BY 2.0)

Sources:
Boyce, G.R., E. Gluck-Thaler, J.C. Slot, J.E. Stajich, W.J. Davis, T.Y. James, J.R. Cooley, D.G. Panaccione, J. Eilenberg, H.H. De Fine Licht, A.M. Macias, M.C. Berger, K.L. Wickert, C.M. Stauder, E.J. Spahr, M.D. Maust, A.M. Metheny, C. Simon, G. Kritsky, K.T. Hodge, R.A. Humber, T. Gullion, D.P.G. Short, T. Kijimoto, D. Mozgai, N. Arguedas & M.T. Kasson, 2018. Discovery of psychoactive plant and mushroom alkaloids in ancient fungal cicada pathogens. BioRxiv preprint, July 24. Doi: 10.1101/375105
Cooley, J.R., D.C. Marshall & K.B.R. Hill, 2018. A specialized fungal parasite (Massospora cicadina) hijacks the sexual signals of periodical cicadas (Hemiptera: Cicadidae: Magicicada). Scientific Reports 8: 1432. Doi: 10.1038/s41598-018-19813-0
Cooley, J.R. & D.C. Marshall, 2001. Sexual signaling in periodical cicadas, Magicicada spp. (Hemiptera: Cicadidae). Behaviour 138, 827-855. Doi: 10.1163/156853901753172674

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Flamingos use cosmetics

Females apply more colourful make-up than males

Flamingos prefer colourful mates

To catch the attention of possible mates, flamingos use make-up. They produce a colourful oil which they apply over the feathers to reinforce their colour, signalling their quality. For females this is more important than for males, Juan Amat and colleagues write.

Flamingos, both males and females, are keen to find the best mate they can get. Mate selection is a cumbersome process. Months before breeding, the birds join large mixed groups to see each other and to be seen. They exhibit their plumage with outstretched necks and stuffed feathers. And when they selected a mate, the game is not finished yet. They stay alert, and if possible they exchange their mate for a better one. Mutual assessment and selection continue until they actually start breeding.

It is important to stand out with a beautiful pink plumage in such displaying group, because a colourful bird is preferred and will quickly acquire an equally attractive partner. Together they can occupy a good nesting place in the breeding colony, enjoying an advantage over less popular birds.

A beautiful colour is attractive for good reason. The feather colour arises during moult at the end of the summer, when the birds incorporate pigments (carotenoids) that they ingested with their food into their feathers. A beautiful colour is proof that the bird has been successful in obtaining food. It can afford to incorporate the pigments into the feathers, which means that it is not under pressure, because in that case it would have to use the pigments to prevent cell damage caused by stress. The substances are antioxidants, which eliminate harmful oxygen radicals that arise during stress. In short, a bird that has beautiful a colour after moult is healthy and in good condition.

However, a long time passes by between the periods of moult and mate choice during which the original colour fades, and in this time the condition of a bird may either improve or deteriorate. The original feather colour is no good indicator of condition during display. How is it possible to make a good choice?

Cosmetics

There is a solution to this problem. The birds are able to reinforce the colour of their feathers, Juan Amat and colleagues showed in 2011; the team studies a large colony of greater flamingos (Phoenicopterus roseus) that breeds on islands and dikes in the salty South Spanish lagoon Fuente de Piedra, a nature reserve.

Flamingos produce a preen oil in the uropygial gland with pigments that were ingested with their food. They apply the preen oil over the feathers by rubbing their cheeks first on the gland and then along neck, chest and back, using the oil as cosmetics. The feather colour now is an up-to-date indicator of health and condition, because only strong birds find sufficient food to obtain pigments and can use them to tinge their plumage. They also have the time to reinforce the colour of their feathers frequently, which is necessary as the applied pigments quickly bleach.

Amat showed that the more time the birds spend rubbing, the deeper pink the colour of their plumage is. They produce preen oil with highest pigment concentrations in the period of display, when they use their make-up extensively and are most colourful. Once they have started breeding – each pair produces one young -, they stop maintenance behaviour of plumage and the colours fade. The parents stay together until their young is independent, after about three months. They then split up – and in October the long-lasting game of display and mate choice starts again.

Effort

Now, Amat shows that on average females are more colourful than males. They exhibit the same rubbing behaviour, but their uropygial gland contains pigments in higher concentrations. Apparently, it is more important for females to signal their quality.

As the researchers explain, the care for the young is more demanding for the mothers than it is for the fathers. The wetlands where the birds forage are no less than 150 to 400 kilometres away from the breeding colony. So, provisioning the chicks is quite an effort. The female makes the trip more frequently than the male and as she is smaller, the journey is heavier for her. That is why, during pair formation, she has to convince males beforehand that she can handle this task by showing a beautiful pink colour.

After the chick hatched, the female’s colour fades faster than that of her mate because now she is under more pressure and needs the pigments to combat stress damage. She doesn’t need to be attractive anymore – until the next display period starts.

Willy van Strien

Photo: Bernard Dupont (Wikimedia Commons, CC BY-SA 2.0)

Watch flamingos parading their plumage

Sources:
Amat, J.A., A. Garrido, F. Portavia, M. Rendón-Martos, A. Pérez-Gálvez, J. Garrido-Fernández, J. Gómez, A. Béchet & M.A. Rendón, 2018. Dynamic signalling using cosmetics may explain the reversed sexual dichromatism in the monogamous greater flamingo. Behavioral Ecology and Sociobiology 72: 135. Doi: 10.1007/s00265-018-2551-1
Amat, J.A., M.A. Rendón, J. Garrido-Fernández, A. Garrido, M. Rendón-Martos & A. Pérez-Gálvez, 2011. Greater flamingos Phoenicopterus roseus use uropygial secretions as make-up. Behavioral Ecology and Sociobiology 65: 665-673. Doi: 10.1007/s00265-010-1068-z

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Modest carnivore

Shepherd’s purse seedling benefits from animal proteins

Shepherd's purse is carnivorous during early development

Shepherd’s purse seeds derive nutrients from small animals by attracting, ensnaring, killing and digesting them, Hattie Roberts and colleagues discovered. The plant is carnivorous during early development.

Most carnivorous plants have a striking appearance: bladderworts, Venus flytrap, pitcher plants and sundews capture small critters with ingenious traps or sticky leaves. But who would suspect shepherd’s purse of having a carnivorous diet? The plant, which occurs almost everywhere, looks innocent. Still, it captures small invertebrates and uses their proteins when germinating, Hattie Roberts and colleagues write. Apparently, also less spectacular carnivores exist among plants.

Animal proteins

shepherd's purse seeds attract, ensnare, kill and digest small invertebratesA shepherd’s purse plant (Capsella bursa-pastoris) does not capture any bugs, but the seeds do. In moist soil, they are covered with a tough, sticky mucus layer. Years ago, John Barber already showed that germinating seeds excrete an attractive substance that lure small invertebrates, which subsequently are entrapped and killed by a toxin – Barber used mosquito larvae in his experiments. The seeds also release enzymes that digest animal proteins and take up the building blocks, amino acids.

The seeds seem to use animal proteins for growth, Barner stated. They also attract and kill nematodes (roundworms that live in soil), unicellular organisms and bacteria.

Food supply

Now, Hattie Roberts completes the story. She germinated seeds in presence or absence of nematodes and monitored germination and growth of the seedlings. The experiments showed that the seeds do better when animal nutrients are available. In soils in which nematodes were present, more seeds germinated successfully than in soils without nematodes, and the seedlings were bigger and heavier when measured ten days after germination. After three weeks, young plants that had germinated in soil with nematodes had longer roots and larger leaves.

Although seeds of shepherd’s purse are able germinate without animal nutrients, they do better with such nutrients. On soils with low nutrient levels, seeds derive more benefits from animal nutrients than on soils with high nutrient levels, as shown by the experiments.

Shepherd’s purse seeds are small and contain only a minimal food supply for the seedling. That is why the plants profit from extra nutrients during early development.

Willy van Strien

Photos:
Large: shepherd’s purse flowers. Harry Rose (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: shepherd’s purse seeds. Kinori (Wikimedia Commons, public domain)

See also:
Carnivorous plants with spectacular traps: bladderwort and Venus flytrap

Sources:
Roberts, H.R., J.M. Warren & J. Provan, 2018. Evidence for facultative protocarnivory in Capsella bursa-pastoris seeds. Scientific Reports 8: 1012. Doi: 10.1038/s41598-018-28564-x
Barber, J.T., 1978. Capsella bursa-pastoris seeds. Are they “carnivorous”? Carnivorous Plant Newsletter 7: 39-42.

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Healer

Wound heals faster in presence of cleaner shrimp

Cleaner shrimp helps wound healing

In case of injury, fish get extra benefits from the services of cleaner shrimp, David Vaughan and colleagues demonstrate. Even though the cleaner does not specifically clean the wound, its treatment aids healing.

Cleaner shrimp, just like cleaner fish, occupy cleaning stations for fish clients on coral reefs. With their mouthparts, they pick parasites and dead or damaged tissue from the skin of their clients, enjoying a morsel of food: a win-win situation. Such helper is the Pacific cleaner shrimp Lysmata amboinensis, which lives on coral reefs in the Pacific Ocean, Indian Ocean and Red Sea; in the film Finding Nemo, Jacques is representing this species.

How will this cleaner behave to a fish that sustains an injury, David Vaughan and colleagues wondered. Does it take advantage of an injured client by biting off some exposed living tissue? Or might his cleaning treatment be beneficial?

Inflammation

The researchers took cleaner shrimp into the lab, and also a number of sea goldies (Pseudanthias squamipinnis), a fish species that lives around coral reefs. They inflicted a small, superficial wound to one side of some fish, under anaesthesia; in the field, such wounds often occur. Half of the injured fish was then transferred individually to a tank where a cleaner was present for one hour each day; the remaining fish were housed in tanks without a cleaner. For control, uninjured fish were also placed in tanks with or without daily visits of a cleaner shrimp. The behaviour of fish and shrimp was observed, and healing of the wound was monitored.

A fish that wants its skin to be treated, will visit a cleaner shrimp and adopt an inviting attitude, presenting the side of the body it wants to be cleaned. Just after injury, it turns out, fish solicit cleaning less often. They keep the damaged side away from the shrimp.

But within 24 hours, the wound is closed. The spot turns red, indicating an inflammation; the redness increases during the first two days.

A wounded fish that has access to cleaner shrimp now wants to be cleaned at both sides. And after a few days, cleaning turns out to have health benefits: the redness of the wounded site decreases from the second day on, so inflammation subsides. After six days, a clear difference is seen between fish that were cleaned and fish that were not; in the latter fish, the redness has remained high. In other words: thanks to the activities of cleaner shrimp, a wound heals faster. There was no trace of abuse: the shrimp don’t aggravate an existing wound, nor do they cause any new damage.

Positive effect

Cleaner shrimp don’t focus cleaning specifically around the injury site, but treat an injured fish like they treat an uninjured one. The researchers think that the cleaning has an indirect positive effect, by keeping pathogens at bay that would otherwise invade the wound. Moreover, it is known that cleaner shrimp reduce stress in their clients. That will also help the healing process. So, by cleaning, cleaner shrimp also offer healing services.

Willy van Strien

Photo: Bernard Dupont (Wikimedia Commons, Creative Commons CC BY-SA 2.0)

Source:
Vaughan, D.B., A.S. Grutter, H.W. Ferguson, R. Jones & K.S. Hutson, 2018. Cleaner shrimp are true cleaners of injured fish. Marine Biology 165: 118. Doi: 10.4225/28/5b2c885b32331

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Flying over sand and sea

Painted lady travels between Europe and tropical Africa

painted lady is long-distance traveller

It was discovered two years ago that the painted lady butterfly migrates to the south in autumn and reaches the tropical savannahs of Africa. Now, Gerard Talavera and colleagues proved that their offspring returns back in spring.

Most European insects spend a resting period in winter. But the painted lady doesn’t. The butterflies, which can be found almost everywhere in Europe during summer, leave when autumn arrives. At high altitudes and benefiting from downwind, they fly over Europe, including mountain areas; they cross the Mediterranean and then the Sahara, enduring extremely low and high temperatures along their way. An individual painted lady can travel four thousand kilometres within a week: an incredible achievement for these fragile-looking creatures.

Eventually, they massively arrive in the savannahs of tropical Africa south of the Sahel, as Gerard Talavera and colleagues showed two years ago. In this area, the wet season is just about to end and the vegetation is exuberant. The butterflies lay eggs and the caterpillars feed on fresh green leaves. A new generation emerges while it is winter in Europe.

Cycle

But it was unclear what happened to the descendants of the autumn migrants. After the start of the dry season, the savannahs dry out and the area rapidly becomes unsuitable for the painted lady. The butterflies disappear, but the question was: where do they go to? Perhaps the butterflies that moved into tropical Africa chose a dead-end path and go extinct. Perhaps they travel further south to find fresh green plants. Or maybe they cross the sand and the sea again to return to Europe, where they are seen in spring.

Talavera and colleagues suggested the latter possibility to be true. The painted lady population would undertake a migration flight two times a year to be able to exploit both the European summer and the green period south of the Sahara. Such a cycle would cover at least six successive butterfly generations. As yet, there was no proof that it really happened.

But now, the researchers have been able to demonstrate that painted lady butterflies indeed migrate northwards from the African savannahs in springtime. The chemical composition of the wings of a butterfly reveals where it grew up as a caterpillar. Painted ladies that are found in early spring around the Mediterranean did develop in tropical Africa, according to such chemical analysis. And they are on their way to the north.

Flying ability

So, the painted lady outperforms the monarch butterfly, a well-known long-distance traveller of North America. It covers a distance of up to about twelve thousand kilometres per cycle, the monarch covers ‘only’ ten thousand kilometres.

The monarch butterflies have a distinct wing pattern, but with the same colours: mainly black and orange. For the monarchs it was found that the more black they have on the wings and the more intense their orange colour is, the greater is their flying ability. The same might be true for the painted lady: an intriguing question for further research.

Willy van Strien

Photo: Painted lady, Vanessa cardui. Fritz Geller-Grimm (Wikimedia Commons, Creative Commons CC BY-SA 2.5)

A video made by the researchers: Vanessa’s Odyssey

Sources:
Talavera, G., C. Bataille, D. Benyamini, M. Gascoigne-Pees & R. Vila, 2018. Round-trip across the Sahara: Afrotropical Painted Lady butterflies recolonize the Mediterranean in early spring. Biology Letters 14: 20180274. Doi: 10.1098/rsbl.2018.0274
Talavera, G. & R. Vila, 2016. Discovery of mass migration and breeding of the painted lady butterfly Vanessa cardui in the Sub-Sahara: the Europe–Africa migration revisited. Biological Journal of the Linnean Society 120: 274-285. Doi: 10.1111/bij.12873
Stefanescu, C., D.X. Soto, G. Talavera, R. Vila & K.A. Hobson, 2016. Long-distance autumn migration across the Sahara by painted lady butterflies: exploiting resource pulses in the tropical savannah. Biology Letters 12: 20160561. Doi: 10.1098/rsbl.2016.0561
Hanley, D., N.G. Miller, D.T.T. Flockhart & D.R. Norris, 2013. Forewing pigmentation predicts migration distance in wild-caught migratory monarch butterflies. Behavioral Ecology 24: 1108-1113. Doi:10.1093/beheco/art037

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Conspicuous, but also undetectable

Brightly coloured frog is invisible against background

Colourful poison dart frog is invisible from a distance

In spite of its bright colouration, predators have difficulty detecting the poison dart frog Dendrobates tinctorius from a distance, according to research by James Barnett and colleagues. The colourful animal turns out to have a cryptic colouration.

The bright colour patterns of poison dart frogs function as a warning signal to predators: don’t eat me, I’m poisonous. Natural enemies learn that they’d better leave these colourful prey alone.

Yet, the striking appearance of these frogs does not offer them complete protection, as James Barnett and colleagues point out. An inexperienced predator that doesn’t yet understand the message may attack and kill such frog. Moreover, some predators are insensitive to the poison, and others are so hungry that they ignore the warning and take the risk. So, a poison dart frog needs additional protection.

It has. Additional protection is provided by the same bright and distinctive colour pattern, which appears to function, surprisingly enough, as a cryptic colour that minimizes detectability. At least, this is the case in the poison dart frog Dendrobates tinctorius.

Camouflage

At close range, the frog clearly stands out against its natural background of leaf litter on the soil of rainforests in French Guiana, the researchers show, thanks to colours that are hardly found in that background: yellow and blue. The salient colouration is a clear signal.

But from a distance, things are different. Predators no longer are able to discern the pattern and the colours blend together to form an average hue that matches the background colour. So, the colouration turns out to function as distance-dependent camouflage; it makes the frog invisible to birds, snakes and mammals that are not at very close range.

Model frogs

That may be hard to believe, but experiments show that it really is like that. The researchers made frogs of plasticine (modelling clay) and gave their models either a natural colour pattern or painted it plain yellow or brown-and-black. They assembled different backgrounds: leaf litter, paper with a leaf litter print, bare soil and paper in a homogeneous colour. In the field, they put model frogs on different backgrounds and assessed how often wild avian predators attacked these models.

As expected, background had no effect on the number of attacks on yellow models, while brown-and-black animals were safer on leaf litter or paper with a leaf litter print than on other backgrounds.

And what about the frog models with a natural colouration?

Just like the brown-and-black animals, they had the best chance to remain undetected on a leaf litter background.

The bright colour pattern of the poison dart frog Dendrobates tinctorius thus has a dual function. At close range, it is a warning signal, while the colours blend to form a cryptic colour when viewed from a distance.

Willy van Strien

Photo: Dendrobates tinctorius. ©James B. Barnett

Source:
Barnett, J.B., C. Michalis, N.E. Scott-Samuel & I.C. Cuthill, 2018. Distance-dependent defensive coloration in the poison frog Dendrobates tinctorius, Dendrobatidae. PNAS, online June 4. Doi: 10.1073/pnas.1800826115

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Startling

When under attack, skink exposes its entire blue tongue

Blue-tongued skink deters attack by protruding its blue tongue

As their name indicates, blue-tongued skinks possess a blue tongue. The lizards sometimes protrude it to show the striking colour. Arnaud Badiane and colleagues explain why.

The blue-tongued skinks from Australia, Indonesia and Papua New Guinea have a cryptic colour which protects them from hunting predators. But sometimes, they suddenly expose their large tongue, which catches the eye because of a striking blue colour. This behaviour seems odd, as it reveals the animals’ presence after all.

Now, Arnaud Badiane and colleagues argue that also this tongue display offers protection from predators, just because the blue colour stands out against the background. A blue-tongued skink uses its tongue as a defensive strategy at the last moment, they say, when a predator is about to strike. The sudden appearance of the blue tongue startles or overawes the enemy – offering the skink a chance to escape.

Reflexive recoil

The researchers substantiate their arguments with experiments in which individuals of the northern blue-tongued skink, Tiliqua scindoides intermedia, were approached by models of predators: a snake, a monitor lizard, a bird, a fox or, as a control, a piece of wood.

The tested skinks behaved normally until such a predatory enemy came very close. When attack was imminent, they suddenly opened their mouth widely and showed the entire tongue by sticking it out as far as possible. To a piece of wood the threatened skinks responded less strongly than to a predator model. To a bird and a fox they protruded their tongue most often, and to a fox or a snake they exposed the largest area of their tongue. In order to increase the shock effect, they inflated their body and hissed.

The back of the tongue has the most intense colouration, and the tested skunks exposed this part when an enemy was in close proximity. The blue colour is detectable to the visual system of the natural enemies.

Predators cannot learn to ignore such suddenly exposed blue flag, the biologists assume: a recoil reflex is inevitable. They still have to investigate how predators respond in reality. If they really are startled, blue-tongued skins in distress would rightly rely on their tongue as the last defence.

Willy van Strien

Photo: northern blue-tongued skink, Tiliqua scindoides intermedia. ©Shane Black

Source:
Badiane, A., P. Carazo, S.J. Price-Rees, M. Ferrando-Bernal & M.J. Whiting, 2018. Why blue tongue? A potential UV-based deimatic display in a lizard. Behavioral Ecology and Sociobiology 72: 104. Doi: 10.1007/s00265-018-2512-8

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Small bites, huge gulps

Thousands of copepods are ingested each day by little auk

feeding in little auk is similar to that of whale

Little auks have a way to gather food that is unusual in birds, Manfred Enstipp and colleagues show. The birds feed ‘almost like a whale’, as the title of  their publication suggests.

The little auk (or dovekie), a seabird species of arctic regions which gathers its food while diving, does not have easy prey to catch. It feeds mainly on copepods (small crustaceans) and it needs an estimated 60,000 prey items per day. It is difficult to capture these tiny animals, as they respond to threats with fast movements. It’s difficult to grasp something as small like copepods under water anyway: the object is pushed away when you try. How does a little auk get all the copepods it needs?

Just by opening the beak while swimming and filtering the prey from the water, Manfred Enstipp and colleagues assumed. But when they filmed little auks with a high-speed camera in a test pool containing copepods and analysed the footage, their idea turned out to be wrong.

Whale

Little auks, as the researchers observed, search for copepods with their eyes. Upon prey detection, they go after it, stretching their neck. They extend their gular pouch so that under pressure arises in the oral cavity, and open their bill slightly. As a consequence, a big gulp of prey-laden water is sucked in. The bird then retains the prey while it expels the excess water through the nostrils and from the back of the bill. The whole procedure takes about half a second. By capturing prey in quick succession – and with some luck it sometimes has two items in one trial – a little auk gathers its food.

Many fish species use this ‘suction-feeding’ method to catch prey, but for a bird it is unusual. It is reminiscent of the way baleen whales feed: they take in large quantities of water and expel it through the baleens, retaining the plankton.

Willy van Strien

Photo: Allan Hopkins (via Flickr, Creative Commons CC BY-NC-ND 2.0)

Source:
Enstipp, M.R., S. Descamps, J. Fort & D. David Grémillet, 2018. Almost like a whale – First evidence of suction-feeding in a seabird. Journal of Experimental Biology, online May 29 mei. Doi: 10.1242/jeb.182170 

Posted in feeding, predation | Comments Off on Small bites, huge gulps

Collateral benefit

Bird disperses eggs of stick insects it swallowed

brown-eared bulbul disperses eggs of stick insects

Some stick insects are even more like plants than you might think at first glance. Just like plant seeds, the eggs can be dispersed by a bird, Kenji Suetsugu and colleagues show.

Stick insects are perfectly camouflaged: they do not stand out among the plants. Yet insect-eating birds are able to find them and will eat them. And that is the end of the story for such tiny animal.

Well, it may not be, Kenji Suetsugu and colleagues report. If an unfortunate female stick insect is carrying mature eggs, a few of these appear undamaged in the bird’s droppings, and some may even hatch.

Younsters

The researchers, working in Japan, point out that the eggs of stick insects resemble plant seeds: they have the same size and colour and feel the same thanks to a hard shell. Hence their suggestion that the eggs might survive passage through a bird’s digestive tract like plant seeds do. Many plant species produce fruits that are eaten by birds or other animals; the seeds remain intact, are excreted and germinate. Is something similar possible for the eggs of stick insects?

eggs of stick insect after passage through a bird's digestive tractTo find out, they mixed mature eggs of three stick insect species with an artificial diet and fed this to a brown-ear bulbul, one of the main predators of the insects. Afterwards, they examined the bird’s droppings under a stereomicroscope and discovered a small number of intact eggs, and from some of these eggs a young stick insect hatched later on.

Such scenario is also possible when a bird swallowed a gravid female, the authors think. The youngsters that hatch after passage through a bird’s guts would have to find an appropriate food plant to live on, but that is always the case. Normally, a female just drops her eggs to the ground and does not provide any care.

Parthenogenetic

young stick insect, hatched from egg that passed through a bird's gutsSo, sick insects not only look like plants, but they also exhibit a surprising plant-like trait: dispersal of offspring by birds, which is unique in insects.

Dispersal by an avian predator is only possible for species that reproduce parthenogenetically, for in that case females carry eggs that can develop without fertilization. A number of stick insect species exhibit parthenogenesis, including the species that were studied here.

Flyways

Dispersal of insect eggs via a bird’s digestive tract is not entirely comparable to dispersal of plant seeds. Plants produce fruits that have to be eaten to disperse their seeds. In contrast, a female stick insect has no intention to be captured by a bird to have her eggs transported – by being camouflaged, she tries to prevent just that. But if she is unlucky enough to become a bird’s meal, it is a collateral benefit if some eggs survive and young hatch, if only a few.

The hard eggs probably have not evolved to facilitate avian dispersal, the authors suggest, but to decrease the risk of attack by parasitoid wasps, which lay their eggs in other insects’ eggs.

Stick insects are immobile. Thanks to the birds they may reach new places to live. An interesting question is whether distribution patterns in the insects, to be unravelled by DNA research, overlap with birds’ flyways; that would strengthen the idea that the eggs are sometimes dispersed like plant seeds.

Willy van Strien

Photos
Large: Brown-eared bulbul (tongue visible). Alpsdake (Wikimedia Commons, Creative Commons BY-SA 4.0)
Small: stick insect (Ramulus irregulariterdentatus) eggs that passed through a bird’s digestive tract and a young stick insect that hatched from such egg. ©Kenji Suetsugu

Source:
Suetsugu, K., S. Funaki, A. Takahashi, K. Ito & T. Yokoyama, 2018. Potential role of bird predation in the dispersal of otherwise flightless stick insects. Ecology, online May 29. Doi: 10.002/ecy.2230

Posted in growth and development, predation | Comments Off on Collateral benefit