From so simple a beginning

Evolution and Biodiversity

Page 18 of 19

Cleansing hair

30 March 2017 /

Honey bee rubs her eyes after visiting a flower

honey bee quickly cleans herself after visiting a flower

A busy bee gets dirty: she gets covered with the pollen of flowers. But within minutes she has cleaned herself after visiting a flower, as Guillermo Amador and colleagues report, thanks to the hairs on her body.

A bee that has visited a flower to collect nectar or pollen may be completely covered with yellow pollen grains. When the eyes and antennae are dirty, she is not able to see or smell well. But the discomfort lasts only a few minutes, because during flight she manages to quickly remove the pollen, as Guillermo Amador and colleagues show. She puts it in the baskets on her hind legs to it take to the nest as food for the young, or she drops it.

Using high speed cameras, the researchers recorded the cleaning process in a number of honeybees that they had coated in pollen of dandelion or other plants. To keep the bees in front of the cameras, they tethered them temporarily to a thin wire. As the footage showed upon analysis, the bee hairs are essential for the rapid cleaning process.

Brushes

A honeybee that is covered in pollen starts grooming her eyes. The hairs on the eyes are spaced so that the sticky pollen grains are suspended near the tips, where they can be easily wiped away by the pollen brushes on the forelegs. As the hairs of these brushes are closer spaced than those of the eyes, the pollen grains attach to the brushes.

With a fast movement, the bees swipe a foreleg across an eye, from dorsal to ventral, removing almost all the particles that are touched by the brush. As the researchers calculate, about twelve swipes are needed to clean the entire surface of an eye. In reality, the bees rub each eye ten to twenty times. After each swipe, they spend a few seconds to clean the pollen brush with the other legs or the mouth.

Pollination

The hair on the eyes (and on the rest of the body) and the bristle brushes on the forelegs facilitate quick removal of sticky pollen after a flower visit, the conclusion is.

Still, some of the accumulated pollen must be left ungroomed, so that the bee can deliver it on the pistil of the next flower she visits. Otherwise, bees would not pollinate any flowers.

Willy van Strien

Photo: Honey bee collecting pollen. Jon Sullivan (Wikimedia Commons, Public Domain)

On this video, a pollen-covered honey bee rubs her eyes

Source:
Amador, G.J., M. Matherne, D. Waller, M. Mathews, S.N. Gorb & D.L. Hu, 2017. Honey bee hairs and pollenkitt are essential for pollen capture and removal. Bioinspiration & Biomimetics 12:  026015. Doi: 10.1088/1748-3190/aa5c6e

Defensive cocktail

15 March 2017 /

Ants produce powerful antibiotic by mixing resin with acid

Formica paralugubris produces powerful antifungal agent

Workers of the wood ant Formica paralugubris are skilled poisoners. By treating tree resin with formic acid, they produce a powerful disinfectant to control a pathogenic fungus, Thimothée Brütsch and colleagues show.

Pathogenic micro-organisms, such as the common entomopathogenic fungus Metarhizium brunneum, pose a continuous threat to ant nests; because the ants live close together, the risk of epidemics is high. Therefore, ants should keep their nests hygienic.

Resin

And so they do. Workers of the alpine wood ant Formica paralugubris, for instance, incorporate large amounts of solidified resin from coniferous trees, especially spruce, into their nest to fight pathogens, as Michel Chapuisat showed. The distinctive smell of tree resin comes from terpenes and other volatile substances; these are compounds that decrease bacterial and fungal load in wounded trees. And within ant nests, they do as well. In the presence of resin, bacteria and fungi are inhibited, with the result that more larvae survive when exposed to Metarhizium, and adult ants and larvae have a higher chance to survive when a detrimental bacterium invades the nest.

Combination

Now, Thimothée Brütsch and colleagues report that the ants enhance the antifungal activity of the resin considerably by applying formic acid. This acid, which the ants produce into their venom gland, has an antiseptic effect in itself, just like the volatile substances from resin. But the mixture of the resin with formic acid seems to work particularly well; it has greater antifungal activity than you would expect from the separate effects of resin and acid. This means that the acid increases the disinfectant effect of the tree resin.

So, the ants not only collect pieces of resin to disinfect their nest and protect themselves against pathogens, but they also treat it with formic acid to obtain a more powerful antimicrobial agent.

Willy van Strien

Photo: © Timothée Brütsch

Sources:
Brütsch, T., G. Jaffuel, A. Vallat, T.C.J. Turlings & M. Chapuisat, 2017. Wood ants produce a potent antimicrobial agent by applying formic acid on tree-collected resin. Ecology and Evolution, online March 6. Doi: 10.1002/ece3.2834
Chapuisat, M., A. Oppliger, P. Magliano & P. Christe, 2007. Wood ants use resin to protect themselves against pathogens. Proceedings of the Royal Society B 274: 2013-2017. Doi: 10.1098/rspb.2007.0531

Fake present

10 March 2017 /

Male spider cheats female with densely wrapped rubbish

Pisaura mirabilis male cheats female with well-wrapped fake present

A male nursery web spider may offer its partner a worthless package instead of a decent nuptial gift. He wraps such a fake present in many layers of silk, Paolo Ghislandi and colleagues show, so that it takes longer before the female detects the deceit and sends him away.

When you give someone a cheap gift, you’d better wrap it well. At least, that is the rule in the nursery web spider (Pisaura mirabilis), a hunting spider that occurs throughout Europe, as Paolo Ghislandi and colleagues report. A male usually carries a nuptial gift when he is looking for a female to mate with. It should contain one or more prey items that he has caught to offer her and wrapped in white silk. A female, happy to get a nice meal, will allow the male to mate her, while she often rejects a male without a present, as Maria Albo had shown.

Worthless

But instead of a meal, a female often finds the hard leftovers of an arthropod prey or some plant parts after removing the silk – an inedible gift that is worthless. Is a male giving such a gift in bad condition and unable to capture a prey and offer it? Or couldn’t he find anything better?

No, instead of inability it is pure deception, as Ghislandi concludes from field observations and behavioural experiments in the laboratory. Even a male that is well-fed and heavy – and therefore capable to catch and offer a prey – often cheats its partner with wrapped rubbish.

And he is successful, for as a female is unable to determine whether a white package contains something edible or not, she will accept a male with a fake present as readily as a male that carries an edible gift.

Punished

But ultimately, a cheating suitor will still be punished: the mating lasts briefly. A male can transfer its sperm while the female consumes her gift; it she is finished, he has to go. Consequently, when the gift is inedible, the mating will end soon, so a cheating male will transfer less sperm than a honest male. That is a disadvantage, because a female mates with several males and their sperm must compete for the eggs to be fertilized. The more sperm cells a male transfers, the more offspring he will sire.

More silk

Ghislandi also discovered that fake presents are wrapped in more layers of silk than real gifts, so cheating males invest a lot in wrapping. Probably, this is a trick to prolong mating, because the more silk is wrapped around the gift, the longer it takes a female to detect the deceit and stop the copulation.

Still, a really long mating will not ensue. And maybe that’s not so bad after all: a male cheating a female with a fake present may fertilize less eggs, but he saves time and energy to find other females, thereby increasing is lifetime reproductive success as well.

Willy van Strien

Photo: ©Paolo Ghislandi

Sources:
Ghislandi, P.G., M. Beyer, P. Velado & C. Tuni, 2017. Silk wrapping of nuptial gifts aids cheating behaviour in male spiders. Behavioral Ecology, online February 23. Doi:10.1093/beheco/arx028
Ghislandi, P.G., Albo, M.J., Tuni, C. & T. Bilde, 2014. Evolution of deceit by worthless donations in a nuptial gift-giving spider. Current Zoology 60: 43-51. Doi: 10.1093/czoolo/60.1.43
Albo, M.J., G. Winther, C. Tuni, S. Toft & T. Bilde, 2011. Worthless donations: male deception and female counter play in a nuptial gift-giving spider. BMC Evolutionary Biology 11: 329. Doi: 10.1186/1471-2148-11-329

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

Cockeyed

27 February 2017 /

Strawberry squid looks upwards with a bulging eye

Light is scarce in the mesopelagic region of the deep sea, which asks for special adaptations of the eyes of the animals that live there. Squids of the family Histioteuthidae addressed this challenge by developing two different eyes, Katie Thomas and colleagues report.

If symmetry is a characteristic of beauty, then adult deep sea squids of the family Histioteuthidae are really ugly, because in addition to a normal right eye, they have a protruding left eye which is twice as large and usually yellow coloured. They are cockeyed. And, while not very nice, this is functional, as Katie Thomas and colleagues report.

As early as 1975 Richard Young proposed an idea of why these squids, which hunt prey like fish, shrimp and smaller squid, possess dimorphic eyes.

The squids live at a depth of several hundred meters in the oceans where it is dark apart from dim, downwelling sunlight. How do the animals manage to find their food in this nearly complete darkness? When prey animals are swimming above the squids, they may perceive their contrasting silhouette against the almost dark background, provided that their eyes are very sensitive to light. Below, they can only detect prey that produces bright flashes of light, as many deep sea animal species do for various reasons. To be able to localise such prey, the squids need eyes that produce images with high spatial resolution.

Video recordings

The enlarged left eye of cockeyed squids, Young stated, is light sensitive and more apt to detect silhouettes upwards, whereas the small right eye produces images of higher resolution which enable the squids to localise bioluminescent prey below. But as the animals live at great depths, he was not able to access and observe them to determine whether they actually turn their bulging left eye upwards.

Nowadays, this is possible. For 25 years now, the Monterey Bay Aquarium Research Institute (California) has been sending remotely operated underwater vehicles into depth to make video recordings. Thomas used the video footage to observe the strawberry squid Histioteuthis heteropsis and Stigmatoteuthis dofleini and to find out how these squids behave.

She ascertained that adult cockeyed squids almost always oriented the head downwards in an oblique body position, with the ten arms stretched straight ahead. And, as expected, the animals twist their heads so that the large left eye is directed upwards and the small right eye slighty downwards. So, what Young had supposed proved to be right: the animals have two different eyes that are adapted to two different sources of light, dim downwelling sunlight from above and light flashes in the dark below.

Yellow

Then, why has the left eye a yellow colour in most of these squids?

Many prey prevent detection by predators that approach from below by producing a ventral glow that matches the weak downwelling sunlight, so their silhouette is camouflaged against the background (counter illumination). A predator’s yellow eye filters out ultraviolet light, and this probably results in different colours of the ventrally emitted light of prey and the background light, breaking the camouflage and rendering the prey visible.

Willy van Strien

Photo: Young strawberry squid Histioteuthis heteropsis (not in its normal swimming posture) © Katie Thomas

View the strawberry squid Histioteuthis heteropsis on video

Sources:
Thomas, K.N., B.H. Robison & S. Johnsen, 2017. Two eyes for two purposes: in situ evidence for asymmetric vision in the cockeyed squids Histioteuthis heteropsis and Stigmatoteuthis dofleini. Phil. Trans. R. Soc. B 372: 20160069. Doi: 10.1098/rstb.2016.0069
Young, R.E., 1975. Function of the dimorphic eyes in the midwater squid Histioteuthis dofleini. Pacific Science 29: 211-218.

Glow in the dark

16 February 2017 /

Flashlight fish turns headlights on to catch prey

flashlight fish turns headlights on to find prey

It is difficult to find food in the dark. But the splitfin flashlight fish Anomalops katoptron has no problem: it turns its headlights on when it hunts on zooplankton, as Jens Hellinger and colleagues report.

Only in complete darkness, the splitfin flashlight fish Anomalops katoptron will leave its hiding place. During daytime the fish, which lives in shallow coral reefs in the Pacific, resides in cavities and cracks in the reef where it is invisible to its predators, thanks to its dark colour. But in dark moonless nights it ventures to the open water to forage in a school of conspecifics. The diet consists of swimming zooplankton, prey that is difficult to find in the dark.

But Anomalops katoptron has a light organ under each eye that emits blue light, Jens Hellinger and colleagues point out. The light is produced by symbiotic bacteria that live densely packed within these organs. The bacteria have got a safe place to live in, in exchange for producing light.

Blinking

The bacteria glow continuously, but the fish can turn his lights off by rotating them, exposing their dark backsides instead of the transparent sides. During the day, the lights are almost always off, otherwise the fish would be visible in spite of its dark colour. Occasionally, he blinks.

When the splitfin flashlight fish is active, at night, he blinks more often, Hellinger observed when he studied a number of fish in a tank in the laboratory, and the lights shine about half of the time. And if the fish detects prey, it has its lights on almost continuously.

Many animal species exist that emit light, particularly in the sea, and their luminescence has several functions. Most luminescent species emit light to chase off or embarrass predators. Anglerfish lure prey: their dorsal fin is modified to a ‘fishing rod’ with a luminous bulb that attracts little creatures. And still others lure or recognize partners by flashing patterns; male ostracods, for instance, perform a spectacular light show to attract females, much like fireflies do on land.

Until now, it was not clear where the splitfin flashlight fish Anomalops katoptron uses its light for. It now turns out that it is mainly to detect prey in the dark.

Photo: California Academy of Sciences (via Flickr. Creative Commons CC BY-NC-ND 2.0)

Source:
Hellinger, J., P. Jägers, M. Donner, F. Sutt, M.D. Mark, B. Senen, R. Tollrian & S. Herlitze, 2017. The flashlight fish Anomalops katoptron uses bioluminescent light to detect prey in the dark. PLoS ONE 12: e0170489. Doi:10.1371/journal.pone.0170489

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

Selfknowledge in red-backed fairy-wrens

27 January 2017 /

Only old and bright males seek extra-pair mates

in red-backed fairy-wrens old and bright males seek extra-pair matings

Red-backed fairy-wren males know how to behave to maximize their fitness, Denélle Dowling and Michael Dowling show. A male that has a bright breeding plumage invests in courting extra-pair females, whereas a man with a dull appearance invests in mate guarding.

Like most songbirds, red-backed fairy-wrens, which live in Australia, form socially monogamous pairs, and a couple may stay together for years. This doesn’t mean that the birds are faithful, however: roughly half of the young is not sired by the social father. Adultery is the rule.

In the breeding season, a male may adopt one of two alternative strategies. He can either invest in seeking extra-pair copulations to gain extra-pair offspring in addition to within-pair offspring, or he can stay on his own territory to defend it the against other couples together with his mate, to help provision the young – and to keep other males away from his mate to minimize the risk of being cuckolded.

Preference

What strategy is the best strategy? Jenélle Dowling and Michael Webster argued that the answer differs among males. It just depends on how attractive a male is to other females.

And the males differ greatly in attractiveness. Some have a bright, black and red plumage, while others have a dull, brownish plumage, much like a female. Almost all males aged more than two years are brightly coloured, among young males about half is bright. It was already known that females prefer bright males. Also, they prefer old males, as their age indicates that they are of good quality.

So, old black-red males are the most attractive ones. The best strategy for them will be to foray to neighbouring territories and court other females, Dowling and Webster assumed, as they stand a real chance to succeed. For dull males, on the contrary, it will be better to stay with their partner, as other females will be reluctant to copulate with them. Moreover, a dull male runs a high risk of being cuckolded by his social partner whenever an attractive male approaches her when she is alone. Young black-red males can try to gain extra-pair copulations, but they will be less likely to succeed than old males.

The researchers set up an investigation to find out whether red-backed fairy-wren males act in their best interests. And it turns out that they do. Old black-red males frequently leave to search for extra-pair females, while brown males mostly remain on their territory. Young black-red males adopt an intermediate strategy.

Cuckolded

DNA analyses of parents and young birds revealed that black-red males (young and old) sire more extra-pair young, as expected, but less within-pair young than dull males; apparently, bright males are cuckolded more often.

The latter result is not undisputed. In other studies, including that of Jordan Karubian, brown males were found to have less young than black-red males and to be cuckolded more frequently, even though they guarded their mate closely. But still, the best strategy for them is to stay on their territory. Otherwise, they will probably be cuckolded even more.

Willy van Strien

Photo: Red-backed fairy-wren, bright male. Jim Bendon (Wikimedia Commons, Creative Commons CC BY-SA 2.0)

Sources:
Dowling, J. & M.S. Webster, 2017. Working with what you’ve got: unattractive males show greater mateguarding effort in a duetting songbird. Biology Letters 13: 20160682. Doi: 10.1098/rsbl.2016.0682
Karubian, J., 2002. Costs and benefits of variable breeding plumage in the red-backed fairy-wren. Evolution, 56: 1673-1682. Doi: 10.1111/j.0014-3820.2002.tb01479.x

Good friend

18 January 2017 /

Sea anemone grows better with a shy clownfish around

shy clownfish is better partner

The strength of the mutualistic interactions between sea anemones and clownfish depends on the personality of the fish, Philip Schmiege and colleagues report. A shy, cautious partner benefits a sea anemone more than a bold, venturous fish.

Clownfish (also called anemonefish) are safe between the tentacles of sea anemones. The anemones, animals related to jellyfish, hold off the clownfish’s predators with their stinging, toxic nematocysts. The clownfish are insensitive to these cells. Conversely, clownfish chase and bite guests who intend to nibble at the tentacles with which the sea anemones gather their food. So, sea anemones and clownfish are partners that protect each other.

Fertilize and refresh

But the fish deliver extra services. Many sea anemones harbour unicellular microorganisms that, like plants, are able to capture sunlight and to use it to convert carbon dioxide into carbohydrates. They feed these carbohydrates to the anemones in exchange for residence. The microorganisms derive their nutrients from waste products of the clownfish. Moreover, by moving, the fish refresh the water around the sea anemones continuously, guaranteeing the availability of oxygen. By fertilizing the unicellular inhabitants and refreshing the water, clownfish promote the growth of sea anemones.

Now, clownfish, like many other animal species, have personalities. There are bold, venturous individuals as well as shy, passive ones. It matters to the sea anemones what personality the fishes have that associate with them, Philip Schmiege and colleagues assumed. And they proved to be right.

The researchers brought some wild-caught orange clownfish (or clown anemonefish, Amphiprion percula) into the lab, a species living along coasts of Australia, Asia and Japan. Also, they had grown bubble-tip anemones (Entacmaea quadricolor). Though this is not a natural partner of the fish, they associate readily in the lab.

In each of sixty tanks, the researchers placed one anemone and one or two fish; in the field, zero to six fish associate with one anemone. They measured the size of the anemones and kept track of their growth. Also, they examined how bold or shy each fish was by videotaping its activities every day during twenty minutes and assessing from the footage if he ventured away from the sea anemone. The more time a fish spent away from his partner, the bolder its personality.

Shy fish

After eighteen months, the biologists noted a difference in the growth of the sea anemones. Anemones associated with a shy fish had grown better than anemones with a bold partner. Apparently, shy fish supply better services. Because they remain in close proximity to their host anemone, they fertilize its unicellular inhabitants better and refresh the water more efficiently. And perhaps the anemones dare to expand their tentacles for longer periods of time to catch food as long as there is a clownfish nearby.

In conclusion: the strength of mutualistic relationships, of which the association between sea anemones and clownfish is an iconic example, depends on the personality of the partners.

Willy van Strien

Photo: Orange clownfish © Philip Schmiege

Source:
Schmiege, P.F.P., C.C. D’Aloia, P.M. Buston, 2017. Anemonefish personalities influence the strength of mutualistic interactions with host sea anemones. Marine Biology 164: 24. Doi: 10.1007/s00227-016-3053-1

Prepared to have a meal

20 December 2016 /

Even a sedentary antlion has a capacity for learning

Antlion larva builds a pitfall

All that an antlion larva has to do once he has made his pitfall, is sit there and wait for a prey to come. Over the weeks, he learns to anticipate the arrival of a prey, Karen Hollis discovered.

Antlion larvae need a lot of food, consisting of little critters. They don’t go after their prey, but they take what comes along. While some species wait in ambush for their food, others build traps: a larva of such a species digs a funnel-shaped pit with steep walls in loose sandy soil and buries itself at the vertex, only head and jaws remaining visible. Tiny animals that wander along the edge lose their footing and tumble into the pit, from which it is difficult to escape. And when a nearby prey fails to fall in, the antlion larva tosses sand to him, so that the victim is disoriented, stumbles and comes down in a sand avalanche.

Vibrational signal

Once an antlion has dug his pit – which is a big job -, he only needs to wait until a prey is trapped. That’s all, and yet such a buried larva is learning something, as Karen Hollis reports.

adult antlion is a winged insectWorldwide, there are a few thousand species of antlions, many of them with larvae that dig a pit on a sheltered place, for instance under overhanging branches. Ants are a common prey. Adult antlions are graceful, winged insects.

Hollis and colleagues show that larvae learn to perceive when a prey is approaching. They brought a number of larvae into the laboratory and housed each of them in its own sand-filled plastic bowl. Half of the larvae received a prey item each day at a randomly determined time, always a few seconds after the researchers had dropped some sand grains beside their pits. This was an imitation of the natural situation: an animal that approaches a pit, causes a similar vibrational signal. The other half were presented with a daily prey item at the same time as the first group, but received a vibrational cue at a different, randomly selected time. The larvae were treated as described until they pupated.

Prepared

If a victim falls into the pit, an antlion larva will pick it up, drag it under the sand, bite and deliver an immobilizing poison and digestive enzymes. He then sucks the liquefied prey contents and throws the empty exoskeleton out. If it is necessary, he will repair his trap.

Antlions that used to get their prey each day after a vibrational cue, began to prepare themselves after receiving this cue, the experiments revealed. They responded faster than the untrained larvae when a prey arrived and extracted the contents of the prey at a higher rate and more efficiently, probably because they started to produce digestive enzymes earlier. Apparently, they had learned to associate the vibrational cue with the gain of a prey, in contrast to the other group.

Other researchers, Karolina Kuszewska and colleagues, reported that antlion larvae can learn to distinguish between large and small prey, as large prey causes stronger vibrations. Antlions abandoned a small prey when they noticed that a large one was approaching.

Faster

Because antlions learn to anticipate the capture of a prey, they are able to handle it efficiently, the authors conclude. This is advantageous: in the laboratory, the larvae that learned to associate the vibrational cue with prey grew faster, were bigger and pupated sooner than the larvae that had not been given the opportunity to learn. Trained larvae thus shorten the larval stage, which is the most vulnerable stage of their life cycle because larvae are exposed to wind and rain and accessible to predators. Moreover, the more food a female larva consumes, the bigger and stronger the eggs she will produce later as adult.

So, even an animal that captures prey with a sit-and-wait strategy proves to be able to improve this strategy by learning.

Willy van Strien

Photos:
Large: an antlion larva, probably Myrmeleon formicarius. Aiwok (Wikimedia Commons, Creative Commons CC BY-SA 3.0)
Small: adult Myrmeleon formicarius. Gilles San Martin (Wikimedia Commons, Creative Commons CC BY-SA 2.0)

Watch a video of an antlion and its pitfal

Sources:
Hollis, K.L., 2016. Ants and antlions: The impact of ecology, coevolution and learning on an insect predator-prey relationship. Behavioural processes, online December 6. Doi: 10.1016/j.beproc.2016.12.002
Kuszewska, K., K. Miler, M. Filipiak & M. Woyciechowski, 2016. Sedentary antlion larvae (Neuroptera: Myrmeleontidae) use vibrational cues to modify their foraging strategies. Animal Cogntion 19: 1037-1041. Doi: 10.1007/s10071-016-1000-7
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