In need of a ride

Tadpoles are in a great hurry to get away

A male splash-back poison frog transports each tadpole to a pool to grow up

Things go bad if sibling larvae of the splash-back poison frog Ranitomeya variabilis grow up together: only one of them will survive. So, as soon as an adult frog approaches, tadpoles try to climb on its back and to get a ride to a safe place, Lisa Schulte and Michael Mayer write.

Mating pairs of the splash-back poison frog Ranitomeya variabilis, that occurs in Peru, lay two to six eggs at the surface of small water bodies in plants, for instance Bromelia species. In such ‘phytotelmata’ the risk for the eggs to be found by a predator is small. Later, the male returns to retrieve each larva upon hatching and transports it on its back to an unoccupied phytotelm that he already selected. He then returns to fish the next larva out of the water, until all the young are singly housed in different phytotelmata.

It is necessary for the larvae to get separated from each other, as the tadpoles are cannibalistic. If they stay together, only one of them will survive and grow up.

In some cases, however, the male doesn’t return to retrieve the hatching larvae. In such case, the abandoned tadpoles actively seek transport, as Lisa Schulte and Michael Mayer show. They collected clutches of eggs, took them to the lab and kept them in small plastic cups. After the tadpoles hatched, they were kept together and the researchers introduced an adult frog. That frog was either a conspecific male or a conspecific female, or a male of a different species.

In all cases, the tadpoles approached the adult frog, and many of them tried to climb onto its back quickly. Some succeeded. They actually jumped on the frog’s back, the researchers report; it looked like an attack.

The tadpoles have a good reason to be so desperate. In a natural situation, a frog that shows up most likely is the male parent frog that revisits the phytotelm to save its young from cannibalism. The first tadpole to approach will be assisted to mount; the male will bend its back or push it up with its legs. After the male left with this lucky tadpole, there is no guarantee that he will return to get the other ones. If he can’t find an unoccupied phytotelm anymore, he will stay away. Hence the haste of the tadpoles.

But in the experiments, the visiting frog could also be a female, or a male of another species. In such cases, the tadpoles did not get any help. Yet they tried to get transport by mounting this frog on their own.

Obviously, the need to be saved is so high that the tadpoles don’t make any difference between their father and any other frog that happens to appear. And they had better not, because even a frog with no intention to bring tadpoles to a safe place may visit an unoccupied phytotelm, and rescue the hitchhiker.

However, when the researchers offered a plastic frog model, the tadpoles did not respond. They probably recognize a true frog by chemical cues.

Willy van Strien

Photo: John Clare (via Flickr. Creative Commons CC BY-NC-ND 2.0)

Source:
Schulte, L.M. & M. Mayer, 2017. Poison frog tadpoles seek parental transportation to escape their cannibalistic siblings. Journal of zoology, 5 mei online. Doi: 10.1111/jzo.12472

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Rescue heroes

Birds free entangled group members from sticky seeds

Seychelles warbler on the ground runs a risk of becoming entangled in seeds

Seeds of the Pisonia tree can be dangerous for a little songbird like the Seychelles warbler: when these sticky seeds attach to its feathers, such a bird is not able to fly. Fortunately, the risk of entanglement is low, and in case of bad luck, help often arrives, as Martijn Hammers and Lyanne Brouwer observed.

Seychelles warblers lead a low-risk life on the tropical island of Cousin, belonging to the Republic of Seychelles: there are no natural enemies around that prey on the adult birds. High in the trees they safely glean insects from the leaves.

Seychelles warbler entangled in a cluster of seedsStill, they can be in trouble, Martijn Hammers and Lyanne Brouwer report. The most common tree, the Pisonia tree, produces seeds that become very sticky when they are ripe and fall to the ground. For foraging birds the risk of entanglement is low, but when they are on the ground to collect nest material – work performed by females – or to defend their territory, these seeds easily attach to their feathers; a bird may even get stuck in a cluster of seeds. That is bad luck. Just one of a few of these seeds can prevent a bird from flying, and cause it to die.

But if the victim is lucky, help will arrive. The biologists, who observed the behaviour of the Seychelles warblers during several years, sometimes saw a bird with sticky seeds attached. And in a few cases, another bird came to remove the seeds form the victim after having heard its alarm call. The helper picked and pulled the seeds off with his beak, rescuing the unfortunate animal.

Such rescue behaviour is rare and demanding. A helpful bird must be able to perceive what is going on, know what to do to help the victim and be willing to do it, putting itself at risk of becoming entangled as well. The helper is not just a random conspecific: in each case observed, it belonged to the victim’s family group. Often one or more grown-up young stay with their parents; also, a mother or grandmothermay join a breeding couple. In such cases, a family group lives in a territory, and relatives may help to rear the young. A rescue operation means that the family group remains intact and no help is lost.

The sticky Pisonia seeds do have a function. If they stick to a small songbird like the Seychelles warbler, the tree gains nothing. But more often, the seeds become attached to sea birds visiting the island. They have no difficulty flying – and take the seeds to another island. The tree has its seeds dispersed.

Willy van Strien

Photos: © Martijn Hammers

Source:
Hammers, M. & L. Brouwer, 2017. Rescue behaviour in a social bird: removal of sticky ‘bird-catcher tree’ seeds by group members. Behaviour 154: 403-411. Doi:10.1163/1568539X-00003428

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Biting prey

Fish with venomous fangs have many imitators

Fangblenny Petroscirtes breviceps mimics a venomous species

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

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

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

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

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

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

Willy van Strien

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

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

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Micro army

Cloud of semiautonomous pincers protects sea urchin

Collector sea urchin released a cloud of pincers

When a hungry fish approaches, the collector sea urchin releases a cloud of small biting, venomous pincers that deter its enemy before it has attacked. This peculiar defensive strategy is revealed by Hannah Sheppard-Brennand and colleagues.

In addition to their prominent spines, sea urchins and sea stars possess numerous smaller appendages as well: little pincer-like heads on a movable stalk, called pedicellariae. The pincers have different functions, such as catching food or removing debris – and tormenting predators. For in spite of the unattractive appearance that sea urchins and sea stars have, predators such as fish will pick at their tube feet and other soft tissue. Some species have pedicellariae with teethed jaws and a venom sac to deal with such predators, and anyone who once stepped on such a sea urchin will remember the painful experience.

One species, the collector sea urchin Tripneustes gratilla, deploys these venomous pedicellariae in an unique way, as Hannah Sheppard-Brennand and colleagues show: when harassed, this sea urchin will release a cloud of them in the surrounding water. Upon release, the pincer-like heads behave semi autonomously; they are mobile, have sensory structures and will bite and deliver their venom when they touch a supposed enemy.

Fish are deterred by such a swarm, as lab experiments revealed, and they will leave before they have bitten the sea urchin. Protected by his unique defensive army, the collector sea urchin is able to forage safely on grass and eelgrass during the day, when other sea urchin species have to take shelter, as well as during the night.

Willy van Strien

Photo:
Collector sea urchin Tripneustes gratilla with a cloud of released pedicellaria heads. © Hannah Sheppard Brennand

Source:
Sheppard-Brennand, H., A.G.B. Poore & S.A. Dworjanyn, 2017. A waterborne pursuit-deterrent signal deployed by a sea urchin. The American Naturalist 189, online March 27. Doi: 10.1086/691437

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Cleansing hair

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.

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.

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

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Defensive cocktail

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.

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.

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, 6 maart online. 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

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Fake present

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.

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.

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.

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

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Tiny scarecrow

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.

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.

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

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Cockeyed

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.

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.

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.

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Glow in the dark

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.

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

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