Cleaner wrasse cheats client secretly

Female knows if partner observes her behaviour

in a bluestreak wrasse pair, a conflict may arise

A bluestreak cleaner wrasse female sometimes scares a customer away by biting off a bit of its mucus layer. But if she knows that her partner can see what she’s doing, she behaves somewhat better, Katherine McAuliffe and colleagues report.

Bluestreak cleaner wrasses (Labroides dimidiatus) often work in pairs. Male and female jointly inspect their clients, fish that want to be cleaned. With their pointed snout, the cleaners pick up ectoparasites and dead skin cells. It is a textbook example of cooperation between species, called mutualism: clients get rid of their parasites, cleaners have a meal.

In cleaner wrasses that operate as a couple, a conflict sometimes arises because the female bites a client; that client then will leave, causing the male to miss his meal. A female cleaner is more likely to misbehave if she knows that her partner can’t see what she’s up to, Katherine McAuliffe and colleagues found.


When a female cleaner bites, it is for good reason. She takes a mouthful out of a client’s protective mucus layer. This is tempting, especially during breeding season, because she needs a lot of energy and mucus is more nutritious than the parasites she should be eating. But upon being bitten, a client leaves, and the male, that serves the client properly, is the victim: because she cheats, he also loses the client – without the benefit of ingesting a bit of mucus like she has done.

There is also a risk that he will lose his territory, in which several females live. This is because these fishes change sex during their lifetime. Young cleaner wrasses are always females which, after reaching a certain size, become males. A female that eats nutritious mucus grows well. If she is almost the same size as her partner, she can change sex any moment and compete with him; maybe she’ll manage to chase him off and take over his territory.

It is therefore logical for a male not to tolerate that his partner bites a client. When she does, he punishes her by chasing or biting her. It was known from previous research that he punishes more severely when the client is larger, presenting more food. The punishment is also more severe if his partner is about the same size as himself and a risk of takeover exists.

After punishment, the female delivers good service to the clients and the partners cooperate well.

Model clients

McAuliffe already knew that cleaners treat their clients better when other fishes, potential clients, are watching. That is because bystanders leave when they see clients being hurt. Now, she wanted to know whether a bluestraek cleaner wrasse female is less likely to cheat a client when she knows that her partner can see her.

The cleaner fish live on coral reefs, where they occupy a ‘cleaning station’, as single or as a couple. It is difficult to observe exactly what is happening between cleaners and their clients. That is why the researchers did experiments in the lab, where they brought cleaner pairs into contact with artificial clients: plexiglass plates with food items stuck on them. Mashed prawn, which cleaner fish like, served as a model for a client’s mucus; a mixture of fish flakes and prawn, which the cleaners like less, did for parasites.

First, the cleaner fish learned to deal with the model clients. If they ate fish flake mixture, against their preference, that was seen as good cleaning service. But if they took a bite of mashed prawn, it was considered cheating, and the researchers removed the model client.

After training, the researchers first investigated how females behave when their partner was separated from them by either a transparent or an opaque barrier. As soon as a female took a bite of mashed prawn, the model client was removed, and her partner was given access.

Bad service

When their partner was visible and could see them, cleaner females ate a little more fish flake items on average before taking a bite of mashed prawn and chasing off the model client. So, in that case, the females provided a better service. If the partners were invisible to each other, females took less fish flake items. In other words, they cheated more in secret.

Males, that could punish their partner after she had eaten mashed prawn, punished less severely the more fish flake items she had consumed before. Surprisingly, it made no difference whether males had seen their partner’s behaviour or not. Apparently, they still noticed somehow how much their partner had cheated.

Choosing two times

So, it seems that females are aware whether their partner is or is not able to observe what they are doing, and that they are more inclined to cheat a client when the partner cannot see it.

A next, somewhat more complicated test affirmed this finding. In this set-up, the male was again behind a transparent or opaque partition, but now, two model clients were offered behind additional partitions. One of them was visible to the male – if the male himself was behind a transparent partition- behind a transparent partition; the other was hidden from him behind an opaque screen. The female was allowed to choose which model client to serve. She was given the choice twice; in between the male was admitted, having the opportunity to punish her.

The first time, females were more likely to choose the model client behind the opaque partition if their partner could watch them than if he couldn’t. But the second time, they went more often to the model client behind the transparent partition. This was probably because males were more likely to punish their partner after the first time if she had visited the hidden client. And, in accordance with the first experiment, they punished her whether they had been able to see that she went there or not. Apparently, she betrayed herself somehow.

Clever fish

The researchers’ main conclusion: a bluestreak cleaner wrasse female is more likely to cheat a client if she knows that her partner, who punishes bad behaviour, cannot see what she is doing. In the first trial, females more quickly took a mashed prawn item, which equated to the protective mucus layer of a client fish. In the second trial, they initially preferred to visit a model client hidden from the partner to a visible one.

That she realizes what he can see indicates impressive cognitive capacities. Such capacities were already known: the cleaners recognize themselves in a mirror.

But the question is why a female should care about whether her partner can see her bad behaviour or not, because that did not affect the punishment.

So, the story still does not have an end. But it probably will continue, as the research group has been conducting thorough research on these cleaner fish for years.

Willy van Strien

Photo: Bluestreak cleaner wrasse cleaning a blue angelfish (Pomcanthus semicirculatus). Longdongdiver (Vincent C. Chen) (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

More about the behaviour of bluestreak cleaner wrasse

McAuliffe, K., L.A. Drayton, A. Royka, M. Aellen, L.R. Santos & R. Bshary, 2021. Cleaner fish are sensitive to what their partners can and cannot see. Communications Biology 4: 1127. Doi: 10.1038/s42003-021-02584-2
Kohda, M., T. Hotta, T. Takeyama, S. Awata, H. Tanaka, J-y. Asai & A.L. Jordan, 2019. If a fish can pass the mark test, what are the implications for consciousness and selfawareness testing in animals? PLoS Biol 17: e3000021. Doi: 10.1371/journal.pbio.3000021
Raihani, N.J., A.I. Pinto, A.S. Grutter, S. Wismer & R. Bshary, 2012. Male cleaner wrasses adjust punishment of female partners according to the stakes. Proceedings of the Royal Society B 279: 365-370. Doi: 10.1098/rspb.2011.0690

Honeydew with dopamine

Japanese mugwort aphid forces ants to provide extra protection

Japanese mugwort aphid manipulates attending ants

A Japanese mugwort aphid colony makes ants more aggressive, as Tatsumi Kudo and colleagues show. As a result, enemies have less opportunity to feed on the aphids.

The cooperation between aphids and ants is one of the best-known examples of cooperation or mutualism. Aphids, which feed on the plant saps, excrete excess sugars in a sticky substance, the honeydew. This is a great food source for ants. They collect the honeydew: they milk the lice. To secure the harvest, they protect the aphids from predators, as if it were their livestock. The parties thus exchange food for protection, and both sides benefit from this cooperation.

Such mutualism exists between the Japanese mugwort aphid (Macrosiphoniella yomogicola), which feeds on mugwort (Artemisia montana), and several ant species, of which Lasius japonicus is the most important one. This aphid manipulates the ants that protect it into becoming more aggressive against predators by excreting dopamine in their honeydew, Tatsumi Kudo and colleagues discovered. In other words: the aphids manipulate the behaviour of the ants.


Earlier, the Japanese research group had shown how the ant manipulates the aphids. Two colour morphs of the Japanese mugwort aphids exist, and the ants favour the morph that reproduces slower, but produces a better-quality honeydew. Now the team shows that, the other way round, the Japanese mugwort aphids do not quite behave like obedient livestock.

The researchers detected dopamine in the honeydew of the aphids, a substance that acts on the nervous system. The crop of ants that harvested the honeydew also contained dopamine.

And that affected the behaviour of the ants. The researchers conducted experiments to find out how aggressive ants were towards the Asian ladybird (Harmonia axyridis), a major predator of the aphids. Shortly after visiting an aphid colony, ants were more aggressive than ants that had not visited aphids. As other experiments show, this is due to the dopamine. In these experiments, administration of dopamine made the ants more aggressive than normal, whereas artificial honeydew without dopamine did not.

Extra benefit

So, both the Japanese mugwort aphid and the ant Lasius japonicus that protects it benefit from their mutualistic relationship. The aphid forces the ant to provide better protection, the ant manipulates the aphid colony so that an extra amount of high-quality food is produced.

The relationship with ants is especially important for the aphid. A colony wouldn’t survive without its ant bodyguards.

Willy van Strien

Photo: Japanese mugwort aphid. ©Ryota Kawauchiya

On YouTube: ladybird larva consuming aphids is bitten by an ant

See how the ant manipulates the aphid colony

Kudo, T., H. Aonuma & E. Hasegawa, 2021. A symbiotic aphid selfishly manipulates attending ants via dopamine in honeydew. Scientific Reports 11: 18569. Doi: 10.1038/s41598-021-97666-w


Ants translocate their larvae and pupae to a warm bird’s nest

Myrmica ruginodis translocates brood to a wood warbler's nest

In the nest of a wood warbler not only young wood warblers may grow up, but also ants, as Marta Maziarz and colleagues discovered. Ant larvae and pupae probably survive, grow and develop better in the bird’s nest than in their own nest.

Usually, nests of European forest ants, especially Myrmica ruginodis and Myrmica rubra (the European fire ant or common red ant), are so cold in spring that the larvae and pupae do not grow well. Their development only starts at 16°C, but ant nests rarely get that warm before summer. They are located on the forest floor, between fallen leaves of deciduous trees. The ants cannot produce heat, so without sunlight the nests have the same temperature as the environment. A temperature of 20 to 25°C is optimal for raising brood; the nests never reach that temperature in spring.

But warm places are available nearby, Marta Maziarz and colleagues show. On the forest floor, the wood warbler, a songbird that breeds in European forests, makes a domed nest of grasses, leaves and moss. The bodies of bird parents and, later on, their fully feathered young keep the nest warm.


When the bird parents incubate the eggs, in the second half of May, the nest temperature often reaches 16°C or more; especially on cold days, the difference with the ambient temperature is large. Once the young birds are fully feathered, in the first week of June, the nest temperature even rises to 20°C and higher.

This is a nice temperature for the ants, which indeed visit the warm wood warbler’s nest. In cold weather in May and in the first week of June, they move larvae and pupae from their own nest to a bird’s nest and put them in the sidewalls. Translocation is a lot of work, but apparently, it is worth the effort.

After fledging, the vacant nest cools down again. But the ants don’t remove their brood immediately; they delay relocation for up to two weeks. There is no hurry, because the bird’s nest is no longer warm, but it is not colder than the ants’ nest either.

In the primeval forest of Białowieża in Poland, where Maziarz conducted the research, the ants use 10 to 30 percent of wood warblers’ nests as incubators. The birds do not suffer from the inhabitants, but they do not benefit from them either. Therefore, they do not specifically seek the proximity of ant colonies when starting nest building. It is the ants that start the relationship and benefit from it.

Willy van Strien

Photo: Myrmica ruginodis with brood. Jan Anskeit (Wikimedia Commons, Creative Commons CC BY 4.0)

Maziarz, M., R.K. Broughton, L.P. Casacci, G. Hebda, I. Maak, G. Trigos‑Peral & M. Witek, 2021. Interspecific attraction between ground‑nesting songbirds and ants: the role of nest‑site selection. Frontiers in Zoology 18: 43. Doi: 10.1186/s12983-021-00429-6
Maziarz, M., R.K. Broughton, L.P. Casacci, A. Dubiec, I. Maák & M. Witek, 2020. Thermal ecosystem engineering by songbirds promotes a symbiotic relationship with ants. Scientific Reports 10: 20330. Doi: 10.1038/s41598-020-77360-z

Garden or nameplate?

Why vicuñas create communal dung piles

Vicuñas use permanent latrines to defecate and urinate

Vicuñas live in arid, cold and barren areas, high in the Andes. They set up permanent places to defecate and urinate and use those latrines for decades. There is disagreement about why.

High in the South American Andes, where the soil is arid, rocky, and barren, some places stand out because they are green, overgrown with plants. The greens islands developed because vicuñas come there repeatedly to defecate and urinate. Why do they use such latrines? To create gardens with plants that they can feed on, Kelsey Reider and Steven Schmidt suggest. No, the dung piles are kind of nameplates that mark their territory, William Franklin thinks.

Unpalatable bunch grass

Vicuñas are one of the few animal species that live in the Andes at altitudes of more than 4000 meters, right up to the edge of snow. They mainly live in groups that roam over a territory of almost 20 square kilometers. Climate change is also noticeable here; glaciers dwindle and retreat to the mountain tops. Where they melt, a bare bottom appears which is poor in plant nutrients, so that it takes decades before a noteworthy vegetation is formed. Vicuñas are the first to enter the newly exposed soil at the edge of the glaciers.

With their droppings, they enrich the soil with nutrients. They defecate and urinate only on permanent latrines or dung piles which persist for decades. Consequently, fertilized places are created where vegetation can develop more quickly.

First, a vegetation appears that is dominated by the tough and little nutritious Peruvian feather grass, Stipa pichu. It is not until hundreds of years later that a grassier vegetation develops, with the grass Calamagrostis vicunarum, other grasses and herbs.


In those grassy places vicuñas forage preferentially. Because the places are still used as latrines also, the animals run the risk of picking up gastrointestinal parasites. But places with tasty vegetation are so scarce that it is worth the risk.

That is why Reider and Kelsey believe that the vicuñas maintain latrines in order to concentrate their dung and accelerate the development of nutritious vegetation locally. In other words, latrines are gardens where they grow food.

Franklin thinks otherwise, however. Vicuñas that use a young latrine at the edge of a glacier or start a new one will not be able to enjoy a tasty yield themselves, because generations will have passed before there will grow anything edible. When it comes to food breeding, it would be better for an animal to choose an older latrine where plant growth is already substantial.

Instead, he thinks that the dung piles mark the territory of a group. This is important because if an animal enters another group’s territory accidently, it will be violently attacked and chased away and is at risk of serious injury. By marking the territory at fixed places with the characteristic group scent, especially at the borders, a group manages to keep its members within their own safe territory. So, at a border, two groups may be seen peacefully grazing side by side, each in its own area.


Every group member contributes to these scent markings, and whoever contributes benefits from the fact that the nameplate is maintained.

As a result, vegetation develops on bare ground, gradually becoming more attractive. Which is a nice side-effect for future generations and other mammals that visit the grassy places: mountain viscacha (Lagidium viscacia) and Andean fox (Lycalopex culpaeus).

Willy van Strien

Photo: Dick Culbert (Wikimedia Commons, Creative Commons CC BY 2.0)

Franklin, W., 2021. Vicuña dung gardens at the edge of the cryosphere: Comment. Ecology 102: e03522. Doi: 10.1002/ecy.3522
Reider, K.E. & S.K. Schmidt, 2021. Vicuña dung gardens at the edge of the cryosphere. Ecology 102: e03228. Doi: 10.1002/ecy.3228

Crossdressing in white-necked jacobin

Male-like plumage reduces social harassment in females

in white-necked jacobin, males are brightly coloured

Most white-necked jacobin females are distinguishable from males by a less bright colour. But 20 percent of the females looks like a male. Jay Falk and colleagues wanted to know why they deviate from the normal pattern.

In hummingbirds, a bird family with more than 300 species, males tend to be more brightly coloured than females. But in one in four species, some females have a male-like plumage, as reported earlier this year by the research group that Jay Falk is part of. Now, he tried to figure out why these females dress like a male. He discovered that it enables them to forage relatively undisturbed. They experience less harassment of both conspecifics and other hummingbirds.

most white-necked jacobin females are less colourful than males, but some have male-like plumageThat hummingbird females normally are less colourful than males – though they are by no means dull compared to many other bird species – is because they raise the young. If they are on or around the nest, a dull colour provides safety: their predators detect them less easily. Hummingbird males have no such tasks and are free to seduce females. To be attractive, they have flashy colours, which females like.

White-necked jacobin

But in some hummingbird species, females may have a showy male appearance. The white-necked jacobin, Florisuga mellivora, is an example. About 20 percent of adult females has a shiny blue head, white belly and tail and white spots on the neck like males. Would this confer any benefit?

Perhaps also males prefer a brightly coloured partner, Falk thought at first. But that is not the case, as it turned out when he offered males a choice from several stuffed birds: they prefer a female with normal female plumage.


Another possibility is that brightly coloured birds are less likely to be harassed when foraging. Hummingbirds are small animals with a high metabolism that need to consume large quantities of food. So, the birds spend a large part of the day foraging, sucking nectar from flowers. Competition over food is high, and they are quite aggressive around flowers with a high nectar content. Continuously, they are trying to chase each other away.

White-necked jacobin females in female plumage lose out, according to observations. Apparently, they are not impressive. They are more often chased off than brightly coloured animals, both by conspecifics and other hummingbirds. Conversely, they are less aggressive themselves. In addition, they are likely to be sexually harassed more often. Females in male’s outfit, on the other hand, can forage relatively undisturbed.

Accordingly, male-like females were found to visit a place where nectar was offered more frequently than females in female plumage, and they stayed longer. So indeed, male plumage in females is beneficial because it reduces harassment.

A white-necked jacobin female with male plumage does not look exactly the same as a male. When the tail is fanned, a black tail band becomes visible that is wider in these females than in males. They also have some green on the tail.

Brood care

There is another indication that male plumage offers protection against aggression: all young are brightly coloured, while young of animal species usually are camouflaged. Male-like plumage also enables young white-necked jacobins to forage without too much trouble.

So, young females are brightly coloured. As they reach adulthood, 20 percent of females retains that colourful plumage, while the majority, 80 percent, switches to a less conspicuous appearance. Why don’t they all keep looking like males if that increases access to food resources?

Probably because it is still true that during the breeding period a female should not be clearly visible, favouring a less bright colour. Young females don’t have that concern yet.

Willy van Strien

Large: white-necked jacobin male. Kathy & sam (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: white-necked jacobin female in female plumage. Joseph Boone (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Falk, J.J., M.S. Webster & D.R. Rubenstein, 2021. Male-like ornamentation in female hummingbirds results from social harassment rather than sexual selection. Current Biology, online August 26. Doi: 10.1016/j.cub.2021.07.043
Diamant, E.S., J.J. Falk & D.R. Rubenstein, 2021. Male-like female morphs in hummingbirds: the evolution of a widespread sex-limited plumage polymorphism. Proceedings of the Royal Society B 288: 20203004. Doi: 10.1098/rspb.2020.3004

Successful as bird dropping

Crab spider imitates fresh bird’s poo

bird-dung crab spider mimics bird's poo

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

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

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

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

Leaf miner flies

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

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

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

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

Willy van Strien

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

Another crab spider mimics a flower

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


In bright sunlight, a peregrine falcon can see well thank to malar stripes

Peregrine falcon can see well in bright sunlight thanks to dark malar stripes

Solar glare can impede vision. Michelle Vrettos and colleagues make it plausible that the black malar stripes of a peregrine falcon are helpful during hunt.

With an impressive high-speed dive, a hunting peregrine falcon descends to capture a prey in mid-air. It is the fastest flier among the birds – it can reach about 350 kilometres per hour in a hunting stoop – and it hunts other birds and bats while flying. Its striking black stripes below the eyes help it to track its fast-moving, agile prey, Michelle Vrettos and colleagues write.


The idea that those black stripes, the so-called malar stripes, are important for sharp vision already existed. Light feathers would reflect sunlight from the cheeks into the eyes, blurring the image, but dark feathers absorb the light. As a consequence, a hunting peregrine falcon would suffer less from solar glare. Other falcon species and some songbirds and hunting mammals have similar dark stripes or an eye mask. And some American athletes blacken their cheeks with eye black to reduce glare and better track fast balls. Does it help?

Apparently, it does, at least in peregrine falcons. Vrettos used photos that were posted on internet of a few thousand peregrines from all over the world; except in Antarctica, the bird is found everywhere. She measured the malar stripes on each photo. And she found that the malar stripes are larger and darker as the average annual solar radiation in the area where a photo was taken is higher. Even though, in sunny areas, dark feathers have the disadvantage that they absorb heat.

Experiments are required to proof that the malar stripes really help vision by reducing solar glare. But the findings are at least striking.

Willy van Strien

Photo: A peregrine falcon with prominent malar stripes. Kevin Cole (Wikimedia Commons, Creative Commons CC BY 2.0)

Vrettos, M., C. Reynolds & A. Amar, 2021. Malar stripe size and prominence in peregrine falcons vary positively with solar radiation: support for the solar glare hypothesis. Biology Letters 17: 20210116. Doi: 10.1098/rsbl.2021.0116

To hear a mockingbird

Subtle transitions between adjacent song phrases

northern mockingbird composes its song carefully

The northern mockingbird has an extremely lengthy, variegated and complex song. Tina Roeske and colleagues explain why we like this song so much.

For minutes on end, the northern mockingbird, Mimus polyglottos, can sing its song. The song is well known in North America, where the songbird is common in gardens and parks. It makes phrases in which it repeats a syllable (consisting of one or a few sounds) several times, like the European song thrush does, and strings the phrases up to a varied and complex whole.

A beautiful musical whole, in our opinion. Tina Roeske and colleagues know why we enjoy it: the bird orders its phrases carefully.

Car alarm

A singing mockingbird has a repertoire of a few hundred phrase types. These include its own tunes, but it also mimics calls and songs of many other birds. In addition, it mimics sounds of other animals and it can even imitate unnatural sounds, such as a car alarm.

And yet, its singing is not a hodgepodge. The researchers – a neuroscientist, a biologist, and a music philosopher – show that adjacent phrases usually are selected in such a way that they have similar acoustic properties; they sound like repeats that are a bit transformed or morphed. The researchers distinguish four modes of morphing that we can clearly perceive.


Two adjacent phrases often have the same pitch and rhythm but differ in timbre (tone quality). For example, the first phrase has clear tones, the next one has some noise in it.

In other cases, a phrase is a repeat of the previous one, but at a different pitch. Or it has a faster or slower pace. Sometimes a combination of morphing can be heard, for instance a phrase that is faster and higher in pitch than its predecessor. And sometimes, a contrasting element is inserted between two similar phrases.

Because successive phrases are usually acoustically related, transitions are subtle, making the song coherent. Composers use the same strategies to add variety to their music. They use instruments with different timbres (for instance flute and violin), repeat a motif at a different pitch (the well-known beginning of Beethoven’s Fifth Symphony) or they change the tempo.

Both mockingbird males and females sing. But males sing more often and more exuberantly; they do it to enchant females. Undoubtedly, they are successful, but exactly what a mockingbird female appreciates in a male’s singing is not known.

Willy van Strien

Photo: AidenD (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Hear a mockingbird singing and learn how the researchers analyse the song

Another musician bird: pied butcherbird

Roeske, T.C., D. Rothenberg & D.E. Gammon, 2021. Mockingbird morphing music: structured transitions in a complex bird song. Frontiers in Psychology, online May 4. Doi: 10.3389/fpsyg.2021.630115

Bubble on the head

Water anole rebreathes exhaled air when submerged

Water anole re-uses exhaled air

Some Anolis lizard species can stay underwater for a while without drowning. Thanks to a layer of air around their water-repellent skin, they continue to breathe, Chris Boccia and colleagues write.

The water anole, Anolis aquaticus, is not a fast lizard. But it often manages to escape from a predator, such as a larger lizard, snake, or bird. In case of danger, it splashes into the water to be out of sight. Although it may reappear only after more than fifteen minutes, it does not suffer from breathlessness. That is because it makes good use of the air it has with it, Chris Boccia and colleagues show.

The water anole from Costa Rica is one of more than 400 Anolis lizard species which occur in tropical America. Some species, including this one, live close to water and often submerge. The researchers studied how these semi-aquatic species survive submersion and how they differ from species that always remain on dry land.

All Anolis species appear to have a water-repellent skin. If they get into the water, a thin layer of air forms between water and skin across the body surface. In other words, they do not get wet like other lizards. As a consequence, no air bubbles up to the water surface to escape when an anole exhales underwater, as in other animals. Instead, the exhaled air is incorporated into the air layer around the body. This is visible as an air bubble near the nostrils. In the water anole, that bubble appears on top of its snout.


Semi-aquatic species like the water anole use that trapped air. They re-inhale it. And exhale, and inhale, five times at least.

How does that help?

Breathing is necessary to take up oxygen from the air into the blood and to get rid of carbon dioxide. That gas exchange occurs in the lungs. The carbon dioxide exhaled by a diving anole dissolves easily from the air bubble in the water. So, it gets rid of that waste gas.

Also, with each breath, it takes up oxygen from the air bubble, the researchers show: the oxygen content of the bubble slowly decreases. The oxygen supply may be partly replenished if the air that comes from the lungs where it lost oxygen mixes with air that did not pass through the lungs: the air layer around the skin and air from mouth, nose, and windpipe.


And the bubble might act like a gill; perhaps it absorbs oxygen from the water. That will not be enough for a long stay underwater. But it might extend the maximum dive time a bit. A possible indication for this supplemental oxygen is that the oxygen content of the air bubble decreases more and more slowly over time. But that may also be explained by a lowered metabolism underwater, and thus less oxygen consumption.

Terrestrial Anolis species occasionally reuse expired air when submerged, but they do not do so routinely and not for as long as the water anole and other semi-aquatic species – that have to sustain rebreathing until the predator’s patience is gone.

Willy van Strien

Photo: submerged water anole with bubble on snout. ©Lindsey Swierk

On You Tube, the researchers show it here and here

Boccia, C.K., L. Swierk, F.P. Ayala-Varela, J. Boccia, I.L. Borges, C.A. Estupiñán, A.M. Martin, R.E. Martínez-Grimaldo, S. Ovalle, S. Senthivasan, K.S. Toyama, M. del Rosario Castañeda, A. García, R.E. Glor & D.L. Mahler, 2021. Repeated evolution of underwater rebreathing in diving Anolis lizards. Current Biology, online May 12. Doi: 10.1016/j.cub.2021.04.040

Royal matchmaker

Ant worker transports young queen to suitable mates

Cardiocondyla elegans worker carries queen to new nest to mate

Workers of the ant Cardiocondyla elegans make sure that their queen sisters will meet unrelated males, Mathilde Vidal and colleagues show.

Young queens of the ant Cardiocondyla elegans do not leave the natal nest on their own to be inseminated outside. Although they have wings, they make no nuptial flights like queens in many other species. They stay inside. Males have no wings, and they too remain in the natal nest. And so it happens that young queens, or gynes, mate with males that were born in the same nest. But workers intervene to promote outbreeding, Mathilde Vidal and colleagues discovered.

Cardiocondyla elegans, which is mainly found along the Mediterranean, contructs underground nests on river banks. Hundreds of workers, dozens of young queens and a few males share a nest, headed by one fertile queen. This mother queen has mated with several males and stored their sperm to fertilise eggs.

As a consequence, the gynes and males in her nest are full and half siblings. If they mate with each other, this is inbreeding, and prolonged inbreeding has negative effects on the lifespan of mother queens, the survival of brood and the ratio of females (workers and young queens) to males.

Vidal had observed workers walking through the field between nests, carrying a winged young queen on their back. She wondered whether this queen transport could be a way to promote outbreeding. Behavioral observations and genetic research confirmed this idea.

New contacts

The researchers discovered that gynes do indeed mate in the natal nest. But it doesn’t always stop there. A worker regularly drags a young queen out of the nest, takes her head between its jaws and carries her on its back to another nest, where it drops her into the nest entrance.

Just below that entrance, as it turned out, is a chamber with hundreds of young queens and males. It is obvious what is happening there. The nest chambers with mother queen and brood are much deeper, 1 to 2 meters below the surface. By dropping a young queen into the entrance of an alien nest, a worker brings her into contact with males that are not (half) brothers. The nest where a young queen is delivered also profits because males can mate not only with (half) sisters, but also with an unrelated queen.

After delivery, a queen is sometimes picked up again and taken to still another nest.


Young Cardiocondyla elegans queens hibernate in the natal nest or in the nest to which they were brought. They retain their wings. In spring they leave, usually on foot, to found a nest on their own, with a stored stock of sperm from several males: (half) brothers and, if they have been transported to another nest, alien males. Once they have started their own nest, they lose their wings.

Apparently, young queens are able to disperse on their own. Then why don’t they leave the natal nest to mate elsewhere?

Maybe it’s quicker and safer to be carried, Vidal thinks. Workers know the surroundings. Passing by other nests, they walk in a straight line to a nest that they have selected. Often, they will deliver another gyne there later on.

Inhabitants of a preferred nest are no family, so the matchmakers select unrelated partners for their queen sisters. This behaviour is a new and surprising way to promote outbreeding, the researchers state.

Willy van Strien

Photo: Cardiocondyla elegans: worker carrying young queen. ©Mathilde Vidal

Vidal, M., F. Königseder, J. Giehr, A. Schrempf, C. Lucas & J. Heinze, 2021. Worker ants promote outbreeding by transporting young queens to alien nests. Communications Biology 4: 515. Doi: 10.1038/s42003-021-02016-1
J-C. Lenoir, A. Schrempf, A. Lenoir, J. Heinze & J-L. Mercier, 2007. Genetic structure and reproductive strategy of the ant Cardiocondyla elegans: strictly monogynous nests invaded by unrelated sexuals. Molecular Ecology 16: 345-354. Doi: 10.1111/j.1365-294X.2006.03156.x