Fireproof

‘Heart of Flame’ bromelia protects spider against flames

Heart of flame bromelia shelters spiders from fire

In case of a fire event on the Brazilian cerrado, many animals are killed. But the spider Psecas chapoda, which lives on a bromeliad plant, has a chance to survive, Paula de Omena and colleagues write.

Female Psecas chapoda on Bromelia balansaeThe terrestrial bromeliad plant Bromelia balansae and the spider Psecas chapoda are strongly associated with each other. The spider lives almost exclusively on this prickly plant, in the centre of which it is protected against its predators. On the leaves, adult spiders hunt, court and mate, females lay their eggs, and spiderlings grow up. Up to twenty spiders may inhabit one plant. Conversely, although the plant can do without Psecas chapoda, it benefits when it is inhabited by spiders, because it extracts nutrients from their faeces; the predatory spiders also protect the plant against herbivorous critters.

Fires

Now, Paula de Omena and colleagues discovered that this nice mutualism offers an additional benefit to the spider: it can survive a fire on the plant, because the leaves provide shelter and protection from the heat of the flames. Strikingly, the plant is known as ‘Heart of Flame’, as the centre turns bright red when it is about to bloom.

The bromeliads and spiders live in South America, including the Brazilian cerrado: a savanna-like area with trees and shrubs. In the dry period, which lasts about half a year, natural fires frequently rage. The researchers assumed that in the centre of the plants the spiders are sheltered from the heat of flames, and to find out whether they were right, they counted plants and spiders in a small and isolated cerrado fragment before and after a natural fire event.

Recovery

The day after the fire, the number of spiders had strongly decreased, and also the percentage of bromeliads occupied by spiders was low. But in the centre of a number of plants with intact leaf structures, the researchers found spiders that had survived the fire, and thanks to their survival, the spider population recovered within five months.

Without this possibility to hide, far fewer spiders would survive a fire event and it would take much longer for the population to return to pre-fire levels. A new fire would probably break out before the population fully recovered – so that Psecas chapoda would run a risk to disappear completely. Thanks to the plants, this does not happen.

Willy van Strien

Photos
Large: ‘Heart of Flame’, Bromelia balansae. João Medeiros (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: jumping spider Psecas chapoda, female, on Bromelia balansae. ©Gustavo Q. Romero

Sources:
De Omena, P.M., M.F. Kersch-Beckr, P.A.P. Antiquera, T.N. Bernabé, S. Benavides-Gordillo, F. C. Recalde, C. Vieira, G.H. Migliorini & G.Q. Romero, 2017. Bromeliads provide shelter against fire to mutualistic spiders in a fire-prone landscape. Ecological Entomology, online December 20. Doi: 10.1111/een.12497
Romero, G.Q., P. Mazzafera, J. Vasconcellos-Neto & P.C.O. Trivelin, 2006. Bromeliad-living spiders improve host plant nutrition and growth. Ecology 87: 803-808. Doi: 10.1890/0012-9658(2006)87[803:BSIHPN]2.0.CO;2

Hypocritical behaviour

Cheating cleaner wrasse cares about its reputation

cheating cleaner wrasse cares about its reputation

In some circumstances, cleaner wrasse attract clients by presenting themselves as more friendly than they really are – and subsequently provide them a bad service, as research by Sandra Binning and colleagues reveals.

Anyone who runs a business should care about a good reputation, and the bluestreak cleaner wrasse, Labroides dimidiatus, definitely does. These fish try hard to be seen as cooperative partners, especially when they are exploitative partners in reality; in the words of Sandra Binning and colleagues, they have reputation management abilities.

The cleaner fish occupy a cleaning station on a reef and offer a cleaning service to other fish: the cleaners eat ectoparasites off the surface of their clients. It is a flourishing business, with cleaners on average being involved in two thousand interactions a day with more than a hundred clients; some clients come for inspection many times a day. Both partners benefit from the interactions – clients are cleaned, cleaners earn a meal – so, they have a mutualistic relationship. But a cleaner may cheat its client by taking a bite from its mucus, a layer that protects against abrasions or ultraviolet radiation, instead of removing parasites. A cleaner prefers eating the mucus over parasites, as it is more nutritious.

Temptation

Mostly, cleaners provide honest services. They just have to, because if they bite a client, that client will either leave and visit another cleaning station or chase the cleaner away from its station, making it impossible to continue its work for a while; and some clients are predatory fish that may ingest a cheating cleaner. Also, there are bystanders, waiting clients or potential clients, that eavesdrop on ongoing interactions and that notice when a cleaner bites its current client, as that client will involuntary make a short jolt in response. For the audience, the occurrence of a jolt is a reason to avoid that cleaner.

So, most cleaners behave in a decent manner. They will not bite, especially not when other fish are witnessing. Still, some cleaner wrasse sometimes behave badly, mainly females in the spawning season, when their energy demands are high and, accordingly, the temptation to cheat is high.

Friendly

As biting cleaners run a risk to lose their clients, they care about their reputation: they behave friendly towards small clients and provide these clients tactile stimulation by hovering above them and touching them with their pelvis fins.

Clients like this stimulation; it reduces their stress. Cooperative cleaners use to perform this behaviour infrequently to persuade a client to have itself inspected and cleaned, or to reconcile after a bite and prevent the client from fleeing or becoming aggressive, or to appease predatory fish. It is costly behaviour, because cleaners cannot eat while stroking a client.

But a biting cleaner that titillates a small client, does so for another reason, as the researchers found out before. Small clients offer less parasites and less mucus than larger clients. To stimulate them in order to keep friends with them would hardly be worth the effort, and in most cases it is unnecessary. Instead, the service of a cheater towards small clients is meant to attract larger observing clients, by showing them how friendly it behaves. When a large potential client sees the high service quality that the small client receives and approaches to be cleaned, the cheater can take a big bite of that large client’s mucus.

Witnesses

Now, the researchers show that biting cleaners only perform their hypocritical behaviour when it pays, that is: when many clients and many competing cleaners are around to witness. In such circumstances, cheaters often stroke small clients and bite the large clients that are misled by this nice behaviour. But when just a few clients and a few competitors are around, they will bite their small clients as well. They may be friendly, but only when an audience is looking.

Willy van Strien

Photo: Bluestreak wrasse, Labriodes dimidiatus, and clients. Keith Wilson (via Flickr, Creative Commons CC BY-NC 2.0)

Sources:
Binning, S.A., O. Rey, S, Wismer, Z. Triki., G. Glauser, M. C. Soares & R. Bshary, 2017. Reputation management promotes strategic adjustment of service quality in cleaner wrasse. Scientific Reports 7: 8425. Doi: 10.1038/s41598-017-07128-5
Pinto, A., J. Oates, A. Grutter & R. Bshary, 2011. Cleaner wrasses Labroides dimidiatus are more cooperative in the presence of an audience. Current Biology 21: 1140-1144. Doi: 10.1016/j.cub.2011.05.021
Bshary, R. & A.S. Grutter, 2006. Image scoring and cooperation in a cleaner fish mutualism. Nature 441: 975-978. Doi: 10.1038/nature04755
Bshary, R., 2002. Biting cleaner fish use altruism to deceive image-scoring client reef fish. Proc. R. Soc. Lond. B 269: 2087-2093. Doi: 10.1098/rspb.2002.2084
Bshary, R. & M. Würth, 2001. Cleaner fish Labroides dimidiatus manipulate client reef fish by providing tactile stimulation. Proc. R. Soc. Lond. B 268: 1495-1501. Doi: 10.1098/rspb.2001.1701

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.

Willingness

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.

Sea birds

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

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.

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

Good friend

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

Mini garden

Some arboreal ants grow useful plants

A Squamellaria major plant on macaranga, grown by ants

Gardening is an art – and there are ants that master this art. On the branches of trees they cultivate plants to live in or to strengthen their nests, as research teams of Guillaume Chomicki and Jonas Morales-Linares report.

Many ants and plants are partners in a mutualism: the plants provide the ants with a place to live or with nectar, and the ants deposit their droppings as fertilizer or protect the plants from herbivorous insects. Some tropical arboreal ants go a step further and cultivate the plants they live with. As these plants grow upon tree branches (they are epiphytes), it is more difficult for them to obtain nutrients than it is for plants that root in the soil, so the ant-plant mutualism is a good strategy. Many of the ant-grown plants are completely domesticated and would perish without the ants.

Seed collection

Philidris nagasau, native to Fiji, inhabits the hollow stems of Squamellaria species, bulb-shaped plants that grow on trees. The ants live nowhere else, and six Squamellaria species are always inhabited by these residents. The ant fertilizes the plants, as Guillaume Chomicki and colleagues had previously shown.

workers of Philidris nagasau inspect seedlings of SquamellariaNow, they discovered that the ant makes sure that plants are available by farming them. The researchers observed ant workers collecting exclusively the seeds of these six Squamellaria-species, and not those of any other species. They take them out of the unripe fruits, insert them in fissures and cracks in the bark of a tree and patrol the planting sites. Soon after, the seeds germinate and seedlings appear on the tree, and as soon as they form a cavity, a few ants will enter it, likely to leave their droppings. By doing so, they grow the plants they need to live in.

So, this ant-plant mutualism is more intimate than previously thought. The plants need the ant partner not only for nutrition, but also for seed dispersal.

Beautiful flowers

A different kind of plant nurseries can be found in Central and South America: conspicuous little gardens that hang from some trees. They are the overgrown carton nests of certain ant species. The ants collect seeds of epiphytes and insert them in the walls of their nest, where of the seeds germinate and grow up. The plant roots strengthen the nest and take up water when it rains, so that the nests don’t disintegrate. In return, the ants fertilize the plants and protect them against herbivorous insects. Some plants are exclusively dispersed by the ants and only germinate in an ant nest.

Hanging garden of Azreca gnavaAzteca gnava from southern Mexico and Panama is such a gardening ant. His gardens are frequently found in plantations, as Jonas Morales-Linares and colleagues report, mostly on cocoa, mango, sapote and orange trees. The gardens contain twelve plants on average, typically of two or three different species. Two plant species that cannot live outside these gardens are the bromeliad Aechmea tillandsioides and the orchid Coryanthes picturata. Apparently, the gardening ants have a good taste, for these plants have beautiful flowers.

Three million years

The ant Camponotus femoratus of the Amazonian lowland forest plants similar gardens. Mutualism is obligate for the plant Peperomia macrostachya, that only lives in the nests of this ant. Elsa Youngsteadt and colleagues showed that Camponotus femoratus is the only ant species to collect the seeds of this plant. The ant takes them from the plant, from the soil or from the feces of birds and mammals that have eaten the fruits. Probably, the seeds emit volatiles that only only Camponotus femoratus appreciates. The ant inserts many Peperomia seeds in the walls of its nest. Each seed has only a small chance to germinate there, but the seeds that are not brought into the ant’s nests have no chance to sprout at all.

According to Chomicki, Philidris nagasau in Fiji descends from ancestors that, just like their American colleagues, made carton nests in trees and planted seeds in the wall. But at some time, Philidris nagasau stopped making nests and planted the seeds in the bark instead; at roughly the same time Squamellaria species developed the hollow, bulbous stems that can house the ants. So, ant and plants co-evolved; their co-evolution started about three million years ago.

Willy van Strien

Photo’s:
Large: a Squamellaria major plant, grown by ants on macaranga. © Guillaume Chomicki
Small 1: workers of Philidris nagasau inspecting seedlings. © Guillaume Chomicki
Small 2: hanging garden of Azteca gnava. © Jonas Morales-Linares

Sources:
Chomicki, G. & S.S. Renner, 2016. Obligate plant farming by a specialized ant. Nature Plants 2: 16181. Doi: 10.1038/nplants.2016.181
Chomicki, G., Y.M. Staedler, J. Schönenberger & S.S. Renner, 2016. Partner choice through concealed floral sugar rewards evolved with the specialization of ant-plant mutualisms. New Phytologist, online May 9. Doi: 10.1111/nph.13990
Morales-Linares, J., J.G. García-Franco, A. Flores-Palacios, J.E. Valenzuela-González, M. Mata-Rosas & C. Díaz-Castelazo, 2016. Vascular epiphytes and host trees of ant-gardens in an anthropic landscape in southeastern Mexico. The Science of Nature 103: 96. Doi: 10.1007/s00114-016-1421-9
Youngsteadt, E., J. Alvarez Baca, J. Osborne & C. Schal, 2009. Species-specific seed dispersal in an obligate ant-plant mutualism. PLoS ONE 4: e4335. Doi: 10.1371/journal.pone.0004335