From so simple a beginning

Evolution and Biodiversity

Category: feeding

Acid gulp

16 November 2020 /

Ant swallows its own formic acid to stay healthy

Tnaks to formic acid, Formicinae ants are healthy

Formic acid appears to be a great help for ants to prevent infection from contaminated food, Simon Tragust and colleagues discovered. A gulp after each consumption increases their survival chance.

People like sweet desserts, but for ants of the subfamily Formicinae it is different. They take a gulp of formic acid after eating or drinking, Simon Tragust and colleagues witnessed.

This is remarkable, because formic acid is an aggressive substance. Formicinae ants produce it in a venom gland that has an opening at the tip of the abdomen. They were known to spray it at predators, such as birds, spiders, and insects, to defend themselves, and this is understandable. But swallowing?

Disinfect

Tragust and colleagues had shown previously that Formicinae ants use their acid not only against predators, but also against pathogens. Workers apply it in combination with resin to keep an entomopathogenic fungus (Metarhizium brunneum) out of their nest.

Also, they use formic acid to keep the brood clean. If they detect pupae covered with spores of the pathogenic fungus, they clean them and cover them with formic acid, which they had taken up from the abdominal gland opening into the mouth.

If fungal spores have already germinated on a pupa and the fungus has penetrated the cuticle, workers unpack the infected pupa from its cocoon, bite holes in the skin and inject formic acid. In this way, they prevent the fungus from growing and forming spores that will contaminate the rest of the colony. The pupa does not survive the treatment, but it would have been killed by the fungus anyway.

Crop acidity

Now, a new application of formic acid comes to light: Formicinae ants swallow their own formic acid after eating or drinking something. Tragust deduces this from tests in the lab with Florida carpenter ant, Camponotus floridanus. He offered ants honey water or plain water and saw them lick their abdominal tip afterwards. Apparently, they then took up acid into the mouth and swallowed it, as Tragust showed that the contents of their crop, just before the stomach, became very acidic.

Perhaps, the idea was, workers take formic acid to kill bacteria that may be present on food. And that was the case, as became clear from tests in which workers were given food that was contaminated with a pathogenic bacterium species (Serratia marcescens). In ants that then took a gulp of formic acid, bacteria did not survive the crop environment and the rest of the intestinal system remained clean. Ants that were prevented from taking in acid, were at greater risk of a deadly infection.

Only bacteria that thrive in acidic environments survive the acidic crop, and such bacteria populate the ants’ intestines. But these are beneficial bacteria that help digest food. The acid appears to be an excellent remedy against pathogenic microbes.

Fortunately, we don’t have to take an extremely sour dessert like Formicinae ants, because our stomach keeps itself acidic.

Willy van Strien

Photo: Carpenter ant, Camponotus cf. nicobarensis. ©Simon Tragust

Ants also use formic acid to keep fungus out of nest

Sources:
Tragust, S., C. Herrmann, J. Häfner, R. Braasch, C. Tilgen, M. Hoock, M.A. Milidakis, R. Gross & H. Feldhaar, 2020. Formicine ants swallow their highly acidic poison for gut microbial selection and control. eLife 9: e60287. Doi: 10.7554/eLife.60287
Pull, C.D., L.V. Ugelvig, F. Wiesenhofer, A.V. Grasse, S. Tragust, T. Schmitt, M.J.F. Brown & S. Cremer, 2018. Destructive disinfection of infected brood prevents systemic disease spread in ant colonies. eLife 7: e32073. Doi: 10.7554/eLife.32073
Tragust, S., B. Mitteregger, V. Barone, M. Konrad, L.V. Ugelvig & S. Cremer, 2013. Ants disinfect fungus-exposed brood by oral uptake and spread of their poison. Current Biology 23: 76-82. Doi: 10.1016/j.cub.2012.11.034

Saving room for delicacy

20 February 2020 /

Cuttlefish won’t eat crab when there will be shrimp at night

cuttlefish refrains from eating during daytime when the night will bring better food

Common cuttlefish exhibits a clear food preference: shrimp. If shrimp will be available at night, it refrains from eating crab during daytime, as Pauline Billard and colleagues show.

The European common cuttlefish Sepia officinalis, which occurs in Mediterranean Sea, North Sea and Baltic Sea, consumes different types of prey, but not with the same eagerness. Shrimp are its favourite food. It likes them so much, that it will skip a crab meal if it expects shrimp to be available later on, as research of Pauline Billard and colleagues revealed.

In the lab, the researchers conducted two experiments. First, they offered cuttlefish, kept in separate tanks, a crab during daytime. Some cuttlefish received an additional shrimp every night, the others were given shrimp only on some nights, in an unpredictable way.
The cuttlefish that received shrimp every night started to lower consumption of crab during daytime, saving room for their favourite food. The animals that were not sure about getting the delicacy at night maintained the consumption of crab during the day, eating enough in any case.
When the routine was reversed between groups – so, cuttlefish that had received shrimp every night changed to an unpredictable regimen and the other way round – the animals modified their behaviour accordingly.

Hunger

Then a second, more complex experiment was done. The animals again were offered crab during daytime, but now all of them got shrimp every other night. It took some time for them to get used to the regimen, but then they adjusted their behaviour. If they had received shrimp the night before, so when there would be no shrimp the following night, they consumed crab during daytime. Conversely, if there hadn’t been any shrimp the night before, they didn’t eat much crab, expecting to get shrimp the following night.

The animals’ behaviour can’t be explained by their feeding state, because in that case they would have eaten crab when they didn’t eat shrimp the night before, being more hungry.

Willy van Strien

Photo: Common cuttlefish. Amada44 (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Source:
Billard, P., A.K. Schnell, N.S. Clayton & C. Jozet-Alves, 2020. Cuttlefish show flexible and future-dependent foraging cognition. Biology Letters 16: 20190743. Doi: 10.1098/rsbl.2019.0743

Small bites, huge gulps

6 June 2018 /

Thousands of copepods are ingested each day by little auk

feeding in little auk is similar to that of whale

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

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

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

Whale

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

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

Willy van Strien

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

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

Slimy lips

21 June 2017 /

Southern tubelip feeds on corals by kissing

Labropsis autralis feeding on corals

As one of only a few fish species, the tubelip wrasse Labropsis australis is able to feed on corals. Specialised lips protect the fish from being hurt, as Victor Huertas and David Bellwood show.

Lips of Labropsis australis bear lamellaeThe tubelip wrasse Labropsis australis, or Southern tubelip, looks like a normal fish. But it appears to have highly modified lips, as Victor Huertas and David Bellwood reveal after making a high-resolution image of the fish’s mouth. The lips form a protruding tube when the mouth is closed; they are thick and fleshy, bear lamellae much like a mushroom, and are covered with a thick layer of mucus, secreted by mucous glands.

Just like kissing

That’s noteworthy, as most wrasses, the group of fish species to which Labropsis australis belongs, have thin, smooth lips that are neither slimy nor protruding.

The remarkable lips facilitate un unusual diet, the researchers found out. Living on the Great Barrier Reef off the north coast of Australia, Labropsis australis feeds on hard corals – and that’s not easy, because the corals have a sharp skeleton covered by a layer of tissue with venomous stinging nematocysts, like jellyfish have. No wonder that most fishes don’t touch them. But Labropsis australis seems not to care.

The biologists recorded the fish’s behaviour with a high-speed camera to see how it managed to feed on corals. Analyzing the footage, they saw how the fish approaches its meal, closes its mouth, pushes its fleshy lips against the coral, sealing them over a small area, and rapidly sucks off some of the coral’s mucus and flesh. This sucking is accompanied by an audible ‘tuk’; it’s just like kissing.

Mucus is the key factor that enables these fish to feed on corals, the authors suppose. The thick mucus layer prevents the sharp edges and nematocysts of the coral from damaging the fish.

Willy van Strien

Photos: © Victor Huertas and David Bellwood
Large: Southern tubelip Labropsis australis
Small: Image of the lips of Labropsis australis

The kissing tubelip wrasse on a video made by Victor Huertas and David Bellwoo

Source:
Huertas, V. & D.R. Bellwood, 2017. Mucus-secreting lips offer protection to suction-feeding corallivorous fishes. Current Biology 27: R399–R407. Doi: 10.1016/j.cub.2017.04.056

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