From so simple a beginning

Evolution and Biodiversity

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Skilful camouflage artist

6 July 2023 /

Cuttlefish has to search for the best pattern

Common cuttlefish is a master of camouflage

The cuttlefish has an excellent camouflage ability and rapidly modifies its appearance when the background changes. But its change is indirect, Theodosia Woo and colleagues show: the cuttlefish adjusts a new skin pattern a few times before it is good enough.

To defend itself against predators, the common cuttlefish, Sepia officinalis, like many other squids, can use camouflage to blend in with its surroundings. And if a predator still detects it, it sprays ink to block the view.

The common cuttlefish lives in the North Sea, the Baltic Sea, and the Mediterranean Sea. Depending on the substrate, such as sand, rocks, or sea grass, it can take on a uniform colour, have a mottled pattern, or have large dark and light skin areas that disrupt its contours. There are countless variations, and the cuttlefish produces an appropriate camouflage against almost any background, Theodosia Woo and colleagues write.

Pigment sacs

This is possible, among other things, thanks to two or three million pigment cells in the skin, the so-called chromatophores. They come in three colours: yellow, red, and brown. The cells are closed sacs with an elastic wall, surrounded by radial muscles. When the muscles contract on command of the brain, they pull the sac open, and the colour becomes visible.

Woo showed how cuttlefish change their appearance by doing experiments in which she provided animals with a changing background; she filmed the skin at high resolution and measured the skin patterns with robust computer software. The result is remarkable. The lightning-fast transition makes it seem as if a cuttlefish realises a new matching skin pattern in one go. But it is not like that.

Confronted with a new background, a cuttlefish immediately starts to adapt its skin pattern. But after a first change, it waits shortly and then adjusts the created pattern to improve it. Then it waits again and adjusts the pattern further, until a satisfying pattern is found. So, it goes through a search process in the blink of an eye and apparently receives feedback continuously. Search trajectories are not fixed, because when the researchers offered the same background change several times, the animals followed different search trajectories and the result was also different. The difference in final skin patterns was so subtle that we cannot observe it.

Reflection

In addition to the pigment cells that were studied here, the squid skin has two more types of neurally controlled cells that enable changes in appearance. There are cells that, thanks to their nanostructure, reflect light of one specific colour, for example blue: the iridophores. And there are cells that reflect all incident light and are white in daylight: the leucophores. In addition, the skin can be smooth or rough. The sophistication of a squid skin is beyond our imagination.

All these possibilities are not only used for camouflage, but also for communication. Common cuttlefish spend spring and summer inshore to spawn, and the colours the animals display then is an attraction for divers.

Colour blind

The greatest puzzle about squids is how they are capable to mimic their environment so perfectly while being colourblind themselves. Almost nothing is known about this, but there is evidence that small light sensitive organs occur in the skin.

Willy van Strien

Photo: Young common cuttlefish. Magnef1 (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Sources:
Woo, T., X. Liang, D.A. Evans, O. Fernandez, F. Kretschmer, S. Reiter & G. Laurent, 2023. The dynamics of pattern matching in camouflaging cuttlefish. Nature, online 28 June. Doi: 10.1038/s41586-023-06259-2
Gilmore, R., R. Crook & J.L. Krans, 2016. Cephalopod camouflage: cells and organs of the skin. Nature Education 9(2): 1
Chiao, C-C., C. Chubb & R.T. Hanlon, 2015. A review of visual perception mechanisms that regulate rapid adaptive camouflage in cuttlefish. Journal of Comparative Physiology A 201: 933-945. Doi: 10.1007/s00359-015-0988-5

Desert ant builds landmark

14 June 2023 /

Nest hill helps ants to return home in barren salt flats

desert ant Cataglyphis fortis has outstanding navigation skills

Often nothing is visible around a nest of the desert ant Cataglyphis fortis that could help foraging workers to return to the nest. In that case, the ants make a landmark themselves, Marilia Freire and colleagues show.

A foraging trip is a survival trip for the desert ant Cataglyphis fortis, which lives in salt pans in Tunisia; salt pans are vast bare plains where there was once water, but now only a salt crust remains. Ant workers venture out individually to search that barren plain for insects and other small critters that have succumbed to the relentless desert heat. After founding something, they must return to the nest with the loot between their jaws as quickly as possible, otherwise they will succumb themselves.

But the entrance to the underground nest is barely visible. That is why the ants build a landmark, when necessary, Marilia Freire and colleagues discovered.

Navigation

Food is scarce, so foraging desert ants often must move far from the nest to find something. They venture up to 350 meters away. Because they have excellent navigation skills, they usually return safely.

When going out foraging, a worker constantly uses an internal sun compass to keep track of the direction in which she is walking and with a kind of pedometer she measures the distance she covers in that direction. When she finds food, she has usually followed a tortuous path, but thanks to this so-called path integration she can walk back to the nest in a straight line, i.e., via the shortest possible route. At least: she closely approaches the nest.

When within a few meters, she needs visible clues to find the exact place of the nest entrance, because path integration doesn’t work perfectly. The farther an ant has gotten from the nest, the more uncertainty creeps into the route back and thus the greater the chance is that she has to search for too long and succumbs. For the very last bit of the trip homewards, she relies on nest smell.

But in the middle of a salt pan, there is nothing to be seen at all. What to do in this case?

Landmark

desert ant builds nest hill when no other visual landmarks are aroundFreire and the other researchers had noticed that the desert ants often build a hill at their nest, and that nest mounds in the middle of a salt pan are higher than on the edge, where some shrubs grow. A nest mound in the middle of a salt pan is 12 centimeters high on average (the highest they found was 30 centimeters), a nest mound at the edge only 5. So, they wondered if the mounds might serve as visual landmarks for workers returning from a foraging trip.

To find the answer, they captured ants at the nest and placed them at a distance of a few meters. Since the ants had not walked themselves, they could not use path integration. But they were placed at distances where they normally must be guided by landmarks to find the nest entrance anyway. The researchers had removed the mounds at some of the nests to see if that made a difference.

That turned out to be the case, especially for nests in the middle of a salt pan. Without a mound, ants were not able to walk directly to such nest and more often failed to find it at all. The hills therefore serve as landmarks. Next question: do ants build them specifically for that purpose? It is possible that the mounds have another main function, such as regulating the nest temperature.

Only when needed

But the researchers show that the desert ant does build its mounds as landmarks by conducting experiments in which they removed the mounds at sixteen nests in the middle of a salt pan. At eight of those nests, they placed artificial landmarks, namely two black cylinders. Three days later, the ants were found to have built a new mound at some of those sixteen nests, especially at nests without artificial landmarks, and at those nests, the mounds were taller.

Conclusion: desert ants build mounds near their nest as landmarks for foraging workers. But they only make the effort if there are no other landmarks visible, such as bushes or, in the trials, black cylinders.

Willy van Strien

Photos: ©Markus Knaden
Large: Cataglyphis fortis
Small: nest mound in the centre of a salt pan

Sources:
Freire, M., A. Bollig & M. Knaden, 2023. Absence of visual cues motivates desert ants to build their own landmarks. Current Biology 33: 1-4 (31 May online). Doi: 10.1016/j.cub.2023.05.019
Steck, K., B.S. Hansson & M. Knaden, 2009. Smells like home: desert ants, Cataglyphis fortis, use olfactory landmarks to pinpoint the nest. Frontiers in Zoology 6: 5. Doi: 10.1186/1742-9994-6-5
Wittlinger, M., R. Wehner & H. Wolf, 2007. The desert ant odometer: a stride integrator that accounts for stride length and walking speed. The Journal of Experimental Biology 210: 198-207. Doi: 10.1242/jeb.02657
Wehner, R., 2003. Desert ant navigation: how miniature brains solve complex tasks. Journal of Comparative Physiology A 189: 579-588. Doi: 10.1007/s00359-003-0431-1

Evolution of butterflies

31 May 2023 /

Europe has the fewest butterfly species

Mating butterflies, pea blue

The very first butterflies on earth flew in what now is North or Central America. The caterpillars fed on leaves of bean plants, according to research by Akito Kawahara and countless others.

Butterflies can be found everywhere on earth, except Antarctica. Until now, it was poorly known where and when they originated and how they evolved.

Together with a huge team, Akito Kawahara figured this out. The researchers analyzed the DNA of almost 2300 butterfly species to draw up an evolutionary tree. They also gathered a lot of knowledge by studying museum collections and digging through field guides in all languages. This allowed them to unravel how butterflies spread over the earth and how they lived.

The diversity of butterflies is great; nowadays, there are 19,000 species worldwide. They have descended from moth ancestors. On the evolutionary tree, their branch originates about one hundred million years ago, when dinosaurs were still around. Flowering plants were already present; adult butterflies could find nectar on the flowers which, in return, they pollinated.

Caterpillars need a lot of food to grow, and the caterpillars of the first butterflies probably gnawed on leaves of bean plants.

Late in Europe

The great supercontinent of Pangea had broken into two pieces when the first butterflies appeared. Both pieces, Gondwana (Africa, Australia, Antarctica, and South America) and Laurasia (North America, Europe, and Asia), were falling apart and the parts drifted away. Originally, India was part of Gondwana, but came loose and drifted to Laurasia.

According to the research, butterflies have originated in what is now western North America or Central America. They crossed the sea to South America fairly quickly.

About seventy-five million years ago, butterflies also moved from North America to Asia, via the Bering Strait, and then spread to India and Australia, and later Africa. Overland the road to Europe was open, but butterflies took a long time to chose this direction. The reason is unclear, and the research gives no answer. Butterflies arrived in Europe ‘only’ thirty million years ago, and as a consequence, Europe has few species compared to other continents.

Caterpillar diet

The caterpillars of most species feed on plants and are quite choosy. The so-called host plants of these species usually belong to one plant family.

Some species have developed an alternative caterpillar diet. The caterpillars consume organic detritus or lichens, and some blues (Lycaenidae) even are carnivorous and eat other insects.

Willy van Strien

Photo: Pea blues (Lampides boeticus) mating. Atanu Bose Photography (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Kawahara, A.Y. et al., 2023. A global phylogeny of butterflies reveals their evolutionary history, ancestral hosts and biogeographic origins. Nature Ecology and Evolution, 15 May. Doi: 10.1038/s41559-023-02041-9

Sticky hunter

9 May 2023 /

Gorareduvius assassin bug is covered in resin

Gorareduvius assassin bug uses resin to capture prey

A Gorareduvius assassin bug uses resin as a tool to overpower prey. That works fine, as Fernando Soley and Marie Herberstein show.

Assassin bugs prey on insects; they grasp them with their forelegs, stab them with their proboscis and suck them out. Insects that are trapped try to escape, of course, but some species of assassin bugs impede that. They coat their body with sticky resin so that prey items cannot escape so quickly.

One of these resin users is an otherwise poorly known Gorareduvius species. It is successful with its sticky strategy, as Fernando Soley and Marie Herberstein show.

Meticulously applied

Gorareduvius lives in Western Australia, where it resides in hummocks of curly spinifex grass, which produces resin. The assassin bug scrapes resin off the grass leaves and applies it meticulously to its body, particularly onto its forelegs. Every individual does it, a Gorareduvius assassin bug is always sticky.

Soley and Herberstein conducted experiments in which they staged interactions between this assassin bug and two types of fast-moving prey: ants and flies. In some trials the assassin bug was allowed to keep its resin equipment, in other cases the researchers gently removed it.

Equipped with resin, Gorareduvius more successfully captures ants and flies, as it turned out. The prey can still escape, but the resin stops them for a while, giving the assassin bug more chance to stab them. As a result, capture attempts of resin-equipped assassin bugs are more often successful than those of clean assassin bugs.

Tool

The assassin bug family (Reduviidae) contains about 7000 species. Part of these species cover themselves in resin to enhance prey capture, which the researchers consider as tool use. The habit has arisen at least three times independently.

Willy van Strien

Photo: Gorareduvius, an assassin bug; on the forelegs, above the nod, you see small lumps of resin and where the antennae branch you see the large proboscis. ©Fernando Soley

Sources:
Soley, F.G. & M.E. Herberstein, 2023. Assassin bugs enhance prey capture with a sticky resin. Biology Letters 19: 20220608. Doi: 10.1098/rsbl.2022.0608
Zhang, J., C. Weirauch, G. Zhang & D. Forero, 2016. Molecular phylogeny of Harpactorinae and Bactrodinae uncovers complex evolution of sticky trap predation in assassin bugs (Heteroptera: Reduviidae). Cladistics 32: 538-554. Doi: 10.1111/cla.12140

Wet plumage

24 April 2023 /

Namaqua sandgrouse father carries water for the chicks

Male Namaqua sandgrouse fetches water for his chicks with specially adapted belly feathers

As long as the chicks are unable to fly, a Namaqua sandgrouse father will fetch water for them. Jochen Mueller and Lorna Gibson describe the specially adapted belly feathers that enable this.

As their name suggests, sandgrouse species live in dry, almost barren places. The Namaqua sandgrouse (Pterocles namaqua), for example, lives in deserts in Southwest Africa, such as the Kalahari and the Namibian desert. The birds breed up to no less than 30 kilometers from the nearest body of water. Because they mainly eat dry seeds, they have to drink. Adult birds therefore fly to waterholes in the morning and evening. This is how they survive in their arid habitat.

But their chicks can’t go with them to the waterholes for the first month. They are immediately independent after hatching; they walk and forage for food on their own. But they can’t fly yet. It was already known that sandgrouse fathers transport a supply of water for the young in specially adapted belly feathers, which trap and hold water. Now, using various microscopic techniques, Jochen Mueller and Lorna Gibson describe the structure of those feathers in detail, both in wet and dry state.

Fringe

To stock up a supply of water, a Namaqua sandgrouse male steps into the water until it reaches his belly. He fluffs up his belly feathers and rocks his body, soaking the feathers. Then, he presses his belly feathers against his body and leaves. He can store an estimated 25 milliliters of water, 15 percent of his body weight. He flies back at high speed, a trip that can take half an hour. During the flight through dry desert air, some water evaporates, but a lot is still left when he arrives at his nest.

The chicks run up to him and strip the wet feathers with their beaks.

That the belly feathers have a special structure, can already be seen with the naked eye. The feathers have a broad hairy fringe along the side, except at the top. But only under the microscope does the special structure reveal itself completely.

Coiled barbules

A normal bird’s contour feather consists of a shaft on which barbs are implanted, from which barbules branch. These barbules interlock with hooklets and grooves, giving the feather a closed plane. Thanks to the hooklets and grooves, a crumpled feather can be rubbed back into shape.

Under the microscope, the barbs and barbules of the belly feathers of Namaqua sandgrouse males appear to have a different structure. The hairy fringe along the feather is formed by the outer part of the barbs being thin and flexible, and the barbules implanted on the outer part being thin and flexible too.

The inner part of the barbs, where they are attached to the shaft up to just over mid-length, is thicker and stiff. The barbules on this part branch at the upper side, make one helical curl downward and straighten out, running parallel to the barb. The coils of successive barbules intertwine and keep the feather surface closed.

That is how a belly feather looks when it is dry.

Storing water

If such feather gets wet, the picture changes. The barbules on the inner part of the barb uncurl and bend downwards perpendicularly to the feather plane, forming a dense forest of fibers. Due to the so-called capillary force, water is sucked up and held between them.

The fringe of the feather (i.e., the outer parts of the barbs and the barbules that branch from those parts) bends down and inward to the feather shaft, creating a layer to hold the water.

The Namaqua sandgrouse is one of 14 species of sandgrouse (Pterocles), all of which live on arid terrain. In all these species, the males can carry water in their belly feathers, thanks to that unique adaptation of the feather structure.

Willy van Strien

Photo: Pterocles namaqua, male. Bernard DUPONT (Wikimedia Commons, Creative Commons CC BY-SA 2.0)

On YouTube: Namaqua sandgrouse male fetches water for chicks

Sources:
Mueller, J. & L.J. Gibson, 2023. Structure and mechanics of water-holding feathers of Namaqua sandgrouse (Pterocles namaqua). Journal of the Royal Society Interface 20: 20220878. Doi: 10.1098/rsif.2022.0878
Cade, T.J. & G.L. Maclean, 1967. Transport of water by adult sandgrouse to their young. The Condor 69: 323-343. Doi: 10.2307/1366197

Reinforced carton

18 April 2023 /

Crematogaster clariventris grows a fungus that strengthens its nest wall

Crematogaster clariventris grows a fungus that reinforces its nest

Workers of the ant Crematogaster clariventris collect pieces of fresh leaves to grow a fungus, Alain Dejean and colleagues observed. The threads of the fungus reinforce the carton nest of the ants.

Fungus threads as a component of building or insulation material: you hear more and more about it. It is considered to be innovative, but……. ants were ahead of us. Some species strengthen the walls of their nests with fungal hyphae (threads). The African ant Crematogaster clariventris even collects fresh pieces of leaves to feed them to a fungus that forms strong hyphae, Alain Dejean and colleagues discovered.

The ant lives in large colonies, high in trees. On main branches, workers build nests of hard carton, which they make by chewing fibrous plant material, such as hairs (trichomes) or pieces of wood. They add a fungus, with the result that a network of branched fungal hyphae is embedded in the carton walls; the hyphae consist of tubular cells with a sturdy cell wall. The nest wall is a natural composite material.

Fresh leaf

Dejean, who works in Cameroon, noticed that workers of Crematogaster clariventris bring freshly cut pieces of young and nutritious plant leaves whenever a new nest is constructed or a damaged part of a nest is repaired. Other workers add chewed pulp, and the whole hardens into fungus-reinforced carton in a few days. From these observations, the researchers deduce that the ants bring the fresh leaf material as food for the fungus that forms reinforcing hyphae, so that it will grow well in the new nest wall.

After the fungus died, the sturdy hyphae in the nest wall remain intact.

Crematogaster clariventris is not the only ant species to cut off pieces of leaves to grow a fungus. In Central and South America, ant species occur that cut pieces of fresh leaves and carry it to fungus gardens in their underground nests, the leafcutter ants. They grow fungus for food. So, ants also preceded us in agriculture.

Willy van Strien

Photo: Crematogaster clariventris ©Piotr Naskrecki

Source:
Dejean, A., P. Naskrecki, C. Faucher, F. Azémar, M. Tindo, S. Manzi & H. Gryta, 2023. An Old World leaf-cutting, fungus-growing ant: A case of convergent evolution Ecology & Evolution 13: e9904. Doi: 10.1002/ece3.9904

Super white

27 March 2023 /

Woodcock feathers have the whitest white of all birds

Tail feathers of woodcock are brilliant white at the underside

The whitest feathers that exist can be found in the woodcock, which otherwise has an inconspicuous appearance. Jamie Dunning and colleagues investigated how the surprisingly white hue emerges.

An Eurasian woodcock (Scolopax rusticola) is so well camouflaged that it hardly stands out against the forest floor on which it lives. But the tips of its tail feathers are brilliant white on the underside and therefore very visible, even in dim light. No plumage exist with patches that are whiter than those feather tips. Jamie Dunning and colleagues show how that super white hue is brought about by the structure of the tail feathers.

Woodcocks rest during the day, and then it is important not to stand out. Hence their mottled brown plumage. At dawn or dusk, they are active. To show themselves to each other, they raise their short tails or make a courtship flight. Then, the bright white tips on the underside of the tail feathers stand out clearly.

Nanostructure

Those white tail tips are conspicuous at dim light because they reflect much of the scarce light that falls on them. This is possible because of a special structure. A bird’s feather consists of a shaft on which barbs are implanted. The barbs of the super-white feather tips of Eurasian woodcocks are flattened and thickened, and, like the slats of Venetian blinds, they are slanted and overlap. As a result, a maximal amount of light is reflected.

But before the light rays bounce back, they are scattered beneath the surface of the barbs. The barbs have a disordered internal structure of nanofibers and scattered air pockets, which causes incident light rays to change direction frequently and chaotically. This strong so-called diffuse reflection results in a bright white appearance, just as happens in snow.

The barbs are held together by the many Velcro-like barbules that branch from them. These are brownish, but because they are on the upper side of the tail feathers, they do not affect the whiteness of the underside.

The Eurasian woodcock lives in Europe and Asia. There are seven other woodcock species worldwide, all with super white tops at the underside of the tail feathers. Other birds don’t possess such white feather patches, not even species that are closely related to woodcocks, such as common snipe (Gallinago gallinago).

Willy van Strien

Photo: American woodcock, Scolopax minor, with raised tail. Matt Schenck (Wikimedia Commons, Creative Commons CC BY 4.0)

See also: super black feathers also exist

Source:
Dunning, J., A. Patil, L. D’Alba, A.L. Bond, G. Debruyn, A. Dhinojwala, M. Shawkey & L. Jenni, 2023. How woodcocks produce the most brilliant white plumage patches among the birds. Interface 20: 20220920. Doi: 10.1098/rsif.2022.0920

Fairy lantern rediscovered

15 March 2023 /

Unexpectedly, the cheating plant Thismia kobensis still exists

The rediscoverd Kobe fariry lantern is a cheater

It was discovered in 1992 and believed to be extinct because the site where it had been found was destroyed in 1999. But now, it is rediscovered elsewhere: the Kobe fairy lantern. Kenji Suetsugu and colleagues describe the beautiful but cheating tiny plant.

You would hardly recognize them as plants, the small, splendid ‘fairy lanterns’ on the forest floor, often hidden under fallen tree leaves. Fairy lanterns, Thismia species, are indeed remarkable plants. What you see are the flowers, less than a centimeter in size. The plants have no green leaves, only some scales on the very short stem. Most of the plants lives underground.

There are about 90 species, one of which is Thismia kobensis, the Kobe fairy lantern. Small and inconspicuous as it is, it was only discovered in 1992, in an oak forest near the Japanese city of Kobe. The find was small: it consisted of no more than one specimen. The site was destroyed in 1999 when an industrial complex was constructed, and the newly discovered species went extinct. That was what people thought. But fairy tales exist: in 2021 biologists unexpectedly rediscovered the plant on a conifer plantation in the town of Sanda, 30 kilometers from the original site. And this time the find was larger: almost 20 individuals. Now, Kenji Suetsugu and colleagues provide a scientific description of the species.

The loveliness of its flower is deceptive: Thismia kobensis belongs to a group of cheating plants.

Energy requirement

The cheating has to do with the lack of green leaves.

The green leaves of normal plants contain many chloroplasts. In these cellular organelles, photosynthesis takes place: plants extract carbon dioxide from the atmosphere and with the help of sunlight they fix the carbon in carbohydrates such as sugars and starch. From these carbohydrates, they derive energy. Plants without green leaves cannot make carbohydrates, but they do need energy.

Many of these plants solve this problem by extracting sugars with their roots from fungi in the soil. The scientific term for this is mycoheterotrophy.

Fairy lantern is sugar thief

Most mycoheterotrophic plants target fungi that live in a mutualistic relationship with green plants. The fungi get sugars from these plants. In return, the fungi help the green plants to absorb water and nutrients such as nitrogen and phosphorus from the soil. This collaboration, called mycorrhiza, is mutually beneficial and both parties are honest.

However, when mycoheterotrophic plants such as Thismia make contact with mycorrhizal fungi, they don’t cooperate in this way. They do receive water and nutrients, but they do not return sugars. They can’t. Instead, they take up sugars from the fungus in addition to water and nutrients. In other words: they steal. The fungus had received those sugars from green plants, so mycoheterotrophic plants indirectly parasitize on green plants via mycorrhizal fungi.

Difficult alternative

There are about 500 species of mycoheterotrophic plants. They live on nutrient-poor soils in forests, where little sunlight reaches the soil and the ability for photosynthesis, i.e., sugar production, is limited. Sugar theft is the alternative that these plants developed.

sarcodes sanguinea is a myceheterotrophic plantBut it’s not as easy as it seems. It is difficult for a mycoheterotrophic plant to form a relationship with a mycorrhizal fungus. Where a green plant interacts with many mycorrhizal fungi species simultaneously, a mycoheterotrophic plant can make contact with only one or a few fungal species. That’s probably because most fungi detect the cheaters and hold off on the relationship. Therefore, mycoheterotrophic plants are always rare and never widely distributed.

Mycoheterotrophic species often target a fungus that has many different green partners. With so many suppliers, the sugar supply is always guaranteed.

Dust seeds

The vast majority of land plants live in association with mycorrhizal fungi. The mycoheterotrophic mode of life -which abuses this mutualism – has developed dozens of times. In the case of fairy lanterns, this happened many millions of years ago. That is why they have little resemblance to ordinary plants. Other mycoheterotrophic plants emerged much more recently and have a more normal appearance.

the brid's nest is a mycoheterotrophic orchidSome plants are mycoheterotrophic shortly after germination only; this applies to all orchid species. The seeds are as fine as dust and contain no food. After germination, these plants get their sugars from fungi until they have leaves and can make their own sugars. This could be a first step towards a fully mycoheterotrophic lifestyle. There are also orchid species that stay mycoheterotrophic during their whole life, for example the bird’s nest, Neottia nidus-avis.

Broomrape species (Orobanche) look similar to some mycoheterotrophic plants, but are different: with their roots, they parasitize directly on other plants.

Willy van Strien

Photos:
Large:
Fairy lantern of Kobe, Thismia kobensis ©Kenji Suetsugu
Small:
Snow plant, Sarcodes sanguinea, a mycoheterotrophic plant from North-west America. David῀O (Wikimedia Commons, Creative Commons CC BY 2.0)
Bird’s nest orchid, Neottia nidus-avis. BerndH (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Sources:
Suetsugu, K., K. Yamana & H. Okada, 2023. Rediscovery of the presumably extinct fairy lantern Thismia kobensis (Thismiaceae) in Hyogo Prefecture, Japan, with discussions on its taxonomy, evolutionary history, and conservation. Phytotaxa 585: 102-112. Doi: 10.11646/phytotaxa.585.2.2
Gomes, S.I.F., M.A. Fortuna, J. Bascompte & V.S.F.T. Merckx, 2022. Mycoheterotrophic plants preferentially target arbuscular mycorrhizal fungi that are highly connected to autotrophic plants. New Phytologist 235: 2034-2045. Doi: 10.1111/nph.18310
Jacquemyn, H. & V.S.F.T. Merckx, 2019. Mycorrhizal symbioses and the evolution of trophic modes in plants. Journal of Ecology 107: 1567-1581. Doi: 10.1111/1365-2745.13165
Gomes, S.I.F., J. Aguirre-Gutiérrez, M.I. Bidartondo & V.S.F.T. Merckx, 2017. Arbuscular mycorrhizal interactions of mycoheterotrophic Thismia are more specialized than in autotrophic plants. New Phytologist 213: 1418-1427. Doi: 10.1111/nph.14249

Cleaning ants are successful

14 February 2023 /

Metarhizium fungus makes fewer victims

Argentine ant removes sporen of Metarhizium fungus

Ants defend themselves against disease-causing Metarhizium fungus by grooming off fungal spores from each other. Prolonged exposure to that cleaning behaviour makes the fungus less deadly, Miriam Stock and colleagues show.

Metarhizium fungus can quickly spread throughout an ant nest because the ants easily infect each other with fungal spores. But the animals take action to inhibit the pathogen. That does not leave the fungus unaffected, Miriam Stock and colleagues show with experiments.

To counteract the fungus, ants can disinfect nest and brood (eggs, larvae and pupae) with a mixture of formic acid, which they produce in a poison gland, and tree resin. In addition, a sick ant stays away from the brood and spends more and more time outside the nest so as not to endanger its nest-mates. And the animals keep each other clean. If spores of the fungus land on an ant, her nest-mates either groom off the spores, risking infection themselves, or spray them with formic acid.

New spores

These caring nest-mates should act quickly. The spores attach on the affected ant and germinate, after which nothing can be done anymore. The fungus penetrates the body to develop, eventually killing the ant. Then the fungus appears on the cadaver forming spores that make new victims in the next infection cycle.

Conducting experiments with the Argentine ant, Linepithema humile, Stock shows that timely care does indeed help; the presence of other ants reduces the chance that an ant dies after contact with fungal spores.

But, as it turns out, cleaning also causes changes in the fungus.

Metarhizium-fungus adapts

The trials consisted of series in which the Metarhizium fungus passed repeatedly via spores from a dead ant to a new victim. In half of these series, the infected ant was held isolated, in the other half she was accompanied by two nest-mates that could remove the fungal spores. Conducting a final test after ten infection cycles, the researchers allowed the fungus to infect either an isolated ant or an ant with company.

In the final test, fungal lines that had grown on isolated ants caused a lot of mortality among newly infected ants when they did not receive care from others. But fungal lines that had infected ants that were in company of other ants – that could groom them -, had changed. They formed twice as many spores, but nevertheless made fewer victims among ants they came into contact with, even if there were no nest-mates around to help. These fungal lines had become less deadly.

Essential component

And there was something else: the spores of those ‘social fungal lines’ were less well detected and removed by the ants. The researchers discovered that these spores produced less ergosterol; this is a compound that occurs in all fungi and that, apparently, arouses the ants. So, the ‘social fungus lines’ evade defence by the ants.

But this comes at a cost. Ergosterol is an essential component of the spore membrane. The fact that the ‘social lines’ have lower levels of this important component probably explains why they are less deadly.

So, grooming each other to remove Metarhizium fungus spores as ants do is useful in two ways. It works immediately if ants quickly remove spores from a nest-mate, saving her from death. And in the longer term, it makes the fungus less dangerous.

Willy van Strien

Photo: Argentine ants exchanging food. Davefoc (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

See also: ants disinfect their nest with a mixture of resin and formic acid

Sources:
Stock, M., B. Milutinović, M. Hoenigsberger, A.V. Grasse, F. Wiesenhofer, N. Kampleitner, M. Narasimhan, T. Schmitt & S. Cremer, 2023. Pathogen evasion of social immunity. Nature Ecology & Evolution, online February 2. Doi: 10.1038/s41559-023-01981-6
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 7: 2249-2254. Doi: 10.1002/ece3.2834
Bos, N., T. Lefèvre, A.B. Jensen & P. D’Ettore, 2012. Sick ants become unsociable. Journal of Evolutionary Biology 25: 342-351. Doi: 10.1111/j.1420-9101.2011.02425.x
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

Red blood cells hided

16 January 2023 /

Glass frog is more translucent when sleeping

Fleischmann's glass frog is extra translucent when sleeping.

A sleeping Fleischmann’s glass frog can hardly be seen. Red blood cells, which would make the animal visible, are stored away temporarily, Carlos Taboada and colleagues write.

Fleischmann’s glass frog has transparent muscles and a transparent ventral skin that transmit light, rendering heart and intestines visible from below. The skin of its back contains a little green pigment. With these qualities, the animal is translucent: a form of camouflage. But red blood cells – which do not transmit the light, but reflect red light and absorb other colours – can spoil the effect.

Carlos Taboada and colleagues show that the frog has a way to solve this problem: when it sleeps, it removes almost all red blood cells from the bloodstream.

Sleep during daytime

Glass frogs belong to the few translucent land animals that exist. Fleischmann’s glass frog, Hyalinobatrachium fleischmanni, is one of them. The animal, which grows up to three centimetres in length, is found in rainforests in Central and South America. Adult frogs live on land. They are active at night and sleep during daytime, hanging upside down under a leaf. The less they stand out against the leaf when sleeping, the harder it is for predators, mainly birds, to spot them.

It is helpfull that the glass frog is translucet. And by removing almost all red blood cells, about 90 percent, from circulation, a sleeping glass makes itself extra translucent. It hides the red blood cells in the liver, which expands considerably as a result. So, the glass frog is more difficult to detect while resting, when it cannot be alert. As soon as the animal resumes activity, the blood cells go back into the bloodstream and translucency diminishes.

Oxygen

Red blood cells are red because they contain the pigment haemoglobin, a protein that binds oxygen; red blood cells carry oxygen to all other cells. During sleep, therefore, the cells receive no oxygen. Apparently, they are able to coop with that.

Willy van Strien

Photo: Fleischmann’s glass frog. Esteban Alzate (Wikimedia Commons, Creative Commons CC BY-SA 2.5)

Sources:
Taboada, C., J. Delia, M. Chen, C. Ma, X. Peng, X. Zhu, L. Jiang, T. Vu, Q. Zhou, J. Yao, L. O’Connell & S. Johnsen, 2022. Glassfrogs conceal blood in their liver to maintain transparency. Science 378: 1315-1320. Doi: 10.1126/science.abl662
Cruz, N.M. & R.M. White, 2022.  Lessons on transparency from the glassfrog. Transparency in glassfrogs has potential implications for human blood clotting. Science 378: 1272-1273. Doi: 10.1126/science.adf75
Barnett, J.B., C. Michalis, H.M. Anderson, B.L. McEwen, J. Yeager, J.N. Pruitt, N.E. Scott-Samuel & I.C. Cuthill, 2020. Imperfect transparency and camouflage in glass frogs. PNAS 117: 12885-12890. Doi: 10.1073/pnas.1919417117

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