From so simple a beginning

Evolution and Biodiversity

Shell with windows

10 December 2024 / / 0 Comments

Heart cockle accommodates algae that require light

Shell of heart cockle Corculum cardissa has many tiny windows

The shells of heart cockles (Corculum cardissa) have many transparent windows on their sun-facing side for the benefit of resident algae. The windows have a special structure, Dakota McCoy and colleagues show.

Shells need to be hard and sturdy to protect the mollusk inside. It is a simple function and usually there is nothing special about a shell, apart from the diversity in shapes and colours. But the shells of heart cockles (Corculum cardissa and other species) are remarkable: they contain a large number of transparent windows, orderly arranged. They are there for a reason: they transmit sunlight to the unicellular algae that live within the mollusk. Dakota McCoy and colleagues investigated shape and function of the windows.

But why are algae living in shellfish in the first place?

Algae, like plants, are able to capture carbon dioxide from air to synthesize sugars with the use of sunlight in a process called photosynthesis; the sugars are the basis for energy and building materials. The nutrients that algae and plants need are chemical elements such as nitrogen, phosphorus, and calcium, which they incorporate into complex carbon compounds such as proteins and DNA, carrier of genetic information. Animals are dependent on photosynthesis; they must feed to obtain energy and building materials. Or…..

…. they can accommodate algae, so that they have sugars at their immediate disposal and do not have to feed.

Tiny windows

Some bivalves use this alternative opportunistically. And there are two groups that can only live with algae: the giant clams (Tridacninae, including the large Tridacna gigas) and many heart cockles (Fraginae). They house unicellular algae in fine branches of their intestinal tract. The algae provide sugars in exchange for a safe living place and probably also nutrients.

A prerequisite for successful cooperation is that the algae have access to sunlight. The hosts, which are partially buried, must ensure this. They live in shallow water, where sunlight penetrates to the bottom. Giant clams often keep their shells open, so that the animal is bathed in sunlight. Heart cockles have a different solution. Their shells remain closed, but the algae receive light through minuscule windows in the sun-facing side of the shells.

The researchers wanted to know more about the structure of these windows and examined those of the heart cockle Corculum cardissa.

Optic fibres

The shells of Corculum cardissa consist of aragonite, a calcium compound (calcium carbonate, CaCO3) that forms planar crystals that are crossed in orientation.

The windows have a different microstructure: here, the aragonite forms fibres instead of planar crystals. Each window is a bundle of cables consisting of parallel aragonite fibres that runs perpendicular to the shell surface. The cables transmit light, just like glass fibre cables. Fibre optic cables are exceedingly rare in nature, and cable bundles have never been found before.

Experiments show that the sun-facing shell sides – the windowed sides – transmit colours of sunlight that are important for photosynthesis; on average 31 percent of these colours passes through. In contrast, for ultraviolet light, which is harmful to animal tissue and algae, this percentage is only 14. The sand-facing shell sides transmit hardly any light.

Some individuals have a microlens beneath each window, also consisting of aragonite, which condenses the incoming light and focuses it deeper in the tissue, where the algae are. That completes the design.

You wouldn’t make it up: shells with windows. But it exists.

Willy van Strien

Photo: the sun-facing side of heart cockle Corculum cardissa. Ria Tan, Wildsingapore, via Flickr. Creative Commons: CC BY-NC-ND 2.0

Sources:
McCoy, D.E., D.H. Burns, E. Klopfer, L.K. Herndon, B. Ogunlade, J.A. Dionne & S. Johnsen, 2024. Heart cockle shells transmit sunlight to photosymbiotic algae using bundled fiber optic cables and condensing lenses. Nature Communications 15: 9445. Doi: 10.1038/s41467-024-53110-x
Kirkendale, L. & G. Paulay, 2024. Photosymbiosis in Bivalvia. Treatise Online no. 89: Part N, Revised, Volume 1, Chapter 9. Doi: 10.17161/to.v0i0.6568

Smart building

1 December 2024 / / 0 Comments

Nest mound of Globitermes sulphureus provides a stable indoor climate

Queen of Globitermes sulphureus in a nest that always has an agreeable high humidity level.

Periods of severe drought, periods of heavy rain: a nest mound of the termite Globitermes sulphureus withstands it all. That is thanks to its three-layered structure, Chun-I Chiu and colleagues show.

The savannahs of Thailand are bone dry in winter while the wet summer season brings an extreme amount of rain: a challenging climate. But the termite Globitermes sulphureus prospers, thanks to nest mounds that protect the colonies in the underground nests beneath them. The mounds persist, the animals neither desiccate nor drown, but always enjoy a pleasantly high humidity level in their nest. This has to do with a clever piece of architecture, Chun-I Chiu and colleagues conclude from various measurements.

Like ants, termites live in large colonies, but they are not related to ants; they are related to cockroaches. A termite colony has a king and queen that produce offspring, and workers and soldiers of both male and female sexes. The queen, that has to produce a huge amount of eggs, is much larger than the other termites.

Stability

The mound above a nest of Globitermes sulphureus may look a little plump, but it is a complex structure. It consists of three layers each of which contributes in its own way to the stability of the mound and to the favourable internal climate in the nest.

The thin outer layer consists of plate-like elements of hard material. The animals make it from sand or soil particles, hence it has the same colour as the soil on which it stands. This layer prevents moisture from escaping from the nest, which is very important during dry periods. Underneath this layer, there is a thicker middle layer of irregularly shaped, stuck-together pieces with cavities in between that are also made of soil particles. This layer is waterproof and can withstand pressure, for example when raindrops hit it. It makes the mound robust.

The inside of the mound, the third layer, clearly differs from the outer layer and the middle layer. It is filled with rounded, smooth pellets in which a lot of fibrous organic material is incorporated, such as cellulose from plant remains. This layer is redder in colour than the other two, and it is the most porous one. Like a sponge, it absorbs water vapour that the termites exhale, holds it and releases it at a low rate. This layer forms a water reservoir with which humidity can be maintained at a high level.

Repair

Has the mound to be repaired after damage, the termites work from the outside inwards. Within a few hours, they are fixing the outer layer, after weeks the outer layer and middle layer are ready. The repair of the inner layer takes more time. The researchers think that this is because the animals must collect material that is less easy to find.

Willy van Strien

Photo: Queen of Globitermes sulphureus in nest. © Chun-I Chiu

Source:
Chiu, C-I., K. Attasopa, S. Wongkoon, Y. Chromkaew, H. Liao, K-C. Kuan, P. Suttiprapan, I. Guswenrivo, H-F. Li & Y. Sripontan, 2024. Three‐layered functionally specialized nest structures enhance strength and water retention in mounds of Globitermes sulphureus (Blattodea: Termitidae). Environmental Entomology, online 9 October. Doi: 10.1093/ee/nvae093

The evolution of ant agriculture

29 October 2024 /

The first fungus gardens, adaptations, and innovations

Ant agriculture: Cyphomyrmex species that cultures a yeast

Ted Schultz and colleagues link the emergence of ant farming to an asteroid impact and the domestication of the fungal crop to a period of strong climate change.

You can forage for food, but you can also grow it to make sure it is available. About 250 species of ants from South, Central, and North America do the latter, growing a fungus in their nests for food. The evolutionary history of this ant-fungus relationship was largely known. Now, Ted Schultz and colleagues compare the evolutionary tree of fungus-growing ants with that of cultivated fungus varieties and refine the picture.

It is fascinating how they link the history of ant farming to two major events on Earth.

Pioneers

The fungus-growing ants have a common ancestor that started agriculture. This happened 66 million years ago in wet tropical forests of South America. Shortly before that, an asteroid had hit Chicxulub in Mexico with enormous consequences. Dust in the atmosphere blocked sunlight for months, plants died and many species of plants and animals, including dinosaurs, became extinct.

But fungi that live on dead material, such as fallen leaves, flourished, and some ants took advantage of this. They could not digest organic material themselves, but they allowed a mushroom-like fungus that could do the job to grow in their nest by providing it with detritus. The fungus broke down the material, and the ants consumed breakdown products as well as fungus. All 250 species of ants that currently have a fungus garden in their nest descend from these pioneers.

Soon, ants picked up a second mushroom-like fungus. Virtually all cultivated fungus varieties today – and there are several hundred of them – descend from these two early crops.

Domestication

From the beginning, the farming ants could not do without their crops; they would starve. But conversely, the fungi did not need the ants. They also lived outside ant nests, and fungal crops exchanged genetic material with their wild relatives. Outside they formed mushrooms, within ant nests the ants prevented this and only allowed fungal threads to grow. This is known as lower ant agriculture. Today, roughly a hundred species of ants exist that practice lower farming, with many semi-wild fungal varieties.

But it did not stop there. At some point, there were ants that domesticated their crop. That means that the cultivated fungus became dependent on the grower and can no longer live in the wild. And it produces nutrient-rich food bodies especially for the ants, the so-called gongylidia. These ants and their fungi are inseparable, and a young queen that wants to establish her own colony does not leave the maternal nest without a piece of fungus garden between her jaws. This is called higher ant agriculture.

This agricultural transition only occurred when lower ant agriculture had already existed for 36 million years, now about 27 million years ago. Why didn’t it happen earlier, and why did it suddenly happen then?

Global cooling

The researchers point at the so-called Terminal Eocene Event 33.5 million years ago that preceded the transition. The Earth cooled down rapidly and many species became extinct, although the extinction was not as massive as 66 million years ago. In South America, part of the wet tropical forests made way for landscapes that were seasonally dry, such as savannas.

Some of the fungus-farming ants moved to drier areas. The fungi in their nests retained the same growing conditions, but they lost contact with wild relatives, which lived in wet forests only. Because the cultivated fungi no longer exchanged genetic material with their wild relatives, the ants could select freely for characteristics that were beneficial to themselves, and not necessarily to the fungus. And so, a domesticated crop developed.

Innovation

Finally, 18 million years ago, a new form of higher ant farming appeared: there were fungus growers that started to provide their gardens with pieces of fresh leaves instead of leaf litter. These leaf-cutter ants form complex colonies of millions of individuals; they manage to keep their gardens in perfect order. They all grow the same fungus species, Leucoagaricus gongylophorus, a descendant of the very first fungus with which ant farming ever started.

Schultz does not mention whether there was a special reason for these ants to switch to fresh leaves as a substrate for their fungus. There are now more than fifty species of leaf-cutter ants.

Alternative agriculture

Two other agricultural systems branched off from lower ant agriculture. About 30 million years ago, a group of ants switched to growing fungi in unicellular form – that is: a yeast – instead of in multicellular thread form (there are unicellular and multicellular fungi). This is remarkable, because the mushroom-like fungi of which the cultivated crops are derived grow exclusively in multicellular form. Even the fungi cultivated as yeast never occur in yeast form in the wild.

And 21 million years ago, another group of fungus growers exchanged the usual mushroom-like fungi (from the family Agaricaceae) for coral fungus species (from the family Pterulaceae), which do not break down leaf litter, but wood.

Would there be a reason for these two shifts also? It would be great if a reason was found.

Willy van Strien

Photo: Cyphomyrmex ant species that cultures yeast. ©Alex Wild

See also: leaf cutter ants supply their crop with food according to demand

Sources:
Schultz, T.R., J. Sosa-Calvo, M.P. Kweskin, M.W. Lloyd, B. Dentinger, P.W. Kooij, E.C. Vellinga, S.A. Rehner, A. Rodrigues, Q.V. Montoya, H. Fernández-Marín, A. Ješovnik, T. Niskanen, K. Liimatainen, C.A. Leal-Dutra, S.E. Solomon, N.M. Gerardo, C. R. Currie, M. Bacci, Jr., H.L. Vasconcelos, C. Rabeling, B.C. Faircloth & V.P. Doyle, 2024. The coevolution of fungus-ant agriculture. Science 386: 105-110. Doi: 10.1126/science.adn7179
Branstetter, M.G., A. Ješovnik, J. Sosa-Calvo, M.W. Lloyd, B.C. Faircloth, S.G. Brady & T.R. Schultz, 2017. Dry habitats were crucibles of domestication in the evolution of agriculture in ants. Proceedings of the Royal Society B 284: 20170095. Doi: 10.1098/rspb.2017.0095
De Fine Licht, H.H., J.J. Boomsma & A. Tunlid, 2014. Symbiotic adaptation in the fungal cultivar of leaf-cutting ants. Nature Communications 5, 5675. Doi: 10.1038/ncomms6675
Schultz, T.R. & S.G. Brady, 2008. Major evolutionary transitions in ant agriculture. PNAS 105: 5435-5440. Doi: 10.1073_pnas.0711024105
Villesen, P., U.G. Mueller, T.R. Schultz, R.M.M. Adams & A.C. Bouck, 2004. Evolution of ant-cultivar specialization and cultivar switching in Apterostigma fungus-growing ants. Evolution 58: 2252–2265. Doi: 10.1111/j.0014-3820.2004.tb01601.x

Fruit abundance

10 October 2024 /

White-bearded manakin with rich territory is more successful

White-bearded manakin with rich territorium spends much time to display

A territory with plenty of food is a valuable asset for a male white-bearded manakin. The easier he finds food, the more time he spends on courtship display and the more females will visit him, as Luke Anderson and colleagues show.

In the white-bearded manakin, Manacus manacus, males contribute nothing to the care of the offspring. They occupy a territory in the vicinity of two to dozens of other males and try to attract as many females as possible and seduce them to mate. Females do the rest: after they have selected a male and copulated, they build a nest without help, incubate the eggs and raise the young.

Males with a territory that is rich in the fruits that they eat receive more female visits than males in a place with less food, Luke Anderson and colleagues discovered.

Costly courtship display

The white-bearded manakin, a small songbird, lives in forests in tropical South America. Like in many of the other 55 manakin species, the black-and-white males display spectacular courtship behaviour to attract females during the breeding season. Some males are much more successful than others.

A male possesses a territory in which he has cleared a court – a piece of ground of 15 to 90 centimetres in diameter, surrounded by saplings – down to the bare soil. Clean ground is safe, because a dangerous snake is perceived immediately. Moreover, the male stands out with his show. He puffs out his beard feathers, utters his call and leaps up and down between stems and the ground at lightning speed, his wings snapping and whirring. He can sustain this energetically costly show for up to half a minute at a time.

The olive-green females do best to choose a male of good genetic quality, to maximize the chance to produce successful offspring. An important criterium by which females can judge the quality of males is their courtship performance. The more intense the courtship is, the stronger and healthier the performer will be.

Uneven playing field

But now, Anderson writes that some white-bearded manakin males have an advantage by possessing a rich territory. The birds eat mainly ripe fruits, and territories differ greatly in fruit availability, his research in Ecuador shows. Males with a rich territory have to spend hardly time looking for food and are in good condition, he assumed. And indeed, as camera observations showed: the richer a territory was, the more time its owner spent on his shows.

And the more time a male spent displaying, the higher the frequency of female visits, thus the more reproductive success he had.

So, the displaying males are rivals on an uneven playing field; males with a rich territory are at an advantage. Is courtship performance then an honest signal of their quality?

Competition

It would be an dishonest signal if it is a coincidence whether a white-bearded manakin male occupies a rich territory, his quality having nothing to do with it.

But probably, the males have to compete for the best place, and the highest quality male will obtain the richest territory where he can spend much time on courtship display. In this case, the courtship performance is an honest signal for females to assess male quality.

The birds deposit the seeds of the fruits they eat back into their territory. In this way, places with fruiting plants will continue to exist. Males are long-living and can occupy the same territory for up to eleven years. 

Willy van Strien

Photo: White-bearded manakin male. Félix Uribe (Wikimedia Commons, Creative Commons CC BY -SA 2.0)

Watch a video of a displaying white-bearded manakin male on You Tube

Sources:
Anderson, H.L., J. Cabo & J. Karubian, 2024. Fruit resources shape sexual selection processes in a lek mating system. Biology Letters 20: 20240284. Doi: 10.1098/rsbl.2024.0284
Cestari, C. & M.A. Pizo, 2014. Court cleaning behavior of the white-bearded manakin (Manacus manacus) and a test of the anti-predation hypothesis. The Wilson Journal of Ornithology, 126: 98-104. Doi: 10.1676/13-032.1

Parasol

26 September 2024 /

Male desert locust protects female from sun

Desert locust is heat tolerant

A female desert locust spends more than two hours to lay a batch of eggs in the hot sand of the Sahara. Usually, a male is sitting on her back, acting as a sunshade, Koutaro Ould Maeno and colleagues write.

Desert locust females produce about a hundred eggs at a time. They drill their abdomens into the sand and then sit still for more than two hours on average while the eggs leave her body. If they do the job during daytime, they must endure the scorching heat. How does the insect cope with that, Koutaro Ould Maeno and colleagues wondered.

They studied the behaviour of desert locusts, Schistocerca gregaria, in Mauritania during the so-called gregarious phase, when the animals live in groups. Males gather at leks during the day to attract females and copulate.

Possessive behaviour

With a guarding male on her back, an ovipositing female stays cooler

After mating, a female stores the sperm; one mating provides enough sperm for several egg-laying sessions. A male invests a lot in mating, as it takes him hours. To ensure that she actually uses his sperm, he usually continues to guard her until she has laid eggs, keeping rivals away. This possessive behaviour limits her freedom to choose another partner, but in return she is not harassed by other males.

And it turns out to have still another advantage.

Most females lay their eggs at night, but some wait until the next morning. They avoid predators that are active during the cool night. But another danger is looming: it gets dangerously hot. Desert locusts can withstand much heat, but a temperature of 55°C or more is fatal, and it can get that hot in the sun. This is where the guard helps. When a female lays eggs, he sits on her back and functions nicely as a parasol, the researchers write.

Probably, this is also the case in a mating couple.

Cooler

Females that oviposit during the day cool down a bit because their abdomen extends into the ground; it is less hot there than at the surface. In addition, the researchers now show that an egg-laying female with a male on her back is cooler than a female without a guard. She is also cooler than the sand.

The guard himself also gets less hot than the sand because he is at a greater distance from the ground. When males attract females at a lek, they stand as high on their legs as possible to avoid overheating. In addition, the animals position themselves in such a way that they catch a minimum of solar radiation.

Desert locusts can live gregariously; then they gather, multiply rapidly and can become a plague that eats almost everything that is green, moving fast and far. But in dry periods they are solitary and occur in small numbers; the animals then live longer.

Willy van Strien

Photos:
Large: mating couple of desert locust. Adam Matan (Wikimedia Commons, Creative Commons CC BY-SA 3.0)
Small: ovipositing desert locust female without guarding male. Christiaan Kooyman (Wikimedia Commons, Creative Commons, public domain)

Sources:
Maeno, K.O., S. Ould Ely, S.A. Ould Mohamed, M.E.H. Jaavar, A.S. Benahi & M.A. Ould Babah Ebbe, 2024. Mate-guarding male desert locusts act as parasol for ovipositing females in an extremely hot desert environment. Ecology e4416, online 15 September. Doi: 10.1002/ecy.4416
Maeno, K.O., S. Ould Ely, S.A. Ould Mohamed, M.E.H. Jaavar & M.A. Ould Babah Ebbe, 2023. Thermoregulatory behavior of lekking male desert locusts, Schistocerca gregaria, in the Sahara Desert. Journal of Thermal Biology 112: 103466. Doi: 10.1016/j.jtherbio.2023.103466

Amputation saves ant lives

9 July 2024 /

Florida carpenter ant workers treat leg wounds effectively

Workers of Florida carpenter ant amputate legs when useful

Injured leg? In the Florida carpenter ant, Camponotus floridanus, nestmates treat the patient to prevent lethal infections. If it is useful, they amputate the leg, Erik Frank and colleagues write.

With a wound on a leg, a worker of the Florida carpenter ant, Camponotus floridanus, would have only a small chance to survive if it were not for her nest mates that come to the rescue. To prevent infection, they lick the wound clean and often amputate the leg, significantly increasing the survival chance, Erik Frank and colleagues show. This care is frequently needed because colonies of this ant species fight each other intensively.

The researchers tested the ants’ medical skills by making a small cut in the leg of workers. They then injected a saline solution containing a deadly bacterium, Pseudomonas aeruginosa, into the wound. Infected ants were placed either in isolation or in a nest where two hundred workers were available.

Bitten off

Most of the ants that sat alone after infection succumbed to the injuries. But when placed in a nest, most ants did survive thanks to the care of nest mates. What care they provided turned out to depend on where the wound was.

If the infected wound was on the upper leg, usually one of the nest mates intervened drastically and bit off the leg at the top. If the wound was on the lower leg, this did not happen; instead, workers licked the wound thoroughly clean. In both cases, helpers chose the treatment that was most effective, as became clear in experiments with infected wounds in which the researchers amputated the affected leg.

Bacterial load

If they amputated a leg of an ant with a wound on the upper part, then her chance to survive was as high as it was in the case of amputation by nestmates. But if they removed a leg with an injury on the lower part, it did not help: most patients died. The treatment that the ants apply in that case, extensive cleaning, is much more effective.

Why is amputation only helpful for an infection in the upper leg?

Whether an ant will survive an infection depends on how quickly the bacteria are able to spread through the body: the higher the bacterial load, the higher the mortality. The bacteria spread via the hemolymph, the insect version of blood, which flows through the legs in channels.

In the upper leg, these channels are narrower than in the lower leg, so that bacteria are less likely to enter the hemolymph. Also, the upper leg has much more muscle mass than the lower leg, and blood is pumped around by muscle movements. If the upper leg is affected, circulation is slowed down much more than if the lower leg is affected, impeding the spread of bacteria.

Time enough

Consequently, when the upper leg is affected, ants have enough time to perform an amputation, which takes forty minutes at least, before the bacteria have spread. But timely amputation is unfeasible with an infection in the lower leg. Then cleaning is the best way to help a victim.

The ants also amputated the leg if the researchers injured the upper leg but injected a sterile saline solution instead of a solution with bacteria. That makes sense, because under natural conditions, in the ants’ nest, such a wound is most likely to become infected. The workers err on the side of caution.

The Florida carpenter ant is the only animal species known to apply amputation to treat conspecifics in case of injury.

The researchers previously discovered that also workers of the Matabele ant from Africa, Megaponera analis, treat infected wounds of nestmates. They do so by administering antibiotics from glands on their backs that produce a mix of antimicrobial substances. The Florida carpenter ant does not have such a built-in pharmacy. For this ant, cleaning and amputation are good alternatives.

Willy van Strien

Illustration: ©Hanna Haring

See also: the Matabele ant fights infections with self-made antibiotics

Source:
Frank, E.T., D. Buffat, J. Liberti, L. Aibekova, E.P. Economo & L. Keller, 2024. Wound-dependent leg amputations to combat infections in an ant society. Current Biology, 2 July online. Doi: 10.1016/j.cub.2024.06.021

Successful in the deep sea

11 June 2024 /

Bizarre deep-sea anglerfishes thrive in challenging environment

Deep-sea anglerfishes flourished thanks to sexual parasitism

Deep-sea anglerfishes are a large group of animals with bizarre reproduction modes that live in the inhospitable deep sea. Chase Brownstein and colleagues outline the evolutionary history of this group.

The pitch-dark, oxygen-lacking, cold, almost empty deep sea is a difficult environment to live in. But the common ancestor of deep-sea anglerfishes moved into this environment and the fish became highly successful from an evolutionary perspective: there are about 170 species. Chase Brownstein and colleagues describe how this animal group arised and flourished.

Deep-sea anglerfishes (Ceratioidea) may be the strangest animals around. Females are clumsy animals that can barely swim. They lure their prey with a ‘fishing rod’ growing from their heads with a luminous end. Males are much smaller than females and do not eat anything at all. They swim around looking for a mate. Upon finding a female, a male attaches onto her abdomen with his teeth and when she lays eggs, he fertilizes them. In some species, this biting results in a fusion, in which the male turns into a sperm-supplying appendage to his partner, deriving nutrition from her through a shared circulatory system: sexual parasitism.

It was this bizarre and unique method of reproduction that enabled colonization of the deep sea.

Sex guaranteed

The deep-sea anglerfishes are part of the order of the anglerfishes (Lophiiformes). Their closest relatives live on seafloors, where they lie still or ‘walk’ on their pelvic fins. About 50 million years ago, the ancestor of the deep-sea anglerfishes split from such bottom dwellers and moved to the open deep sea. This happened at a time when the Earth was warmer normal, and many species in oceans went extinct. Perhaps the seafloor became less suitable as a place to live. In any case, the deep sea was a new environment where deep-sea anglerfishes underwent a period of rapid specialization and speciation.

A major problem in the deep sea is reproduction. Because there is little life, fish live in low densities. The chance of encountering a mate is small, and the chance that two conspecifics will meet each other when both are ready to reproduce is extremely small. Here, the unique method of reproduction in deep-sea anglerfishes was helpful. The researchers think that they practiced sexual parasitism from the beginning. As a result, a male only once had to find a female and it did not matter when he met her. Because he attached and did not let go, the two were assured of sex: he was ready to deliver his sperm as soon as she could lay eggs.

This is still the case in many species, but other species arose in which the male attaches to a female only temporarily.

Fortunate combination

Sexual parasitism, with dwarf males attached as sperm sacs, does not otherwise occur in vertebrates. How did it arise in deep-sea angler fishes? The researchers point to two developments that were taking place. First, there was a trend for male anglerfish to be smaller than females. Second, anglerfishes reduced their immune system, especially the acquired part, which builds up protection against specific pathogens or parasites that it has been exposed to. How these fishes do defend themselves against diseases is still unknown.

The deep-sea anglerfishes took both trends to the extreme: males are no larger than necessary to swim to a mate and produce sperm. And the acquired immune system has largely been dismantled, so that males can parasitize on females without any problems.

So, it was a fortunate combination of circumstances and characteristics that drove the deep-sea anglerfishes to the challenging deep sea and made them successful.

Willy van Strien

Photo: Female Humpback anglerfish (Melanocetus johnsonii), which belongs to deep-sea anglerfish. Fernando Losada Rodríguez (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

More about tiny deep-sea anglerfish males that parasitize on females

Source:
Brownstein, C.D., K.L. Zapfe, S. Lott, R. Harrington, A. Ghezelayagh, A. Dornburg & T.J. Near, 2024. Synergistic innovations enabled the radiation of anglerfishes in the deep open ocean. Current Biology 34: 2541-2550. Doi: 10.1016/j.cub.2024.04.066

Beetle mimics noxious moths

31 May 2024 /

Bats leave tasty tiger beetle alone

Tiger beetles imitate ultrasonic sounds of unpalatable tiger moths

By mimicking the ultrasonic sound of noxious tiger moths, nocturnally active tiger beetles protect themselves against foraging bats, as Harlan Gough and colleagues write.

Some tiger beetles fly at night. It means that they must be afraid of hunting bats, predators that search for prey by emitting ultrasonic (very high-pitched) clicks and deducing from the reflected sound where a tree or a building is – or where a tasty insect snack is flying. This so-called echolocation allows bats to ‘see’ in the dark. Many insects perceive the ultrasonic clicks of an attacking bat and respond by fleeing or diving to avoid the enemy.

There are a few tiger beetles that react differently: they produce an ultrasonic sound in response to an approaching bat. Harlan Gough and colleagues wanted to know why.

Ultrasonic response

The only other insects known to respond with ultrasonic sound to a hunting bat are moths; an estimated 20 percent of moths responds, at a pitch that bats hear well. The sounds have several effects. Some moths disrupt the reflected bat sound by their calls, so that the bat no longer can interpret the noise. Other moths warn with their sound that they are distasteful or poisonous; once a bat has tasted such a species, it will leave it alone from then on. And other, non-poisonous moths benefit from this: they imitate the sound of a noxious species so that a bat let them also go.

And what about the tiger beetles that produce ultrasonic sound in response to a bat? What do they achieve by doing so?

The researchers tested nineteen tiger beetle species, beetles from the Cicindelidae family, from southern Arizona (USA). They exposed the beetles in the lab to the ultrasonic clicks of a bat that is about to attack. Seven of these nineteen species responded with their own ultrasonic sound, all being species that are active at night. The other twelve species stay put at night and therefore do not need to defend themselves against bats.

Tiger beetles and tiger moths

Do tiger beetles flying at night disrupt the echolocation of bats by jamming? No, the authors write, because that would require a more intensive sound (in technical terms: a higher duty cycle) than the beetles can produce.

Is their ultrasonic sound a warning that they are unpalatable? That is also not the case. The beetles do contain a repellent substance, benzaldehyde, which has an almond scent. But bats still like to eat them, as is evident from experiments with the big brown bat, Eptesicus fuscus. Apparently, the concentration of benzaldehyde is too low to deter this predator. The substance may help against small enemies such as ants and robber flies.

Unpalatable tiger moth warns bat predator with ultrasonic sound

Maybe they imitate the ultrasonic sound of noxious moths? To evaluate that hypothesis, the researchers compared the sounds of tiger beetles with existing sound records of sympatric tiger moths, moths of the subfamily Arctiinae, some of which are poisonous. And yes: the sound produced by tiger beetles is similar to that of poisonous tiger moths. The beetles seem to practice acoustic mimicry.

Wings

Moths that produce ultrasonic sounds do so in diverse ways. They have special structures, such as tiny combs. Tiger beetles produce sounds by brushing their beating hindwings along the back edges of the rigid forewings, the elytra. Normally, they hold the elytra up during flight, but to make sound, they lower them slightly.

Definitive evidence for acoustic mimicry by tiger beetles is still lacking. This would require behavioural tests with bats to find out whether they indeed ignore the beetles after having tasted an unpalatable tiger moth.

Willy van Strien

Photos:
Large: Ellipsoptera marutha, Aridland Tiger Beetle, is one of the species that mimics tiger moths. Laura Gaudette (Wikimedia Commons, Creative Commons CC BY 4.0)
Small: unpalatable tiger moth Cisthene martini, Martin’s Lichen Moth. Ken-ichi Ueda (Wikimedia Commons, Creative Commons CC BY 4.0)

Sources:
Gough, H.M., J.J. Rubin, A.Y. Kawahara & J.R. Barber, 2024. Tiger beetles produce anti-bat ultrasound and are probable Batesian moth mimics. Biology Letters 20: 20230610. Doi: 10.1098/rsbl.2023.0610
Barber, J.R., D. Plotkin , J.J. Rubin, N.T. Homziak, B.C. Leavell, P.R. Houlihan, K.A. Miner, J.W. Breinholt, B. Quirk-Royal, P. Sebastián Padrón, M. Nunez & A.Y. Kawahara, 2022. Anti-bat ultrasound production in moths is globally and phylogenetically widespread. PNAS 119: e2117485119. Doi: 10.1073/pnas.2117485119
Corcoran, A.J., W.E. Conner & J.R. Barber, 2010. Anti-bat tiger moth sounds: form and function. Current Zoology 56: 358-369. Doi: 10.1093/czoolo/56.3.358

Different flower colour, different visitor

16 May 2024 /

Camouflaged fritillary still attracts pollinators

Fritillary Fritillaria delavayi has brown leaves in many places

Flowers of the Chinese fritillary Fritillaria delavayi can be as brown or grey as the stony soil. But there are still pollinators that manage to find them, Tao Huang and colleagues show.

At high altitudes in the Hengduan Mountains in southwest China, plants grow on bare, stony soil. Green leaves are very noticeable here, and to escape from herbivores such as caterpillars, many plant species have developed an unusual brown or grey leaf colour that matches the background. An example is Corydalis hemidicentra.

The fritillary Fritillaria delavayi goes one step further than other plant species: in some places not only the leaves, but also the flowers are stone-coloured. Tao Huang and colleagues wondered whether pollinators could find such camouflaged flowers.

Lung diseases

Fritillaria delavayi is a perennial bulb plant that may have regular green leaves and a bright yellow flower. It grows at an altitude of 3700 to 5600 meters. It is easy to see why this fritillary took on camouflage colours in many places. The small bulbs are used in traditional Chinese medicine, because they contain substances that are beneficial for lung diseases. There is a great demand for them. The plant is difficult to grow because it requires cold and dry air. And so, bulbs are dug out in accessible places.

In some places, Fritillaria delavayi even has brown flowers

In such places the plant developed a stone-coloured appearance. Brown or grey plants are not noticeable, especially if also the flower is brown or grey. But the flowers must be detectable by pollinators, that transfer pollen from one flower to the pistil of another. The flowers cannot fertilize themselves.

Field observations show that two species of bumblebees come to yellow flowers to collect nectar, pollinating the flowers in the process. But they cannot perceive brown or grey flowers, so they do not visit them. How can these flowers be pollinated?

Frequent visits

By other insects, it turns out. The camouflaged flowers of Fritillaria delavayi attract three species of the Anthomyiidae fly family. The flies are looking for nectar and pollen and sometimes mate within the flowers. They do not perceive brown or grey flowers any better than bumblebees do, but they are attracted to the smell. Huang shows that the camouflaged flowers are smaller than the yellow ones, an adaptation to the small bodies of the flies. The flies are less efficient pollinators than bumblebees, but this is compensated for by more frequent flower visits.

As a result, stone-coloured flowers set seed just as well and produce as many seeds as yellow ones. This means that camouflage is not at the expense of reproduction. And camouflaged flowers do indeed protect the plant from human collectors, according to previous research with slides: people clearly have more difficulty finding brown or grey flowers than yellow ones.

Willy van Strien

Photos:
Large: Fritillaria delavayi with brown leaves and yellow flower
Small: Fritillaria delavayi with brown leaves and brown flower
©Yang Niu

See also: Corydalis hemidicentra with cryptic leaf colour

Sources:
Huang, T., B. Song, Z. Chen, H. Sun & Y. Niu, 2024. Pollinator shift ensures reproductive success in a camouflaged alpine plant. Annals of Botany, 9 May online. Doi: 10.1093/aob/mcae075
Niu, Y., M. Stevens & H. Sun, 2021. Commercial harvesting has driven the evolution of camouflage in an alpine plant. Current Biology 31: 446-449. Doi: 10.1016/j.cub.2020.10.078

Nest architectural traditions

9 April 2024 /

Stingless bee follows existing construction plan

Nest of Scaptotrigona depilis with combs in corkscrew form

Workers of the stingless bee Scaptotrigona depilis build their nests according to the architectural style they perceive, Viviana di Pietro and colleagues show. And so, a tradition is born.

The brood cell complex in nests of the stingless bee Scaptotrigona depilis, which lives in South America, can have two distinct forms. In most colonies, workers build combs (plates with brood cells) horizontally one above the other, each comb starting from a central pillar: the parallel form. But in some colonies, they construct a continuous spiral comb without a central pillar: the corkscrew form. So, the workers that build the combs follow one of two possible architectural styles.

This is not a matter of hereditary makeup, Viviana di Pietro and colleagues write, nor is it an adaptation to the location of the nest or to the environmental temperature. The workers simply continue to build in the style that has already been applied, continuing a tradition.

Like honeybees, stingless bees are highly social species with queens that reproduce and workers that do the other tasks. These tasks include construction and maintenance of the nest, which they make in cavities. Workers of Scaptotrigona depilis construct combs from a mixture of wax and plant resin. They build them from the bottom up, and as said in one of two ways. They put food in each cell and close it after the queen has added an egg. The egg develops into a larva and pupa, and finally a young bee emerges.

Switching

Combs are much more often built in the parallel form than in the corkscrew form: about 95 per cent of the colonies have the parallel form.

Scaptotrigona depilis: combs in parallel form

Sometimes a colony switches from one type to another. On average, the parallel form lasts for almost two years. The corkscrew shape is maintained for a month and a half; that is much shorter, but still longer than a cohort of workers is building, namely two to three weeks. Both architectural styles are passed on from generation to generation for some period.

The researchers wanted to determine whether this is because workers are guided by the structure that already exists. They therefore conducted experiments in which they took experienced workers from one colony and placed them in another colony, the brood cell complex of which had either the familiar or the alternative form. The result was clear: workers that were placed with the type they were not familiar with, immediately continued that construction plan, instead of adhering to the building plan they were used to. Apparently, they didn’t have to learn that different architectural style from their new nest mates.

Default

In a second experiment, the researchers changed the parallel form of the combs to the corkscrew form in a number of colonies by making a cut in the top comb from the edge to the centre and placing one end on top of the other. In most cases, the workers continued to build following the corkscrew form.

The conclusion is that not much is needed to maintain a tradition. It is sufficient if the animals are guided by what exists, in this case: they apply the building plan of the existing structure. It requires no understanding, planning or communication. The technical term for this form of self-organization is stigmergy.

Probably, the parallel form of the brood cell complex is default. The researchers think that sometimes a corkscrew shape arises by error. Instead of breaking things down, the bees than continue to build according to that model.

Willy van Strien

Photos:
Large: Rare corkscrew shape comb; open cells at the margin still have to be filled
Small: Parallel combs with central pillar, the dominant form
©Viviana di Pietro

Source:
Di Pietro, V., C. Menezes, M.G. de Britto Frediani, D.J. Pereira, M. Fajgenblat, H. Mendes Ferreira, T. Wenseleers & R. Caliari Oliveira, 2024. The inheritance of alternative nest architectural traditions in stingless bees. Current Biology, online 19 March. Doi: 10.1016/j.cub.2024.02.073

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