From so simple a beginning

Evolution and Biodiversity

All eggs welcome

27 May 2025 / / 0 Comments

Caring fathers aplenty in Japanese giant water bug

In Japanese giant water bug, males take care for the eggs.

Males of the Japanese giant water bug take care of eggs – even of eggs that have been fertilized by other males. Publications by Shin-ya Ohba and Tomoya Suzuki describe this exceptional paternal care.

In the Japanese giant water bug, males care for eggs until they hatch, and they meet the need for care adequately, Shin-ya Ohba and colleagues write. This is remarkable, because care for offspring is rare among insects, and care provided exclusively by the father is even more so.

More peculiar, a third of the eggs a male cares for was fertilized not by himself, but by other males, as Tomoya Suzuki and colleagues were surprised to find.

The Japanese giant water bug, Appasus japonicus, lives in freshwater bodies in Japan and Korea. Within the family of giant water bugs (the Belostomatidae) it is only a small one. It grows to a maximum length of 2 centimeters, while there are also species that measure up to 12 centimeters. Paternal care occurs in many species in this family.

Investment

A male Japanese giant water bug begins his caregiving task by inviting a female to mate with him. He advertises himself with an up-and-down movement. After mating, she sticks fertilized eggs on his back, starting in the middle. When she is finished, he looks for another female to mate with. She adds her eggs. After an average of four matings, his back is fully occupied. A male can carry 100 to 150 eggs, a female lays a few dozen at most.

The eggs require careful treatment: on the one hand, the male must keep them wet and on the other hand, expose them to the air to provide them with sufficient oxygen. He gets this done by staying at the water surface and, with a slow pumping motion, holding the eggs now just above water level and then just below water level. It takes a week to a month for them to hatch, depending on the temperature. During this period, the father can hardly swim and forage because of his burden. He also runs a greater risk of falling victim to a predator. The care therefore requires considerable investment.

Because a male is busy with the eggs for weeks, you would expect that the number of available males is limited, and females must fight for a back where they can lay eggs on. But that turns out not to be the case: males keep up well with females’ egg production and there are enough unoccupied places.

Sperm storage

A male allows a female to lay eggs only if he has mated with her, so that he can be the father of the offspring. Still, on average one in three eggs is ‘foreign’: fertilized by another male. This is not what the researchers had expected when they allowed forty animals – twenty males and twenty females – to mate freely in a tank and determined the relationships between hatched young and adult animals using DNA analyses.

The explanation is that females store sperm and can use sperm from a previous partner instead of the male on which she is currently laying her eggs. And so virtually every male cares for young that are not all his own.

But would not only behavior continue to exist that results in a large number of own offspring? Does paternal care for young make evolutionary sense if paternity is so uncertain?

Yes: in the case of the Japanese giant water bug, it is understandable that a male takes care of other males’ offspring. First, most of the eggs he carries will be fertilized by himself. If he does not take care of them, they are lost. Foreign eggs automatically benefit, but that is just the way it is.

Egg carrier is attractive

In addition, females prefer a male that is carrying eggs over a male with an empty back, previous research has shown. So, eggs on his back – whether fertilized by himself or by another male – increase his chances. And perhaps a female that mates with him will later fertilize eggs with his sperm too and stick them on another male. He may carry some eggs of another father, but another male may take care of his offspring.

The preference of females for males that are already carrying eggs is understandable. A male aims to fill his back within a single day, so that all eggs are the same age and will hatch at the same time. If he collects only a few eggs on a certain day, it is not worth the effort to care for them. He removes them, and they die. By choosing a male that is already carrying eggs, a female reduces that risk for her eggs.

Because foreign eggs are hardly an extra burden and increase a male’s attractiveness, the care for other bugs’ young persists. Ultimately, it benefits a male.

Willy van Strien

Photo: Appasus japonicus, male carrying some eggs and female. © Shin-ya Ohba

Sources:
Ohba, S., R. Hayashida & T. Suzuki, 2025. Female-female competition in two giant water bug species. Ecological Entomology, online 19 May. Doi: 10.1111/een.13454
Suzuki, T., S. Ohba & K. Tojo, 2025. Reproductive strategies in paternal care and remarkably low paternity level in a giant water bug. Ecology and Evolution 15: e71316. Doi: 10.1002/ece3.71316
Ohba, S., N. Okuda & S. Kudo, 2016. Sexual selection of male parental care in giant water bugs. Royal Society Open Science 3: 150720. Doi: 10.1098/rsos.150720

Demand for pollen

15 April 2025 /

Bumblebee queens force plants to accelerate blooming

Queen of buff-tailed bumblebee

Early spring is a crucial time for bumblebee queens. Their larvae need pollen while flowering plants are scarce. But bumblebees can accelerate pollen production, Priska Flury and colleagues report.

In mid-March, bumblebee queens wake up from their hibernation. They had mated in fall and stored sperm cells and then spent the winter alone in rest. Now it is time to start a colony. Each bumblebee queen looks for a place, makes a nest, lays eggs in it and feeds the larvae, which grow on a diet of pollen. They pupate and five weeks after the queen started the nest, the first workers emerge and help her. Until then, it is toiling.

And it is precisely during this busy period that only few plants are flowering and pollen for the larvae is difficult to find. That is unfortunate. But bumblebee queens have a special trick. They accelerate the flowering of plants so that pollen becomes available sooner, Priska Flury and colleagues show. They manipulate plants.

Crescents

A bumblebee queen does so by cutting holes in leaves of non-flowering plants, using her tongue and jaws. These holes have a characteristic crescent shape. What exactly happens in the plant is not clear, but the effect is: the plant flowers a few weeks earlier.

The researchers, who work in Switzerland, first investigated in the lab the clipping behaviour of commercially bred queens of buff-tailed bumblebees (Bombus terrestris) on non-flowering specimens of black mustard and tomato. When queens had little pollen in stock, they would make holes. When there was enough pollen, they would not.

They then captured queens of other bumblebee species in the field and tested in the lab whether they also clipped holes when they were deprived of pollen. Of the forty-one bumblebee species living in Switzerland, they tested seventeen, and the queens of twelve species appeared to make holes, including red-tailed bumblebee (Bombus lapidarius), white-tailed bumblebee (B. lucorum), and early bumblebee (B. pratorum). The other species did not cut holes in the lab, but that does not rule out that they do so in the field.

Plants in which queens had cut holes flowered a few weeks earlier than plants that had not been cut. As a control, the researchers themselves made holes in some plants, but that had almost no effect.

Critical period

So, bumblebee queens ‘order’ pollen when they need it. Previous research had shown that workers of a number of bumblebee species make holes in leaves when there is a high demand for pollen to advance flowering. They do so to survive periods with few flowers when bumblebee colonies are growing rapidly. At the end of April, it is over, because from that time on there is always enough pollen to be found.

That bumblebee queens cut holes is probably more important than the cutting behaviour of workers because early spring, whith no workers around, is a critical period. It depends on this period whether a young colony will survive and grow into a large and successful colony.

Workers and queens have special ‘baskets’ (scopae) on their hind legs to store and transport pollen. They need pollen not only for the larvae, but it is also a source of protein for themselves; they get energy from nectar. When collecting pollen and nectar, they pollinate the flowers. Therefore, it will also be an advantage for plants if the flowering coincides with the time that bumblebees are foraging. The manipulation by bumblebees improves synchronization.

Willy van Strien

Photo: buff-tailed bumblebee queen on small-leaved linden. Ivar Leidus (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Sources:
Flury, P., S. Stade, C.M. De Moraes & M.C. Mescher, 2025. Leaf-damaging behavior by queens is widespread among bumblebee species. Communications Biology 8: 435. Doi: 10.1038/s42003-025-07670-3
Pashalidou, F.G., H. Lambert, T. Peybernes, M.C. Mescher & C.M. De Moraes, 2020. Bumble bees damage plant leaves and accelerate flower production when pollen is scarce. Science 368: 881-884. Doi: 10.1126/science.aay0496

Caterpillar look

2 April 2025 /

Young white-necked jacobin defends itself with appearance and behaviour

White-necked jacobin builds cup-shaped open nest

A young white-necked jacobin looks like a caterpillar with urticating hairs and behaves like one. It is to deter its predators, Jay Falk and colleagues hypothesize.

A newly hatched white-necked jacobin hummingbird looks little like a young bird at first glance. It is a hairy creature that lifts its head and shakes it from side to side as soon as something approaches. Only when its mother announces her arrival with a special signal does it behave normally: it opens its mouth wide to beg for food.

The white-necked jacobin, Florisuga mellivora, lives in the Amazon region. The mother builds a nest and takes care of it on her own, as in other hummingbird species. She lays one or two eggs and incubates them. The young hatch after about two weeks and fledge a few days later.

Chick of white-necked jacobin resembles caterpillar

Jay Falk and colleagues suggest that a chick’s peculiar appearance and behaviour are a response to its vulnerable position. It lies in a cup-shaped nest that is exposed on a plant leaf. The mother regularly flies away to eat, leaving the young in plain sight and unattended.

Deterrent

A white-necked jacobin chick first tries not to stand out. Its ‘hairs’ are exceptionally long natal down feathers that grow on its back. They are the same colour as the seed fluff that lines the nest, camouflaging the young bird well. Also, it may be a physical barrier that prevent small predators from reaching its body.

When predators discover and approach the creature despite its camouflage, it has another trick: mimicry. Due to its hairy appearance and the way it shakes its head, the young bird looks like a caterpillar with urticating hairs. There are several types of caterpillars with irritating stinging hairs in the area, and predators prefer to leave them alone.

The extent to which white-necked jacobin chicks benefit from this fear response and deter predators through their imitation needs further investigation. It seems to work, because the researchers saw how a carnivorous wasp that can overpower young birds approached a white-necked jacobin nest. The wasp inspected the nest but made off when the young started playing caterpillar.

Other caterpillar mimics

The behaviour and the long down feathers of white-necked jacobin chicks are unusual. The only other hummingbird species with young that have such feathers is the black hummingbird, Florisuga fusca. This related species also makes an open, cup-shaped nest on a plant leaf, and its young also appear to imitate a caterpillar.

Strange as it may be, these two hummingbird species are not the only birds with young that resemble caterpillars. The same phenomenon has been extensively described for the South American cinereous mourner (Laniocera hypopyrra), whose orange, hairy young mimic a poisonous caterpillar species. The shrike-like cotinga (Laniisoma elegans) also has young that resemble a hairy caterpillar.

Willy van Strien

Photos
Large: white-necked jacobin (male-like female) on nest. Caspar S (Wikimedia Commons, Creative Commons CC BY 2.0)
Small: nest with young and egg. © Michael Castaño-Diaz

More about white-necked jacobin: crossdressing

Sources:
Falk, J.J., M. Castaño-Diaz, S. Gallan-Giraldo, J. See & S. Taylor, 2025. Potential caterpillar mimicry in a tropical hummingbird. Ecology: 106: e70060. Doi: 10.1002/ecy.70060
Londoño, G.A., D.A. García & M.A. Sánchez Martínez, 2015. Morphological and behavioral evidence of Batesian mimicry in nestlings of a lowland Amazonian bird. The American Naturalist 185: 135-141. Doi: 10.1086/679106
D’Horta, F.M., G.M. Kirwan & D. Buzzetti, 2012. Gaudy juvenile plumages of cinereous mourner (Laniocera hypopyrra) and Brazilian Laniisoma (Laniisoma elegans). The Wilson Journal of Ornithology 124: 429-435. Doi: 10.1676/11-213.1

Food aid

24 March 2025 /

Clark’s anemonefish feeds its sea anemone

Clark's anemonefish in bubble-tip anemone

Clark’s anemonefish pass animal food that they do not consume to the sea anemone in which they live, Yuya Kobayashi and colleagues write. It is an extra service.

Anemonefish (or clownfish) and sea anemones are partners for life. The fish protect the sea anemones from predators and parasites, keep them clean, fertilize the water with their excrement and refresh it. Now, Yuya Kobayashi and colleagues show that Clark’s anemonefish, Amphiprion clarkii, also provisions its partner with food. The fish live in large sea anemones on coral reefs in the western Pacific Ocean, the Indian Ocean and the Red Sea, among other places, and have mutual relationships with several species of sea anemones.

In exchange for their services, anemonefish can live safely in an anemone. That is not self-evident, because sea anemones, relatives of jellyfish, have rings of tentacles with stinging cells full of poison around a mouth opening. With these tentacles, they defend themselves and catch prey, which is paralyzed by the poison. But anemonefish move unhindered among the tentacles.

Suitable snacks

That Clark’s anemonefish occasionally attach food to the tentacles, was demonstrated by Kobayashi and colleagues with experiments in the sea off the coast of Japan. The partner of Clark’s anemonefish there is the bubble-tip anemone, Entacmaea quadricolor, named after the bulbous tips of its tentacles. The researchers offered the Clark’s anemonefish pieces of animal food of different sizes: shrimp, squid, clam, fish or sea urchin. They observed what happened or made video recordings that they analyzed afterwards.

The fish can only ingest small pieces, up to about half a centimeter. They ate small pieces of shrimp, squid, clam and fish until they were satiated; if they got more, they placed excess pieces on the tentacles of the sea anemone. Larger pieces, up to 2 centimeters, were provided immediately to the sea anemone. The anemonefish ignored small pieces of sea urchin, but picked up large pieces and gave it to the sea anemone; the fish cannot eat pieces of sea urchin because of their hard armor. Sea anemones usually transported the animal food that was given to the mouth opening and consumed it.

The researchers also offered pieces of plant food to the anemonefish: green algae. The fish ate small pieces but ignored larger pieces. They didn’t give any piece to the sea anemone, which wouldn’t have used it, because it is carnivorous.

So, Clark’s anemonefish feed the sea anemone with food that is suitable: large pieces of animal food including sea urchin, but no green algae.

Extra growth

The food provision is an extra service, but not without self-interest. Clark’s anemonefish are permanent residents of a sea anemone and live in groups of males and one female that deposits her eggs between the tentacles of the sea anemone. If the female disappears, the largest male becomes a female and takes her place. A sea anemone that is fed grows faster and therefore offers more space for fish and eggs.

The question still is whether this feeding in the field frequently happens under natural conditions, without researchers offering bits of animal food. The researchers have observed it, but not very often.

Willy van Strien

Photo: Clark’s anemonefish in bubble-tip anemone. Diego Delso (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

More about anemonefish: good friend

Source:
Kobayashi, Y., Y. Kondo, M. Kohda & S. Awata, 2025. Active provisioning of food to host sea anemones by anemonefish. Scientific Reports 15: 4115. Doi: 10.1038/s41598-025-85767-9

Birds-of-paradise are glowing

14 March 2025 /

Fluorescence enhances the splendour of a bird-of-paradise male

western parotia is one of the birds-of-paradise thet show fluorescence

Most species of birds-of-paradise have feathers and skin patches that are fluorescent, Rene Martin and colleagues discovered. They can emit light.

Birds-of-paradise are known for their bright colours, striking ornamental plumage and exuberant courtship behaviour. But as if that wasn’t enough, it now turns out that they also emit light. Some areas of their plumage or skin can emit a green, yellow or blue glow, Rene Martin and colleagues discovered. It is a case of fluorescence, which means that an object absorbs light of a certain wavelength (i.e. colour) and re-emits the light with a somewhat longer wavelength.

There are 45 species of birds-of-paradise; they are found in New Guinea, northeastern Australia and parts of Indonesia. For the study, the researchers used the large collection of birds-of-paradise of the American Natural History Museum in New York. In a dark room, they shone blue and ultraviolet light on the birds to see if areas of their body glowed and if so, they analysed the light emitted.

ribbon-tailed astrapia also is a fluorescent bird-of-paradise

Impress and seduce

In no less than 37 of the 45 species of birds-of-paradise they had success. Especially white and bright yellow feathers appeared to be fluorescent. When irradiated with blue light, fluorescent parts gave off a green or yellow-green glow, when irradiated with ultraviolet they lit up blue.

The phenomenon is stronger in males than in females. In most species, head, neck, belly, ornamental feathers and legs of males are luminous, as are spots on the inside of the mouth and throat. In females usually only the chest and belly can glow up. If females have the same pattern as males, the fluorescent area is smaller and less bright.

Fluorescence occurs in bird-of-paradise species where females take all care of the young and males can spend all their time seducing partners and impressing each other. The phenomenon reinforces the colourful image of a male trying to impress and therefore has a function in communication, the researchers state. They have a number of arguments.

Contrast

To start with, birds-of-paradise live in shadow-rich tropical forests. They are active on the forest floor or among tree leaves, where there is a lot of blue and ultraviolet light that can excite fluorescence.

Furthermore, fluorescent parts are located in conspicuous places or places that are displayed during rivalry or courtship. For example, dancing males often open their beaks wide to show the luminous spots inside. The birds can discern the emitted colours – green, green-yellow and blue – very well. And the luminous parts have a dark background for contrast. Other research has shown that many birds-of-paradise have super-black feathers against which their colours stand out extra brightly. That super-black is often seen around fluorescent feathers too.

Birds-of-paradise males have more features that enable a spectacular show than was known up to now. They are not the only birds that show fluorescence; parrots, puffins and nightjars, among others, also do. And other animals too; chameleons for example have blue glowing bone bumps on their heads.

Willy van Strien

Photos: fluorescent white and yellow feathers
Large: western parotia, Parotia sefilata. J.J. Harrison (Wikimedia Commons, Creative Commons CC BY-SA 4.0)
Small: ribbon-tailed astrapia, Astrapia mayeri. Gailhampshire (Wikimedia Commons, Creative Commons CC BY 2.0)

See the courtship dance of Parotia sefilata on YouTube

See also:
Super black feathers in birds-of-paradise
Chameleon’s head emits a pattern of blue light

Source:
Martin, R.P., E.M. Carr & J.S. Sparks, 2025. Does biofluorescence enhance visual signals in birds-of-paradise? Royal Society Open Science 12: 241905. Doi: 10.1098/rsos.241905

Zombie spider

20 February 2025 /

Newly discovered fungus species manipulates cave spiders

Orb-weaving cave spider may be manipulated by fungus Gibellula attenboroughii

The newly discovered fungus Gibellula attenboroughii infects cave spiders and forces them to help spread its spores, Harry Evans and colleagues report.

Animals that are infected with parasites may behave like zombies. The parasite manipulates their behaviour so that they cooperate to their own demise, to the benefit of the parasite. The ability of parasites to do this is amazing; it shows that they are able to control their host’s nervous system. There are multiple examples, as you will see in the category manipulation; they are gruesome tales.

Also some parasitic fungi do it. Gibellula attenboroughii, named for the renowned wildlife documentary filmmaker David Attenborough, is a newly found parasitic fungus that lives in spiders. Harry Evans and colleagues describe this species.

The researchers discovered the fungus Gibellula attenboroughii in an abandoned gunpowder store in Ireland, growing on the orb-weaving cave spider Metellina merianae. This European spider lives in caves, hollows, and cellars, where it hides near its web. But a fungal infected spider, it turns out, leaves its safe place and settles on the ceiling or wall near the entrance, where air circulates. It becomes covered with fungal mass and special spore-bearing fungal threads and dies. Air currents take up the fungal spores and disperse them.

Spore dispenser

The fungus has thus transformed the spider into a spore disperser. We already knew this type of manipulation. Notorious are fungal species of the genus Ophiocordyceps that infect carpenter ants (of the genus Camponotus). A sick ant is often forced to leave the nest, make its way onto the vegetation next to an ant trail, and bite down; the jaws lock, and the ant dies. A kind of mushroom grows out of its body, producing fungal spores. The dead ant’s location is favourable for spreading to new victims.

Fungi are known that infect spiders and turn them into a spore dispenser in a similar way. The recently discovered fungus species Gibellula attenboroughii is specific to cave spiders. It is remarkable that a pathogen can spread among these spiders, which live isolated, in contrast to ants. Besides the orb-weaving cave spider, the fungus also infects the European cave spider, Meta menardi, a larger species.

Willy van Strien

Photo: Orb-weaving cave spider Metellina merianae. -serwacy01- (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

See also: cicadas that are manipulated by a fungus

Sources:
Evans, H.C., T. Fogg, A.G. Buddie, Y.T. Yeap & J.P.M. Araújo, 2025. The araneopathogenic genus Gibellula (Cordycipitaceae: Hypocreales) in the British Isles, including a new zombie species on orb-weaving cave spiders (Metainae: Tetragnathidae). Fungal Systematics and Evolution 15: 153–178. Doi: 10.3114/fuse.2025.15.07
Hughes, D.P., J.P.M. Araújo, R.G. Loreto, L. Quevillon, C. de Bekker & H.C. Evans, 2016. Chapter eleven. From so simple a beginning: the evolution of behavioral manipulation by fungi. Advances in Genetics 94: 437-469. Doi: 10.1016/bs.adgen.2016.01.004

Hidden eyes

3 February 2025 /

Eye spots are effective only from a refuge

Eyespots of spicebush swallowtail caterpillar are effective only when he hides.

The eyespots of a spicebush swallowtail caterpillar protect the animal from hungry birds – but only when the caterpillar is concealed, Elizabeth Postema shows.

An older caterpillar of the spicebush swallowtail butterfly Papilio troilus has an appealing swollen head with two eyespots. It is obvious that these eyespots serve to deter predators. But they do so only under special conditions, Elizabeth Postema writes.

Adult spicebush swallowtail

The swallowtail occurs in North America; the caterpillars live on leaves of trees and shrubs such as sassafras and American tulip tree. A common predator of caterpillars is the black-capped chickadee (Poecile atricapillus), a tit species.

Frightening

A spicebush swallowtail caterpillar sitting openly on a leaf is visible; it is green, but in a slightly different shade than the leaf. The eye spots make it even more conspicuous. That is why a caterpillar hides during the day to escape detection by hungry tits and other predators. Lying on the midrib of a leaf with its head turned towards the tip, it exudes silk. The silk dries and shrinks, forcing the leaf to fold around the caterpillar.

But what is the use of eyespots to a hidden caterpillar? Postema assumed that these eyespots are important when a bird peers into a leaf roll or picks it open. It will then suddenly see a snout with two eyes – an imitation of a snake – and be startled by it. Two eyespots that suddenly appear, the idea is, have a completely different effect than two eyespots that are continuously visible from far away.

Caterpillars of modelling clay

She tested this hypothesis with artificial caterpillars. She made hundreds of green caterpillars of modelling clay with and without eyespots and attached them to tree leaves, which she then folded around the caterpillar or not. So, there were four experimental groups: visible caterpillar without eyespots, visible caterpillar with eyespots, hidden caterpillar without eyespots and hidden caterpillar with eyespots. After five days, she looked for her artificial caterpillars and checked whether they showed bite marks from birds.

As expected, she discovered that a leaf roll offers protection. Caterpillars that were sitting on a leaf in the open were attacked more often than caterpillars that were hidden.

Eye spots did not help the visible caterpillars: tits did not care. But caterpillars in a leaf roll – which were already safer – were even better off with eyespots. Eye spots made the chance of an attack smaller. Postema’s assumption appears to be correct.

The conclusion is that spicebush swallowtail caterpillars protect themselves by combining eyespots with a refuge, so that the ‘eyes’ suddenly pop out in the event of acute danger.

Young caterpillars have no eyespots, but use a different defense strategy: predators overlook them because they are brown and resemble bird droppings.

Willy van Strien

Photo:
Large: caterpillar of spicebush swallowtail Papilio troilus. NCBioTeacher (Wikimedia Commons, Creative Commons, Public Domain)
Small: adult spicebush swallowtail. Robert Webster (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Postema, E.G., 2024. Eyespot peek-a-boo: Leaf rolls enhance the antipredator effect of insect eyespots. Journal of Animal Ecology, online December 25. Doi: 10.1111/1365-2656.14232

The longer the better

28 January 2025 /

Red-cheeked cordon-bleu male shows his ability to collect nesting material

Red-cheeked cordon bleu shows nesting material at courtship

A red-cheeked cordon-bleu often holds a grass stem in its beak during courtship. It chooses the longest object it can get, Masayo Soma and colleagues found.

A male and female red-cheeked cordon-bleu work on their relationship continuously. They sing and dance for each other; dancing entails simply hopping up and down. Song and dance play a role in mutual mate selection and serve to strengthen the pair bond afterwards; a courtship session rarely results in copulation. Couples are close and male and female raise young together.

During courtship, birds often hold a grass stem or straw in their beak, and Masayo Soma and colleagues investigated the significance of this courtship element.

Grass nest

The red-cheeked cordon-bleu (Uraeginthus bengalus) is a songbird that lives in sub-Saharan Africa. It belongs to the estrildid finches, a group of species of which most have beautiful colour patterns. Many species strengthen the pair bond, like the red-cheeked cordon-bleu, with song and dance during which they may hold a grass stem. Males hold a stem during dance more often than females.

Previous research had shown that species performing a stem-holding display are mainly species in which males work intensively on building the nest. Many species of estrildid finches make a nest of grass; the males have the task of collecting the nesting material, while females remain on the nest and weave in the stems that were brought in. This is also the case in red-cheeked cordon-bleu.

The idea is therefore that a male holds a grass stem in his beak while dancing to show that he is well able to perform his task. For females, handling a grass stem does not have that meaning.

The longest

That idea is now gaining additional support. Because if a male intents to advertise his nest material collecting ability by performing nesting material holding display, a long stem is more convincing than a short one. And indeed: a long stem is preferred, red-cheeked cordon-bleus showed in choice tests. The birds, which are about 13 centimetres long, were offered strings of 5, 10 and 20 centimetres. They mostly chose a string of 20 centimetres. If they picked up a short string, they immediately threw it away.

The researchers did similar experiments with the star finch (Bathilda ruficauda, ​​synonym Neochima ruficauda), an estrildid finch from northern Australia and also a grass nest builder, and got the same result.

The story is not yet complete. For instance, the researchers do not know whether a bird that displays with a long grass stem will get a better partner or be more successful in maintaining the pair bond. Moreover: it is not clear whether long stems are preferred for nest building. If not, then handling a long stem would serve to embellish the display rather than to prove collecting ability.

Willy van Strien

Photo: red-cheeked cordon-bleu (Uraeginthus bengalus). Carlos Vermeersch Santana (Wikimedia Commons, Public Domain)

See also: blue-capped cordon-bleu (Uraeginthus cyanocephalus), closely related to red-cheeked cordon-bleu, performs tap dance

Sources:
Soma, M., M. Nakatani & N. Ota, 2025.  Choice of props for courtship dancing in estrildid finches. Scientific Reports 15: 219. Doi: 10.1038/s41598-024-81419-6
Soma, M., 2018. Sexual selection in Estrildid finches, with further review of the evolution of nesting material holding display in relation to cooperative parental nesting. The Japanese Journal of Animal Psychology, 68: 121-130. Doi: 10.2502/janip.68.2.2

Slingshot

19 December 2024 /

Theridiosoma gemmosum catapults its web to passing prey

Theridiosoma gemmosum uses her web as a catapult

A Theridiosoma gemmosum female does not wait for a mosquito to fly into her web. If she hears one approaching, she strikes her web at it, Sarah Han and colleagues write. The mosquito cannot escape.

Most female spiders that construct a web, feed on the insects that have flown into it. But Theridiosoma gemmosum takes a different approach: this spider catapults her web at a passing prey, usually a mosquito, to capture it.

If she did not, such a mosquito would escape the web. A mosquito flies with its front legs extended forward, and as soon as the legs touch a spider’s web, the mosquito reverses its flight and the spider misses her prey. But Theridiosoma gemmosum is ahead of this avoidance strategy by taking action when she hears a mosquito coming close, Sarah Han and colleagues show.

Theridiosoma gemmosum belongs to the ray or slingshot spiders (Theriodiosomatidae), small spiders that use their web as a catapult. Theridiosoma gemmosum is only a few millimetres in size. The web is also small, and it is difficult to find one. The species is widely distributed in wet environments such as river banks and swamps in the northern hemisphere.

Ready to strike

A slingshot spider makes a planar orb web, spins a thread from the centre and attaches the end to a twig. Then she sits in the middle of the web, grabs the centre with her four back legs and the anchor thread with her four front legs. By letting her front legs run over the thread, she stretches the web a few centimetres; the web becomes cone-shaped and is now ready to strike. The spider, sitting on top of the cone, holds the loose piece of thread between front and back legs with her pedipalps (the ‘boxing gloves of spiders).

And then she waits until a flying insect passes the base of the cone. If this happens, she releases the thread; the web snaps back, the spider whizzing backwards with it. The more the web was stretched, the more powerfully it shoots back. If it hits the unfortunate passer-by, the spider has captured her prey; the insect sticks to the threads and cannot escape. Otherwise, she immediately picks up the thread to tighten the catapult again.

Sound

The researchers wondered what exactly made the spider release her web. They conducted experiments in which they tethered a mosquito to a paper strip, in such a way that it could make normal flying movements. They moved it towards a web of Theridiosoma gemmosum. High-speed camera footage shows that the spider shoots its web at lightning speed at a mosquito when it is within reach, but before it touches it with its front legs and realizes the danger.

How does a slingshot spider perceive that a mosquito is within reach? Not with her eyes: the spider does not see sharply and, moreover, she is facing away from the mosquito. But she has special long hairs on the hind legs that sense the airborne vibrations caused by the wing beats. Moreover, the vibrations propagate over the threads of the web, and she detects that too. From the combination of this information, she probably infers where a mosquito is.

There is another piece of evidence that slingshot spiders respond to sound: they shoot their webs also at the snap of a finger or at the sound of a tuning fork. This does not produce any result, but apparently, slingshot spiders take every chance.

Willy van Strien

Photo: Theridiosoma gemmosum. ©Portioid (via iNaturalist, Creative Commons CC BY-SA)

The catapult in slow motion on YouTube

Sources:
Han, S.I. & T.A. Blackledge, 2024. Directional web strikes are performed by ray spiders in response to airborne prey vibrations. Journal of Experimental Biology 227: jeb249237. Doi: 10.1242/jeb.249237
Alexander, S.L.M. & M.S. Bhamla, 2020. Ultrafast launch of slingshot spiders using conical silk webs. Current Biology 30: R928-R929. Doi: 10.1016/j.cub.2020.06.076

Shell with windows

10 December 2024 /

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

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