Higher quality nectar

Evening primrose responds to sound of insects’ wing beats

beach evening primrose detects a bee approaching

When a flying moth or bee is close to the evening primrose Oenothera drummondii, the flowers detect their buzz. Within minutes, they will produce nectar that is more rich in sugars, Marine Veits and colleagues discovered.

Plants have no ears and therefore they are unable hear. Yet, as it turns out, they perceive sound. The wing beats of a passing moth or bee produce sound waves that are detected by the beach evening primrose Oenothera drummondii, Marine Veits and colleagues show. Rapidly, the plant will change the quality of its nectar  by increasing the sugar content. The researchers suspect that, by doing so, the plant increases its reproductive success.

The beach evening primrose, which grows on beaches in Israel, relies on insects for the pollination of its flowers, to be able to set seed. It blooms at night and attracts hawk moths. Flying from flower to flower, they pick up pollen from one flower and deliver it on the pistil of the next one. At dusk, bees visit the flowers.

Energy drink

To keep the pollinators busy, plants must maintain a supply of nectar as a reward for their services. Preferably no soft stuff, but an energy drink: nectar with a high sugar content. But it takes the plant energy to synthesize it, and there is a risk that the precious nectar will be degraded by microorganisms or robbed by ants if it is not picked up by pollinators soon enough.

So it would be nice if a plant would produce high-quality nectar only if there were pollinators nearby. But how can it know?

The researchers hypothesized that plants might be able to detect the sound waves produced by the wing beats of flying insects and respond to it. An unusual idea, but with a series of experiments they showed this to really happen.

When they played back the recorded sound of flying bees to a beach evening primrose plant, the yellow petals of the flowers started vibrating. Soon after, within three minutes, the sugar content of the nectar had increased; before the sound, the flowers produced nectar with a sugar concentration of 16 percent, after the buzz it was 20 percent. Artificial sound at frequencies similar to the sound of flying moths and bees had the same effect, but sound with much higher frequency did not. Nothing happened in silence either.

Soundproof

The nicest test perhaps was with flowers that were contained in soundproof glass jars padded with acoustically isolating foam. These flowers did not respond when the sound of a bee or moth was play backed.

An increased sugar content is an extra reward for flower visitors. They probably will stay longer or go on to visit another flower of the same species. That increases the chance that they pick up or deliver pollen, augmenting the plant’s reproductive success.

If an insect passes by, it does not necessarily make sense for a plant to rapidly increase the sugar content of its nectar. That is only useful if this insect will remain in the area for a while or if it is not alone, because in that case, pollinators will taste the sweet nectar. Video recordings in the field showed that when one insect passes by, there usually are others around. If the weather is fine, many bees or moths are active simultaneously.

Now, more fieldwork is needed to assess whether the evening primrose’s response to insect buzz actually results in more offspring.

Willy van Strien

Photo: © Lilach Hadany

Source:
Veits, M., I. Khait, U. Obolski, E. Zinger, A. Boonman, A. Goldshtein, K. Saban, R. Seltzer, U. Ben-Dor, P. Estlein, A. Kabat, D. Peretz, I. Ratzersdorfer, S. Krylov, D. Chamovitz, Y. Sapir, Y. Yovel & L. Hadany, 2019. Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration. Ecology Letters, online, July 8. Doi: 10.1111/ele.13331

The art of pest control

Fungus-growing termites keep their gardens clean

Termites that grow fungus for food manage to keep their crops free from pests, such as weeds, pathogens and fungus-eating nematodes, Saria Otani and Natsumi Kanzaki and their colleagues report. Bacteria in the termites’ gut play a role in pest control.

Some termites species practice agriculture by growing a fungus in their nests for food. And just like human farmers, they have to protect their crop against pests. As is known, they perform well. Saria Otani and colleagues show how a number of African termite species keep their fungal gardens free from non-edible, proliferating or pathogenic fungal species. And Natsumi Kanzaki and colleagues report that the Asian termite Odontotermes formosanus suppresses fungus-eating nematodes.

One way by which the termites control these pests, is by ingesting the plant material on which they grow the fungus crop, so that it passes through their gut. Gut bacteria produce substances that inhibit harmful fungi and nematodes, to ensure that the pre-digested stuff is pretty clean.

Agriculture in termites

Just like ants and some bee and wasp species, termites are eusocial. They live in large colonies that can exist for decades. Most residents are sterile: they are either workers that maintain the nest, take care of the brood and forage for food, or soldiers that defend the nest. Reproduction is a privilege of the royal couple, that has no other duties. The queen is nothing more than an egg laying machine, the king’s task is to mate with her.

Winged sexual individuals (alates) appear once a year. They make a nuptial flight, and couples form that may found a new colony.

More than three hundred species of termites from Africa and Asia have a special way of life: in indoor gardens, they grow fungi in highly productive monocultures. In these species, the workers have the additional task of taking care of the crop. They forage for tough plant-derived material on which they grow the fungus: dry grass, wood and leaf litter. The gardeners consume the stuff and deposit it with their faeces on top of the garden. They are unable to degrade the cellulose and lignin of plants, but the fungus grows well on the pre-digested and fertilized material. It forms nutritious buds, the nodules, which are consumed by the termites. The nodules contain asexual spores, which pass the termites’ gut undamaged; by dropping them on top of the fungal garden, the termites maintain the crop. They also consume older, lower garden parts that are whitish with fungal mycelia.

Cleaning process

Both termite and fungus profit from this agriculture: it is a mutualistic relationship. The fungus has a safe and comfortable living place, the termites have a food supply. But a problem is, that the well attended fungal gardens are suitable as a living place or food source also to other parties.

A garden, for instance, is attractive to fungi that are of no use to the termites, but are competitive with or pathogenic to the crop. The plant material that the workers bring in from the field is not free of such species. Yet, Otani could hardly find harmful fungi in the gardens of three African species, including Macrotermes natalensis. He shows that both the fungal crop and the garden contain substances that inhibit the growth of foreign fungi.

The termites do not synthesize such substances, but their gut bacteria do. By eating the plant material before provisioning the fungus crop, the gardeners probably subject it to a cleaning process. Gut bacteria are deposited on the garden with the faeces, and continue to produce fungicidal substances.

Grooming

Because the fungal crop is full of carbohydrates, proteins and fats, it is an attractive food source for other animals, such as fungus-eating nematodes. Their presence would reduce the harvest. Natsumi Kanzaki shows, in the Asian termite species Odontotermes formosanus, that workers that leave the nest to forage for plant material often carry such nematodes upon return, as does their load.

The fungal crop is not toxic to the nematodes. But they don’t get a chance to eat it, because the termites will groom returning colony mates to remove hitchhiking nematodes. Also, the foragers are not in direct contact with the garden. And when the gardeners consume the new plant material, gut bacteria will suppress nematodes that cling on it.

Obligate

Termite farming originated in Africa. The farming is obligate for both partners: fungi-growing termites and cultivated fungi no longer are capable to live on their own.

Although termites look a bit like ants, they are not related to them. On the evolutionary tree of life, they are close to cockroaches. That is why certain differences exist between termites and ants. Whereas male ants are not engaged in colonial life (all workers are females), sterile male termites help their nest mates as workers or soldiers. Juvenile termites do not go through larval and pupal stages, but are nymphs, small versions of adult animals.

Willy van Strien

Photos:
Large: Odontotermes formosanus, young alates and workers. ©Wei-Ren Liang
Small: Macrotermes natalensis: fungus garden with nodules, soldiers and nymphs. ©Saria Otani

Sources:
Kanzaki, N., W-R. Liang, C-I. Chiu, C-T. Yang, Y-P. Hsueh & H-F. Li, 2019. Nematode-free agricultural system of a fungus-growing termite. Scientific Reports 9: 8917. Doi: 10.1038/s41598-019-44993-8
Otani, S., V.L. Challinor, N.B. Kreuzenbeck, S. Kildgaard, S. Krath Christensen, L. Lee Munk Larsen, D.K. Aanen, S. Anselm Rasmussen, C. Beemelmanns & M. Poulsen, 2019. Disease-free monoculture farming by fungus-growing termites. Scientific Reports 9: 8819 . Doi: 10.1038/s41598-019-45364-z
Aanen, D.K. & J.J. Boomsma, 2006. Social-insect fungus farming. Current Biology 16: R1014-R1016. Doi: 10.1016/j.cub.2006.11.016
Aanen, D.K., P. Eggleton, C. Rouland-Lefèvre, T. Guldberg-Frøslev, S. Rosendahl & J.J. Boomsma, 2002. The evolution of fungus-growing termites and their mutualistic fungal symbionts. PNAS 99: 14887-14892. Doi: 10.1073/pnas.222313099

Stripe suit or mohawk

Jumping spider males have two ways to approach cannibalistic females

Striped male Maevia inclemens reduces female aggression

The jumping spider Maevia inclemens is peculiar by having two types of males. They look different and they behave differently. Why would that be? The morphs have developed alternative strategies to reproduce safely, Laurel Lietzenmayer and colleagues think.

Tufted male Maevia inclemens signals its qualityIn the North American jumping spider Maevia inclemens, two types of males exist that differ so much, that they seem to be different species. Some males are black with pale legs and have three tufts of setae on their head, a bit like a cross-positioned mohawk. Other males have black-and-white striped legs and orange pedipalps (the ‘boxing gloves’).

So, females have the opportunity to choose between a punker and a male in a stripe suit. But the ladies are not choosy at all: they respond to the first male they happen to see.

The difference in appearance is linked to a different courtship behaviour. According to Laurel Lietzenmayer and colleagues, alternative strategies to reproduce are behind the differences, each male type being successful in its own way.

Signaling quality

The males face a difficult problem. To be able to reproduce, they must attract the attention of a female. But Maevia inclemens is a predatory species, and males are potential prey for females. Therefore, a male must manage to elicit a female’s mating behaviour – and not her appetite.

The tufted male will stay at a safe distance if he aims to mate a female, about 9 centimetres; the males are only half an inch in length, females are slightly larger. He makes himself as tall as possible by standing on three leg pairs and lifting himself tall, raising and clapping his front legs rhythmically; he also moves his pedipalps and abdomen.

The larger a male is, the higher his quality, the researchers assume. A female will probably prefer to copulate with a large male, because his offspring will inherit his superior qualities. The mohawk may give the female an extra clue about his size, because, as measurements show, the larger the male, the longer his tufts.

Avoiding cannibalism

A striped male has to come closer to a female to attract her attention, because she is not able to discern him easily at a great distance. He courts at only 3 centimetres from her, running the risk of being cannibalized. He makes himself as small as possible by crouching and he slides in semicircles, while holding his front legs in a triangle-like configuration.

Experiments with prey (termites) in different capes of coloured paper show that potential prey with a black-and-white stripe pattern is more conspicuous. Still, it is not attacked more frequently than prey with a solid gray or orange colour. Apparently, the stripes suppress the aggression of female Maevia inclemens, perhaps because many striped prey species are venomous.

Two solutions

Both types of males seem to have a different solution for the problem of approaching a cannibalistic female, the researchers write, which is reflected in their dimorphic appearance and behaviour. The tufted male signals his quality at a far distance, while the striped male attracts her attention while reducing her aggression from nearby. In other words: the tufted male tries to stimulate her mating behaviour, the striped male to temper her appetite.

If a female is willing, the encounter follows the same pattern for both male types. They behave the same, have the same chance of mating successfully and on average sire the same number of offspring. After mating, they again run the risk of being consumed, but in almost all instances they are able to escape.

Genetic determined?

The story about the alternative strategies of Maevia inclemens males is not yet complete, Lietzenmayer indicates. Many questions are still open, for example: is a female actually able to estimate the size of a tufted male from his tufts’ length? Are courting males with striped legs really more visible from close distance than solid coloured males?

In addition, it is not yet known whether the difference between the male types is genetically determined and how it originated.

Few animal species are known with different male types. This remarkable jumping spider is one of them, and it will be fascinating to find out why.

Willy van Strien

Photos:
Large: Maevia inclemens, striped male. Opoterser (Wikimedia Commons, Creative Commons CC BY 3.0)
Small: Maevia inclemens, tufted male. Tibor Nagy (via Flickr, CC BY-NC-ND 2.0)

Watch both male types courting

Sources:
Lietzenmayer, L.B., D.L. Clark & L.A. Taylor, 2019. The role of male coloration and ornamentation in potential alternative mating strategies of the dimorphic jumping spider, Maevia inclemens. Behavioral Ecology and Sociobiology 73: 83. Doi: 10.1007/s00265-019-2691-y
Clark, D.L. & B. Biesiadecki, 2002. Mating success and alternative reproductive strategies of the dimorphic jumping spider, Maevia inclemens (Araneae, Salticidae). The Journal of Arachnology 30: 511-518. Doi: 10.1636/0161-8202(2002)030[0511:MSAARS]2.0.CO;2
Clark, D.L., 1994. Sequence analysis of courtship behavior in the dimorphic jumping spider Maevia inclemens (Araneae, Salticidae). The Journal of Arachnology 22 : 94-107.

Pair bonds in bats

Female Egyptian fruit bat selects male that shared its food

In Egyptian fruit bat, a fruit-eating mammal, males take the initiative to mate, but females determine whether mating occurs. They strongly prefer a friend that often offered them food, Lee Harten and colleagues write.

Bats are social animals, and so is the Egyptian fruit bat (Rousettus aegyptiacus), which occurs in Africa and the Middle East. The fruit-eating mammals live in large colonies of up to thousands of specimens. Individuals within a group maintain friendship bonds with a few others, meaning that they share food.

Lee Harten and colleagues previously reported that the animals have two ways to obtain food. A risky way is to get fruit from a tree on their own. When a bat lands in a tree to collect food, it runs the risk of being caught by a predator, such as a snake or a cat. Therefore, the bats forage high in the trees. And when a fruit tree has thin foliage, they fly with their catch to a safe place to consume it.

There is also a funky method that the bats often use. If a colony mate holds a fruit in its mouth, they approach it and try to steal it. The bat that has obtained the fruit may respond aggressively, but sometimes it will have its catch scrounged.

Faint-hearted

Individuals differ in their strategy. Some usually pick their own fruit, while others are more likely to try to scrounge it. The scroungers are more anxious. They are afraid to land on a place with food, and if they do, they are so vigilant that most times, they will not be able to pick any fruit. For faint-hearted bats, scrounging from others is the better option.

Often scroungers don’t approach any arbitrary colony member, but they have one or two partners that they regularly approach, and that tolerate it. So, a network of affiliations exists.

Overall, Egyptian fruit bat males and females use different strategies. Males are more likely to collect fruit on their own than to scrounge, while for females it is the other way around. Only during lactation – a female produces one pup once or twice a year – they shift to collecting food on their own; they then need extra energy. Outside that period, they prefer to scrounge, each from its own set of favorite males.

Reciprocity

Now, Harten shows that those relationships have big consequences. In his lab, he kept a colony of wild-born Egyptian fruit bats, fifteen males, ten females and the young that were born in the lab. Genetic paternity analysis of the pups showed that in most cases, the father was one of the males that the mother preferred to get food from. The transfer of food from father to mother had been most intensive in the period just before pregnancy.

It is not a direct exchange of food for sex, because not all food-sharing bonds result in a descendant. But by tolerating a few females to prig food, a male has a chance to sire offspring later. Although a male takes the initiative to mate, a female decides whether or not to accept it. If she does, the male gets something in return for its generosity. Such delayed reciprocity is probably an explanation, but maybe not the only one, that the animals share food with some others.

Each male has a number of regular scroungers and a chance to produce a young with one of them. The relationships persist during a breeding season, but when a new period starts, females select another male to sire their young.

Willy van Strien

Photo: Egyptian fruit bat with fig. Artemy Voikhansky (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Sources:
Harten, L., Y. Prat, S.B. Cohen, R. Dor & Y. Yovel, 2019. Food for sex in bats revealed as producer males reproduce with scrounging females. Current Biology, online May 23. Doi: 10.1016/j.cub.2019.04.066
Harten, L., Y. Matalon, N. Galli, H. Navon, R. Dor & Y. Yovel, 2018. Persistent producer-scrounger relationships in bats. Science Advances 4: e1603293. Doi: 10.1126/sciadv.1603293

Vine avoids spider mites

Tendrils curl away from herbivore-infested plants

Vine Cayratia japonica prevents spider mites from invading

When the Asian climbing plant Cayratia japonica stretches its tendrils to other plants, it is careful. The tendrils withdraw as soon as they detect the presence of spider mite, as Tomoya Nakai & Shuichi Yano observed.

The Asian vine Cayratia japonica is an excellent climber: in America, where it was introduced, it is known as bushkiller. Tendrils of the plant coil around stems of neighboring plants, enabling the vine to grow towards the light. The tendrils grab onto everything they can.

Well, not everything really. The tendrils withdraw when they touch upon a plant that is infested with two-spotted spider mite, Tomoya Nakai & Shuichi Yano show. Two-spotted spider mite or red spider mite (Tetranychus urticae) is a small arachnid hat sucks up plant sap from leaves, which often don’t survive it. The mites occur on hundreds of plant species. If their number at some place is too high, they will walk to another place. As they follow each other’s trails, a group will soon aggregate at this new site.

Spider mite web

Because of its physical contact with other plants, a vine could easily get infested by these harmful critters. But Cayratia japonica appears to have an effective way to prevent mites from invading. As soon as a tendril touches a plant that is occupied by mites, it withdraws and curls away from the infested plant. The researchers could show this in the lab, by placing a number of vines each next to a bean plant that was either clean or bearing many mites. They filmed the movement of the vine’s tendrils using time-lapse photography, making one film frame per minute.

The next question was: what cue does a tendril use to detect the presence of spider mite? Does it pick up the volatile compounds that a bean plant releases into the air when infested? Or does it feel the web with which the mites cover the plant surface to be safe underneath from predators?

Experiments showed that the volatile compounds released by infested bean plants have no effect on the stretching tendrils. But mite silk does: after contact with a spider mite web, the tendrils immediately withdraw. Nakai and Yano also tried spider silk, but the tendrils did not respond to it. The vine thus responds directly and specifically to the presence of spider mite.

This reduces the chance that mites disperse in groups from support plants to the climbing plant. A few of them will cross over during the short contact, but they are not save without the web and will disappear.

Willy van Strien

Poto: 石川 Shihchuan (via Flickr. Creative Commons CC BY-NC-SA 2.0)

Source:
Nakai, T. & S. Yano, 2019. Vines avoid coiling around neighbouring plants infested by polyphagous mites. Scientific Reports 9: 6589. Doi: 10.1038/s41598-019-43101-0

Suicidal repair team

Young aphids die when closing a hole in their nest

Soldier nymphs in Nipponaphis monzeni repair their nest with their body fluid

Japanese aphids, Nipponaphis monzeni, inhabit galls on hazel. A hole in the gall wall would mean the end of the colony living there, were it not for aphid soldiers that give their lives to close it. Mayako Kutsukake and colleagues show how.

The Japanese aphid Nipponaphis monzeni is a social species, living in colonies. Juveniles, called nymphs, serve as soldiers for a period before they become adults and reproduce. It is their task to defend the nest, which is located in galls on the branches of evergreen witch hazel (Distylium racemosum), and to repair it in case of damage.

To close a hole, they show a spectacular and unique behaviour. In a self-destructive action, they discharge their body fluid to plug the gap. The liquid solidifies, forming a scab. Mayako Kutsukake and colleagues were curious about the mechanism.

Vulnerable nest

Colonies of Nipponaphis monzeni are founded by females that reproduce parthenogenetically. A colony of sisters is formed that are genetically identical and produce identical daughters.

gall on hazel in which Nipponaphis monzeni livesThe aphids induce the hazel on which they live to form a closed, hollow tumour, a gall. The animals inhabit this gall, sucking plant sap from the inner wall; in this phase, they are wingless. The gall remains small for a long time, but after three to five years it begins to grow rapidly during spring months and the following summer, it is fully grown – up to eight centimetres long – and home to thousands of aphids.

Winged aphids then appear in autumn. They make an opening in the wall and fly away to a second host tree, an oak, where they mate and produce a new generation of colony foundresses.

A full-grown gall has a lignified, hard wall, offering safety. But during growth, the wall consists of soft plant tissue and the nest is vulnerable. Moth caterpillars consuming hazel tree leaves easily tunnel into such gall, ingesting aphids as well. The soldiers will not tolerate this and attack the enemy: they climb onto it and sting it to death with their mouth parts.

But the hole that the caterpillar gnawed in the gall wall still remains. It has to be closed, otherwise enemies or pathogens may invade, or the nest may desiccate.

Skilful plastering

Japanese researchers had already shown how the soldier nymphs repair the hole with a self-sacrificing behaviour. Dozens or hundreds of them gather around the hole and eject large amounts of white body fluid (hemolymph, which is comparable to our blood) through two tubes on the abdomen. They mix the secretion with their legs and skilfully plaster it over the hole. Some soldiers are buried, others are locked out in the process. And all shrivel after losing their body fluid and will die.

Any way, the hole is fixed; the plug hardens and turns black. As a result, the colony is likely to survive the damage. After the sealing, the gall wall is healed, as the soldiers trigger the tree to cover the plasterwork on the inside by regenerating plant tissue.

Coagulation

Now, Kutsukake investigated the substances with which the soldiers repair a hole. The body fluid, she shows, contains many peculiar large cells of a hitherto unknown type that are packed with fat droplets and the enzyme phenoloxidase; the fluid contains long proteins and tyrosine, an amino acid.

When the soldiers discharge their body fluid, the cells rupture and the fat globules are released; the soldiers plug the gap immediately with a soft lipidic clot. At the same time, the other components come into contact with each other, and a coagulation process starts in which the proteins are linked to form a network that reinforces the lipid plug so that it becomes a scab.

The researchers assume that the process is derived from the process by which wounds heal. But in soldier nymphs’ hemolymph, the components are accumulated in extremely large quantities, far beyond what is necessary for wound healing.

With their unique repair behaviour, the soldier nymphs of Nipponaphis monzeni exhibit extreme altruism to defend the colony: they give their lives. Thanks to this sacrifice, a large part of their family survives. Otherwise the entire colony would have been lost.

Willy van Strien

Photos : ©Mayako Kutsukake
Large: Nipponaphis monzeni soldier nymphs plastering their hemolymphe over a hole
Small: gall in which Nipponaphis monzeni lives

On YouTube, the researchers show how soldiers fix a hole in the gall wall

Sources:
Kutsukake, M., M. Moriyama, S. Shigenobu, X-Y. Meng, N. Nikoh, C. Noda, S. Kobayashi & T. Fukatsu, 2019. Exaggeration and cooption of innate immunity for social defense. PNAS, 15 april online. Doi: 10.1073/pnas.1900917116
Kutsukake, M., H. Shibao, K. Uematsu & T. Fukatsu, 2009. Scab formation and wound healing of plant tissue by soldier aphid. Proceedings of the Royal Society B 276: 1555-1563. Doi: 10.1098/rspb.2008.1628
Kurosu, U., S. Aoki & T. Fukatsu, 2003. Self-sacrificing gall repair by aphid nymphs. Proceedings of the Royal Society London B (Suppl.) 270: S12-S14. Doi: 10.1098/rsbl.2003.0026

Discrete invitation

Arabian babbler leads partner to hidden place

Arabian babbler invites partner in an unobtrusive way

Unlike other animals, the Arabian babbler keeps its sex life private. It has a subtle way to invite another bird for a concealed copulation, as Yitzchak Ben Mocha and colleagues observed.

Animals do not seek to conceal their sexual behaviour. But the Arabian babbler, Argya squamiceps, is an exception. The birds, which live in stable kin groups of two to twenty individuals, do not want to be detected when copulating. A couple that is going to mate will take care to be out of sight of their group mates: at a certain distance or behind thick vegetation.

Yitzchak Ben Mocha and colleagues describe how the birds take a partner to such hidden place without revealing their intention to the other birds.

Arabian babblers live in open, dry landscapes across the Arabian Peninsula and Israel, where each group defends a territory. Within a group, only one pair, the dominant pair, will breed. They are the parents of nearly all young in the group. The other adult group members are subordinates and help raise the young. After hatching, the young stay in the nest for two weeks. And after fledging, it takes another eight weeks until they reach independency. During this period, they need care: protection and food.

Unobtrusive

Observing a population, the researchers witnessed that the birds have a subtle way to invite another bird to copulate. They place themselves in a location that is visible to that specific bird only while holding an object in the beak; often they slightly shake their head. The object can be anything, such as a twig, leaf, fruit, small animal or eggshell. The signalling behaviour is unobtrusive, but the partner grasps the message. When he or she accepts the invitation and approaches, the initiator moves away or hides behind the vegetation and the partner will follow. If they lose contact, the initiator comes back, places itself within the other’s visual field and repeats the invitation.

Usually, a copulation follows. But when another group member appears, the  signaller drops the object and stops the mating behaviour.

The object presented is nothing special, just something that happens to be abundant. So, it is not intended to impress. Neither is it a gift; although it may be edible, that does not affect the partner’s response. The presentation is just a subtle way to invite a mate for a concealed copulation.

Crucial help

Even dominant birds, which don’t have to fear that subordinates will dare to disturb a copulation, take great care to hide their mating behaviour. Why is that? The authors offer an explanation. The care of subordinate group members is crucial for raising the offspring. Without that care, the young have a smaller chance to reach adulthood. Moreover, they gain less weight and will be less capable to acquire food once they are independent.

The dominant pair does not want to lose that precious help. With overt mating behaviour, the researchers suggest, they would cause social tension in the group and increase the chance that subordinates leave or fight, which would be undesirable. So, the parents prefer to keep peace by keeping their love life private.

Willy van Strien

Photo: Greg Schechter (Wikimedia Commons, Creative Commons CC BY 2.0)

See invitation for concealed copulation on YouTube

Sources:
Ben Mocha, Y. & S. Pika, 2019. Intentional presentation of objects in cooperatively breeding Arabian babblers (Turdoides squamiceps). Frontiers in Ecology and Evolution 7: 87. Doi: 10.3389/fevo.2019.00087
Ben Mocha, Y., R. Mundry & S. Pika, 2018. Why hide? Concealed sex in dominant Arabian babblers (Turdoides squamiceps) in the wild. Evolution and Human Behavior 39: 575-582. Doi: 10.1016/j.evolhumbehav.2018.05.009
Ridley, A.R., 2007. Factors affecting offspring survival and development in a cooperative bird: social, maternal and environmental effects. Journal of AnimalEcology 76: 750-760. Doi: 10.1111/j.1365-2656.2007.01248.x

Who dares?

Black-headed female takes the lead in Gouldian finch

Black-headed Gouldian finch is most courageous

When Gouldian finches have to drink, not every bird is willing to leave the safe trees first. There is a pattern in the order in which they venture to a waterhole, Andrias O’Reilly and colleagues show.

Drinking water is a perilous adventure for the Gouldian finch, a songbird from north-western Australia. It is a colourful species. If the birds are on the ground near a creek or pond, birds of prey will spot them easily, so they are less safe there than in the trees. But they have no choice: they have to drink. Once a day, early in the morning, they take the risk, coming in flocks. Some of them are more courageous than others, as Andrias O’Reilly and colleagues saw.

Personality

That was already known from experiments in the lab. Gouldian finches have different head colours; most birds (70 percent) have a black head, others (30 percent) a red one and a few (less than 1 percent) a yellow one. Research had shown that the colour is linked to personality: animals with a red head are more aggressive, whereas black-headed birds are more explorative and more courageous. The researchers wondered if this is also the case in the wild. If it is, a difference in courage should be visible in a risky activity, such as drinking water.

So, they observed the birds at their daily drinking party and noted what type of bird descended first to the waterhole, taking the greatest risk. They conducted their research at the end of the breeding season, when the young had fledged.

Apparently, Gouldian finches are no heroes. They will not land on the ground to drink untill other birds are present at the waterhole. If no bird is there, they will remain in the trees and wait for other birds to appear.

Risk

Only in that case, they dare as well. And then, the black-headed birds are most likely to take the lead, as it turned out. That is in agreement with what was found in the lab. The black-headed birds run less risk because they are less conspicuous than the red-headed ones, the explanation is.

Young birds have not yet full colours and are even less conspicuous. Still, juveniles let the adult birds precede; probably the young birds are more cautious because they have little experience.

At the start of the research period, mainly females are the first birds to descend to the water. Fathers primarily care for the young for a while after fledging; during this period, males will stay with the cautious young, so females have to take the lead. And the black-headed females will take it.

Willy van Strien

Photo: Gouldian finch, black-headed male. Linda de Volder (via Flickr; Creative Commons CC BY-NC-ND 2.0)

Source:
O’Reilly, A.O., G. Hofmann & C. Mettke-Hofmann, 2019. Gouldian finches are followers with blackheaded females taking the lead. PLoS ONE 14: e0214531. Doi: 10.1371/journal.pone.0214531

Costs before benefits

By guarding stepkids, bee male may get the mother

In bee Ceratina nigrolabiata, the male takes care of other males' offspring

Ceratina nigrolabiata bee males guard the nest of their female partner. This seems surprising, as the brood consists mainly of other males’ offspring, as Michael Mikás and colleagues show. Still, the males have good reason.

Bee males don’t do much. Okay, they mate with females and of course that is important, but that’s it. The females construct a nest and take care of the offspring. In solitary species, such as the species that visit a bee hotel, each female makes her own nest; social species, such as the honeybee, live in groups in which queens produce eggs and workers do the work.

There is one exception, Michael Mikát and colleagues report: in the solitary bee species Ceratina nigrolabiata, males do participate in care – but, surprisingly, mainly by protecting other males’ offspring.

Guard

A Ceratina nigrolabiata female makes her nest in the hollow stem of a plant. She goes inside, lays an egg, brings food for the larva that will hatch, closes the space by building a wall and lays another egg in the next part of the stem. Ultimately, a nest consists of six to seven cells in a row, with young in a descending stage of development when viewed from the inside out. The mother leaves when the nest is completely provisioned.

In the majority of nests in which a female is active, a male is present, as the researchers observed during their studies in the Czech Republic. When the female performs foraging trips, the male stays inside the nest to protect it from predators such as ants, driving them away when they come near. He is sitting near the entrance with the head facing inwards. When she returns, she will scratch his abdomen and he will let her pass.

The benefit for her is clear: thanks to this guard, she can leave to forage without having her nest unattended.

For him, it is different. DNA analyzes show that in most cases the brood that he protects does not contain any offspring that he fathers. So he takes care of other males’ offspring, and in general, that is not a good strategy from an evolutionary point of view.

Male switches

In fact, the bee males have no interest in the brood at all; it is the mother that captivates them. A male only has a chance to mate if he finds a female and stays with her until she is willing; in Ceratina nigrolabiata, a female will mate several times in her life. So he has to stay at her nest. While he certainly participates in care by actively protecting the brood, this stepfather care is a by-product of monopolizing a female, according to the researchers.

And indeed, if they removed a female from her nest, the male abandoned the brood.

So, every female is assured of a helpful lover. If a male disappears, his place is usually taken by another within a day.

These stepfathers are not ideal helpers, because they stay on average for only seven days, while a female needs about forty days to complete her nest. As a consequence, the male inhabitant of most nests changes one or more times, and in fatherless periods the female spends less time collecting food, staying on the nest instead. The more changes, the fewer offspring she therefore can produce. But at least she gets help, which is unique among solitary bees.

Willy van Strien

Photo: Ceratina nigrolabiata, female returns at her nest in a hollow plant stem and scratches the guarding male. ©Lukáš Janošík

Source:
Mikát, M., L. Janošík, K. Cerná, E. Matoušková, J. Hadrava, V. Bureš & J. Straka, 2019. Polyandrous bee provides extended offspring care biparentally as an alternative to monandry based eusociality. PNAS: 116: 6238-6243. Doi: 10.1073/pnas.1810092116

Care for everyone

Earwig mother tends foreign eggs and adopts orphans

earwig female cares for another female's offspring 

An earwig mother will treat another female’s eggs as caring as her own eggs, Sophie Van Meyel and colleagues write. Previously, Janine Wong and Mathias Kölliker had discovered that she is willing to accept young orphans in her family.

Earwigs are not very popular animals, but actually they are lovely creatures. The extensive and complex care that females provide to their offspring is impressive.

In late autumn, a female European earwig, Forficula auricularia, lays twenty to forty eggs in a burrow. She then remains in that nest and tends her clutch during winter. And that pays off: without her presence, almost all eggs would be lost, Sophie Van Meyel and colleagues show. A mother cleans the eggs with her mandibles to prevent growth of fungi and pathogens. She protects her clutch against predators. She ensures that the eggs will not desiccate. And she relocates them if necessary.

This nice maternal behaviour is not directed exclusively to a mother’s own clutch.

Weight loss

When the clutch of an earwig female is replaced by that of another female, she provides the same care with the same dedication, as Van Meyel witnessed when she conducted cross-fostering tests in the lab with five-day-old clutches. The eggs have their mother’s odour, so a female should be able to recognize foreign eggs. But she does not reject them. When tending eggs, a female faces a tough task, because she will not leave to forage until the young have hatched, which takes a few months. So, she will lose weight.

But strangely enough, the weight loss during winter is even greater for a female that has no eggs to tend. Apparently, food is scarce outside. A tending mother probably cannibalizes  some of her eggs to survive. This may explain that she is willing to care for a foreign clutch as well as for her own clutch, as the possession of eggs is a guarantee that she does not have to starve. She will be forgiven for consuming a small part of the clutch, since without her care almost no egg would make it through the winter months.

Orphans

The young hatch in early spring. Earwigs do not go through a complete metamorphosis with larval and pupal stages, but the juveniles resemble adult animals. They are nymphs.

After hatching, the nymphs usually stay in their burrow for a week. The mother protects them, regurgitates food for them and accompanies them when foraging at night. The nymphs can do without that care; they are mobile shortly after hatching and can search for food independently. But they do better if their mother attends them during the first week.

However, not every mother survives until spring, so some nymphs are orphans from the start of their life. Many such nymphs leave their natal nest during the first night. If they survive, they often join another family. Then again something remarkable happens: the mother of that family typically accepts them, and most orphaned nymphs end up well, as Janine Wong and Mathias Kölliker have shown.

Most motherless nymphs appear to choose an adoptive family with smaller juveniles. They are safe there, because when food is scarce, nymphs may cannibalize each other, preferring nonsibling smaller nymphs. By accepting foreign nymphs, an earwig family therefore runs a certain risk. Apparently,  group augmentation confers an advantage to the adoptive family that outweighs that risk, but it is not clear yet what that advantage might be.

Willy van Strien

Photo: European earwig female with eggs. ©Joël Meunier

Watch an earwig mother tending her eggs on You Tube

Sources:
Van Meyel, S., S. Devers & J. Meunier, 2019. Love them all: mothers provide care to foreign eggs in the European earwig Forficula auricularia. Behavioral Ecology, online 9 February. Doi: 10.1093/beheco/arz012
Wong, J.W.Y. & M. Kölliker M., 2013. The more the merrier? Condition-dependent brood mixing in earwigs. Animal Behaviour 86: 845-850. Doi: 10.1016/j.anbehav.2013.07.027