From so simple a beginning

Evolution and Biodiversity

Category: reproductive behaviour (Page 1 of 4)

Fish without males

15 July 2025 / / 0 Comments

Amazon molly is a sexual parasite

In Amazon molly, only females exist.

All Amazon mollies are female. A female mates with a male of another species—and then gives birth to daughters that are clones of herself. What sustains this sexual parasitism? Waldir Berbel-Filho and colleagues solve a piece of the puzzle.

The tropical fish Poecilia formosa, the Amazon molly, has a peculiar sex life. The species consists only of females that reproduce asexually: they produce daughters that are genetic copies of the mothers. However, a female must mate with a male to initiate the development of the embryos. Since there are no males of their own species, she will mate with a male of a related species. His sperm triggers the development of her eggs, but his genetic material (DNA) is sidelined. He does not contribute to the genetic make-up of the offspring.

Amazons thus sexually parasitize males of other species. Researchers like Waldir Berbel-Filho and his colleagues are puzzled by how this situation can persist.

Hybrid

The Amazon molly is a freshwater fish averaging about 5.5 centimetres in length that lives in southern Texas and northeastern Mexico. The species is a hybrid, resulting from a single mating event of a male Poecilia latipinna (sailfin molly) and a female Poecilia mexicana (shortfin molly). These parental species are the ‘hosts’ on which the Amazones sexually parasitize.

Where Amazon mollies live, typically only one of the parent species is found, either the sailfin molly or the shortfin molly. The silvery-gray females of all three species look quite similar, but they differ in body shape: the shortfin molly is longer and thinner than the sailfin molly, and its shorter dorsal fin is inserted more posteriorly. Amazon mollies are intermediate in body shape between the two parental species, but their shape varies across locations.

Miracle

Hybridization occurred 100,000 to 200,000 years ago, meaning that the Amazon molly has gone through approximately 500,000 generations.

That’s a miracle. Because male sailfins and shortfins that mate with an Amazon do not sire any offspring, you’d expect them to learn to distinguish between an Amazon molly and a female of their own species and avoid mating with an Amazon molly. But if they would mate only with females of their own species, the Amazon molly can’t reproduce and becomes extinct.

In addition, the Amazon molly competes with its parental species for food; the fish mainly eat algae and small insects. And because Amazons only have daughters, their populations can grow twice as fast as those of the parental species, which produce equal numbers of sons and daughters. The Amazons could therefore displace the parental species, but then, due to a lack of males, they also perish.

Body shape

It seems like a hopeless situation. To explain why Amazon mollies still manage to survive, Berbel-Filho investigated three possibilities.

First possibility: to attract males, Amazons in each location most closely resemble females of the parental species that is present there. So, where they coexist with sailfin molly, they resemble female sailfin molly, and where they coexist with shortfin molly, they resemble female shortfin molly. In other words, they deceive males through mimicry.

Second possibility: to diminish competition for food, Amazon mollies differ from females of the parental species that they coexist with. If that parental species is sailfin molly, they resemble female shortfin mollies, and vice versa. The underlying idea is that a different body shape is associated with a slightly different diet, so that species with different body shapes at least have some of the available food for themselves, and the species can coexist.

Third possibility: the shape variation of Amazon mollies is random and independent of the parental species with which they occur.

Detailed measurements showed that the second possibility is correct. Amazon mollies are less similar in body shape to females of the parental species with which they coexist. The conclusion is that Amazons do not displace the locally present parent species through food competition, although it still needs to be proven that a difference in body shape indeed reduces competition for food.

Waste

But then there is the other danger: the danger that males of the parental species won’t mate with Amazons. The difference between females in each location helps males distinguish the sexual parasite from their own species. Previous research has shown that males indeed mate more often with females of their own species. So how does the Amazon molly manage to survive?

There is no clear answer to that yet. It could be, I think, because females differ on average. The fish vary in body shape, and there is some overlap between females of the local parental species and Amazons. If males were so choosy as to avoid any mating with an Amazon, they would also reject some females of their own species and miss out on paternity. If the amount of sperm they produce isn’t limiting, they’d be better off wasting some sperm to the wrong females than losing fertilisation opportunities with good ones.

Willy van Strien

Photo: Amazon molly, Poecilia formosa. ©Tyler Reich

Sources:
Berbel-Filho, W.M., M. Tobler, T. Reich, A. Eghbalpour, M.J. Ryan, K. Heubel, F. Garcia-De León & I. Schlupp, 2025. Converging or diverging? Shape coevolution between a sperm-dependent asexual and its sexual hosts. Proceedings of the Royal Society B 292: 20250432. Doi: 10.1098/rspb.2025.0432
Riesch, R., M. Plath, A.M. Makowicz & I. Schlupp. 2012. Behavioural and life-history regulation in a unisexual/bisexual mating system: does male mate choice affect female reproductive life histories? Biological Journal of the Linnean Society 106: 598-606. Doi: 10.1111/j.1095-8312.2012.01886.x
Riesch, R., I. Schlupp & M. Plath, 2008. Female sperm limitation in natural populations of a sexual/asexual mating complex (Poecilia latipinna, Poecilia formosa). Biology Letters 4: 266-269. Doi: 10.1098/rsbl.2008.0019

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

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

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

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

Perfume makers

3 April 2024 /

Young orchid bees create a precious collection of fragrances

Male orchid bees concoct a precious perfume

To seduce females, male orchid bees release a self-made perfume during courtship. Young males are the most fanatical perfume makers, Jonas Henske and Thomas Eltz write.

A beautiful colour with a metallic sheen appears to be insufficient for male orchid bees to impress females. They must also have an attractive scent. Orchid bees (Euglossini, about two hundred species) are found in tropical America. They do not live in colonies, like the honeybee. Males occupy a territory and try to attract females.

A wonderful smell is provided by a self-made perfume, which consists of a mixture of scents that males collected from flowers, rotting wood, sap from trees and – weird enough – faeces. Males differ in the intensity and complexity of their perfume, and only a few males have an outstanding blend. That’s no wonder, because it takes a lot of time and energy to find and collect the dozens of aromatic components, most of which are scarce. Young bees in particular work fanatically to concoct their perfume, as Jonas Henske and Thomas Eltz discovered during their research on Euglossa imperialis in Costa Rica. Males of this species can live for six weeks to three months.

Complex mixture

Hundreds of species of orchids benefit from the male orchid bees’ urge to collect scents. They are pollinated exclusively by these bees, in exchange for a precious fragrance.

Males capture volatile odours by spitting lipids onto a sweet-smelling surface. The fragrances are absorbed by the lipids. The bees then use their legs to stuff the scented fat into special pouches on their hind legs. They regularly take out the content to enrich it with new odours, creating an extensive and complex mixture of fragrances.

A male that wants to mate makes hovering flights in his territory, moving his legs in a characteristic way. Underneath its body, the right and left middle legs alternately sweep the pouches of the opposite hind leg. Tufts of hair on the middle legs absorb some fat. The fluttering wings then spread the perfume that is released.

Experiments in the lab showed that females are interested. The perfume allows them to determine whether they are dealing with a male of their own species; each species of orchid bee has its characteristic scent bouquet. The species Euglossa dilemma and Euglossa viridissima, for example, look similar, but can be distinguished by smell. This indicates that the males carefully compose their scent mixture: all components in exactly the right proportions.

Improvement

The researchers had assumed that the oldest male orchid bees would have the largest supply and the most complex perfume, because they had had the most time to create it. Such a precious perfume would be evidence that its owners had lived a long time, a signal of good hereditary quality and good condition. But that idea turns out to be wrong.

To test their assumption, Henske and Eltz attracted Euglossa imperialis males, captured them, estimated their age, and sealed the perfume pouch on the right hind leg with glue. They then released the animals and waited for them to reappear at the original capture site. Half of the males returned within five days, some stayed away for more than twelve days. The researchers could capture about a third for the second time, and then they compared the contents of both perfume pouches.

Between the first and second measurement, young males had improved the perfume in the pouch on the left hind leg, which had been left open: the supply had become larger, and the perfume had a more varied composition than that in the sealed right pouch. The perfume in the left pouch of old males had deteriorated in quantity and quality.

Trade-off

Perhaps young orchid bee males have a sharper sense of smell, or are more efficient at finding and storing odours, the researchers think. But it may also be a trade-off. Males collect scents and court females throughout their lives, expanding their perfume supply continuously on the one hand and using bits of it up on the other. The balance can change. For males that do not have much time left to live, it may not be worth acquiring more scent; they better use the perfume supply they have.

Unfortunately, it is not known whether females prefer a more complex scent.

Willy van Strien

Photo: Euglossa species male. Thomas Shahan (Wikimedia Commons, Creative Commons BB BY 2.0)

Sources:
Henske, J. & T. Eltz, 2024. Age-dependent perfume development in male orchid bees, Euglossa imperialis. Journal of Experimental Biology 227: jeb246995. Doi: 10.1242/jeb.246995
Eltz, T., C. Bause, K. Hund, J.J.G. Quezada-Euan & T. Pokorny, 2015. Correlates of perfume load in male orchid bees. Chemoecology 25:193-199. Doi: 10.1007/s00049-015-0190-9
Eltz. T., Y. Zimmermann, J. Haftmann, R. Twele, W. Francke, J.J.G. Quezada-Euan & K. Lunau, 2007. Enfleurage, lipid recycling and the origin of perfume collection in orchid bees. Proc. R. Soc. B 274: 2843-2848. Doi: 10.1098/rspb.2007.0727
Eltz, T., D.W. Roubik & M.W. Whitten, 2003. Fragrances, male display and mating behaviour of Euglossa hemichlora: a flight cage experiment. Physiological Entomology 28: 251-260. Doi: 10.1111/j.1365-3032.2003.00340.x

Sacrificing sleep

5 February 2024 /

Dusky antechinus male gives himself little rest

Male dusky antechinus reduces sleep in mating season

A male dusky antechinus must do everything he can in the only short mating season he experiences. He sacrifices hours of sleep, Erika Zaid and colleagues show.

As for all species, producing as many offspring as possible is what life is all about for the dusky antechinus, Antechinus swainsonii. For males, which do not care for young, this means that they have to mate with as many females as possible, because every successful mating may increase the number of young they sire. To achieve this, only three weeks are available, because this is the period in which all females are fertile. Males experience fierce competition; as a consequence of the pressure to face this, they are twice as heavy as females.

This short and intensive mating season has a very bizarre ending for males: they all die. Females, that carry the young in a flap of skin (they have no complete pouch), stay alive and many of them experience a second reproduction season the next year. But for males, it is over after one time.

To score as many partners as possible in that single mating season, males cut back on rest, Erika Zaid and colleagues discovered.

Testosterone

The dusky antechinus, a species of broad-footed marsupial mice, is an insectivorous predator that lives in Australia. Before the mating season, male and female sleep an average of more than 15 hours per day. During the mating season, measurements of physical activity and EEGs show that males reduce this to 12 hours on average: 20 percent less. The increased activity, which they exhibit especially at night, is accompanied by a higher level of the male sex hormone testosterone in the blood, giving them extra time and strength to find females and get access.

Unfortunately, the researchers do not know whether males that sacrifice much sleep actually father more offspring. Also, they did not investigate whether males compensate for the lack of sleep by sleeping more deeply.

Sleeping less jeopardizes health. The concentration of corticosteroids, which suppress the immune system, increases, with ultimately fatal consequences. But because males will die soon anyway, staying healthy is no longer important. Mating more often is now a better strategy than getting enough sleep.

Sustaining

You might think that dusky antechinus males die after the mating season because they have been acting so unhealthy. But that is not how it works, according to the researchers. Their death is a certainty. The increase in corticosteroids hardly contributes anything to this fate, but it does ensure that they can sustain their increased activity.

Willy van Strien

Photo: Antechinus swainsonii. Catching the eye (Wikimedia Commons, Creative Commons CC BY 2.0)

Source:
Zaid, E., F.W. Rainsford, R.D. Johnsson, M. Valcu, A.L. Vyssotski, P. Meerlo & J.A. Lesku, 2024. Semelparous marsupials reduce sleep for seks. Current Biology, January 25 online. Doi: 10.1016/j.cub.2023.12.064

Purple-crowned fairywren assists dear breeders

23 November 2023 /

Subordinate works not always equally hard

purple-crowned faiywren helps parent and potential partner

Purple-crowned fairywrens living with breeding parents often help raise offspring. A subordinate works hardest when father or mother has a new, valuable partner, Niki Teunissen and colleagues show.

The number of territories available is limited for purple-crowned fairywren, a small passerine bird that lives in northern Australia in dense vegetation along rivers and creeks. The territories are linearly aligned, are kept all year round and are all occupied. Out of necessity, young birds often stay with their parents for a few years; most breeding pairs have a few male and female subordinates around them. Purple-crowned fairywrens, Malurus coronatus, eat insects; males have a beautiful purple crown during the breeding season.

Subordinates can assist the breeding pair during the busiest time, the two weeks when the young need to be provisioned. But not all of them offer help, and not all helpers work equally hard. Group members that don’t help are still allowed to stay in the group. Niki Teunissen and colleagues investigated under which circumstances group members do or do not help well. They show that a purple-crowned fairywren subordinate ‘knows’ precisely when it pays to be helpful.

The researchers provided birds with colour rings to make them individually recognizable and of each bird, they knew its parents and its brothers and sisters. They observed the behaviour of fifty groups during three breeding seasons.

Brothers and sisters

If young in the nest have the same parents as a subordinate, or share one parent with it, that subordinate will help feed them. And that is worth the effort. Because with help, more young fledge per clutch on average. A helper shares in this greater success, because those young are full siblings or half-siblings. But in the few years that children stick around, both parents may have died or disappeared and been replaced. And sometimes young birds do not join their parents, but another couple. In such cases, the young are unrelated and a subordinate will not help raise them.

Kinship with the young does not fully explain the willingness to help, though, because, on average, group members work harder for a clutch of half-brothers and half-sisters than for a clutch of full brothers and sisters. That seems enigmatic, but something else is going on. Whether a subordinate will support a breeding pair and how hard it will work, also depends on the value that the pair itself has.

Main prize

When both the breeding male and female are not its parents, it is not going to help feed the young, as we already saw. If both are its parents, it will help; the young are then full siblings. Thanks to this help, the parents reduce their workload. Their chance of survival increases, and so does the chance that a new clutch of brothers and sisters will be produced. This is also a win for the helper.

Things get interesting, the researchers discovered, when one parent is gone and the other parent has a new partner. How hard a resident purple-crowned fairywren will work now depends on which parent is left: the same-sex parent or the other one.

A female purple-crowned fairywren living with her mother and her new partner works much harder than a subordinate in a group with both parents. That is because that new male partner is interesting. If her mother dies, the helper may inherit her place and her partner, become the owner of the territory and produce the next clutch. That’s the main prize!

With a father and a new partner, she has less to gain. That new female partner is of no use to her, in fact: she is a rival if a new male ever comes into play. So, she works less hard.

Likewise, a male fairywren puts in most effort in helping when living with a father with a new partner.

Sophisticated

And therefore, a subordinate purple-crowned fairywren works hardest when the breeding pair consists of a parent and a potential mate – which is very sophisticated. Such couple has great value to him or her. That is why he or she often helps provisioning a nest with half-siblings more intensively than a nest with full siblings.

In line with this, the researchers had previously shown that a young purple-crowned fairywren is less willing to join a group with a same-sex stepparent. Subordinates affiliate with parents and a potential mate. Also, when they help defend the nest against predators, it is to protect (half)siblings as well as parents and a potential mate.

Willy van Strien

Photo: Female (left) and male purple-crowned fairywren. P. Barden (Wikimedia Commons, Creative Commons CC BY 4.0)

Sources:
Teunissen, N., M. Fan, M.J. Roast, N. Hidalgo Aranzamendi, S.A. Kingma & A. Peters, 2023. Best of both worlds? Helpers in a cooperative fairy-wren assist most to breeding pairs that comprise a potential mate and a relative. Royal Society Open Science 10: 231342. Doi: 10.1098/rsos.231342
Teunissen, N., S.A. Kingma, M. Fan, M.J. Roast & A. Peters, 2021. Context-dependent social benefits drive cooperative predator defense in a bird. Current Biology 31: 4120-4126. Doi: 10.1016/j.cub.2021.06.070
Teunissen, N., S.A. Kingma, M.L. Hall, N. Hidalgo Aranzamendi, J. Komdeur & A. Peters, 2018. More than kin: subordinates foster strong bonds with relatives and potential mates in a social bird. Behavioral Ecology 29: 1316-1324. Doi: 10.1093/beheco/ary120
Kingma, S.A., M.L. Hall, E. Arriero & A. Peters, 2010. Multiple benefits of cooperative breeding in purple-crowned fairy-wrens: a consequence of fidelity? Journal of Animal Ecology 79: 757-768. Doi: 10.1111/j.1365-2656.2010.01697.x

Promotion for buff-tailed bumblebee worker

23 October 2023 /

If the queen is lost, a worker can take over

When the queen is lost, a buff-tailed bumblebee worker can take over

Normally, buff-tailed bumblebee workers do not mate. But if the queen disappeared, they may mate, Mingsheng Zhuang and colleagues show, enabling the colony to survive.

A bee queen mates and lays eggs; fertilized eggs develop into females, unfertilized eggs into males. Her workers, also females, refrain from reproduction; they defend the nest, care for the brood and forage for food. Thanks to this strict division of labour, a colony runs well. If workers also would produce eggs, too little work would be done. Because the offspring of the queen are related to each other, workers have indirect reproductive success. They do not have a spermatheca, the vesicle in which females store sperm after mating, and are unable to mate. Once a worker, always a worker.

At least, this is how it is in honeybees.

But it does not apply to all bee species that live in colonies with a division of labour between queen and workers, so-called ‘eusocial’ species. In bumblebees (which belong to the bees), workers do have a spermatheca.

It was a mystery why. Now, Mingsheng Zhuang and colleagues argue that bumblebee workers sometimes are promoted to queen.

Artificial insemination

Zhuang shows that workers of several bumblebee species have a spermatheca that is functional. When he artificially inseminated workers, they responded in the same way as queens. They laid fertilized eggs from which daughters emerged and founded a colony. He thinks that workers of all bumblebee species still have a functional spermatheca, even though bumblebees have existed as a eusocial group for tens of millions of years.

The logical next question is whether bumblebee workers can actually mate and function as queens. And under what circumstances they will do.

The researchers conducted much of their research on the buff-tailed bumblebee, Bombus terrestris. This species, which occurs in Europe, North Africa, and parts of Asia, has colonies that exist for one year. In the spring, each queen that has mated and hibernated starts a colony on her own. She makes a nest in the ground, lays eggs and takes care of the larvae that hatch. These larvae develop into workers. Once they are present, the queen is dedicated to laying eggs. The colony grows to a size of hundreds of workers.

At the end of the season, the queen lays eggs from which males develop, and young queens appear. Workers also will lay eggs then, which are unfertilized and produce males. Young queens leave, mate and search a place to hibernate. Males and workers die.

Replacement

Buff-tailed bumblebee workers normally do not mate. But they can, as experiments of Zhuang show, if they have been separated from the queen and egg-laying workers for a while. In this regard, they differ from young queens, which do not need such a period of isolation. And if a worker has been in the company of nest mates for more than 24 hours before isolation, a switch is not possible anymore. So, opportunities for promotion are limited. Moreover, the chance of workers surviving a mating appears to be small.

But it may be enough to be able to provide a replacement and rescue the colony if a queen dies prematurely, Zhuang and colleagues think; that chance is probably quite high. In that case, workers will lay eggs that develop into early males and if one of the workers takes over the role of queen, mating and producing daughters, the colony can finish the season. According to them, this explains why workers have retained a functional spermatheca. It is difficult to determine whether such replacement often occurs in the wild, they write. It would require locating and digging out colonies and conducting DNA research.

Smaller

Why doesn’t a worker leave the natal colony and start her own? She would have to leave soon after eclosion, meet a male and survive the mating. But workers are much smaller than queens and produce fewer eggs. Being part of a large colony as a worker will yield greater reproductive success than heading a small colony as a queen.

Willy van Strien

Photo: Buff-tailed bumble bee queen on small-leaved lime. Ivar Leidus (Wikimedia Commons, Creative commons CC BY-SA 4.0)

Source:
Zhuang. M., T.J. Colgan, Y. Guo, Z. Zhang, F. Liu, Z. Xia, X. Dai, Z. Zhan, Y. Li, L. Wang, J. Xu, Y. Guo, Y. Qu, J. Yao, H. Yang, F. Yang, X. Li, J. Guo, M.J.F. Brown & J. Li, 2023. Unexpected worker mating and colony founding in a superorganism. Nature Communications 14: 5499. Doi: 10.1038/s41467-023-41198-6

Two-spotted spider mite male in a hurry

11 July 2023 /

He strips off her old skin to be the first to mate

A female two-spotted spider mite often is undressed by a male

When a two-spotted spider mite female is about to moult into an adult, a male is often already waiting to undress her and mate, Peter Schausbergen and colleagues write.

Males of the two-spotted or red spider mite, Tetranychus urticae, have to exert every effort to produce offspring, because only the one who is the first to copulate with a female can fertilize her eggs. So, it is important to be present as soon as a female matures. Often, a male is already around before that time, according to observations by Peter Schausbergen and colleagues.

Mites are arachnids. They start life as an egg, become a larva and then go through two nymphal stages. They moult between the stages and emerge from the old skin a bit bigger; after the last moult they are sexually mature. Females develop from fertilized eggs, males from unfertilized eggs.

Silvery appearance

A female two-spotted spider mite is often joined in the last nymphal stage by a male that claims her by sitting on top of her. He spends time and energy on guarding her, and these would be wasted if a rival appears after the last moult and succeeds in mating first. That danger is real, because a newly emerged adult female secretes pheromones that attract males. The guarding male must prevent this.

To shorten the precious waiting time and secure the first mating, a guarding male acts decisively when her final moult is coming. A day before moulting, the nymph enters a resting phase, and in the last few hours she takes on a silvery colour due to air getting between the old skin, which she will shed, and the new skin.

She initiates the moult by bulging, causing the old skin to crack along a crossline. If she is alone, she first pulls off the anterior part of the old skin and then the posterior part, exposing her genital opening. But if a male is guarding, things go different. He drums her back with his forelegs, and in response she bulges earlier. When the old skin has cracked, he quickly strips off the posterior part with his pedipalps (the ‘boxing gloves’ that also spiders also possess). And then, with a bit of luck, he will indeed be the first to mate.

Fighters and sneakers

In our view, this undressing behaviour of the male two-spotted spider mite is very indecent. But he has no choice. Prudent behaviour is punished by natural selection: if he waits patiently for her to undress herself, it is more likely that another male takes over and sires the offspring.

There are two types of guards. Some are fighters, that are often disturbed by other males when they sit on a female and dismount to fight. Others are sneakers, that are not attacked by rivals and are never disturbed. Maybe other males mistake them for females because they do not respond, or maybe they smell like females. It would be interesting to find out whether fighters and sneakers display the same pushing behaviour when the nymph they guard is about to moult.

Pest

The two-spotted spider mite is less than half a millimetre long. It feeds by piercing plant cells and sucking their contents. It is a worldwide pest on many agricultural crops. A single mite does little harm, but the bugs multiply quickly and in a brief time, there are many of them.

Willy van Strien

Photo: Two-spotted spider mite female, Tetranychus urticae. Gilles San Martin (Wikimedia Commons, Creative Commons, CC BY-SA 2.0)

Sources:
Schausberger, P., T.H.H. Nguyen & M. Altintas, 2023. Spider mite males undress females to secure the first mating. iScience, 107112, 7 July. Doi: 10.1016/j.isci.2023.107112
Sato, Y., M.W. Sabelis, M. Egas & F. Faraji, 2013. Alternative phenotypes of male mating behaviour in the two-spotted spider mite. Experimental and Applied Acarology 61: 31-41. Doi: 10.1007/s10493-013-9673-y

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