Category: reproductive behaviour (Page 1 of 4)

Young orchid bees create a precious collection of fragrances

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

If the queen is lost, a 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

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

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

Young spotted bowerbird joins older male

In company of a subordinate, a spotted bowerbird male stands stronger: his bower is safe, and more females are impressed, according to observations by Giovanni Spezie and Leonida Fusani.

Bowerbird males keep themselves to themselves. To seduce females, they each build their own bower with courtship platforms. They keep a far distance from each other; in the spotted bowerbird, the average distance is no less than 1 kilometre. Yet the owner of a bower often has company of a subordinate male. Giovanni Spezie and Leonida Fusani wondered what such male is doing there. Is he a younger male learning skills from an older one? Or does he actively participate in the activities, is it a form of collaboration?

The spotted bowerbird (Ptilonorhynchus maculatus or Chlamydera maculata) is one of 21 species of bowerbirds that exist, and it lives in eastern Australia. It has an erectile lilac crest on the nape.

A male builds a lane of grass and twigs with a platform on both sides of mainly greyish objects, such as bones and stones. He decorates the place with berries, leaves and pieces of glass. Females will visit and enter the bower to watch the male calling and dancing next to his bower. The performance can last an hour. With his elaborate bower and energetic courtship display, he shows his quality. If she likes it, she will mate.

Males can devote all their time to show off, because taking care of the young is a females’ task. Some males attract several females, but all the effort of many others are in vain.

Adequate reaction

To find out what subordinate males are doing at bowers, the researchers made motion-activated video recordings. They analysed the footage to see if such male just watches, or also participates in bower maintenance and courtship. And if he helps, is he, like the bower owner, able to adapt his behaviour to the reaction of a visiting female, for example if she threatens to leave? Does the bower owner benefit from the help? And the helper himself?

Although subordinate males are less active than bower owners, they behave similar and respond to female behaviour in the same way (unless the researchers missed subtle differences). So, the relationship between an owner and subordinate seems unlike that of teacher and apprenticeship, the researchers suggest.

Both participants benefit

Rather, the subordinate seems to be a helper. In his presence, the bower is less likely to be plundered by competing males. Males often destroy each other’s bower or steal precious ornaments to embellish their own place. In the spotted bowerbird, marauding is less common than in other species, but the presence of an extra male even reduces the risk. That is why a bower owner may tolerate the presence of another male.

In addition, an owner with a helper has more courtship success.

The owner thus benefits from the company of a subordinate. In turn, the auxiliary male also benefits; sometimes he has an opportunity to mate with a visiting female. In addition, there is a chance that he will gain ownership of the bower. A partnership between males may last for years.

Related?

The collaboration would be most useful if the males were related, for example brothers, so that the subordinate indirectly has some reproductive success via the bower owner. But researchers have not yet investigated whether that is the case.

It is questionable. Other research had shown that males pay little attention to family relationships. They don’t necessarily place their bower near relatives, but they don’t avoid them either. And if they maraud a bower, it is the neighbour’s bower, regardless of whether the birds are relatives.

Willy van Strien

Photos:
Large: spotted bowerbird. Greg Miles (Wikimedia Commons, Creative Commons CC BY-SA 2.0)
Small: bower of spotted bowerbird. Davidgregsmith (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Sources:
Spezie, G. & L. Fusani, 2022. Male–male associations in spotted bowerbirds (Ptilonorhynchus maculatus) exhibit attributes of courtship coalitions. Behavioral Ecology and Sociobiology 76: 97. Doi: 10.1007/s00265-022-03200-x
Madden, J.R., T.J. Lowe, H.V. Fuller, R.L. Coe, K.K. Dasmahapatra, W. Amos & F. Jury, 2004. Neighbouring male spotted bowerbirds are not related, but do maraud each other. Animal Behaviour, 68: 751-758. Doi: 10.1016/j.anbehav.2003.12.006

Spider male escapes from cannibalism

With a catapult mechanism, a male of the spider Philoponella prominens manages to escape his hungry partner after copulation. Shichang Zhang and colleagues recorded it on video.

For many male spiders, mating is life-threatening. Because to a female, a male not only is a supplier of sperm that she can use to fertilize her eggs, but also a tasty snack. And when he has given his sperm, he is just a meal. Dying without siring offspring is no option. So, he has to proceed with caution, and leave immediately after finishing copulation.

A Philoponella prominens male, a spider species from woods of central China, is very accomplished. After mating, he swiftly leaps away, out of her reach, Shichang Zhang and colleagues show. They recorded mating and leaping with a high-speed camera.

High pressure

During mating, which lasts half a minute, he folds his two front legs against her, the researchers observed. By suddenly stretching them afterwards, he pushes off and shoots away. He had already secured himself before with a safety line of silk, which he had tied to the edge of her web. After leaping, he crawls back via that line to mate with her again. He is able to repeat the action up to six times.

Spiders move their legs not only with muscles, but also use hydraulics. They bend the legs by contracting flexor muscles but lack extensor muscles. Instead, they fill the joints with body fluid at high pressure, so that the legs stretch by released hydraulic power as the flexor muscles are relaxed. In this way, a male Philoponella prominens jumps from his partner. He reaches a speed of about seventy centimeters per second, spinning around at high speed. A female is unable to grasp him.

The leap is lifesaving, as the researchers showed. If they prevented a male from leaping with a fine brush, he was grabbed by his partner and eaten. As if he were just prey.

Willy van Strien

Photo: Philoponella prominens, mala above female. © Shichang Zhang

Emergency leap on video

Another spider male that has to be careful: Maevia inclemens

Source:
Zhang, S., Y. Liu, Y. Ma, H. Wang, Y. Zhao, M. Kuntner & D. Li, 2022. Male spiders avoid sexual cannibalism with a catapult mechanism. Current Biology 32: R341-R359. Doi: 10.1016/j.cub.2022.03.051

Dance fly female advertises quality by inflating her body

Shaped like flying saucers, long-tailed dance fly females seek the attention of males. Their wide shape indicates their quality, Jessica Browne and colleagues write.

Females of the long-tailed dance fly (Rhamphomyia longicauda), which lives in North America, possess ornaments that make them attractive to males. They have sacs on either side of their abdomen and feathery black scales on their legs. By inflating the sacs and wrapping the legs along them while flying, they become laterally expanded. In this way, they show their quality, Jessica Browne and colleagues argue.

Sex roles reversed

In most animal species, females are choosy and males try to impress them by showing off. But in long-tailed dance flies, it is just the other way around: the males are choosy, the females try to seduce them to mate.

The reason is that females are unable to gather their food on their own. They need food to produce eggs, but cannot hunt for the smaller insects on which they live. That is why they have to to be provisioned by males. A male intending to mate brings a prey as a nuptial gift. Females mate frequently, because every mating yields a meal. But males have to catch prey first. That is hard for them, and a male that has gone to all that trouble will offer his gift only to a female that deserves it.

Silhouette

In order to seduce males, females gather in a lek. At dawn or dusk they form a swarm of dozens of flies in a clearing in the forest and ‘dance’ about half a meter above ground level. Males that have captured a prey will approach such swarm from below and see the females silhouetted against the dimly lit sky. Upon detection of an attractive female, a male will hover just below her. She doesn’t miss the chance and immediately drops on him. Together they leave the swarm to mate. She stores his sperm to fertilize eggs with later.

Males prefer large females. To be attractive, females inflate their sacs, lift their legs and wrap them along the laterally expanded sacs, so that their silhouette becomes much wider. They look like flying saucers. The wider a female is, the greater her chance of being chosen.

But what exactly does a large silhouette signify? Why is it beneficial for males to choose such inflated female?

Magnified difference

The higher the quality of a long-tailed dance fly female is, the wider she can make herself, as Browne and colleagues show. A dance fly begins its life as a larva. After pupation, an adult fly emerges with dimensions that are fixed; also the size of the sacs and the scales on the legs of females is fixed. Probably, the size of an adult fly is an indication of quality and a result of how good conditions were during its larval stage. Now, it turns out that the larger a female is, the larger her expandable sacs and leg scales are in proportion. Because large females can make themselves relatively wider, the differences in quality that exist between females are magnified.

Males preferring inflated females are choosing quality.

Paternity not guaranteed

Their choice is a good one, because a wide female potentially produces many eggs. And because she is attractive, she will be chosen frequently and fed many meals, so she will be able to indeed develop those eggs. She also has a good chance of surviving long enough.

But a male that chooses an attractive female can only hope that he will sire some of that progeny. If he is the first to mate her, she will use his nuptial gift to initiate egg development, but by the time she is going to lay them, she has stored sperm from many more males and his chances are small. A male probably has the best chance to sire much offspring if he is the last to mate with her before she starts laying eggs, when they are almost mature.

But in what state of development the eggs of an attractive female are, a male cannot infer from her size. He must be choosy, but he must also be lucky.

Willy van Strien

Photo: Female Rhamphomyia longicauda with inflated sacs. ©Heather Proctor

Sources:
Browne, J.H. & D.T. Gwynne, 2022. Deceived, but not betrayed: static allometry suggests female ornaments in the long‑tailed dance fly (Rhamphomyia longicauda) exaggerate condition to males. Evolutionary Ecology, online Jan. 7. Doi: 10.1007/s10682-021-10148-3
Murray, R.L., J. Wheeler, D.T. Gwynne & L.F. Bussière, 2018. Sexual selection on multiple female ornaments in dance flies. Proceedings of the Royal Society. B 285: 20181525. Doi: 10.1098/rspb.2018.1525
Funk, D.H. & D.W. Tallamy, 2000. Courtship role reversal and deceptive signals in the long-tailed dance fly, Rhamphomyia longicauda. Animal Behaviour 59: 411-421. Doi: 10.1006/anbe.1999.1310