From so simple a beginning

Evolution and Biodiversity

Fruit abundance

10 October 2024 /

White-bearded manakin with rich territory is more successful

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

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

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

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

Costly courtship display

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

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

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

Uneven playing field

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

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

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

Competition

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

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

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

Willy van Strien

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

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

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

Parasol

26 September 2024 /

Male desert locust protects female from sun

Desert locust is heat tolerant

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

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

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

Possessive behaviour

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

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

And it turns out to have still another advantage.

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

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

Cooler

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

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

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

Willy van Strien

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

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

Amputation saves ant lives

9 July 2024 /

Florida carpenter ant workers treat leg wounds effectively

Workers of Florida carpenter ant amputate legs when useful

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

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

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

Bitten off

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

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

Bacterial load

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

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

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

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

Time enough

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

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

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

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

Willy van Strien

Illustration: ©Hanna Haring

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

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

Successful in the deep sea

11 June 2024 /

Bizarre deep-sea anglerfishes thrive in challenging environment

Deep-sea anglerfishes flourished thanks to sexual parasitism

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

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

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

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

Sex guaranteed

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

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

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

Fortunate combination

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

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

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

Willy van Strien

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

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

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

Beetle mimics noxious moths

31 May 2024 /

Bats leave tasty tiger beetle alone

Tiger beetles imitate ultrasonic sounds of unpalatable tiger moths

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

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

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

Ultrasonic response

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

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

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

Tiger beetles and tiger moths

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

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

Unpalatable tiger moth warns bat predator with ultrasonic sound

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

Wings

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

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

Willy van Strien

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

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

Different flower colour, different visitor

16 May 2024 /

Camouflaged fritillary still attracts pollinators

Fritillary Fritillaria delavayi has brown leaves in many places

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

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

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

Lung diseases

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

In some places, Fritillaria delavayi even has brown flowers

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

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

Frequent visits

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

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

Willy van Strien

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

See also: Corydalis hemidicentra with cryptic leaf colour

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

Nest architectural traditions

9 April 2024 /

Stingless bee follows existing construction plan

Nest of Scaptotrigona depilis with combs in corkscrew form

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

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

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

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

Switching

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

Scaptotrigona depilis: combs in parallel form

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

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

Default

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

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

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

Willy van Strien

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

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

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

Suckling amphibian

25 March 2024 /

Ringed caecilian-mother produces milk for her young

Ringed caecilian feeds milk to her young

Females of the ringed caecilian secrete a fluid rich in fats and carbohydrates for their hatchlings, Pedro Mailho-Fontana and colleagues discovered. Like mammal’s milk.

Mammals suckle their young. This behaviour distinguishes them from other vertebrates: fish, amphibians, reptiles, and birds. Yet that distinction is not watertight, as a few bird species exist that produce a kind of milk to feed their young: some pigeons and doves, some flamingos, and the emperor penguin. And now, Pedro Mailho-Fontana and colleagues report that females of the ringed caecilian, an amphibian, feed their young with something that resembles mammalian milk. Thanks to this ‘milk’, the youngsters grow rapidly.

It is not surprising that this peculiar trait, which is easily observable, is only now coming to light. The biology of caecilians is poorly known because the animals live underground. Caecilians (Gymnophiona) form a third group within the amphibians, next to frogs & toads and salamanders. They have no legs, have reduced eyes, and are blind; they have two tentacles with which they find their way underground.

Spoon-shaped teeth

The caecilian in question here is the ringed caecilian (Siphonops annulatus). It is widespread in South America. The animal grows to over forty centimetres in length. A female lays eggs, on average ten at a time, in an underground round nest chamber. She is a devoted mother: she lays coiled up with the eggs on her body, and when the young have hatched, she stays with them for another two months; then the young are independent. Until that moment, she will not even leave for a brief time to find food for herself.

A female changes colour when she is attending hatchlings. Normally, ringed caecilians are bluish grey, but a mother turns whitish grey. It was already known that this colour is caused by fat droplets accumulating in her epidermis. Every few days, the young are allowed to scrape off that skin; for this purpose, they have spoon-shaped teeth in the lower jaw. They all do at the same time, ferociously; within ten minutes it is over, and peace returns until the mother’s skin is ready for consumption again. This ‘skin feeding’ occurs in more caecilian species.

But ringed caecilians hatchlings also get other food, Mailho-Fontana discovered: milk. He kept a number of animals in the lab and filmed their behaviour.

Oviductal milk

Hatchlings often assemble near their mother’s rear end, he observed. Further research revealed that glands in the mother’s oviduct walls produce a white, viscous fluid that emerges through the genital opening, the cloaca, several times a day. The stuff is rich in fats and carbohydrates.

The young imbibe it voraciously. This ‘milk’ is a more important source of nutrition than the mother’s skin, and it is thanks to the milk that the young grow very fast, the researchers think. Their weight doubles within a week after hatching. The mother, eating nothing, loses a third of her weight.

The mother releases milk when hatchlings touch her tail, often producing high-pitched sounds, which probably is begging behaviour. She then raises her body end vertically, and the hatchlings compete for a good place. On average, three of them drink at the same time until they are fully satiated.

Viviparous caecilian species in which the young drink milk in the oviducts before birth were already known. The discovery of oviductal milk in the egg-laying ringed caecilian was unexpected.

Willy van Strien

Photo: Ringed caecilian, female with young. ©Carlos Jared

Sources:
Mailho-Fontana, P.L., M.M. Antoniazzi, G.R. Coelho, D.C. Pimenta, L.P. Fernandes, A. Kupfer, E.D. Brodie Jr. & C. Jared, 2024. Milk provisioning in oviparous caecilian amphibians. Science 383: 1092-1095. Doi: 10.1126/science.adi5379
Jared, C., P.L. Mailho-Fontana, S.G.S. Jared, A. Kupfer, J.H.C. Delabie, M. Wilkinson & M.M. Antoniazzi, 2019. Life history and reproduction of the neotropical caecilian Siphonops annulatus (Amphibia, Gymnophiona, Siphonopidae), with special emphasis on parental care. Acta Zoologica. 100: 292-302. Doi: 10.1111/azo.12254
Wilkinson, M., A. Kupfer, R. Marques-Porto, H. Jeffkins, M.M. Antoniazzi & C. Jared, 2008. One hundred million years of skin feeding? Extended parental care in a Neotropical caecilian (Amphibia: Gymnophiona). Biology Letters 4: 358-361. Doi: 10.1098/rsbl.2008.0217

Repurposed

16 February 2024 /

Tree fern Cyathea rojasiana transforms dead leaves into roots

Tree fern Cyathea rojasiana transforms dead leaves into roots

Brown, dried leaves are not worthless for the tree fern Cyathea rojasiana. On the contrary: the tree fern uses them as extra roots, James Dalling and colleagues discovered.

The tree fern Cyathea rojasiana, which grows in Panama, has a crown of leaves on a trunk. Sometimes a new frond sprouts, sometimes an old leaf dies. But dying is not the end for a leaf, James Dalling and colleagues discovered: the decayed leaf gets a second life. At least: the rachis.

The tree fern grows to a height of two meters, the leaves are more than two meters long. A senescent leaf will bend down, the leaf tip touching the ground. The leaf rots away, but the rachis remains. A tree can have a ‘skirt’ of twenty to thirty of those remains. They look lifeless, but when Dalling tried to remove them, they were found to be firmly stuck in the ground.

Reversed flow direction

Vascular bundles run through the rachis of a green leaf, transporting water and nutrients absorbed by the roots to the leaf tissue. These vascular bundles appear to be intact in the ground-stuck leaf remains of Cyathea rojasiana. They are surrounded by a black layer that apparently protects them from rotting. And, surprisingly, at the end, i.e., in the soil, a bunch of finely branched roots has sprouted from each vascular bundle.

The conclusion is that the former leaf rachises have been transformed into roots, in which the direction of the water flow is reversed: in green leaves, it flowed from stem to leaf tip, now it is from leaf tip to stem.

Cyathea rojasiana grows in wet, extremely nutrient-poor soil. Extra roots are not so much useful to absorb water, the researchers think, but to extract nutrients from a larger area of soil. They showed that the new roots indeed absorb nitrogen and transport it upwards.

For many plant species holds: you can stick a piece of stem or leaf in the ground, and roots will grow. But converting a leaf rachis into a root is something that, as far as we know, only Cyathea rojasiana does.

Willy van Strien

Photo: Tree fern Cyathea rojasiana with decayed leaves, now functioning as roots. ©James Dalling

James Dalling tells about his discovery on YouTube

Source:
Dalling, J.W., E. Garcia, C. Espinosa, C. Pizano. A. Ferrer & J.L. Viana, 2024. Zombie leaves: novel repurposing of senescent fronds in the tree fern Cyathea rojasiana in a tropical montane forest. Ecology e4248, 18 January online. Doi: 10.1002/ecy.4248

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