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.
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
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.
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.
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
Dung ball roller female helps male when things get difficult
Together, a male and female dung ball roller are able to transport a dung ball over a path with obstacles.He leads, she moves along and assists where necessary, Claudia Tocco and colleagues show.
Dung ball rollers (Sisyphus species) have a striking habit. The dung beetles form pairs, take a piece of mammal droppings, construct a ball larger than themselves and roll it away in a straight line to make sure not to collide with other pairs that have taken a part of the same dung pile. When, often after demanding work, they arrive at a suitable place, they bury their ball in the soil together with an egg. The larva that will hatch from the egg is surrounded by excellent food.
Claudia Tocco and colleagues wanted to know more about the harmonious cooperation that male and female exhibit. They investigated how partners divide tasks in two species: Sisyphus fasciculatus from South Africa and Sisyphus schaefferi, that lives in North Africa, Southern Europe, and Asia Minor. In an outdoor test setup, they offered cow dung to groups of dung ball rollers. The beetles formed pairs, constructed a dung ball and started rolling.
The male, which is slightly larger than the female, is always the one driving the dung ball transport, as the researchers saw. He determines the course. He walks backwards and pulls the dung ball with his front legs. His partner walks on the other side, also backwards, with her head down and her hind legs on the ball. On flat terrain, she contributes nothing. If the male stops rolling, she also stops. So, you never see a female dragging a dung ball by herself. Conversely: if she stops, he goes on alone, rolling the dung ball as quickly and staying on course as well as a couple.
Mostly, she does move along, maintaining contact with the ball. Consequently, she can help immediately when things get difficult. And they do, because Sisyphus fasciculatus and Sisyphus schaefferi live in woodlands and forests, with all kinds of objects lying on the ground. A couple of dung ball rollers often encounters obstacles. The researchers conducted experiments to simulate these situations to see how the pair cleared them.
First, they placed two 2.6 centimeter high obstacles one behind the other on the path. That is quite a challenge, because a dung ball roller is less than a centimeter long. At these obstacles, the female no longer followed passively, as it turned out, but assisted by pushing or steering, and as a result, a pair cleared the double obstacle faster than a male working alone. Moreover, a male alone often gave up.
In a next series of experiments, the beetles were challenged with a wall of 3.9, 6.5 or 9.1 centimeters high. The higher the wall, the less likely a pair was to climb over it with the ball and the less likely it was to succeed if it tried. A male alone declined more often than a pair, but if he tried to clamber over the wall, he usually succeeded.
A couple could get over a high obstacle faster than a male alone, mainly because the female helped at the start. When the male pulled himself up along the wall and lifted the dung ball from the ground, she stabilized the ball with her hind legs and pushed it, in a headstand position. Then he worked his way up, while she hung on the ball. Despite that extra burden for the male, a pair climbed as quickly as a male alone. If he was in danger of falling, she would provide support. Once she got to the top, she became active and pushed the ball over the edge with her head. The beetles then fell down and continued their path.
Dung ball rollers manage to get their ball over difficult obstacles. Unlike the Greek mythical king Sisyphus, after whom the beetles are named. Because of his brutality towards the gods, he was punished by having to push a boulder up a slope in the underworld for eternity, while the boulder kept falling back. He could not do it alone and he did not have a partner to lend a hand.
Willy van Strien
Photo: Sisyphus schaefferi couple with dung ball, male at left side, female at right side. Daniel Ballmer (Wikimedia Commons, Creative Commons, CC BY-SA 4.0)
Sources: Tocco, C., M. Byrne, Y. Gagnon, E. Dirlik & M. Dacke, 2024. Spider dung beetles: coordinated cooperative transport without a predefined destination. Proceedings of the Royal Society B 291: 20232621. Doi: 10.1098/rspb.2023.2621 Dacke, M., E. Baird, B. el Jundi, E.J. Warrant & M. Byrne, 2021. How dung beetles steer straight. Annual Review of Entomology 66: 243-256. Doi: 10.1146/annurev-ento-042020-102149
Matabele ant heals infection of injured conspecifics
Workers of the Matabele ant treat infected wounds of nest mates with self-made antibiotics, Erik Frank and colleagues saw.That saves the lives of those nest mates.
Groups of Matabele ants (Megaponera analis) hunt termites, which fight back fiercely. Consequently, foraging trips cause many casualties. An ant colony would perish if it were not for the fact that ‘slightly’ injured specimens, for instance ants that lost one or two legs, are picked up and carried back to the nest. Thanks to the care they receive there, most of them recover from their injuries; without help, they would be dead within 24 hours in all probability.
Erik Frank and colleagues previously discovered that workers lick and groom the wounds immediately after arrival in the nest. Now, it appears that they also treat the wounds medically. The Matabele ant lives in Africa south of Sahara; the research was done in Ivory Coast.
Video recordings in artificial nests in the lab show that workers groom victims’ wounds again after 10 to 12 hours, and then often apply a substance after cleaning that they take from glands on the back, the metapleural glands. They use their own glandular product or that of the wounded individual. They mainly treat ants with wounds that have become infected, for example with the deadly bacterium Pseudomonas aeruginosa.
The glands of the Matabele ant form a well-supplied pharmacy. They turn out to produce more than a hundred compounds, many of which have an antimicrobial or healing effect. Tests show that the antibiotic mix suppresses the growth of the bacteria. Most other ant species also have metapleural glands, but with a less extensive arsenal of substances.
How do nursing workers know whether a wound is infected or not? Probably because the composition of the outer layer that ants have – a waxy layer of hydrocarbons – changes during infection. Colony mates can smell that.
Conclusion: Matabele ant workers can effectively treat wounds of conspecifics with self-made antibiotics. This ability is unique among insects and other invertebrates.
Willy van Strien
Photo: Matabele ant worker with termites. ETF89 (Wikimedia Commons, Creative Commons CC BY-SA 4.0)
Source: Frank, E.T., L. Kesner, J. Liberti, Q. Helleu, A.C. LeBoeuf, A. Dascalu, D.B. Sponsler, F. Azuma, E.P. Economo, P. Waridel, P. Engel, T. Schmitt & L. Keller, 2023. Targeted treatment of injured nestmates with antimicrobial compounds in an ant society. Nature Communications 14: 8446. Doi: 10.1038/s41467-023-43885-w
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.
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.
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
Horsehair worm manipulates mantis with its own genes
Horsehair worms, which live parasitically in various insects during their larval stage, drive their host to suicide. Tappei Mishina and colleagues wondered how they acquired the potential to make this happen.
A striking and gruesome example of parasites that manipulate their host are horsehair worms. During their larval stage, they live in crickets, grasshoppers, and mantises, but as adult worms they live freely in water. To get there, they drive their hapless host to commit a self-destructive act: it jumps into the water. Horsehair worms can disrupt the behaviour of their host so dramatically thanks to genes they picked up from it, Tappei Mishina and colleagues show.
In water, adult horsehair worms (Nematomorpha) mate in a knotted mass of males and females; that is why they are also called Gordian worms. The females then lay eggs from which microscopic larvae hatch. In order to develop further, they must move to insect hosts that live on dry land. The hosts can ingest the larvae directly with their food or via a ‘transporter’, for instance a mayfly. Living in water during its larval stage, this insect is exposed to horsehair worm larvae. The adult mayfly flies out and may be grabbed by an insect host, which then becomes infected with a parasitic horsehair worm larva.
And then, a horror story starts. The horsehair worm larva grows into an extremely thin worm that can reach several times the length of the host. By the time the parasite matures, it forces its host to behave unnaturally. The host, no longer in charge of himself, starts wandering until it comes across water. Then it enters the water body, often with death as a result. If it survives, it will be infertile.
But the worm is in its element. It wriggles out of the insect’s body and starts looking for conspecifics. If the host is attacked by a predatory water insect before the worm is out, it will emerge more quickly. And if the host is swallowed by a fish or frog, the worm manages to escape from that fish or frog also.
How can horsehair worms so dramatically manipulate the behaviour of their hosts, from which they differ greatly from an evolutionary perspective, Mishina wondered.
His research on mantis Tenodera angustipennis and horsehair worm Chordodes fukuii shows that the worm literally took over the biochemistry of its host.
The researchers first examined which genes are activated or deactivated in the horsehair worm and in the mantis brain, and how this pattern changes during host manipulation. They show that only in the worm does the expression pattern change: during manipulation, many genes are read and transcribed to be translated into proteins that were previously inactive, while other genes are silenced. The worm produces proteins to influence the praying mantis’ brain, is the conclusion.
They then compared genes from Chordodes species with information about known genes and proteins stored in databases. This yielded a surprising result: more than 1,400 genes of the parasites are very similar to genes of mantises. Especially these genes are expressed differently during manipulation; most are more strongly activated, others are suppressed. Other horsehair worm species than Chordodes species, which have other hosts, do not possess these mantis genes.
Horizontal gene transfer
It seems that Chordodes has picked up genes from its hosts, mantises, over the course of its evolutionary history – and not just a little. That happened not once, but many times. It is not surprising that the proteins encoded by these genes have an effect in mantises.
Gene transfer between animal species, which is called horizontal gene transfer, is a special and, as far as we know, very rare phenomenon. The researchers suggest that it may also play a role in other cases of host manipulation.
Sources: Mishina, T., M-C. Chiu, Y. Hashiguchi, S. Oishi, A. Sasaki, R. Okada, H. Uchiyama, T. Sasaki, M. Sakura, H. Takeshima & T. Sato, 2023. Massive horizontal gene transfer and the evolution of nematomorph-driven behavioral manipulation of mantids. Current Biology, online 19 October. Doi: 10.1016/j.cub.2023.09.052 Sánchez, M.I., F. Ponton, D. Missé, D.P. Hughes & F. Thomas, 2008. Hairworm response to notonectid attacks. Animal Behaviour 75: 823-826. Doi: 10.1016/j.anbehav.2007.07.002 Ponton, F., C. Lebarbenchon, T. Lefèvre, D.G. Biron, D. Duneau, D.P. Hughes & F. Thomas, 2006. Parasite survives predation on its host. Nature 440: 756. Doi: 10.1038/440776a Biron, D.G., L. Marché, F. Ponton, H.D. Loxdale, N. Galéotti, L. Renault, C. Joly & F. Thomas, 2005. Behavioural manipulation in a grasshopper harbouring hairworm: a proteomics approach. Proceedings of the Royal Society B 272: 2117-2126. Doi: 10.1098/rspb.2005.3213
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.
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.
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.
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
Lancet liver fluke turns ant into zombie, but not during the day
Larvae of the lancet liver fluke, a parasite, have to transfer from ant to deer.They manipulate the behaviour of infected ants to maximize the chance of transmission, Simone Nordstrand Gasque and Brian Fredensborg report.
An ant carrying lancet liver fluke larvae is no longer itself. At the parasite’s command, it climbs up in the grass and stays there motionless. This makes it more probable for the parasite to reach the host in which it matures, a grazer. The manipulation is complex, as Simone Nordstrand Gasque and Brian Fredensborg show: an infected ant only remains high up in the vegetation when it is chilly; when it is warm, it comes back and behaves normally.
The lancet liver fluke (Dicrocoelium dendriticum, a flatworm) has a complicated life cycle with three larval stages in three different hosts; it cannot live outside a host. It develops successively in a land snail, an ant, and a grazing mammal, such as a deer, sheep, or a cow. So, it has to transfer several times.
Adult liver flukes live in bile ducts in the livers of grazers. They mate and produce eggs that are excreted with the feces. The eggs are picked up by a land snail that nibbles on the droppings. The eggs hatch in the snail’s body into so-called miracidium larvae. They multiply asexually and thousands of larvae of the next stage, the cercaria larvae, appear. They migrate to the snail’s lung where they are packed in slime balls.
The snail coughs up the slime balls, and then it is the turn of the next host, which also comes by itself: the slime balls are tasty snacks for ants, which take them with them to their nest. Adult ants and larvae consume the balls and become infected. In ants, the cercaria larvae develop into the next stage, the metacercaria larvae.
Now comes the most difficult transmission, which is necessary to complete the cycle: from ant back to grazer. That doesn’t happen easily. Ants reside in their nest or walk around on the ground. A grazer does not take a bite of that. The cycle could stop here, but now the parasite intervenes.
The larvae – there may be hundreds of them –safely encapsulate in the ant’s abdomen. But one of them moves to a ganglion in the ant’s head. It is unclear exactly how it manages, but this larva gains control over the ant’s behaviour. Like a zombie, the ant climbs up a blade of grass for no reason and locks its jaws to the vegetation. And so, a grazer may ingest the ant with the larvae on board along with the grass.
The larva that enabled the transfer dies in the grazer’s stomach. It sacrificed itself for the others, which emerge from their capsule in a safe place, develop into adult worms and settle in the bile ducts of the grazer: the circle is complete.
It is extraordinary that a parasite changes the behaviour of its host so drastically. But the lancet liver fluke does even more: it makes sure that the change is only expressed when it makes sense.
Gasque and Fredensborg conducted research into the behaviour of the European red wood ant (Formica polyctena) after infection with lancet liver fluke in woods in Denmark, where roe deer live. They show that an infected ant only stays high up in the vegetation when it is cool, i.e., early in the morning and in the evening. During the day, it unlocks its jaws, goes down and behaves like the other ants.
It turns out that the temperature determines whether an infected ant is itself or becomes a zombie. Time of day, humidity and amount of sunlight do not matter. The warmer it is, the fewer infected ants persist in their biting behaviour. Only on chilly days at the end of the season, do many infected ants stay attached to vegetation all day.
This is beneficial from the parasite’s point of view. Because on hot days an exposed ant could overheat and die, and then the parasitic larvae would not survive either. Since deer mainly graze at dusk, there is no point in taking that risk. It is better to release the ant and let it ant behave normally, and only send it back up again in the evening.
Smelly Gastrodia orchid provides food for fly larvae
For its pollination, Gastrodia foetida, attracts female flies that normally visit mushrooms to lay their eggs on.The orchid seems deceptive, but it is not, Kenji Suetsugu discovered.
Many orchids are cheaters. Whereas most plants cooperate with insects and offer them nectar as a reward for pollination, such orchids have their flowers pollinated without offering a reward in return. They lure their pollinators with false pretences. For example, some orchids mimic female insects to abuse males who want to mate and, in their futile attempts, pick up pollen from one flower and deposit it on another.
Another type of deception is perpetrated by orchids of the genus Gastrodia. They attract fly females who want to lay eggs by mimicking the smell of material in which fly larvae grow up, such as fermenting fruits or decaying mushrooms. But the promise is false, as turns out when females visit these flowers. If they lay eggs on them, which they do occasionally, the larvae that hatch die of starvation.
Gastrodia foetida is a rare plant from the forests of Japan and Taiwan. As do other Gastrodia species, the plants have no normal leaves, and the succulent flower does not look like much to us: it is inconspicuous and brown. But to females of some fly species the flower is attractive because of its musty smell; foetida means stinky. A common visitor is Drosophila bizonata, a species with larvae that develop in decaying mushrooms.
When a female fly enters the flower, the hollow lip in the flower bends up to the column that carries pistil and stamens. The female is stuck in the resulting channel between column and lip. To escape from that trap chamber, she has to crawl through a narrow opening along the stamens, and then the pollen, which is packed in two clumps, gets attached to her back (unless there had been another fly before, because then the clumps are already gone). If she then visits another flower in which she is locked up again, the pollen clumps end up on the pistil and this flower will produce many seeds. In other Gastrodia species, things go in the same way.
But unlike those other species, the stinky orchid really is a suitable place to lay eggs on. Suetsugu frequently found eggs on flowers of Gastrodia foetida that had been visited by a female fly. And surprisingly, the eggs hatch and the larvae do not die, but grow well. Three or four days after pollination, the flowers fall off, leaving only the ovary behind. As the flowers decompose on the soil, the larvae feed on the floral tissue until they mature and pupate. Two weeks after pollination they emerge as adult flies.
Although the larvae of Drosophila bizonata are mushroom eaters, these flowers apparently meet their needs.
It is not clear why mushroom eating fly larvae can also grow well on these flowers. It may have to do with the fact that the orchid cannot make its own sugars through photosynthesis, like normal plants, because it does not have the green leaves necessary for this process. Instead, it steals sugars from fungi. Suetsugu suggests that, as a result, the plant tissue may have chemically similarities to that of mushrooms.
In any case, Gastrodia foetida appears to have gone from deception back to mutualism with pollinators, but with a reward other than nectar. Flies pollinate the flowers, and the succulent decomposing flowers then serve as food for their larvae. It is the first time that this form of ‘nursery pollination’ has been demonstrated.
The mutualism is indispensable for the plant, but not for the fly; it still can lay its eggs on mushrooms also.
Hunting trumpetfish swims closely alongside other fish to remain undetected
By swimming next to another fish, the trumpetfish can approach its prey closer without them noticing.It works, Samuel Matchette and colleagues observed.
In order to ‘surprise’ its prey when attacking, a trumpetfish keeps itself invisible. The elongate, extremely slender fish, typically just over half a meter long, often waits in vertical position between corals and sponges for prey to come close enough to strike; its prey are smaller fish and shrimp. As the predator fish takes on the background colour while waiting, it does not stand out.
But that strategy is useless in water with little cover. In such scenery, the predator applies another camouflage trick: it shadows a harmless fish by swimming very closely alongside it. And that works well, as Samuel Matchette and colleagues show: prey do not see their enemy approaching.
The trumpetfish, Aulostomus maculatus, is related to seahorses and pipefish; it lives in the western part of the Atlantic Ocean. It was already known that it often swims aligned with other fish. It arches for instance over the back of a large fish, taking on that fish’s colour. The idea already existed that in doing so, it conceals its characteristic outline to approach its prey undetected. Fish that it hides behind are usually harmless herbivores, such as parrotfish, from which prey animals do not flee.
But the question still was: does it really work? Does it enable the predator to approach its prey more closely undetected?
On coral riffs near Curaçao, the researchers conducted tests that answered these questions in the affirmative.
They studied the defensive behaviour of bicolour damselfish (Stegastes partitus). These fish live in colonies, are on the menu of trumpetfish and react clearly when seeing a predatory fish: a few individuals inspect the predator and then all quickly seek shelter.
Matchette and colleagues exposed damselfish colonies to a three-dimensional printed and painted model of a trumpetfish alone, a parrotfish alone, or a parrotfish with a trumpetfish attached. They moved those models over a colony, one at a time, and videotaped the colony’s reaction.
As might be expected, damselfish were not much startled by a parrotfish passing on its own. In contrast, they responded strongly to a trumpetfish; they inspected it intensively and then quickly retreated.
And the combination of parrotfish and trumpetfish? This did not elicit a stronger reaction than a parrotfish alone. Conclusion: bicoloured damselfish do not notice a trumpetfish that shadows a parrotfish. The camouflage trick – hiding behind moving fish – works well.
That is: as long as the parrotfish tolerates the company. It often chases the trumpetfish away.
Sources: Matchette, S.R., C. Drerup, I.K. Davidson, S.D. Simpson, A.N. Radford & J.E. Herbert-Read, 2023. Predatory trumpetfish conceal themselves from their prey by swimming alongside other fish. Current Biology 33: R781-R802. Doi: 10.1016/j.cub.2023.05.075 Aronson, R., 1983. Foraging behavior of the west Atlantic trumpetfish, Aulostomus maculatus: use of large, herbivorous reef fishes as camouflage. Bulletin of Marine Science 33: 166-171.