Help when needed

Crab spider makes itself useful on infested flower

crab spider hunts prey on flowers

Lying in ambush on a flower, a crab spider will grab every visitor and eat it. Its victim may be a useful guest, such as a bee, as well as a harmful one. In buckler mustard, the presence of a crab spider turns out to be beneficial if flowers are infested by caterpillars, Anina Knauer and colleagues show.

Crab spiders have an effective way to acquire food. They reside in a flower, usually inconspicuously as their colour matches that of the flower, and wait for visitors to arrive. They grab them with the two pairs of large legs to which their name refers, kill them with a poisonous bite and eat them. They can handle prey that is much larger than they are. It is a disadvantage for a plant when such a spider settles on a flower, you would guess, for many flower visitors that they hunt are useful visitors, such as bees that pollinate the plant to enable it to set seed; it would be a disaster if those pollinators could not do their job.

But Anina Knauer and colleagues show that the presence of a crab spider can be a blessing. That is because a flower also gets visitors with bad intentions, and a resident crab spider can eliminate them. Therefore, they discovered, a flower will attract crab spiders in case of unwelcome visitors.

buckler mustard attracts crab spider if infested by caterpillarsThe researchers investigated how the presence of the crab spider Thomisus onustus affects the fitness of the plant it usually occurs on, buckler mustard (Biscutella laevigata), an alpine herb with yellow flowers and fruits that look like spectacles. The plant interacts with several insect species that are potential prey for the spider. The scent of the flowers attracts bees that take care for pollination in exchange for nectar. But the seed setting often fails because the flowers are consumed by caterpillars of the diamondback moth (Plutella xylostella). What happens when a crab spider is present?

The researchers conducted experiments in which they placed three caterpillars on flowers of plants with or without a crab spider every morning and counted the caterpillars in the evening. On plants with a crab spider, most of the caterpillars disappeared – apparently, they were eaten by the spider -, and after four weeks, as a consequence, those plants had suffered much less damage than plants without a spider and developed seeds normally. The crab spider rescued the flowers.

In the field, the researchers also found, plants call the voracious spider for help when the flowers are infested. This call is chemical: infested flowers emit increased amounts of one of the scent compounds, beta-ocimene. The crab spider is attracted by that compound and will settle on such flowers. Indeed, a larger proportion of plants with caterpillars is occupied by a crab spider compared to plants without a spider. So, plant and spider have a mutualistic relationship: an infested plant asks for help and receives it, while the spider that comes to the rescue gets a meal.

But what about the bees, which are the most important pollinators? Aren’t they in danger when a spider is present? They hardly are, as it turns out. They usually detect the presence of a spider on a flower, despite its camouflage, and avoid a visit, and the spider almost exclusively feeds on caterpillars. Still, despite the reduced visit rates of bees, the flowers set seed. Apparently, there is no lack of pollen. The presence of the spider therefore turns out to be beneficial for plants that are infested by caterpillars.

High in the mountains Thomisus onustus does not occur, while buckler mustard does. Upon attack by caterpillars, plants of highland populations increase the amount of beta-ocimene to a much less extent than plants of lowland populations.

Willy van Strien

Photos:
Large: Thomisus onustus (not on buckler mustard). Paco Gómez (via Flickr, Creative Commons CC BY-SA 2.0)
Small: buckler mustard. Isidre blanc (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Knauer, A.C., M. Bakhtiari & F.P. Schiestl, 2018. Crab spiders impact floral-signal evolution indirectly through removal of florivores. Nature Communications 9: 1367. Doi: 10.1038/s41467-018-03792-x

Posted in mutualism | Leave a comment

Inequality

Red-capped plover invests more in young of opposite sex

male red-capped plover will provide more parental care to daughters

Fathers care more when they have daughters, mothers care more when they have sons. Such is the case in the red-capped plover, in which both parents divide the tasks of raising their two chicks, as Daniel Lees and colleagues witnessed.

In the red-capped plover, a bird that inhabits coastal areas of Australia, parents divide the care for their young. The nest is a shallow scrape on the ground wherein the female usually lays two eggs, open and exposed. The eggs are well camouflaged thanks to their yellowish-brown colour and black spots. They have to be, otherwise they would be easily detected during daytime by visually-foraging predators, such as the little raven. The female also has a protective coloration. But the male has a bright red head to impress females and help him acquire a high-quality mate. When he would incubate the eggs, his ornamentation would disclose their presence to predators.

In order to prevent this from happening, the birds have divided the breeding duties properly, Kasun Ekanayake and colleagues showed. During the day, the inconspicuous female breeds and only at night the male will take over. The one enemy that forages in the dark, the red fox, uses olfactory cues, and for this peril, it does not matter whether the father or the mother is sitting on the nest. Many clutches fall prey to the red fox, which isn’t a native species of Australia, but has been introduced and now poses a major threat to many bird and mammal species.

young red-capped plover is vulnerable to predatorsAs soon as the young red-capped plovers have hatched, they are mobile and they have to feed themselves. One of the parents is with them to keep them warm, to warn of danger and to lead them to places with food. The chicks fledge at approximately 35 days.

During the first few weeks after hatching, the chicks, which are camouflaged, are very vulnerable to predators. In that period, it is mainly the mother who accompanies them. Later, when the chicks become able to escape from danger, the father gradually takes over the care until they are independent. So, the care for the young birds seems to be equally divided between parents.

But there still is some inequality, as Daniel Lees and colleagues point out. For the division of care between parents, it matters whether they have daughters or sons.

The mother, who takes care of the chicks during the first weeks, will decrease her contribution over time at a lower rate when both young are males; in that case she continues to invest more than she would do if she had had two daughters or a son and a daughter. And the father, who gradually takes over her job, will provide more care if both young are female.

So, both parents care more for young of the opposite sex. No difference is to be seen between male and female chicks, and the researchers needed a blood sample to be able to determine the sex of the young. Apparently, however, the birds can distinguish between sons and daughters and treat them differently.

How to explain this? The researchers suggest that the parents may provide more care to young of the opposite sex because these young will not be rivals later on, on the wedding market. Fathers will then have to compete for attractive partners with their sons and mothers with their daughters. It is an possibility that still has to be investigated.

Willy van Strien

Photos:
Large: Red-capped plover, male. ©Daniel Lees
Small: Red-capped plover, chick. Benjamint444 (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Sources:
Lees, D., C.D.H. Sherman, K. Kostoglou, L.X.L. Tan, G.S. Maguire, P. Dann & M.A. Weston, 2018. Plover parents care more for young of the opposite sex. Behavioral Ecology, online April 5. Doi: 10.1093/beheco/ary052
Ekanayake, K.B., M.A. Weston, D.G. Nimmo, G.S. Maguire, J.A. Endler & C. Küpper, 2015. The bright incubate at night: sexual dichromatism and adaptive incubation division in an open-nesting shorebird. Proceedings of the Royal Society B 282: 20143026. Doi: 10.1098/rspb.2014.3026

Posted in parental care | Comments Off on Inequality

Unrewarded services

Orchid utilizes fungi and fruit flies without paying

Drosophila fly on flower of the deceptive orchid Gastrodia pubilabiata

The orchid Gastrodia pubilabiata lives at the expense of other species. It steals sugars from fungi, which also attract fruit flies that provide pollination service, as Kenji Suetsugu shows, without receiving any reward in return.

While most plants produce sugars from carbon dioxide using energy from sunlight in a process called photosynthesis, the orchid Gastrodia pubilabiata leaves the job to others. The small and inconspicuous plant, which grows in Japan and Taiwan, does not have green leaves, as it lacks chloroplasts, the cell organelles that conduct photosynthesis. With its roots, it steals sugars from the underground hyphae of a number of mushroom forming fungi species; the fungi obtained these sugars from dead organic material. The fungi get nothing in return.

And while most plants produce nectar as a food resource for insects (or other animals) that pollinate the flowers in return, this orchid doesn’t. To be pollinated, it exploits fruit flies (Drosophila species) without rewarding them. The flies need fermenting fruit or decaying mushrooms to lay their eggs in, and their larvae will consume that stuff. Apparently, the brown-coloured flowers of Gastrodia pubilabiata smell like fermenting and decaying substrates, as the flies are deceived into laying their eggs on the flowers. Consequently, the larvae will find no suitable food and die. But the orchid has been served. While visiting a flower, the flies pick up pollinia, masses of pollen grains, which they deliver to the next flower they visit, thereby pollinating that flower.

The orchid thus takes nutrients from mushrooms and is pollinated by fruit flies, and neither of these partners receives any reward for its services. Both are victims of a parasitic and deceptive plant.

Now Kenji Suetsugu shows that mushroom-forming fungi still provide another service. Old mushrooms attract fruit flies that have to lay their eggs, and upon arrival, they will also visit the orchid flowers that mimic fermenting and decaying material. Suetsugu conducted experiments in which he removed decaying Mycena mushrooms from the orchids’ proximity or added extra specimens; Mycena species are the main victims of theft by the plant. He found that the more decaying mushrooms are around, the more pollen is removed from and delivered to orchid flowers by flies that are misled, and the more seeds are produced.

So, the fungi not only function as food providers, but also as magnets that attract pollinators – without reward.

Willy van Strien

Photo: Gastrodia pubilabiata, flower and fruit fly bearing pollinia. © Kenji Suetsugu

Source:
Suetsugu, K., 2018. Achlorophyllous orchid can utilize fungi not only for nutritional demands but also pollinator attraction. Ecology, online March 25. Doi: 10.1002/ecy.2170

Posted in mimicry, parasitism, pollination | Comments Off on Unrewarded services

Deceit, abuse and benefits

Complex relationships between arum, blowflies and lizard

Dead-horse arum flower is attractive to lizard

With its smell of rotting carrion, the dead-horse arum Helicodiceros muscivorus is irresistible to blowflies and a lizard. The blowflies will be abused, the lizard benefits. Ana Pérez-Cembranos and colleagues unraveled these complex relationships.

On islands in the Mediterranean Sea, a plant occurs with a very bad smell, the dead-horse arum, Helicodiceros muscivorus. Its odour contains chemical components that are also emitted by a decomposing dead animal. It irresistible to a female blowfly searching for carcasses to lay her eggs on to make sure that the carnivorous larvae will have food. The dead-horse arum takes advantage of that behaviour.

The plants release their odour on the first day of blooming. Blowflies that perceive the smell cannot ignore it. Upon approaching the source, they find a pink or red curved bract, the spathe, with the hairy end of the spadix (inflorescence), which produces the smell. When they land, the spadix turns out to be warm. To blowflies, the imitation is perfect: this is rotting carrion. Guided by the heat, they crawl into the tube that is formed by the base of the spathe around the lower part of the spadix, which bears female and male florets.

Once inside, the blowflies don’t find what they need, which is decaying meat. But if they want to leave, they cannot. Spikes on the spadix keep the door closed. The blowflies are trapped.

Unintentionally, they provide a service to the arum during their imprisonment in the floral chamber. The female flowers at the bottom of the spadix are blooming this first day, and blowflies that had been misled by the arum before, now deliver the pollen that they picked up on that occasion. The plant has its female flowers pollinated.

The next day, the female flowers have faded and the male flowers are mature. The stench and the heat disappear, the spikes wilt and the blowflies escape, and while passing the male flowers, they are loaded with pollen. And here is the second benefit to the plant: the blowflies take the pollen with them to female flowers elsewhere – if at least they find another foul smelling arum on their way and are again misled into visiting it.

So, the blowflies are coerced to pollinate the dead-horse arum without receiving any reward such as nectar. On the contrary: they lose time that they should have spent on searching for genuine carcasses.

Now Ana Pérez-Cembranos and colleagues show that the Balearic lizard Podarcis lilfordi is also misled by the arum’s odour. The animal is omnivorous and sometimes forages on carcasses, which are also attractive as a heat source; lizards are cold-blooded and when the weather is cool, they may use a rotting carcass as a perching site for basking. In addition, they capture the blowflies that arrive at the cadaver in search for a site for oviposition.

The lizards respond to the smell of the dead-horse arum as they do to the smell of a carcass and will approach the source. If that turns out to be a dead-hors arum instead of a dead animal body, they will not find a meat meal, but they do find a basking place and blowflies, which they take from the spathe or grab from the tube. The lizards thus take away a number of pollinators, but, according to the researchers, enough are left to ensure pollination.

So, the lizard isn’t an enemy of the arum. And after the flowering period, when fruits are ripe, a mutualism even develops between both. The lizards consume the fruits and disperse the seeds in their faeces; passage through the lizard’s intestine increases the probability of germination. On Aire Island, a the small island off the southeastern coast of Menorca, where the research was done, the dead-horse arum is a newcomer. It is estimated to have grown there for only about fifty years. In that period, it spread rapidly over the island and nowadays it locally occurs in great densities. That is because of the lizard, which has learned to eat the fruits and now is the main disperser of the seeds, the researchers think.

Willy van Strien

Photo: Balearic lizard on the spathe of the dead-horse arum © Ana Pérez-Cembranos

Sources:
Pérez-Cembranos, A., V. Pérez-Mellado & W.E. Cooper, 2018. Balearic lizards use chemical cues from a complex deceptive mimicry to capture attracted pollinators. Ethology  124: 260-268. Doi: 10.1111/eth.12728
Angioy, A-M.,  M. C. Stensmyr, I. Urru, M. Puliafito, I. Collu & B. S. Hansson, 2004. Function of the heater: the dead horse arum revisited. Proceedings of the Royal Society London B 271: S13-S15. Doi: 10.1098/rsbl.2003.0111
Stensmyr, M.C., I. Urru, I. Collu. M. Celander. B.S. Hansson & A-M. Angioy, 2002. Rotting smell of dead-horse arum florets. Nature 420: 625-626. Doi: 10.1038/420625a

Posted in mimicry, mutualism, pollination, predation | Comments Off on Deceit, abuse and benefits

Nutritious two-component glue

Queen larva is firmly attached to her ceiling

Royal jelly, fed to a queen larva, holds her in place

A bee larva that is to become a queen receives large quantities of royal jelly. And that is not only because the stuff is nutritious, as Anja Buttstedt and colleagues show.

A female honeybee larva can become a worker or a queen, her fate depending on the food she receives. During the first days, all larvae are treated to the so-called royal jelly, a nutritious mixture that the nurse bees produce in their head glands; it is rich in proteins, sugars and fats. After the third day, larvae that will grow up to be worker bees are raised on a different diet. When they pupate, nurse bees close their cells with a layer of wax. But a larva that is destined to become a queen is fed on royal jelly exclusively; the nurse bees bring it to her in generous quantities. Thanks to that nutritious diet, she grows bigger than worker bees.

The royal jelly has still another function, Anja Buttstedt and colleagues discovered: it holds the queen larva in place.

And that is badly needed. The cells in the comb, in which worker larvae grow up, are too small for a developing queen larva. For her, the bee workers will build a special cell, a so-called queen cell or queen cup. It is not only wider, but also differently oriented: vertically, opening downwards. Therefore, her royal highness could easily fall out of her cell.

Buttstedt shows why that does not happen: the royal jelly, which the workers deposit on the ceiling, is so sticky that it keeps the larva hanging from the ceiling until it pupates and the cell is sealed with wax. The stickiness arises because two proteins, royalactin (the main protein in royal jelly) and apisimin, form long fibrous structures that make the jelly viscous.

The workers produce and store the proteins in their hypopharyngeal glands. The gland mixture is liquid, enabling the bees to excrete it. But when they deposit it in a brood cell, they combine it with fatty acids which they produced in the mandibular glands, and in those acidic conditions, the proteins royalactin and apisimin form a fiber network.

So, royal jelly is a two-component adhesive, as the authors conclude, serving as excellent food as well. It is just what a queen larva needs to grow up safely.

Willy van Strien

Photo: Honeybee, comb and two queen cells. Piscisgate (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Source:
Buttstedt, A., C.I. Muresxan,H. Lilie, G. Hause, C.H. Ihling, S-H. Schulze, M. Pietzsch & R.F.A. Moritz, 2018. How honeybees defy gravity with royal jelly to raise queens. Current Biology, online March 15. Doi: 10.1016/j.cub.2018.02.022

Posted in growth and development | Comments Off on Nutritious two-component glue

Helpers in the nest

Thanks to helpers, cichlid mothers acquire more food

In Neolamprologus obscurus, young fis stay with their mother to help

When young of the cichlid species Neolamprologus obscurus have grown up, they are allowed to remain in the territory of their mother for a while because of their help. Hirokazu Tanaka and colleagues wanted to know why that help is important.

Neolamprologus obscurus, a cichlid fish that occurs in Lake Tanganyika in Africa, lives in groups in which each breeding female owns a territory along a steep bank, where she has dug out several cavities under stones. In those safe shelters, she spends almost all her time and she uses them for breeding. She guards her eggs and fry, and chases conspecifics out of her territory.

But her grown up young are allowed to stay. They help her defend the territory and maintain the shelters by removing sand that continuously enters from the edges.

The removal of sand from the shelters is most beneficial to her, Hirokazu Tanaka and colleagues discovered. The shelters not only serve as a safe residence and as a breeding ground, but they are also a means to acquire food. The fish feed on small benthic invertebrates, especially shrimp. These tiny animals move up to the water surface at night to forage, but in the full light of the day they are not safe there and before dawn, they sink back to the bottom to hide in cracks and cavities – such as cavities in which Neolamprologus obscurus lives. The food comes to the fish by itself.

Tanaka shows that the larger a cavity is, the more benthic invertebrates immigrate at dawn. Because of this increased food abundance, it is desirable for a breeding female to have helpers that maintain the shelters and even enlarge them.

Of course, helpers take some of the food that they acquire, so part of the gain is lost for the breeding female. But she still profits, because the more helpers are present to remove sand from the edges of the cavity, the longer those edges can be. And the area and content increase even more: with a double number of diggers, maintaining a cavity with a circumference that is twice as large, the area and the volume become four times larger, and as a consequence, more food is available per fish when more helpers are around.

But there is a limit to the number of helpers a female will tolerate; it will be no more than ten. So, when young fish have become larger, they will disappear from her territory to start for themselves.

Willy van Strien

Photo: Neolamprologus obscurus, helper. ©Hirokazu Tanaka

Sources:
Tanaka, H., J.G. Frommen & M. Kohda, 2018. Helpers increase food abundance in the territory of a cooperatively breeding fish. Behavioral Ecology and Sociobiology 72: 51. Doi: 10.1007/s00265-018-2450-5
Tanaka, H., J.G. Frommen, L. Engqvist & M. Kohda, 2017. Task-dependent workload adjustment of female breeders in a cooperatively breeding fish. Behavioral Ecology 29: 221–229. Doi: 10.1093/beheco/arx149
Tanaka, H., D. Heg, H. Takeshima, T. Takeyama, S. Awata, M. Nishida & M. Kohda, 2015. Group composition, relatedness, and dispersal in the cooperatively breeding cichlid Neolamprologus obscurus. Behavioral Ecology and Sociobiology 69: 169–181. Doi: 10.1007/s00265-014-1830-8

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Males in transition

Squid male changes its mating tactic when growing larger

Males in the squid Doryteuthis pleii adopt alternative mating tactics, depending on their age

When becoming sexually active, male squids are little successful at first. Only later they perform better, increasing their chances to sire offspring. This development includes major changes, Lígia Apostólico and José Marian discovered.

In squid like Doryteuthis pleii, a species living off the coast of Brazil, small males are able to mate, but they have to do it at an inappropriate time and in a little successful way, as sneakers. Large males act much more effectively as real partners or consorts, as Lígia Apostólico and José Marian report.

When squid mate, s male delivers sperm packages to a female. With a special arm, a male takes the packages, spermatophores, from the spermatophoric sac, where they are produced, and places them on the body of a female with a rapid movement. Then he is done, the sperm packages themselves will do the rest of the work. With a shooting mechanism (ejaculatory apparatus), a package turns inside out, and when evaginated, it attaches onto the female’s body and the sperm cells swim out.

A large male delivers its sperm packages neatly. He approaches a female that is about to release her eggs, places himself next to her with his head pointing in the same direction as hers, moves his special arm behind her head under the mantle that surrounds her body and places his spermatophores near the opening of the oviduct from which the eggs will be released in capsules. The sperm cells have immediate access to the eggs. The male guards the female and tries to keep rivals at bay with flickering colour patterns, because if another male also mates with her, his sperm will have to compete with that other male’s sperm.

A small man does not stand a chance against a large one, so he can only mate at a less exciting time, when no eggs are to be released soon. He doesn’t put his arm under the female’s mantle, but he assumes a head-to-head position and places his sperm packages under her beak, that is between the arms. When she releases the eggs, she holds the capsules for a while near the beak before depositing them on the substrate, and then a sneaker’s sperm cells have a chance – as far as the eggs are not fertilized already by a consort’s sperm.

The sperm cells of sneakers are adapted to the unfortunate site where they are placed and the wide time interval between mating and fertilization chances, and their spermatophores differ from those of consorts. Sneakers have smaller and thinner spermatophores; after evagination, they are short and club-like shaped. The sperm cells come out slowly and aggregate at the exit, having nothing to do there for the time being. The spermatophores of consorts, in contrast, are larger and after evagination, they are long and hook-like shaped. The sperm is quickly discharged in a powerful flow and sperm cells immediately diffuse, so the eggs that are released will pass through a cloud of them.

Now in Doryteuthis pleii, Apostólico and Marian found some males, intermediate in size between sneaker and consort (about 17 centimetres mantle length), that produce sneaker-like spermatophores as well as consort-like spermatophores, and often also an intermediate form. The sneaker-like packages are oldest and stay in the anterior part of the spermatophoric sac, the consort packages are youngest and reside in the posterior part, and the intermediate packages are to be found in between.

This indicates that a male starts as a sneaker and, if he exceeds a certain size limit, he will go on as a consort, implementing all changes that are required by the transition. Age estimates show that sneakers are indeed younger than consorts; the estimates are based on the size of small particles in the organs that enable the animals to control their position and balance; every day these particles, statoliths, increase a little in size. The switch from sneaker to consort must take place very fast, as only few males are found that are in transition.

So, during their lives, which lasts less than a year, the males go through a major development. They are small when at summer the mating season starts, but still they mature sexually, so that they can begin to reproduce – although for the time being only as little successful sneakers.

But perhaps not all males follow that path, Apostólico and Marian think. Males that were born early, in late summer or autumn, have much time before the mating season starts. They can grow to a large size before they become sexually active, and then they can be consorts from the start.

Willy van Strien

Photo: Alvaro E. Migotto (Cifonauta. Creative Commons CC BY-NC SA 3.0)

Sources:
Apostólico, L.H. & J.E.A.R. Marian, 2018. From sneaky to bully: reappraisal of male squid dimorphism indicates ontogenetic mating tactics and striking ejaculate transition. Biological Journal of the Linnean Society 123: 603-614. Doi: 10.1093/biolinnean/bly006
Apostólico, L.H. & J.E.A.R. Marian, 2018. Dimorphic male squid show differential gonadal and ejaculate expenditure. Hydrobiologia 808: 5-22. Doi: 10.1007/s1075
Apostólico, L.H. &  J.E.A.R. Marian, 2017. Dimorphic ejaculates and sperm release strategies associated with alternative mating behaviors in the squid. Journal of Morphology. 278: 1490-1505. Doi: 10.1002/jmor.20726

Posted in reproductive behaviour | Comments Off on Males in transition

First aid

Hunting ant workers rescue lightly injured nest-mates

termite-hunting ant Megaponera analis rescues lightly-wounded nest-mates

Groups of the African ant Megaponera analis undertake hunting parties that are risky because of the fierce resistance of the termites that are attacked. Some ant workers get injured, but they are carried back to the nest and treated if possible, Erik Frank and colleagues report.

Workers of the large African ant Megaponera analis, also known as Matabele ant, face a heavy task. The ants prey on termites that they detect and overpower at their foraging sites. The ants approach the termites in a column formation consisting of hundreds of individuals. When the first ants reach a site, they wait until all participants have arrived and then they attack. The large individuals, the majors, break open the protective layer of earth that covers the termites’ foraging site; the small ants, the minors, then go inside to seize, kill, and pull out the termites.

And that is a risky job, as Erik Frank and colleagues write. Termite soldiers with strong head and mandibles will fight fiercely. Some ants, almost all of them being minors, get injured; some ants are bitten off one or more legs or antennas, others are hindered by a termite that clings to them.

The ants limit losses by rescuing many injured nest-mates. After the fight, the ants gather before they jointly return to the nest, because an ant travelling alone easily falls prey to predators, for example spiders. Majors run over the place to pick up and carry dead termites and nest-mates that lag behind. If all ants have joined the column, they start walking. But ants that lost one or two legs and ants with a termite clinging to them are unable to keep up with the group, according to observations and experiments in the field and in the lab. By excreting certain substances they signal to others that they need help.

Majors that are not yet carrying anything will pick up these lightly-injured nest-mates, which tuck in their legs to facilitate transportation.

Ants who are severely injured and can no longer stand on their legs, don’t emit an emergency signal and they don’t let themselves to be picked up: they keep on twisting and turning. These unhappy ants are left behind, so that only victims that have a chance to recover are taken home. Almost all of them safely reach the nest, whereas without help many injured ants would not be able to complete the journey.

As soon as the victims are brought into the nest, they are taken care of. A termites that clings to an ant mostly is pulled off successfully and the ant doesn’t suffer any long-term consequences of the adventure. An ant that lost a leg or antenna receives a thorough treatment: nest mates groom the open wound for a long time, cleaning it and probably also applying antimicrobial substances that they produce in special glands. Experiments show that an ant with an untreated open wound almost always dies, probably due to an infection. But when treated, it usually survives and it will learn to walk on four or five legs as fast as the others – and soon enough, it will join termite raiding parties again.

When heavily injured ants are brought in, which happens only infrequently, they will get no treatment, but are carried out of the nest instead. The ants only help injured nest mates that will survive.

The rescue behaviour in Megaponera analis is unique. It could develop in these ants because they conduct short and space-limited raids on a dangerous prey. There are many casualties, but the injuries are rarely fatal when the victims get help – and help is available. Without rescuing behaviour, the colony would be much smaller and fewer workers would be available to join a raiding party. To give an idea of the importance: the number of ants that are rescued on a day roughly equals the number that is born.

Willy van Strien

Photo: Megaponera analis: major carrying injured nest mate back to the nest. ETF89 (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

Videos of Megaponera ants that carry and treat injured nest mates

Sources:
Frank, E.T., M. Wehrhahn & K.E. Linsenmair, 2018. Wound treatment and selective help in a termite-hunting ant. Proceedings of the Royal Society B 285: 20172457. Doi: 10.1098/rspb.2017.2457
Frank, E.T., T. Schmitt, T. Hovestadt, O. Mitesser, J. Stiegler, K.E. Linsenmair, 2017. Saving the injured: Rescue behavior in the termite-hunting ant Megaponera analis. Science Advances 3: e1602187. Doi: 10.1126/sciadv.1602187

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Multi-coloured livestock

Thanks to tending ants, mixed aphid colonies persist

Lasius japonicus tending its two-coloured livestock

The aphid milking ant Lasius japonicus ensures long-lasting coexistence of two colour morphs of the mugwort aphid, from which it harvests honeydew, Saori Watanabe and colleagues write. Without intervention, its favourite colour would be displaced.

Like many other ants, the Asian ant Lasius japonicus has a mutualistic relationship with aphids. The aphids suck sap from their host plant and excrete excess sugars, dissolved in a liquid: honeydew. The ant fights off their natural enemies and harvests (‘milks’) the sugary honeydew. One of its mutualistic partners is the Japanese mugwort aphid, Macrosiphoniella yomogicola, which lives on mugwort, a common plant of Europe and Asia. The protection of the ant is of crucial importance to the aphids; each colony will fall victim to its enemies if not protected.

The mugwort aphid occurs in different colours, with red and green as the most common types; large green specimens will turn black. The ant has a preference for the green morph, Saori Watanabe and colleagues show, because it excretes a higher quality honeydew. But as a consequence, the red morph, which retains a larger proportion of the sugars that it obtains from the host plant, can reproduce at a higher rate. All aphids are females that reproduce parthenogenetically, their young being clones of their mother. Red aphids produce red daughters, green aphids green daughters – and the green morph runs a risk to be displaced by the red one.

But, as it turns out, the ants prevent this from happening. The researchers show that the red aphids indeed are able to multiply faster than the green ones. As a consequence, in laboratory experiments, the proportion of green aphids in a mixed colony decreased, but only if the researchers withheld attending ants. If, however, ants were allowed to join the aphids, the reproduction rate of the green morph increased, and the green aphids now reproduced as fast as the red aphids. Thus, in the presence of ants, the proportion between green and red morphs was stable.

It is not clear how the ants improve the reproduction rate of the green aphids, but it saves the green morph from local extinction.

In the field, almost all colonies are mixed. It is understandable that no pure red colonies are to be found. No ant would be interested in such colony, which produces only low quality honeydew, so it would be lost. But why don’t green colonies exist? Why wouldn’t the ants remove the red aphids from a mixed colony by eating them, so that only high quality honeydew would be produced?

Apparently, the presence of red aphids is advantageous for some reason. That has to do with the winter period, the researchers suggest. At the end of the season, the aphids give birth to daughters and sons, which mate and produce fertilized eggs that can overwinter if the host plant survives. However, after flowering in autumn, mugwort dies off. The researchers hypothesize that red aphids may suppress flowering, so that the plant persists. They are now going to test that idea.

It would mean that the ant needs both aphid morphs, the green one for high quality honeydew, the red one to maintain the colony to the next season. It would also mean that the two types of aphids need each other. The red morph cannot do without the green one, which attracts attending ants, and the green morph cannot do without the red one, which prevents the host plant from dying off in winter.

But as dependent the aphid morphs may be on each other, they cannot live together for a long time without the ant interfering.

Willy van Strien

Photo: aphid tending ant Lasius japonicus and two colour morphs of Macrosiphoniella yomogicola. ©Ryota Kawauchiya

Bronnen:
Watanabe, S., J. Yoshimura & E. Hasegawa, 2018. Ants improve the reproduction of inferior morphs to maintain a polymorphism in symbiont aphids. Scientific Reports 8: 2313. Doi: 10.1038/s41598-018-20159-w
Watanabe, S., T. Murakami, J. Yoshimura & E. Hasegawa, 2016. Color polymorphism in an aphid is maintained by attending ants. Science Advances 2: e1600606. Doi: 10.1126/sciadv.1600606

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Hidden beauty

Chameleons are characterized by glowing bony tubercles

Calumma crypticum possesses glowing bony tubercles

Many chameleon species are discovered to possess bony bumps that emit blue light through the skin. The glowing bumps enable the animals to recognize conspecifics and males probably show them off to females. We don’t perceive them in natural light, but the animals do, David Prötzel and colleagues think.

There are many ways in which an animal can make itself stand out, for instance with scent, colour, song, dance, decorative feathers or eyes on stalks. But here is a new one: chameleons appear to have small bumps on their skull that emit blue light, David Prötzel and colleagues report.

The glowing tubercles of Calumma crypticum become visible under UV lightThat may sound like horror, but there is nothing ghostly about it. Bone tissue is fluorescent: if it is hit by ultraviolet light, it is excited and will emit blue light. Chameleons use this natural phenomenon. The bumps, or tubercles, on their skull protrude through most of the skin and are covered only by a thin, transparent layer of cells, which is like a window. If ultraviolet passes that window and falls on the tubercles, they will glow blue.

Normally we don’t see it, as the amount of ultraviolet (UV) in natural light is too small. Therefore, the phenomenon was only discovered when the researchers illuminated heads of chameleons with a UV lamp. But natural light does contain enough ultraviolet to make the glowing bumps visible to the chameleons themselves, the researchers suspect, as their eyes are more sensitive to blue light than ours. Many chameleon species in Madagascar and in Africa have such glowing bumps, especially species that inhabit humid forests, where the component of ambient UV light is relatively high; the emitted blue light contrasts well with the dark background.

The pattern of bony bumps is species specific; most bumps are seen around and behind the eyes, but some species have such blue glowing tubercles not only on the skull, but on the entire body. Chameleons will recognize their conspecifics by the distinctive pattern of tubercles, which is a stable signal for these animals with their colour changing behaviour.

As in the nearly all species males posses on average more tubercles than females, the researchers assume that males display them to seduce a female.

So, chameleons possess glowing bone bumps as ornamentations used for recognition and display; it is possible that other lizards and snakes will be discovered to show fluorescencent bony bumps.

Willy van Strien

Photos:
Large: Calumma crypticum, male. Axel Strauβ (Wikimedia Commons, Creative Commons CC BY-SA 3.0)
Small: head of Calumma crypticum, preserved specimen from the Zoologische Staatssammlung München (Germany), under ultraviolet light. Copied from David Prötzel et al. (Creative Commons, CC BY 4.0) and mirrored, so that head is oriented in the same direction as in the large picture

On this YouTube video, the researchers illuminate Furcifer pardalis and two Brookesia species to elicit the blue glow. And on this video you see the knobby skull of Calumma globifer.

Source:
Prötzel, D., M. Heß, M.D. Scherz, M. Schwager, A. vant Padje & F. Glaw, 2018. Widespread bone-based fluorescence in chameleons. Scientific Reports 8: 698. Doi: 10.1038 / s41598-017-19070-7

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