From so simple a beginning

Evolution and Biodiversity

Month: February 2018

First aid

27 February 2018 /

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.

Emergency signal

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.

Care

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 worth the effort. 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

Multi-coloured livestock

19 February 2018 /

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 by the ant is of crucial importance to the aphids; each colony will fall victim to its enemies if not protected.

Quality

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. The green morph runs a risk to be displaced by the red one, which multiplies faster.

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.

Winter

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.

Need each other

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

Hidden beauty

12 February 2018 /

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.

Blue light

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.

Seduce

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

Family ties

6 February 2018 /

Caring treehopper mother recognizes her offspring

female treehopper, Alchisme grossa, guarding her eggs

Females of the treehopper Alchisme grossa exhibit complex maternal care. If a mother has been separated from her offspring, she can localize and recognize them, as Daniel Torrico-Bazoberry and colleagues show.

The treehopper Alchisme grossa occurs in Central and South America, where it lives on a number of host plants, feeding on plant sap. The females lay their eggs on the host plants; they cut a slit in the midrib at the underside of a leaf, deposit the eggs in it and cover the egg mass with a frothy secretion.

Alchisme grossa females exhibit extensive brood careThey then will exhibit extensive brood care for a few months, Daniel Torrico-Bazoberry and colleagues write. The caring behaviour is unique for such a small creature. A female positions herself over the eggs and shields them with an enlarged pronotum (dorsal plate of the thorax) which bears two horns at the front side. If parasites or predators, such as spiders or predatory bugs, try to reach the eggs of a guarding mother, she will behave like a hero. She moves her body, fans her wings and kicks with strong legs to scare off the enemies. A batch of eggs is certainly lost without its mother; if it does not fall prey to enemies, it will desiccate.

Sap feeders

The offspring rely on maternal care until they have completed development. The treehoppers undergo an incomplete metamorphosis. The nymphs that hatch from the eggs resemble adults, but are smaller. They undergo five instar stages before they are fully grown. Just like adult treehoppers, nymphs are sap feeders. Shortly before they hatch, the mother cuts a number of small holes in the midrib near the batch of eggs, so that the tiny nymphs can easily puncture the vein to tap the sap flow. And she stays with them. If the nymphs feel threatened, they drum on the leaf with their legs and the mother will come.

Now Torrico-Bazoberry shows that a female can localize and recognize her offspring after having been separated from them. This is useful, because often several females start a family on a single host plant, each on her own leaf. Torrico-Bazoberry put ten to fifteen nymphs from a single family on a host plant in the lab and a female on 20 centimetre distance on the same plant; in some cases she was the mother, in others she was not.

Trample

Separated from their mother, the nymphs often started to trample; one or a few began, the rest joined in producing a wave-like synchronized behaviour. Upon this rocking behaviour, the nymphs gathered. If the female that was put on the plant was their mother, they aggregated more closely; apparently they detected her presence. The female responded to the rocking behaviour if she was the mother: each mother approached the nymphs. Some non-mothers also did, but not all of them.

Nymphs of treehopper Alchisme grossa receive maternal care throughout developmentApparently, mother and nymphs discriminate kin from non-kin, probably on the basis of the composition of the chemical compounds of the outer skin layer, the researchers suggest. Chemical analyses revealed that this composition differs between individuals, differences between nymphs of a single family being much smaller than differences between nymphs of different families. Because the nymphs aggregate more closely in presence of their mother, it is easier for her to defend them and prevent them from desiccation.

Sometimes, the nymphs stay on their natal leaf until reaching maturity, but sometimes they disperse over the plant stem before that time. The mothers follow their young and together they form mixed aggregations with nymphs of other families and their mothers.

Willy van Strien

Photos: Treehopper Alchisme grossa. Andreas Kay (via Flickr. Creative Commons CC BY-NC-SA 2.0)
Large: female with eggs on midrib of leaf
Small, first: female
Small, second: older nymphs on plant stem

Sources:
Torrico-Bazoberry, D., L. Caceres-Sanchez, L. Flores-Prado, D. Aguilera-Olivares, F.E. Fontúrbel, H.M. Niemeyer & C.F. Pinto, 2018. Kin recognition in a subsocial treehopper (Hemiptera: Membracidae). Ecological Entomology, online Jan. 23. Doi: 10.1111/een.12506
Torrico-Bazoberry, D., C.F. Pinto, L. Flores-Prado, F.E. Fontúrbel & H.M. Niemeyer, 2016. Natural selection in the tropical treehopper Alchisme grossa (Hemiptera: Membracidae) on two sympatric host-plants. Arthropod-Plant Interactions 10: 229-235. Doi: 10.1007/s11829-016-9427-y
Torrico-Bazoberry, D., L. Caceres-Sanchez, D. Saavedra-Ulloa, L. Flores-Prado, H.M. Niemeyer & C.F. Pinto, 2014. Biology and ecology of Alchisme grossa in a cloud forest of the Bolivian Yungas. Journal of Insect Science 14: 196. Doi: 10.1093/jisesa/ieu031
Camacho, L., C. Keil & O. Dangles, 2014. Factors influencing egg parasitism in sub-social insects: insights from the treehopper Alchisme grossa (Hemiptera, Auchenorrhyncha, Membracidae). Ecological Entomology 39: 58–65. Doi: 10.1111/een.12060

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