From so simple a beginning

Evolution and Biodiversity

Month: March 2017

Cleansing hair

30 March 2017 /

Honey bee rubs her eyes after visiting a flower

honey bee quickly cleans herself after visiting a flower

A busy bee gets dirty: she gets covered with the pollen of flowers. But within minutes she has cleaned herself after visiting a flower, as Guillermo Amador and colleagues report, thanks to the hairs on her body.

A bee that has visited a flower to collect nectar or pollen may be completely covered with yellow pollen grains. When the eyes and antennae are dirty, she is not able to see or smell well. But the discomfort lasts only a few minutes, because during flight she manages to quickly remove the pollen, as Guillermo Amador and colleagues show. She puts it in the baskets on her hind legs to it take to the nest as food for the young, or she drops it.

Using high speed cameras, the researchers recorded the cleaning process in a number of honeybees that they had coated in pollen of dandelion or other plants. To keep the bees in front of the cameras, they tethered them temporarily to a thin wire. As the footage showed upon analysis, the bee hairs are essential for the rapid cleaning process.

Brushes

A honeybee that is covered in pollen starts grooming her eyes. The hairs on the eyes are spaced so that the sticky pollen grains are suspended near the tips, where they can be easily wiped away by the pollen brushes on the forelegs. As the hairs of these brushes are closer spaced than those of the eyes, the pollen grains attach to the brushes.

With a fast movement, the bees swipe a foreleg across an eye, from dorsal to ventral, removing almost all the particles that are touched by the brush. As the researchers calculate, about twelve swipes are needed to clean the entire surface of an eye. In reality, the bees rub each eye ten to twenty times. After each swipe, they spend a few seconds to clean the pollen brush with the other legs or the mouth.

Pollination

The hair on the eyes (and on the rest of the body) and the bristle brushes on the forelegs facilitate quick removal of sticky pollen after a flower visit, the conclusion is.

Still, some of the accumulated pollen must be left ungroomed, so that the bee can deliver it on the pistil of the next flower she visits. Otherwise, bees would not pollinate any flowers.

Willy van Strien

Photo: Honey bee collecting pollen. Jon Sullivan (Wikimedia Commons, Public Domain)

On this video, a pollen-covered honey bee rubs her eyes

Source:
Amador, G.J., M. Matherne, D. Waller, M. Mathews, S.N. Gorb & D.L. Hu, 2017. Honey bee hairs and pollenkitt are essential for pollen capture and removal. Bioinspiration & Biomimetics 12:  026015. Doi: 10.1088/1748-3190/aa5c6e

Defensive cocktail

15 March 2017 /

Ants produce powerful antibiotic by mixing resin with acid

Formica paralugubris produces powerful antifungal agent

Workers of the wood ant Formica paralugubris are skilled poisoners. By treating tree resin with formic acid, they produce a powerful disinfectant to control a pathogenic fungus, Thimothée Brütsch and colleagues show.

Pathogenic micro-organisms, such as the common entomopathogenic fungus Metarhizium brunneum, pose a continuous threat to ant nests; because the ants live close together, the risk of epidemics is high. Therefore, ants should keep their nests hygienic.

Resin

And so they do. Workers of the alpine wood ant Formica paralugubris, for instance, incorporate large amounts of solidified resin from coniferous trees, especially spruce, into their nest to fight pathogens, as Michel Chapuisat showed. The distinctive smell of tree resin comes from terpenes and other volatile substances; these are compounds that decrease bacterial and fungal load in wounded trees. And within ant nests, they do as well. In the presence of resin, bacteria and fungi are inhibited, with the result that more larvae survive when exposed to Metarhizium, and adult ants and larvae have a higher chance to survive when a detrimental bacterium invades the nest.

Combination

Now, Thimothée Brütsch and colleagues report that the ants enhance the antifungal activity of the resin considerably by applying formic acid. This acid, which the ants produce into their venom gland, has an antiseptic effect in itself, just like the volatile substances from resin. But the mixture of the resin with formic acid seems to work particularly well; it has greater antifungal activity than you would expect from the separate effects of resin and acid. This means that the acid increases the disinfectant effect of the tree resin.

So, the ants not only collect pieces of resin to disinfect their nest and protect themselves against pathogens, but they also treat it with formic acid to obtain a more powerful antimicrobial agent.

Willy van Strien

Photo: © Timothée Brütsch

Sources:
Brütsch, T., G. Jaffuel, A. Vallat, T.C.J. Turlings & M. Chapuisat, 2017. Wood ants produce a potent antimicrobial agent by applying formic acid on tree-collected resin. Ecology and Evolution, online March 6. Doi: 10.1002/ece3.2834
Chapuisat, M., A. Oppliger, P. Magliano & P. Christe, 2007. Wood ants use resin to protect themselves against pathogens. Proceedings of the Royal Society B 274: 2013-2017. Doi: 10.1098/rspb.2007.0531

Fake present

10 March 2017 /

Male spider cheats female with densely wrapped rubbish

Pisaura mirabilis male cheats female with well-wrapped fake present

A male nursery web spider may offer its partner a worthless package instead of a decent nuptial gift. He wraps such a fake present in many layers of silk, Paolo Ghislandi and colleagues show, so that it takes longer before the female detects the deceit and sends him away.

When you give someone a cheap gift, you’d better wrap it well. At least, that is the rule in the nursery web spider (Pisaura mirabilis), a hunting spider that occurs throughout Europe, as Paolo Ghislandi and colleagues report. A male usually carries a nuptial gift when he is looking for a female to mate with. It should contain one or more prey items that he has caught to offer her and wrapped in white silk. A female, happy to get a nice meal, will allow the male to mate her, while she often rejects a male without a present, as Maria Albo had shown.

Worthless

But instead of a meal, a female often finds the hard leftovers of an arthropod prey or some plant parts after removing the silk – an inedible gift that is worthless. Is a male giving such a gift in bad condition and unable to capture a prey and offer it? Or couldn’t he find anything better?

No, instead of inability it is pure deception, as Ghislandi concludes from field observations and behavioural experiments in the laboratory. Even a male that is well-fed and heavy – and therefore capable to catch and offer a prey – often cheats its partner with wrapped rubbish.

And he is successful, for as a female is unable to determine whether a white package contains something edible or not, she will accept a male with a fake present as readily as a male that carries an edible gift.

Punished

But ultimately, a cheating suitor will still be punished: the mating lasts briefly. A male can transfer its sperm while the female consumes her gift; it she is finished, he has to go. Consequently, when the gift is inedible, the mating will end soon, so a cheating male will transfer less sperm than a honest male. That is a disadvantage, because a female mates with several males and their sperm must compete for the eggs to be fertilized. The more sperm cells a male transfers, the more offspring he will sire.

More silk

Ghislandi also discovered that fake presents are wrapped in more layers of silk than real gifts, so cheating males invest a lot in wrapping. Probably, this is a trick to prolong mating, because the more silk is wrapped around the gift, the longer it takes a female to detect the deceit and stop the copulation.

Still, a really long mating will not ensue. And maybe that’s not so bad after all: a male cheating a female with a fake present may fertilize less eggs, but he saves time and energy to find other females, thereby increasing is lifetime reproductive success as well.

Willy van Strien

Photo: ©Paolo Ghislandi

Sources:
Ghislandi, P.G., M. Beyer, P. Velado & C. Tuni, 2017. Silk wrapping of nuptial gifts aids cheating behaviour in male spiders. Behavioral Ecology, online February 23. Doi:10.1093/beheco/arx028
Ghislandi, P.G., Albo, M.J., Tuni, C. & T. Bilde, 2014. Evolution of deceit by worthless donations in a nuptial gift-giving spider. Current Zoology 60: 43-51. Doi: 10.1093/czoolo/60.1.43
Albo, M.J., G. Winther, C. Tuni, S. Toft & T. Bilde, 2011. Worthless donations: male deception and female counter play in a nuptial gift-giving spider. BMC Evolutionary Biology 11: 329. Doi: 10.1186/1471-2148-11-329

Tiny scarecrow

6 March 2017 /

Red-winged blackbird flinches from whistling caterpillar

red-winged blackbird s scared by whistling caterpillar

It is funny when the tiny caterpillar of the walnut sphinx Amorpha juglandis suddenly emits a high-pitched noise. Thus sound scares birds, as Amanda Dookie and colleagues witnessed, so that they will refrain from picking the caterpillar. Why are birds startled by this whistling caterpillar?

caterpillars od walnut sphinx can make whistling soundsNormally birds are not afraid of a caterpillar, but caterpillars of the moth Amorpha juglandis can scare them, Amanda Dookie and colleagues report, by starting to scream when they are touched – a most peculiar behaviour.

A few years ago, Veronica Bura investigated how the caterpillars produce their high pitched sound. Their respiratory system consists of a network of tubes with on each side a row of openings, the spiracles. When screaming, Bura assessed, walnut sphinx caterpillars contract the front end of their bodies, close all spiracles except the rear pair and expulse the air forcefully through these openings, producing a whistling sound. The posterior spiracles are enlarged compared to the others, which probably is an adaptation for sound production. Often the caterpillars also thrash their heads to defend themselves while whistling, and Dookie wanted to know if the whistle sound in itself is enough to frighten birds, and how great the startling effect is.

Startle response

To find out, she exposed a number of male red-winged blackbirds to playbacks of caterpillar whistles that had been recorded before. Just like the walnut sphinx, red-winged blackbirds are to be found throughout North America. The experimental birds were housed in individual cages and provided mealworms on a small platform for four days before the tests started. Then the platform was equipped with a sensor and a speaker, and as soon as a bird touched the dish during a test, the whistling sound was played back.

That had a huge effect: the sound evoked a startle response in all birds. Most flew away, hopped backwards or clapped their wings. After a while they tried again to pick a mealworm and then they heard the whistle sound again. The birds got habituated a bit and the startle response decreased over time, but when they were exposed to the sound after two days of rest, they were as frightened as they had been the first time.

Danger

Can the caterpillars protect themselves from hungry birds by whistling? Probably so. In the wild, the birds scurry around and when they are scared by a noisy caterpillar, they will abandon that prey and move on in search of another.

But why are birds scared by a whistling caterpillar that is not dangerous or venomous, as far as is known? The birds may associate the short, high-pitched sound with danger, the researchers propose, because the sound is similar to the alarm call that many birds emit when they are threatened. A fright response to such alarm call is hard-wired in birds, and this seems to be exploited by the caterpillars when they mimic the call.

Willy van Strien

Photos:
Large: red-winged blackbird Agelaius phoeniceus. Janet Beasly (Wikimedia Commons, Creative Commons CC BY-SA 2.0)
Small: caterpillar of walnut sphinx, Amorpha juglandis. © Jayne Yack

Sources:
Dookie, A.L., C.A. Young, G. Lamothe, L.A. Schoenle & J.E. Yack, 2017. Why do caterpillars whistle at birds? Insect defence sounds startle avian predators. Behavioural Processes, 138: 58-66. Doi: 10.1016/j.beproc.2017.02.002
Bura, V.L., V.G. Rohwer, P.R. Martin & J.E. Yack, 2011. Whistling in caterpillars (Amorpha juglandis, Bombycoidea): sound-producing mechanism and function. The Journal of Experimental Biology 214: 30-37. Doi:10.1242/jeb.046805

© 2024 From so simple a beginning

Theme by Anders Norén — Up ↑