From so simple a beginning

Evolution and Biodiversity

Month: April 2018

Cooling down

26 April 2018 /

Blowfly blows bubbles to prevent overheating

blowfly cools down by bubbling behaviuour

 

A blowfly often extrudes a liquid bubble between its mouth parts and then takes it back. By exhibiting this bubbling behaviour, it gets rid of excess heat, Guilherme Gomes and colleagues show.

How can a buzzing blowfly avoid getting overheated? Few people will ever have wondered, but as it happens, Guilherme Gomes and colleagues did. And they discovered that the oriental latrine blowfly Chrysomya megacephala manages to lower its body temperature by blowing a bubble.

At high air temperatures, a blowfly can expel a drop of liquid out of its oral cavity and hold it with its mouthparts. As some liquid evaporates, the droplet will rapidly cool down, whereupon the fly will take it in. The cycle is often repeated, and a droplet may tidally move out and back up to six times until eventually the fly swallows it and its body temperature decreases. The liquid is a complex mix of fluids derived from ingested meals and saliva.

Daytime and night-time

The blowfly applies this trick during the day when ambient temperature exceeds 25 °C. At that temperature, the animal is warmed-up and busy, so that its muscles produce a lot of heat, which makes cooling necessary. When it gets really hot, above 30 °C, the fly becomes inactive and no longer generates heat. It then stops blowing bubbles.

At night, it bubbles more than during the day to stay cool, in order to decrease its metabolism and save energy.

If air humidity is high, the liquid will not evaporate well and a bubble will not cool down. If the fly still expels a drop, it will not re-ingest it, but spit it out instead.

Small animals only

Cooling down by extruding a droplet is only feasible in small animals, and a number of insect species seem to exhibit such behaviour. For larger animals, it is impossible to produce and handle a liquid drop that is large enough for a cooling effect. To us, it would make no sense to trying it – fortunately. We cool down by sweating, which is impossible to an insect because of its chitinous exoskeleton and wax covering.

Willy van Strien

Photo: Blowfly Chrysomya megacephala. gbohne (via Flickr, Creative Commons CC BY-SA 2.0)

Source:
Gomes, G., R. Köberle, C.J. von Zuben & D. V. Andrade, 2018. Droplet bubbling evaporatively cools a blowfly. Scientific Reports 8: 5464. Doi: 10.1038 / s41598-018-23670-2

Help when needed

20 April 2018 /

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.

Seed set

buckler mustard attracts crab spider if infested by caterpillars
The 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.

Bees

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

Inequality

12 April 2018 /

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.

Red fox

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.

Wedding market

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

Unrewarded services

6 April 2018 /

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.

Deceived

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 sometimes 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.

Service

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

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