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.

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 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

Useful cigarette butts

House finch has to accept harmful side effects

House finches add cigarette butts to their nests to repel parasites

Smoked-trough cigarette filters are noxious, still some bird species add them to their nest lining, where the nicotine will repel blood-sucking parasites. They do so only when they need to, as Monserrat Suárez-Rodríguez and Constantino Macías Garcia show.

Spent cigarette filters are popular among some bird species, for instance the house finch. The birds weave cellulose fibres from discarded butts into the lining of their nests, together with more conventional soft materials such as feathers, fur or cotton. Monserrat Suárez-Rodríguez en Constantino Macías Garcia wondered whether the birds collect cellulose from butts accidently, or whether they do it to protect their young against blood-sucking parasites: lice and ticks. From earlier research, they knew that ectoparasites are repelled by nicotine, and the more smoked-through cigarette butts could be found in a nest, the smaller the amount of parasites was. Weight gain and fledging success of young increased with the proportion of cellulose from butts in the nest lining.

But they also knew that the butts are harmful to adult birds and their offspring. Next to nicotine, the butts contain more than 400 different substances such as heavy metals and insecticides, many of which are toxic. The substances may enter the birds’ bodies through the skin or the lungs.

Damage

The research team had analysed blood samples of parents and young and found nuclear abnormalities in many red blood cells (in contrast to human red blood cells, those of birds contain a nucleus with dna). The larger the proportion of butts in the nest lining, the more genotoxic damage was seen. Red blood cells live for only two to four weeks, so the damage may have no serious consequences. But other cells types likely are damaged too. The question is whether the benefits of adding cigarette butts to the nest lining – less parasites, resulting in better growth – are large enough to outweigh these costs.

The answer will depend on how much the butts are needed to fight off parasites.

Ticks

Now, experiments reveal that house finches act accordingly: they bring more smoked-through cellulose fibres from cigarette butts to their nests if parasites are present than if they’re not. The researchers removed the nest lining from a number of nests shortly after the young hatched, and added a piece of felt instead; by doing so, they removed the bulk of the tick population from the nest as well. They measured the amount of butts in the original lining. They added living ticks to some of the artificial felt nest linings, dead ticks to other linings and nothing to the remaining linings. After the young fledged, they collected the artificial linings to investigate how much butts the parents had added.

It appeared that the birds collected more butts if the researchers had added living ticks to their nest, so when it was useful to bring butts. Also birds that had brought a large amount of butts into their original nest lining, collected many butts now as well; apparently, they had experienced a high parasitic load during incubation.

The birds don’t collect cigarette butts randomly, the conclusion is, but in response to the presence of ectoparasites; so, it is a form of self-medication.

Willy van Strien

Photo: house finch male feeding young. Susan Rachlin (Wikimedia Commons, Creative Commons CC BY 2.0)

Sources:
Suárez-Rodríguez, M. & C. Macías Garcia, 2017. An experimental demonstration that house finches add cigarette butts in response to ectoparasites. Journal of Avian Biology, online September 1. Doi: 10.1111/jav.01324
Suárez-Rodríguez, M., R.D. Montero-Montoya & C. Macías Garcia, 2017. Anthropogenic nest materials may increase breeding costs for urban birds. Frontiers in Ecology and Evolution 5: 4. Doi: 10.3389/fevo.2017.00004
Suárez-Rodríguez, M. & C. Macías Garcia, 2014. There is no such a thing as a free cigarette; lining nests with discarded butts brings short-term benefits, but causes toxic damage. Journal of Evolutionary Biology 27: 2719–2726. Doi: 10.1111/jeb.12531
Suárez-Rodríguez, M., I. López-Rull & C. Macías Garcia, 2013. Incorporation of cigarette butts into nests reduces nest ectoparasite load in urban birds: new ingredients for an old recipe? Biology Letters 9: 20120931. Doi: 10.1098/rsbl.2012.0931

Double deceit

Female cuckoo chuckle call is embarrassing for songbirds

female cuckoo vocally mimics a hawk

By first laying her egg secretively and then giving a loud chuckle call while leaving, a female cuckoo doesn’t seem to behave in a consistent way. But her call adds to her trickery, as Jennie York and Nicholas Davis show.

A female common cuckoo that lays an egg in the nest of a songbird, for instance a reed warbler, behaves as secretly as she can, because if the intended foster parents detect her presence, they will chase her away; and if she has laid her egg already, the parents will either try to eject it or leave their clutch to start a new one somewhere else. With a cuckoo young in the nest, their own young cannot survive. So, a cuckoo visits the nest and quickly dumps her egg when the owners are away, mostly within a minute.

Vigilant

But while she tries to be unseen when laying, she gives a conspicuous chuckle call when flying away afterwards – quite different from the ‘cuck-oo’ call of the male. This seems paradoxical, as the songbirds may notice her presence after all. Why is she seeking their attention now? Jennie York en Nick Davis answer this question.

They reasoned that a calling female cuckoo may be mimicking the call of a sparrowhawk, to which it is quite similar. If the parents hear that sound, they are concerned about their safety. They become vigilant and scan the surroundings to detect the predator, and their attention is diverted away from their clutch. If they perceive a foreign egg in the clutch, they respond in the same way as when they have seen a female cuckoo on their nest: they try to eject the foreign egg or leave the clutch. But when worrying about their own safety, they will pay less attention to their clutch and may overlook a foreign egg.

Less attention

York and Davis could demonstrate that this idea is right. A few meters from reed warblers’ nests, they placed speakers and play backed the call of a male cuckoo, the call of a female cuckoo, the call of an Eurasian sparrowhawk, or the call of an Eurasian collared dove, a harmless bird; they recorded the songbirds’ responses. The results are clear: the sound of a male cuckoo or a dove elicited no response, while the call of a sparrowhawk provoked vigilance – as did the call of a female cuckoo. So, it appears that indeed a female cuckoo vocally mimics a sparrowhawk. Also great tits and blue tits, which are not exploited by cuckoos as foster parents for their young, get alarmed by the female cuckoo’s chuckle.

After such a frightening experience, reed warblers pay less attention to their clutch, as further experiments revealed. When the researchers exposed the reed warblers to the calls again, put a foreign egg in the nests and checked the nests afterwards to see whether this egg was accepted or rejected, they discovered that parents that had been exposed to the call of a sparrowhawk or a female cuckoo were less likely to notice the foreign egg than birds that had heard a male cuckoo or a collared dove.

So, a chuckling female cuckoo deceits the foster parents twice, first by secretly laying her egg and then by vocally mimicking a sparrowhawk, tricking the victims into defending themselves instead of their clutch, while in fact the clutch is in danger.

Willy van Strien

Photo: Trebol-a (Wikimedia Commons, Creative Commons CC BY-SA 3.0)

Source:
York, J.E. & N.B. Davies, 2017. Female cuckoo calls misdirect host defences towards the wrong enemy. Nature Ecology & Evolution, online September 4. Doi: 10.1038/s41559-017-0279-3