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Last Updated: Thursday, 18 March, 2004, 13:14 GMT
Why ants make great gardeners
Leafcutter ants, Earth birthday project
The ants use leaves to grow their fungus on
Leafcutter ants have evolved several gardening techniques in order to become successful.

The insects - sometimes called parasol ants - cut half-moon-shaped pieces of leaf from trees and carry them to their nest on their backs.

The leaves are used to make a sponge-like "fungus garden" - the leaves are mashed up to support the growth of a special fungus which the ants then eat.

But the ants will only eat one type of fungus, leaving them exposed - much like human farmers - to the risks of pathogens, micro-organisms that cause disease.

The effects of such pathogens can be devastating, but what has amazed scientists is the way most ant colonies appear able to stay either free of disease or to keep problems under control.

"We discovered that the ants employed two very different behaviours to defend the fungus garden," Professor Cameron Currie, of Kansas University, told BBC World Service's Discovery programme.

"The first is weeding - this involves the ants removing infected parts of the fungus garden and discarding it into their 'dump'.

"The other behaviour we called 'fungus grooming' - this is where the ants actually clean the fungus garden, and lap up the spores of the pathogen from within the fungus garden."

Chemical defence

An ant colony may include eight million individuals and go through two tonnes of leaves a year. The garden is a hugely important place. It is where the larvae are kept.

But this remarkable garden is a monoculture, and like all monocultures it is open to attack. For the ants, the enemy comes in the form of other fungal species.

Leafcutter ants, Tom Davis
If we can work out how the social insects manage their labour, I think it could give us some really deep insights for the organisation of our own factories
Professor Nigel Franks
To study the ants' gardening techniques, Currie and colleagues have sprayed leaves in ants' nests with pathogens, and videotaped the insects' behaviour.

Initially, the ants become very excited - Currie describes them as seeming to "panic" - but after 72 hours almost all traces of the pathogen are removed.

The Kansas ecologist and evolutionary biologist said he had also discovered how the ants use antibiotics to fight off the fungal infection. They have evolved a mutualistic association with a third organism, a bacterium.

"The ants actually culture and grow this bacterium on their bodies," he stated.

"These bacteria actually produce antibiotics that suppress the specialised pathogens of the fungus garden.

"So the ants also employ chemical defences."

Human networks

Like all good gardeners, ants also have a compost heap. This is a waste chamber located next to the fungus garden. "Undertaker ants" take dead ants to this site, while others remove fungus which is no longer useful.

Research at Sheffield University has found that there are ants who work on the tip, turning it over, helping it to degrade as fast as possible.

Leafcutter ant garden, Earth birthday project
The fungus garden is the home of the queen ant and the larvae
These ants have a never-ending task. As a source of potential infection, they are not allowed back into the colony and are attacked if they try to do so.

"You have individual ants on rubbish detail," said Adam Hart, a research assistant at Sheffield.

"If a parasite or a pathogen takes hold, or if this fungus garden is destroyed, the ant colony no longer exists. So they're very scrupulous in keeping the place hygienic and very clean."

Ants do, however, have no bosses directing operations or policing the gardeners.

Professor Nigel Franks, of Bristol University, told Discovery he believed ant organisation could have huge lessons for humans.

"These different jobs, particularly in the leafcutter colony, have different risks," he pointed out.

"Imagine you're a waste disposal operative in human society. You might have your clothing or outer surfaces contaminated by nasty substances.

"You shouldn't - even if somebody asks you to do it - immediately go and work in a kitchen.

"So it's an immense management problem. If we can work out how the social insects manage their labour, I think it could give us some really deep insights for the organisation of our own factories, or networks of computers or whatever."




SEE ALSO:
Ants in special delivery
25 Feb 04  |  Devon
Ant history revealed
10 May 03  |  Science/Nature
Killer ants threaten Australia
28 Feb 03  |  Asia-Pacific


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