London, September 17 : Using high-speed cameras, scientists have revealed that fungi spores are the fastest flyers in nature, and can achieve record-breaking acceleration to escape dung.
According to a report in New Scientist, the images show in detail how microscopic dung-loving, or coprophilous, fungi use a squirt-gun action to propel their spores.
The fungi degrade the millions of tons of dung produced by cows and other herbivores each year. To reproduce, their spores must be eaten by herbivores, yet few animals will graze on the grass next to their own dung.
To overcome this obstacle, dung-dwelling fungi have evolved tiny catapults, trampolines and squirt guns that propel spores and spore packets up to 2.5 meters away.
Nicholas Money at Miami University in Oxford, Ohio, and colleagues filmed the squirt gun action of four species at 250,000 frames per second.
They found that the spores, measuring between 10 micrometres and half a millimetre, are launched at up to 25 metres per second. Although impressive, that makes them slower than had been estimated by mathematical models.
But, the acceleration of the spores still puts them in a class of their own.
"One minute they're standing still on a cow pie, and a millionth of a second later, they are travelling at 25 metres per second," said Money.
His colleagues measured accelerations up to 180,000 g - the fastest airborne acceleration seen in the living world.
In comparison, a jumping antelope accelerates at 1.6 g, astronauts experience maximum acceleration of less than 4 g during a Space Shuttle launch, and fleas accelerate at 200 g. Jellyfish stingers are fired at 40,000 g in water.
"The fastest spores travelled more than 1 million times their own 'body' length in one second," said Money.
To understand why mathematical estimates based on the distances travelled by the spores had been wrong, Money's colleague Diana Davis looked at the droplets of liquid expelled with them.
The squirt guns expel their contents by osmotic pressure. So from the composition of the sap, Davis was able to calculate the pressures that would develop inside.
The mathematical calculations had suggested that these pressures must be very high in order for them to spit the spores metres away.
Instead, Davis found that the squirt cells are under no greater pressure than other kinds of fungal cells. The researchers said that the models must have over estimated the drag that air exerts on the tiny droplet.