Scientists have measured the fastest launch acceleration known in nature — a tiny fungal spore that is squirted eight feet away from its home on a dung heap to greener pastures.
The researchers used very high-speed video capturing 250,000 frames per second to record the spore-flinging, which can't be seen with the naked eye because it happens in one-millionth of a second.
The recordings allowed them to calculate the acceleration, which ranged from 20,000 to 180,000 times the acceleration of gravity in the four fungal species tested.
"In terms of velocity, there are other things that move faster," said study lead author Nicholas Money of Miami University in Oxford, Ohio. "It's the acceleration here that's really astonishing. These microscopic spores are stationary, and one millionth of a second later, they are moving at 25 meters per second [56 miles per hour]."
Given the size of the spores, this acceleration would be equivalent to a person traveling at 5,000 times the speed of sound, Money said.
Because the spores are so tiny, air exerts a huge amount of drag on them — imagine firing a cannonball through syrup — so the spores need a lot of acceleration to overcome the slowdown.
It is the need to get their spores away from the pile of poo on which these fungi live that drove the evolution of their dramatic ability. These fungi live in the dung of herbivores, performing the critical function of helping to degrade the manure, but their spores must be eaten by herbivore hosts for the fungi to reproduce.
For their part, the herbivores won't graze too near their own droppings, maintaining a "zone of repugnance" around their dung heaps. The spores must clear the zone to more appetizing ground where they can be munched by a cow or an elephant to complete the cycle.
The spores are propelled by the release of osmotic pressure within a cell at the tip of a fungal stalk. Accumulation of salts and sugars in the cell draws water inside, building the pressure.
At the right time, a miniscule lid opens in the tip of the cell, letting loose a tiny-but-mighty water cannon that shoots the spores away.
The results are published in the journal PLoS ONE.
"It's incredible to think about this," said mycologist Joey Spatafora of Oregon State University in Corvallis. "It affects and improves our understanding of how these organisms disperse. "I get excited about it, too, as a teaching and public demonstration tool — as a way of engaging students and members of the general public about how amazing and cool fungi are."