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Tuesday, January 13, 2009

The Magic of Mushroom Spores

By Brandon Keim Email


High-speed video has revealed that the incredible variety of fantastic forms taken by fungal spores helps them catapult themselves into the air.

For hundreds of years, scientists have described the spectrum of spore shapes — a different one for each of 15,000 known varieties of fungi, an assortment so astounding as to have sprung from the mind of Willy Wonka rather than Charles Darwin.

But for all their observations, they've known relatively little about why spores took those shapes. Some mycologists suspected it was merely evolutionary noise. But the first comparative analysis of fungal spore form and reproductive dispersal shows that shapes are no evolutionary accident.

"What people have done for 200 years is volume after volume of taxonomic work with descriptions of spore shape and size, without reference to why it's there. You've just got these weird and wonderful forms, but nothing about why," said botanist Nicholas Money of Miami University in Ohio.

Money's team used high-speed video analysis to study spores thrown into the air by a biomechanical process as elegant as it is miniscule. A single bead of water condenses on a spore's surface; when the bead touches a film of water on another part of the spore, the bead pours into it, like raindrops merging on a windowshield. The resulting shift in weight distribution is so sudden and massive as to hurl the entire conglomeration — called the ballistospore — airborne.

That process is part of the asexual reproduction of fungi, and the many different shapes may serve to help different species grow and reproduce in different conditions. A single mushroom can launch 31,000 ballistospores per second, adding up to some 2.7 billion spores per day. This process is already understood, but Money and his colleagues are among the first researchers to break it down in frame-by-frame resolution.

What made their paper special, said Money, is their description of variation in this mechanism. They found that tiny changes in spore shape produced profound alterations in water droplet shape. Changes in water droplet shape then affected the the trajectory of dispersed spores.

At one level, the findings are literally microscopic; at another, they're universal.

"Mushrooms are masterpieces of natural engineering," said Money, "and we are just beginning to understand how they work."

The research, published Thursday in Public Library of Science ONE, was funded in part by the National Institutes of Health. They are interested in using Money's insights to develop methods of fungal control. That, however, will be done by others; Money's focus is purely on the magic of mushroom biomechanics.

Asked whether spore trajectories could be scaled up to thrown baseballs or other reader-friendly terms, Money replied that mushroom spores don't go far at all.

"If the viscous drag of air acted upon a baseball with the same intensity that it impedes the flight of a mushroom spore, you would see the pitched ball slow after an arm's length of motion, stop dead, and fall vertically to the ground," he said. "In my seminars I refer to this flight path as the Wile E. Coyote trajectory."

This makes sense, Money said, because it ensures that spores will fall cleanly downward from the densely packed gills where they originate.

"Speaking technically, this is a ****ing beautiful mechanism," he said.

Citation: "Adaptation of the Spore Discharge Mechanism in the Basidiomycota." By Jessica L. Stolze-Rybczynski, Yunluan Cui, M. Henry H. Stevens, Diana J. Davis, Mark W. F. Fischer and Nicholas P. Money. Public Library of Science ONE, Vol. 4 No. 1, Jan. 8 2009

Image: Plate detail from Ernst Haeckel's Kunstformen der Natur, depicting Basimycetes / WikiMedia Commons

Videos: 1. Ultrahigh-speed video clip (50,000 f.p.s.) showing ballistospore discharge in gilled mushroom of Armillaria tabescens / PLoS ONE 2. Ballistospore discharge in the stinking smut fungus Tilletia caries. Video captured at 24 frames per second; shows drop behavior before discharge / Nicholas Money, Miami University. 3. Spore release from cap of fairy ring mushroom captured with conventional digital camera in video mode / Nicholas Money, Miami University.