Monthly Archives: February 2009

Endless forms most beautiful and most wonderful

Charles Darwin 

Endless forms most beautiful and most wonderful. Charles Darwin invoked those very words in the pages of his seminal opus, On the Origin of Species, published 150 years ago this year. Darwin was struck by the diversity of life and how disparate niches had so often been filled by modified forms of related species. Islands of course come to mind. Or take the icy, snowy habitats near glacial ice and melting seeps. At first glance, you wouldn’t dream of finding mushrooms growing there, let alone flourishing. Nevertheless, natural selection has driven groups of mushrooms to adapt to this habitat numerous times over the previous millennia. We’re highlighting these amazing fungi in this issue with a report by Cathy Cripps and photos by Steve Trudell. Furthermore, in this issue and all issues for 2009 we will be celebrating the 200th anniversary of the birth of Charles Darwin and his tremendous contributions to the field of biology. Besides pictures and articles directly related to Darwin, the 2009 issues of Fungi will feature articles on basic fungal taxonomy and genetics that will appeal to amateur and expert alike.

Artillery Fungi: Fastest Flights in Nature!

Artillery Fungi SlidesWhen he’s not busy writing terrific stories on fungi and those who study fungi (eg. Mr. Bloomfield’s Orchard, Triumph of the Fungi, and Carpet Monsters), Nik Money spends his time investigating the mechanisms of spore dispersal in fungi. The research team in his lab at Miami University in Oxford, Ohio, recently has employed an ultra-high-speed video camera to film a number of fungi as they blast their tiny progeny at tremendous velocities.

The nature of spore release mechanisms among fungi has been investigated since the eighteenth century. Long thought to rely mostly by passive means, it was assumed that mushrooms—as one example—simply dropped their spores from gills, with the ensuing clouds of spores carried off on a current of air. Money has shattered that myth. First off, it should be noted that a variety of spore discharge processes have evolved among the fungi. Those with the longest ranges are powered by hydrostatic pressure and include “squirt guns” that are most common in the Ascomycota and Zygomycota. In these fungi, fluid-filled stalks that support single spores or spore-filled sporangia, or cells called asci that contain multiple spores, are pressurized by osmosis. Because spores are discharged at such high speeds, most of the information on launch processes from previous studies could only be calculated using mathematical models, at best, or pretty much guessed at by others.

In their report, recently published in the prestigious on-line research journal Public Library of Science ONE (Yafetto et al.; 2008; PLoS ONE 3[9]: e3237), Money and colleagues have used ultra-high-speed video cameras running at rates of 250,000 frames per second (!) to analyze the entire launch process in four species of fungi that grow on the dung of herbivores. For the first time ever, they were able to take direct measurements of launch speeds and empirical estimates of acceleration in these fungi. Get this: launch speeds ranged from 2 to 25 meters per second with incredible corresponding accelerations of 20,000 to 180,000 times the force of gravity which propelled spores over distances of up to 2.5 meters. (Little wonder that Nik has dubbed fungal spores the “fastest flights in nature.”) Additionally, quantitative spectroscopic methods were used to identify the organic and inorganic osmolytes responsible for generating the turgor pressures that drive spore discharge. The new video data allowed the team to test different models for the effect of viscous drag and identify errors in the previous approaches to modeling spore motion. Spectroscopic data showed that high speed spore discharge mechanisms in fungi are powered by the same levels of turgor pressure that are characteristic of fungal hyphae and do not require any special mechanisms of osmolyte accumulation.

Contemporary analysis of these extraordinary processes has implications for the fields of plant disease control, terrestrial ecology, indoor air quality, atmospheric sciences, veterinary medicine, and biomimetics. Mechanisms include a catapult energized by surface tension that launches mushroom spores, the explosive eversion of a pressurized membrane in the artillery fungus (Sphaerobolus stellatus, see color photo with multiples stages in readiness prior to blastoff) and the discharge of squirt guns pressurized by osmosis. Squirt gun mechanisms are responsible for launching spores at the highest speeds and are most common in the Ascomycota, including lichenized species, but have also evolved among the Zygomycota, including the loveable “hat thrower,” Pilobolus (see image sequences). In the so-called “coprophilous” fungi in both phyla, specialized for growth on herbivore dung, these squirt gun mechanisms propel spores over distances of many centimeters or even meters onto fresh vegetation (and thus away from the “zone of repugnance” surrounding the grazers’ dung) where they may be consumed by their host animals. The range of these mechanisms necessitates very high launch speeds to counteract the otherwise overwhelming influence of viscous drag on the flight of microscopic projectiles. Money is now taking a look at the mechanisms of ballistospore discharge within the Basidiomycetes, and you can too. Check out the sequence of images Dr. Money supplied to Fungi that show spores being shot from the gills of Armillaria tabascens, one of the honey mushrooms. Last summer at the annual meeting of the Mycological Society of America, Nik brought down the house with his Cannon Fungus Opera, featuring ultra-high-speed film of fungi blasting away, set to the tune of the “Anvil Chorus.”

Watch the video HERE: