ScienceDaily (Jan. 4, 2009) —
The reproductive spores of many species of fungi have evolved remarkably
drag-minimizing shapes, according to new research by mycologists and
applied mathematicians at Harvard University.
In many cases, the scientists
report in the Proceedings of the National Academy of Sciences, the drag
experienced by these fungal spores is within one percent of the absolute
minimum possible drag for their size. But these sleek aerodynamic shapes
are seen only among fungus spores distributed by air flow, not those which
are borne by animals.
"We set out to answer a very
simple question: Why do fungal spores have the shapes that they do?" says
co-author Marcus Roper, who contributed to the research as an applied
mathematics graduate student in Harvard's School of Engineering and
Applied Sciences. "It turns out that for forcibly ejected spores, the
shape can be explained by simple physical principles: The spores need to
have a close to minimum possible air resistance for their size. As
projectiles, they are close to perfect."
Roper is now a postdoctoral
researcher at the University of California, Berkeley.
Together with colleagues at
Harvard, Roper studied the airborne spores of more than 100 species of
ascomycetes, the largest phylum of fungi. These fungi enter the sexual
phase of their life cycle when they deplete nutrients in the deposits of
feces or decaying matter where they reside.
In these species, spores are
held in fluid-filled sacs where pressure builds until they eventually
explode, ejecting the spores into the surrounding air. An optimal
drag-minimizing shape ensures that the spores can traverse several
millimeters of still air surrounding the fungus' fruiting body; once past
that point, the 10-micron spores are light enough to be propelled by even
the gentlest breeze.
While Roper and his
colleagues found that ascomycetes eject spores at an unexpectedly forceful
1.24 meters per second, the spores decelerate very rapidly, heightening
the importance of aerodynamics in reproductive success.
Spores transported by animals
lack the drag-minimizing shapes seen among airborne spores, says co-author
Anne Pringle, a mycologist.
"A well known ascomycete, the
truffle, spreads its spores when it is eaten and egested by animals," says
Pringle, assistant professor of organismic and evolutionary biology in
Harvard's Faculty of Arts and Sciences. "Other ascomycetes encase their
spores in a goo which is then spread by insects. These animal-dispersed
spores do not exhibit particularly drag-minimizing shapes."
"We can see the signature of
natural selection in this very simple principle that cuts across a range
of species," Pringle says. "It is a real leap forward in our understanding
of the biology of a mega-diverse group of microorganisms, showing how they
manipulate and respond to their environment."
The unusual marriage of
mycology and applied mathematics was fostered at Harvard by the physical
proximity of disparate facilities such as high-speed cameras Roper used to
photograph spore release and the 130-year-old Farlow Library, which ranks
among the world's strongest mycological and botanical collections.
represents exactly the type of opportunity that is unique and special
about Harvard," says co-author Michael P. Brenner, Glover Professor of
Applied Mathematics and Applied Physics in Harvard's School of Engineering
and Applied Sciences. "The work combines diverse fields -- mycology and
applied mathematics -- in synergistic and truly collaborative ways, with a
critical contribution coming from Harvard's remarkable collections."
In addition to Roper,
Pringle, and Brenner, Rachel Pepper of Harvard's Department of Physics
contributed to the research, which was funded by Eastman Kodak, the
Harvard University Herbaria, the Harvard Materials Science and Engineering
Center, and the National Science Foundation.
University (2009, January 4). In Many Fungi, Reproductive Spores Are
Remarkably Aerodynamic. ScienceDaily. Retrieved January 7, 2009,