''Pilobolus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

that commonly grows on herbivore dung.

Life cycle

The

life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring * Life-cycle hypothesis ...

of ''Pilobolus'' begins with a black sporangium that has been discharged onto a plant substrate such as grass. A

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

animal such as a horse then eats the substrate, unknowingly consuming the sporangium as well. The ''Pilobolus'' sporangium survives the passage through the gastrointestinal tract without germinating, and emerges with the excrement. Once outside its host, spores within the sporangium

germinate Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...

and grow as a mycelium within the excrement, where it is a primary colonizer. Later, the fungus fruits to produce more spores. left, ''Pilobolus'' sporangium The asexual fruiting structure (the sporangiophore) of ''Pilobolus'' species is unique. It consists of a transparent stalk which rises above the excrement to end in a balloon-like

subsporangial vesicle A ''subsporangial vesicle'' is a vesicle which is below the sporangium on a fungus. Is often used in the turgor-building and release to launch the sporangium from the stalk of the fungus using this spore-dispersal method. An example of this is t ...

. On top of this, a single, black sporangium develops. The sporangiophore has the remarkable ability of orienting itself to point directly towards a light source. The shape and transparency of the subsporangial vesicle allow it to act as a

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

, focusing light into carotenoid pigments deposited near the base of the vesicle, which absorb the photons and allow cells to detect the light level in the direction of the lens. The developing sporangiophore grows such that the maturing sporangium is aimed directly at the light. When

turgor Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called ''hydrostatic pressure'', and is defined as the pressure in a fluid measured at a certain point within itself when at equilibri ...

pressure within the subsporangial vesicle builds to a sufficient level (often 7 ATM or greater), the sporangium is launched, and can travel anywhere from a couple of centimeters to a distance of 3 meters (10ft). For a sporangiophore less than 1cm tall, this involves acceleration from 0 to 20 km/h in only 2 µs, subjecting it to over 20,000 G, equivalent to a human being launched at 100 times the speed of sound. The orientation of the stalk towards the early morning sun apparently guarantees that the sporangium is shot some distance from the excrement, enhancing the chances that it will attach to vegetation and be eaten by a new host. Another adaptation of ''Pilobolus'' is that the sporangium is covered in calcium oxalate crystals. Besides serving as a protective mechanism, their

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, t ...

nature also leads the sporangium to flip over onto its sticky bottom after landing in a drop of dew, thus allowing it to cling to a plant substrate. ''Pilobolus'' species can be grown in artificial culture, but only when the growth medium is supplemented with some form of chelated iron, or with sterilized herbivore dung. The forcible discharge mechanism of ''Pilobolus'' is exploited by parasitic nematodes including lungworms in the genus ''

Dictyocaulus ''Dictyocaulus'' is a genus of nematode parasites of the bronchial tree of horses, sheep, goats, deer, and cattle. ''Dictyocaulus arnfieldi'' is the lungworm of horses, and ''Dictyocaulus viviparus'' is the lungworm affecting ruminants. ''Dic ...

''. Larval lungworm nematodes excreted by infected deer, elk, cattle, horses, and other hosts climb up ''Pilobolus'' sporangiophores and are discharged with the sporangium. They complete their life cycle when they and their ''Pilobolus'' vector are eaten by a new host.

References

*Bruce, V. G., F. Weight, and C. S. Pittendrigh. 1960. Resetting the sporulation rhythm in ''Pilobolus'' with short light flashes of high intensity. Science 131:728–30. *Uebelmesser, E. R. 1954. Über den endogenen Tagesrhythmus der Sporangienbildung von ''Pilobolus''. Arch Mikrobiol 20:1–33.

External links

''Pilobolus crystallinus'', "The Fung in the Dung"
by Tom Volk
''Pilobolus'' and the Lungworm
at the Cornell Mushroom Blog (with time lapse video)

Zygomycetes:''Pilobolus''
at Zygomycetes.org {{Taxonbar, from=Q3273234 Zygomycota genera