''Pilobolus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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

that commonly grows on herbivore dung.

Life cycle

The life cycle of ''Pilobolus'' begins with a black

sporangium A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...

that has been discharged onto a plant substrate such as grass. A

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

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 The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

without germinating, and emerges with the

excrement Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...

. 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 flowering plant, angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the sp ...

and grow as a

mycelium Mycelium (: mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are fo ...

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. On top of this, a single, black

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 that 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 equilib ...

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 Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula or . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydr ...

crystals. Besides serving as a protective mechanism, their

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

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 A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

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. ''Dict ...

''. 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