Pilobolus
Encyclopedia
Pilobolus is a genus
of fungi that commonly grows on herbivore dung
.
of Pilobolus begins with a black sporangium
that has been discharged onto a plant substrate such as grass. A herbivorous 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 and grow as a mycelium
within the excrement, where it is a primary colonizer. Later, the fungus fruits to produce more spores.
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 sporangium
develops. The sporangiophore has the remarkable ability of orienting itself to point directly towards a light source. The subsporangial vesicle acts as a lens
, focusing light via carotenoid pigments deposited near the base of the vesicle. The developing sporangiophore grows such that the maturing sporangium is aimed directly at the light.
When turgor 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 2 meters (6 feet), an amazing achievement for a sporangiophore less than 1 cm tall. The orientation of the stalk towards the light 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 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 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
. 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of fungi that commonly grows on herbivore dung
Coprophilous fungi
Coprophilous fungi are a type of saprobic fungi that grow on animal dung. The hardy spores of coprophilous species are unwittingly consumed by herbivores from vegetation, and are excreted along with the plant matter...
.
Life cycle
The life cycleBiological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
of Pilobolus begins with a black sporangium
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
that has been discharged onto a plant substrate such as grass. A herbivorous 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
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
without germinating, and emerges with the excrement. Once outside its host, spores within the sporangium germinate and grow as a mycelium
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
within the excrement, where it is a primary colonizer. Later, the fungus fruits to produce more spores.
The asexual fruiting structure (the sporangiophore) of Pilobolus species is unique. It consists of a transparent stalk
Stalk
Stalk may refer to:* Plant stem, one of two main structural axes of a vascular plant* Leaf stalk, also known as Petiole* Flower stalk, also known as Peduncle* Stalking, an act of intrusive behavior or unwanted attention towards a person...
which rises above the excrement to end in a balloon-like subsporangial vesicle
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.e.g...
. On top of this, a single, black sporangium
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
develops. The sporangiophore has the remarkable ability of orienting itself to point directly towards a light source. The subsporangial vesicle acts as a lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...
, focusing light via carotenoid pigments deposited near the base of the vesicle. The developing sporangiophore grows such that the maturing sporangium is aimed directly at the light.
When turgor pressure within the subsporangial vesicle builds to a sufficient level, (often 7 ATM
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...
or greater) the sporangium is launched, and can travel anywhere from a couple of centimeters to a distance of 2 meters (6 feet), an amazing achievement for a sporangiophore less than 1 cm tall. The orientation of the stalk towards the light 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
Calcium oxalate is a chemical compound that forms needle-shaped crystals, known in plants as raphides. A major constituent of human kidney stones, the chemical is also found in beerstone, a scale that forms on containers used in breweries...
crystals. Besides serving as a protective mechanism, their hydrophobic 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 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
Dictyocaulus is a genus of nematode parasites of the bronchial tree of horses, sheep, goats, deer, and cattle. Dictyocaulus arnfeldii is the lungworm of horses, and Dictyocaulus viviparus is the lungworm affecting ruminants....
. 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.
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)
- Interview with a Fungus
- Zygomycetes:Pilobolus at Zygomycetes.org