The Fungi Kingdom presents a variety of spore types that utilize mechanisms that are not seen in any other group of organisms. Chytridiomycoda, Blastiocladiomycota, Neocallimastigomycota, Ascomycota, Zygomycota, Glomeromycota, and Basidiomycota make up the major phyla of fungi. Sexual and asexual spores of these fungi are dispersed into the environment by varying mechanisms, from forcibly dispersing spores to attracting other organisms to do the fungi’s dirty work of spore dispersal. Spores are released from the sporophore by an active or passive release.
There are two types of spore release: ballistospore release and spore discharge. Ballistospore release is essentially a “gunshot” maneuver. The basidia houses the development of basidiospores, a reproductive spore that is discharged from the sterigmata by a forcible mechanism. Hence, the name “ballistospore”, like ballistics. The force is driven by a change in the center of gravity of the spore. A droplet of fluid called the Buller’s drop accumulates at the tip of the basidiospore, created by the sugars in the cell wall attracting water vapor from the surrounding air during maturation. The Buller’s drop develops into a water droplet at the hilum (the tip of the spore) and while this is occurring, condensation is also occurring on the adaxial side of the basidiospore. Once these water droplets combine, the center of mass and the surface tension rapidly change, which leads to the release of the basidiospore.
Spore discharge is common in Ascomycetes. When a cell becomes turgid, a spore is released from it due to the hydrostatic pressure building up inside of the cell. At the hymenium or ostiole, asci emerge at the tip of the ascus and are ejected over some distance. In the case of fungi such as Pilobolus (a dung fungi), the sporangiophore forms a sporangium that has a gooey interior. The gooey interior begins to dry, which causes the tension to increase. Over time the gel will crack and the sporangium is released into the atmosphere. Both the ascophores and sporangiophores are aimed towards sunlight to increase their likelihood of jumping over the big guys (i.e. plants and trees) and finding a new home to grow up and repeat the process upon.
Passive spore release either occurs in a dry condition or a mucilage, which is a polymer produced by the fungi that helps store water and spores. This is commonly seen in a giant puffball mushroom. When the puffball cracks open, it allows the wind to carry away the spores. Another passive mechanism is use of water. The spore walls have a “waterproof” exterior that allows them to float along the surface of the water to a place suitable for germination. Rain can squish the spore sack, leading to a rebound that pushes the spores out, which is seen commonly in Bird’s Nest Fungi. Those that use a passive mechanism heavily rely on external support from wind or water and have to produce billions, even trillions of spores just to get a few successful germinations to occur.
Another passive mechanism is the utilization of animals. Truffles, a delicious mushroom that people around the world love to consume, are produced under the surface of the soil and have to get above ground in order to disperse their spores. They have an animal friendly scent that attracts animals to their site, at which point they are dug up by the animal and are consumed. Because the spores do not get digested by the animal, they are excreted and can germinate. Stinkhorn mushrooms have spores that contain a foul smelling goo that resembles a rotten meat smell, which attracts flies. The flies become coated with the slime as they consume it and carry away the spores in the goo. This is a much more successful way of passive dispersal because the dispersal can be over a wider range and their chance of success is much higher than just hoping for the best.
Whatever their dispersal mechanism may be, fungi have something that they are doing right, as they are found in every condition, everywhere in the world. From soil to home, shorelines to plants, they make up a diverse group of organisms that have a wide range of capabilities. Penicillin is derived from the fungi Penicillium, along with other antibiotics. Fungi can cause a range of infections, from yeast infections to ringworm. They can be delightfully delicious, and can put people in a hallucinogenic state. Some produce toxins so deadly that just one can kill you. Whatever the case, the fungi kingdom contain some of the most fascinating eukaryotic organisms. So next time when you tip back a beer, eat a slice of bread, take an amoxicillin for an ear infection, or consume a chunk of brie, remember what those fungi had to do to get there. For more information on dispersal mechanisms, check out: http://herbarium.usu.edu/fungi/funfacts/Dispersal.htm