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| Fig. 12: Pilobolus, the howitzer, ejects its entire sporangium. |
Spore Dispersal in Fungi (continued)
Active Mechanisms of Spore Release
Active mechanism of spore release refer to those fungi that are able to eject their spores using energy from within their mycelium or fruitbody. These can be divided into subcategories:
Explosive Mechanisms: A common means of forcible spore discharge is that in which a cell contains a large vacuole through which greater and greater pressure is applied as water comes into the cell. Eventually, the vacuole will explode releasing the spores in a jet stream of water and the fruiting structure collapses. You saw an example of such a fungus in the video, The Moldy World About Us.
The genus Pilobolus (Figure 12) forcibly ejects an entire Sporangium (Zygomycota) approximately 4 feet away and the swollen portion of the sporangium also serves as a light receptor that curves the stalk of the sporangium so that it shoots the spores in the direction of the light. The spores of the sporangium are in a slime layer so that the entire mass of spores are dispersed as a unit. As you recall the distance here is important because Pilobolus is a dung inhabiting species and the spores must be dispersed beyond the dung heap that it is growing on because the cow will not graze within a certain distance of their dung heaps. And it is important that the cow eat the spores, in order that they will go through their digestive system, and come out with the dung to start the next generation. An animated "gif" demonstrating dispersal in this genus can be found here that was created by Bob Fogel, at the University of Michigan:
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| Fig. 12: Pilobolus, the howitzer, ejects its entire sporangium. |
Animal Dispersal
By examining the fruitbodies of some puffballs, there do not always appear an obvious means of dispersal (Figs. 13a and b). In some genera, it is believed that such puffballs are adapted for dispersal by animals. Foraging animals often consume these fruiting bodies. The spores of these fungi are able to pass through their digestive systems unharmed and will be dispersed in their fecal material.
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| Fig. 13a: Rhizopogon, a puffball that does not have an obvious dispersal mechanism is thought to be dispersed by small mammals. | Fig. 13b: Tuber melanosporum (truffle), the most expensive fungus in the world is animal dispersed |
Speaking of fecal material, there are a large number of species that grow only on animal dung. and utilize the dung as their food.
I hope that you can now appreciate the means by which fungi are able to get around. There are more interesting mechanisms and we do not have time to cover these others. The mechanisms mechanisms covered represent the most common I have included a few of the more interesting ones.
Literature Cited and Further Readings
Christensen, C.M. 1975. Molds, Mushrooms, and Mycotoxins. University of Minnesota Press, St. Paul.
Feinberg, S.M. 1946. Allergy in Practice. 2nd. Ed. Chicago. The Yearbook Publisher, Chicago.
Ingold, C. T. 1965. Spore liberation. Clarendon Press, Oxford. 210 pp.
Kendrick, B. 2002. The Fifth Kingdom, 3rd edition. Focus Publ., Newburyport, MA. ISBN 1-58510-022-6.
Important Terms and Concepts
Aerobiology
(âr´o-bì-òl´e-jê)
noun
The study of the sources, dispersion, and effects of airborne biological
materials, such as pollen, spores, and microorganisms.
- aer´obiolog´ical (-e-lòj´î-kel) adjective
- aer´obiolog´ically adverb
The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992
by Houghton Mifflin Company. Electronic version licensed from InfoSoft International, Inc. All rights reserved.
Funiculus
Hapteron
Hydrophilic (hì´dre-fîl´îk) adjective Having an affinity for water; readily absorbing or dissolving in water. - hy´drophile´ (-fìl´) noun - hy´drophilic´ity (-fe-lîs´î-tê) noun
The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992
by Houghton Mifflin Company. Electronic version licensed from InfoSoft International, Inc. All rights reserved.
Hydrophobic (hì´dre-fo´bîk, -fòb´îk) adjective 1. Repelling, tending not to combine with, or incapable of dissolving in water. 2. Of or exhibiting hydrophobia. - hy´drophobic´ity (-bîs´î-tê) noun
The American Heritage® Dictionary of the English Language, Third Edition copyright © 1992
by Houghton Mifflin Company. Electronic version licensed from InfoSoft International, Inc. All rights reserved.
Marker Fungus: a fungus such as Cladosporium resinae that has specific nutritional requirements so that it can be selected for in a given medium and at the same time exclude other species of fungi utilizing the same medium.
Ostiole
Peridiole: Egg-shaped structure containing basidiospores, in bird's nest fungi.
Peridium
Pseudoflower: Vegetative leaves, stimulated by the rust fungus, Puccinia monoica, to morphologically mimics a flower, thereby attracting insect pollinators that complete the sexual life cycle of the fungus
Questions to Think About
Relative to other organisms, the number of species is not large, but fungi appear to be everywhere. What characteristics do fungi have that enable them to be just about everywhere?
Although fungi have many mechanisms by which they disperse their spores, wind dispersal is the most common. Describe some of the mechanisms that are used by fungi to propel their spores into the air so that they can be carried away by wind.
The term hydrophobic refers to spores that repel water. This is a characteristic of wind dispersed spores. If that is the case, how does it absorb water so that they can grow.
Some fungi do not utilize wind to disperse their spores, at all. Describe some mechanisms of spore dispersal that some fungi have that do not utilize wind.
