Symbiosis in lichens is the mutually helpful symbiotic relationship of green algae and/or blue-green algae (cyanobacteria) living among filaments of a fungus. The nature of the symbiotic relationship in lichens Algae and Symbioses: Plants, Animals, Fungi, Viruses, Interactions Explored, Biopress, Bristol (), pp. The tiny lichen is a critical part of the food chain, but how do algae and fungi work together to form these symbiotic organisms?.
Apothecia are structures that produce a palisade of asci that are openly exposed to the environment. Lichens producing apothecia are discussed further in the section dealing with lichen-forming discomycetes. In the case of L. Although appearing whitish, the margin contains green algae, the photobiont, and will be seen to be green if cut lengthwise. Some lichens produce their asci in perithecia such as those in the photograph of Hydropunctaria maura at right.
Perithecia are flask-shaped structures that open to the outside by a pore called an ostiole. Lichens producing apothecia are discussed further in the section dealing with lichen-forming pyrenomycetes. The ostioles in both perithecia at right can be seen as small circular areas at their tops.
Mutualisms between fungi and algae
There are some other ways that asci can be produced by lichens, but perithecia and apothecia are by far the most common. The photographs above illustrate two other types you may encounter. The first are structures called lyrellae. These are similar to apothecia but are greatly elongated. In the case of Graphis scripta, shown in the photo, the lyrellae are highly branched and may resemble some kind of mysterious writing. The second photograph, of Calicium trabinellum, illustrates a mazaedium, a kind of stalked apothecium in which the asci dissolve and leave the ascospores to pile up in a powdery mass.
A few basidiomycetes are also capable of forming lichens.
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These are not generally considered to be highly-developed relationships yet there is no doubt they function as lichens. The first of the two photos above shows Multiclavula mucida.
In this species the basidia and basidiospores line the surface of the upright "fingers" and under cool moist conditions release the spores to drift in the wind. The photobiont, a green alga, forms a thick crust of the the substrate, in this case rotten wood. The algae are enclosed by the hyphae of the mycobiont.
In the second picture the mycobiont is Lichenomphalia umbellifera, a mushroom. The photobiont and its relationship with the phytobiont are the same as in M. Since these sexual structures reproduce only the fungus, the resulting spores must be fortunate enough to land on an appropriate alga, or perish. However, there is another way. If the lichen can disperse propagules containing both myco- and photobionts then it will be able to develop in any suitable habitat.
However, this type of reproduction is strictly clonal and does not allow for the kind of genetic recombination that occurs during sexual reproduction. Clonal reproduction of lichens can occur in several ways.
Symbiosis in lichens - Wikipedia
The simplest of these is simply to separate a piece of the thallus containing both alga and fungus and send it off by wind or water to develop in a new place. This kind of reproduction is common among lichens and generally effective. There are more highly developed forms of clonal reproduction, two of which are represented in the photographs above. In the first the lichen has produced soredia.
- Symbiosis in lichens
- MUTUALISMS BETWEEN FUNGI AND ALGAE
Soredia are small bundles of algae held together by fungal hyphae. They are small enough to be carried by wind yet guarantee the presence of both partners. The illustration above left shows a young thallus of the foliose lichen Peltigera didactyla. In this species the upper surface becomes dotted with soralia, special structures for the production of soredia.
In the photograph, the soralia have released granular masses of soredia. The other photograph above is a highly magnified view of isidia, small coral-like branches containing both mutualists that can break off and drift to a new habitat.
The lichen in the picture is Xanthoparmelia conspersa, a common lichen on exposed rock in New Brunswick. Lichen habitats One of the fascinating aspects of lichen biology is the ability of these organisms to occupy habitats that would be totally in inhospitable to other organisms. Thus we can find them growing on the ground in deserts, on the sides of dry rock, hanging from the branches of trees and and even growing on the backs of turtles. They are nearly as easy to find and study in the middle of winter as during the warmer months.
The first of the three photographs above was taken in Saskatchewan, out in an open prairie. The rock in the forground is the highest point in the immediate area; animals sitting there get a panoramic view of the grassland and all that is taking place there.
It is a favourite place for birds, especially birds of prey waiting for a mouse or vole that might be moving through the grass. The orange lichen is a species of Xanthoria that thrives on nitrogen-rich bird droppings left on the rock. Similar species of Xanthoria, as well as members of the related genus Caloplaca, can be found on our seacoast on rocks frequented by gulls and cormorants.What's in a Lichen? How Scientists Got It Wrong for 150 Years - Short Film Showcase
The second of the two pictures above is of White Horse Island, a small island in the Bay of Fundy supporting large colonies of nesting birds. The white colour of the rock is due to a thick layer of bird droppings; the orange material is a species of Caloplaca. The gravestone at left marks the resting place of Roland ThaxterProfessor at Harvard University and brilliant mycologist, known in particular for his monumental studies on the Laboulbeniales.
Beside Roland's grave is that of his brother Karl. Both gravestones have become colonized by lichens and are now difficult to read.
Click on the photograph to get an enlarged version of Roland's gravestone Another interesting thing about our coastal lichens is that some of them are highly tolerant of salt, a substance that is toxic to most fungi, including lichenized ones. The picture at right depicts some coastal rocks on the Bay of Fundy near Saint John. At the bottom of the picture are bunches of brown algae, mostly Fucus vesiculosus and Ascophyllum nodosum, commonly called rockweed.
These rockweeds grow in areas along the shore where they will be immersed in seawater, at least at high tide. At the very top of the rock is a patch of orange, probably Xanthoria parietina. In between is a black zone consisting of the custose lichen Hydropunctaria maura. The algae or cyanobacteria benefit their fungal partner by producing organic carbon compounds through photosynthesis.
In return, the fungal partner benefits the algae or cyanobacteria by protecting them from the environment by its filaments, which also gather moisture and nutrients from the environment, and usually provide an anchor to it. All the algae and cyanobacteria are believed to be able to survive separately, as well as within the lichen; that is, at present no algae or cyanobacteria are known which can only survive naturally as part of a lichen.
The most commonly occurring genus of symbiotic cyanobacteria is Nostoc. Depending on context, the taxonomic name can be meant to refer to the entire lichen, or just the fungus that is part of the lichen. The alga or cyanobacterim bears its own scientific name, which bears no relationship to either the name of the lichen or the fungus. The fungal partner may be an Ascomycete or Basidiomycete.
Next to the Ascomycota, the largest number of lichenized fungi occur in the unassigned fungi imperfecti. Comparatively few Basidiomycetes are lichenized, but these include agaricssuch as species of Lichenomphaliaclavarioid fungisuch as species of Multiclavulaand corticioid fungisuch as species of Dictyonema.
Other lichen fungi occur in only five orders in which all members are engaged in this habit Orders GraphidalesGyalectalesPeltigeralesPertusarialesand Teloschistales. Lichenized and nonlichenized fungi can even be found in the same genus or species. TrebouxiophyceaePhaeophyceaeChlorophyceae have been found to associate with the lichen-forming fungi.