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Index >> Population Interactions >> Mutualism

Mutualism

	Mutualism It is an extended synergism which shows a highly specific and obligatory relationship. The mutualistic organisms lose their individuality and become a single organism. Some of the relationships are explained below: Lichens Lichens are organisms of symbiotic association in which a highly specialised fungal partner (mycobiont) inhabits in itself an algal partner (phycobiont). It is a thallus of undifferentiated tissues because of two symbionts. The fungal component mostly belongs to class Ascomycetes. Few Basidiomycetes members are also seen. It forms the main skeleton or framework of the lichen thallus.
The algal component is either a member of green or blue-green algae (mostly single-celled green algae or filamentous blue-green algae). Some of the algal members which form symbiotic relationship with fungi are Protococcus, Gloeocapsa, Nostoc, Rivularia, etc. Lichens are cosmopolitan in distribution, found in varied habitats from mountain tops to sea shores based on which they are of 3 different types: Saxicoles which grow on rocks, usually in cold areas.
Corticoles which grow on barks of trees usually in the tropical and subtropical areas and Terriclies which grow in soil, in hot areas. Lichens are varied in colours¾white, gray, yellow, black, green, etc. They do not thrive in or near polluted industrial areas. Lichens are perennial and slow growing and long lived.
They can inhabit areas where normal plants cannot grow. For example, Cladonia rangifera grows in the Tundra region. They grow luxuriantly under moist conditions. Physiologically, lichens are a symbiotic unit of algae and fungi, algae supplying the photosynthates to the fungi and in return, fungi provide protection, water (absorbed from the moisture) and nitrogenous substrate, and anchors the lichen thallus firmly to the substratum. On the basis of the fungal component, lichens are classified as Ascolichens, where Ascomycetes member is the fungal component (e.g. Dermatocarpon), and Basidiolichens where Basidiomycetes member is the fungal component (e.g. Cora, Corella).
	On the basis of the distribution pattern of the partners, lichens are classified as homoiomerous thallus, where algae and fungi are uniformly distributed throughout the thallus (e.g. Ephebe), and heteromerous thallus, where algal cells are few in number and are distributed on the upper side of the lichen thallus in contrast to the fungal members that are dominant (e.g. Parmelia). On the basis of the morphology, lichens are classified as Crustose/ Crustaceous, where the lichen thallus is firmly adhered to the substratum and resembles crusts (e.g. Verrucaria); Foliose, where thallus has a flat leaf-like appearance which is slightly adhered to the substratum (e.g. Gyrophora) and Fructicose, where the lichen thallus is cylindrical or flat/ribbon-like resembling a little shrub and is very loosely adhered to the substratum (e.g. Usnea, Cladonia).

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