Mutualisms between fungi and algae
Interactions between fungi and green algae have already been described for the De- obvious similarities, some mutualistic relations between free-living algae. The tiny lichen is a critical part of the food chain, but how do algae and fungi work What are these strange, plant-like green things? Like the slime molds, lichens are a hybrid; a symbiotic relationship between an algae and a fungus. The symbiotic relationship between algae and fungi is lichen. The fungal component is called mycobiont while the algae component is called phycobiont.
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.Simple plants - the algae - Describes the characteristics of algae and fungi
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. Hydropunctaria maura can grow where it is periodically immersed in seawater but is also able to grow in an area just above that where it receives only splash from waves.
This "black zone" occupies an area that often goes for days or even weeks without immersion in seawater but will eventually get splashed. This is a tough place to live: Just the place for a lichen!
The picture at right depicts yet another species of Verrucaria mucosa, a close relative of H. In fact, it releases its ascospores when it is above the water and thus depends upon being exposed to air. However, it does not grow in the upper areas of the tide like H.
In the picture V.
Symbiosis in lichens
On parts of the rock that have dried it is harder to see but you may notice that it is slightly green, revealing the presence of the photobiont. The red spots are the alga Hildenbrandia polytypa, similar is size and growth habit to V.
The last picture again shows Verrucaria mucosa, this time growing under water at high tide. Note that even this lichen has its limits; most of the rocks in the picture have no lichens at all.
MUTUALISMS BETWEEN FUNGI AND ALGAE
This may be because the rocks are too small and may be moved by currents as the tide ebbs and flows or it may be that their surfaces are unsuitable for lichens. Another problem that lichens face is being eaten by animals. Many contain acids and other compounds that make them unpalatable to animals but V. Notice the large rock above the one with lichens on it. On its surface is a small snail called a periwinkle.
Some periwinkles, notably the rough periwinkle, eat V. This has not happened here yet but there are in fact several periwinkles present, as well as the white barnacles and a mussel. How many periwinkles are here? Not many at first glance, but you might be surprised.
Click on the picture to get an enlarged view and see how many periwinkles you can count. One of the more intriguing mutualisms found in our region is the one between the brown alga Ascophyllum nodosum and the fungus Mycophycias ascophylli. Ascophyllum nodosum, commonly called rockweed, occurs in the intertidal zone where it is left exposed to the air when the tide goes out.
Mycophycias ascophylli, a member of the lichen-forming order of fungi Verrucarialesgrows within the body thallus of A. In return the fungus has access to carbohydrates and other nutrients within its protective environment. Garbary and colleagues at St.
Francis Xavier University in Nova Scotia have studied this mutualism in detail and have shown that the fungus not only forms relationships with the rockweed but also seems to form a mutualism with Polysiphonia lanosa, a common epiphyte found attached to the A. At far left is a thallus of A. You may wish to look further back on this page to see the habitat photo of A. The next picture shows a detail from the first panel. The small almond-shaped structures along the stem are receptacles.
Each receptacle bears a number of conceptacles, structures that release sperm and egg into the ocean each spring. These are seen as bumpy areas in the second photo but in the third more highly magnified panel they can be seen more easily and reveal the pores through which the sperm and egg escape.
The next panel is even further magnified and the conceptacles are even clearer. In this panel it is also possible to see tiny black dots, resembling grains of pepper; these are the perithecia fruiting bodies of Mycophycias ascophylli.
The blue box drawn on around one of these leads to the next photograph, taken with a compound microscope, showing a detailed view of one perithecium partially submerged in the receptacle. The perithecia contain asci and ascospores. The last panel shows one ascus containing eight 2-celled ascospores. The ascospores are not very clear in this picture but are nevertheless nearly mature. In our region Ascophyllum nodosum releases its sperm and eggs in late May.
Fungi Symbiosis ( Read ) | Biology | CK Foundation
On a warm day at low tide these tiny cells ooze out of the conceptacles like toothpaste out of a tube. When the tide comes in they are released into the water. The sperm, released in numbers large enough to colour the water orange, swim activly in search of eggs and attach to them when they find one. Eggs can be observed spinning wildly, powered by hundreds of sperm attached to their surface. Finally one sperm succeeds in fertilizing the egg, which then sinks to the bottom to grow into a new plant.
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. One fungus, for example, can form lichens with a variety of different algae.
The thalli produced by a given fungal symbiont with its differing partners will be similar, and the secondary metabolites identical, indicating that the fungus has the dominant role in determining the morphology of the lichen.