Fungal symbiosis

fungus comb soldiers and nymphs

Macrotermes colonies host a remarkable symbiotic relationship with a basidiomycete fungus, Termitomyces. The termites cultivate the fungi in a fungus garden, comprising a few hundred fungus combs, structures built from chewed up grass and wood, and inoculated with fungal spores. Each year, these fungi produce a crop of large mushrooms (pictured at left), known locally as omajowa, which are highly prized as a delicacy.

Unlike the fungi cultivated by leaf-cutter ants, which the ant colony uses as food, the Termitomyces culture in a Macrotermes nest aids in the breakdown of cellulose and lignin into a more nutritious compost which serves as the termites actual food. The fungus garden is, therefore, a kind of extracorporeal digestive system, to which termites have 'outsourced' cellulose digestion.

The fungi also play a significant role in the social homeostasis in Macrotermes colonies, in particular aiding in water balance for the colony. This has made Macrotermes colonies much more tolerant of dry conditions than other termites, which enables them to exist in dryer environments than termites are commonly found.

What the fungi do

fungus comb in gallery

A fungus comb in its gallery

comb collection

A small portion of the fungus combs from a single colony

The fungi are part of an extracorporeal digestive system that converts undigested woody material in plants into higher quality oligosaccharides and more easily digestible complex sugars. There is some nitrogen fixation that also takes place.

The fungi are grown in structures called fungus combs. Combs are made from macerated woody material, gathered by foraging workers, that is chewed up and swallowed. When the foragers return to the nest, they evacuate this material very quickly as pseudofeces, passing it on to nest workers, which take this material and mold it into the fungus comb.

scheme of fungal symbiosis

Somewhere along the way, perhaps in the digestive tracts of foragers or nest workers, this woody slurry is inoculated with a variety of fungal spores. Once deposited in the comb, the Termitomyces spores germinate and begin spreading hyphae through the comb. As these grow, they delignifiy and digest cellulose, converting it to simpler sugars and nitrogen. The termites then consume this enriched fodder for food. The structure of the combs is dynamic. Fresh material is continually added to the top, and digested material is consumed from the bottom. Food "flows through" the comb, just as silage flows through a silo.

A colony amasses a large number of fungus combs, gathered into a series of galleries atop the nest called a fungus garden. The collection of fungus combs in the photograph to the right (Figure 2) represents a small sample of a single colony's fungus garden.

Each fungus comb is placed in a semi-enclosed space called a gallery. The total mass of fungus combs typically exceeds the colony's entire mass of termites by about eight fold - roughly 25-40 kg of fungus comb per colony.

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Termite pages

Termite home

Structure

Endocasting

Social homeostasis

Nest temperature

Water homeostasis 1

Water homeostasis 2

Water homeostasis 3

Fungal symbiosis

Fungal symbiosis and water 1

Fungi and water homeostasis 2

Gas exchange 1

DC vs AC Gas Exchange

Gas exchange 2

Gas exchange 3

Gas exchange 4

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