Symbiosis With Fungi

Abstract

Associations between termites and fungi are considered in two categories: firstly, interactions that affect the discovery and consumption of food or its nutrient value, but which fall short of mutualism; secondly, the cultivation of fungus-combs (Termitomyces spp.) within the nesting system by Macrotermitinae, where there is an obligate reliance on the fungus and which in most cases appears to contribute to the degradation of plant structural compounds, especially xylans. In the first category most information is available for pest termites and it is possible to show, in different species or circumstances, roles for fungal colonizers of decaying wood (or for their metabolic products) as attractants, repellents, conditioners, toxins, and nutritional supplements. Some entomophagous fungi are pathogenic to termites and may be potential agents of biological control, despite low host specificities. In the second category of association, the structures and dynamics of Macrotermitine fungus-combs are classified and data presented to illustrate the variety of net enzymatic synergisms (i.e. final hydrolytic activities and specificities in the termite gut) achieved by the mutualism in different host species and feeding groups. To reconcile the conflicting evidence on possible enzyme acquisition from the fungus by the termite, it is proposed that symbiosis in the Macrotermitinae shows evolutionary diversification, with some species of fungus producing a range of enzymes according to substrate and environmental conditions (generalists), others with a fixed range of enzymes not responsive to substrate (constitutive specialists) and yet others which produce little, if any, enzyme for termite use. The assay of enzyme productions in pure cultures of Termitomyces, and the host specificities of different species of the fungal partner are also reviewed.