Invertebrate Assistance In Dispersal And Facilitation Of Colonization Of Resources

Propagules, be they asexual or sexual spores, hyphal fragments or yeasts, of many Basidiomycota are dispersed by invertebrates on their bodies, passing through their guts, and even in special structures on their bodies. Propagule carriage can thus be incidental (though sometimes with attraction, e.g. Phallales —see above) or obligatory, the latter being most highly developed in the mutualistic associations with termites, ants and wood wasps. Siricidae (wood wasps) carry their symbionts in a pair of pouches, termed mycangia, at the base of the ovipositor, and inoculate both fungus and eggs together into wood (Kajimura, 2000). The importance of wood wasps in dispersing the fungus does, however, appear to be taxon-specific; dispersal through basidiospores is considered of less importance for A. areolatum, but common in A. chailletii (Kajimura, 2000). The Basidiomycota symbionts of ants fruit only rarely, and normally propagate asexually and are spread by dispersing queens (Mueller et al., 2001). Ants carry, for example, Attamyces bromatificus from one leaf-cutter ant colony to a new one in an infra-buccal pocket to ensure successful colonization of new nest material (Cherrett et al., 1989). Termitomyces spp. are carried to new colonies by females in the genus Microtermes and by kings of M. bellicosus (Johnson et al., 1981), but the rest of the Macrotermitinae acquire their symbionts at the nest-founding stage while foraging: sexual spores are consumed and survive passage through the gut, being deposited in a faecal pellet on the fungus comb (Aanen et al., 2002; Mueller and Gerardo, 2002). Spores of some species not involved in tight mutualistic relationships with invertebrates also survive passage through the gut, and sometimes actually require this before readily germinating, e.g. Ganoderma sp. passing through the gut of a fly larva (Nuss, 1982).

Invertebrates can also facilitate colonization by breaching outer protective layers of plants providing infection courts, ranging from minute feeding or ovi-position sites (e.g. wood wasps—mentioned above) to large wounds allowing colonization by ruderal Basidiomycota (Chapter 11). Tunnels within wood can also facilitate tangential spread.

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