NUTRITIONAL-VALUE OF HYPOGEAL FUNGAL SPOROCARPS FOR THE LONG-NOSED POTOROO (POTOROUS-TRIDACTYLUS), A FOREST-DWELLING MYCOPHAGOUS MARSUPIAL

Although mycophagy (fungus-feeding) is widespread among small ground-d welling mammals, there has been little evaluation of the nutritional b enefits of this feeding habit. In Australia, some members of the Potor oidae (or rat-kangaroo family) consume large amounts of hypogeal fungi throughout the year. Hypogeal fungi appear to be of marginal nutritio nal quality for small mammals with simple stomachs but potoroos have a n enlarged forestomach in which microbial fermentation takes place, an d this may allow more effective utilisation of protected nitrogenous c omponents and structural carbohydrates of fungi. In a feeding experime nt, we evaluated the nutritional value of sporocarps of the hypogeal f ungi Mesophellia glauca (Mg) and Rhizopogon luteolus (R1), for the lon g-nosed potoroo (Potorous tridacytlus). Although the concentration of nitrogen was high in both fungi, much of that nitrogen was in non-prot ein form or associated with cell walls and may be either of low nutrit ional value or protected from digestive enzymes. The concentration of cell-wall constituents (fibre) was high in both fungi, suggesting low availability of digestible energy. Despite these features, the digesti bilities of dry matter (Mg 86%, Rl 80%), ingested nitrogen (Mg 72%, Rl 72%) and energy (kJ kg-1) (Mg 93%, Rl 76%) of both fungi were high. C onsequently, P. tridactylus maintained positive nitrogen balance and h igh intakes of digestible and metabolisable energy. We conclude that t he sporocarps of hypogeal fungi represent a nutritionally valuable foo d for rat-kangaroos and suggest that lack of a foregut-fermentation st rategy in other similar-sized ground-dwelling mammals in the forests o f south-eastern Australia explains why they use the hypogeal fungal re source to a lesser extent than do rat-kangaroos.