Nutritional-Value of Hypogeal Fungal Sporocarps for the Long-Nosed Potoroo (Potorous-Tridactylus), a Forest-Dwelling Mycophagous Marsupial

Abstract

Although mycophagy (fungus-feeding) is widespread among small ground-dwelling mammals, there has been little evaluation of the nutritional benefits of this feeding habit. In Australia, some members of the Potoroidae (or rat-kangaroo family) consume large amounts of hypogeal fungi throughout the year. Hypogeal fungi appear to be of marginal nutritional quality for small mammals with simple stomachs but potoroos have an enlarged forestomach in which microbial fermentation takes place, and this may allow more effective utilisation of protected nitrogenous components and structural carbohydrates of fungi. In a feeding experiment, we evaluated the nutritional value of sporocarps of the hypogeal fungi Mesophellia glauca (Mg) and Rhizopogon luteolus (R1), for the long-nosed potoroo (Potorous tridacytlus). Although the concentration of nitrogen was high in both fungi, much of that nitrogen was in non-protein form or associated with cell walls and may be either of low nutritional 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 digestibilities 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. Consequently, P. tridactylus maintained positive nitrogen balance and high intakes of digestible and metabolisable energy. We conclude that the sporocarps of hypogeal fungi represent a nutritionally valuable food for rat-kangaroos and suggest that lack of a foregut-fermentation strategy in other similar-sized ground-dwelling mammals in the forests of south-eastern Australia explains why they use the hypogeal fungal resource to a lesser extent than do rat-kangaroos.