Nutritional Ecology and Digestive Responses of an Omnivorous-Insectivorous Rodent (Abrothrix longipilis) Feeding on Fungus

Abstract

Spore retention by the digestive tract of mycophagous rodents may affect the temporal and spatial dynamics of spore dispersal; rodents may also benefit from consuming a discrete resource rich in minerals and vitamins. Some research suggests that hypogeous fungi are not a nutritionally high-quality food item for small rodents, regardless of being highly consumed by these small mammals. Fungi may be a valuable dietary item when higher-quality food is in low abundance. However, the extent to which fungi are incorporated into diet will ultimately depend on the physiological capacities of organisms for digesting such a resource. Here we investigate digestibility of fungus compared with insects and young foliage of plants, and we draw inferences about digestive constraints in a forestdwelling, mycophagous, habitat-generalist rodent (Abrothrix longipilis) exploiting different diets. We show that the fruiting bodies of fungi are less digestible than young leaves of plants and insects. The intake of fungus, in grams of dry mass per day, did not differ from the intake of plants. However, the wet intake of fungus was 23.8 g wet mass ․ d⁻¹, while the amount of plants consumed was 7.1 g wet mass ․ d⁻¹ and insect intake was 10.7g wet mass ․ d⁻¹. In spite of small mammals' increasing the wet weight of food eaten as the quality and digestibility of the diet decreases, they may be unable to process the required amount of fungus fast enough to maintain their energy or matter budget and minimize the feeding time. Finally, and based on the fact that many insects utilize fungi as oviposition sites, we hypothesize for A. longipilis that a quantity of insect larvae ingested with fruiting bodies of fungi confers a nutritional benefit beyond that of the fungi alone.