Rates of Gut Passage and Retention of Hypogeous Fungal Spores in Two Forest-Dwelling Rodents

Abstract

Alimentary retention of hypogeous fungal spores by small mammals influences the spatial and temporal dynamics of spore dispersal. We investigated, in laboratory experiments, retention of spores of Elaphomyces granulatus by two mycophagous small mammals, the golden-mantled ground squirrel, Spermophilus saturatus, and the deer mouse, Peromyscus maniculatus. The concentration of spores in feces peaked at 20 h and < 12 h after feeding in S. saturatus and P. maniculatus, respectively, but the time for it to fall to half its maximum was similar (approximately 12 h) in both species. Mean retention times of spores were 24 h for S. saturatus and 12 h for P. maniculatus. Alimentary mechanisms that selectively retain small particles such as fungal spores may be common among small mammals, but spores were not retained for longer than the much larger particles of stained alfalfa (Medicago sativa) leaf in either S. saturatus or P. maniculatus. Despite the rapid excretion of most spores, the inoculating potential of feces may remain high for many days after cessation of feeding on fungus if large numbers of spores are ingested initially. Fungal spores ingested by S. saturatus immediately before onset of hibernation are excreted slowly, and a significant proportion may remain in the gut throughout hibernation. These could be dispersed in spring when little dispersal might occur otherwise.