Seasonal differentiation of hypogeous fungi in rodent diet in selected forest reserves of Central Poland

Abstract

Hypogeous fungi are a ecological group which congregates various fungal genera from Ascomycota, hypogeous ‘gasteromycetes’ from Basidiomycota and a few taxa from Glomeromycota. Though taxonomically distant, hypogeous fungi show features of convergent evolution in habitat adaptations, because they occupy a specific ecological niche. They produce underground, closed macroscopic fruit bodies, and are important in the forest ecosystem due to their role as ectomycorrhizal partners for plants, especially forest trees. As their sporocarps remain close, the fungi rely mostly on animals as vectors of dispersion. In case of hypogeous ascomycetes, the asci have no opening mechanisms and remain closed until natural decay or digestion by animals. Hypogeous fungi produce characteristic odours, detectable by animals which feed on them. Most mammals are opportunistic or accidental mycophages which means they feed on fungi when this type of food is abundant in the environment or while foraging for other food source. Examples of mycophages can be found in the mouse family Muridae and the vole family Arvicolinae. The aim of this study is to examine the significance of hypogeous fungi in diet of rodents in the forest ecosystem of Central Poland. The study will verify the hypothesis that hypogeous fungi are an important component of rodent diet and that mycophagy plays a significant role in the forest ecosystem. For this purpose, the Author examined the occurrence of spores in faecal samples from two species of rodents: bank vole Myodes glareolus and yellow-necked mouse Apodemus flavicollis. Both species are widely spread in the Palaearctic, abundant in forest ecosystems and are reported as preferential or opportunistic mycophages. In particular the following issues were of a special concern (1) the diversity of fungal genera in faecal samples; (2) difference in spore occurrence in samples obtained in three seasons: spring, summer and autumn; (3) differences in spore occurrence in relation to study area, animal species, sexes and age. This is the first study of this kind conducted in central Poland and is based on original field research and microscope analysis of samples gathered in the field. The study was carried out by live trapping animals. The study was conducted in the Spała (51°31’37” N 20°08’42” E) and Konewka (51°04’08” N 20°09’26” E) nature reserves, located in Pilica Forest, in Łódzkie Voivodship in central Poland, between July 2013 and May 2015. Once an animal was caught, its species was determined. After the capture, animals were weighed and their sex and age group (juvenile or adult) were determined for later comparisons. The animals were marked with a red dot on the abdomen and released. Faecal samples were then taken from the live traps and placed in a 1,5 ml Eppendorf tube with 1 ml of 90% ethanol for preservation. Samples were examined using NIKON E200 light microscope under x600 magnification. Spores of hypogeous fungi which were found in samples were determined to genus level. Twelve hypogeous genera were present in the samples: Elaphomyces, Hydnotrya, Pachyphloeus, Genea, Tuber, Hymenogaster, Melanogaster, Rhizopogon, Scleroderma, Gautieria, Glomus and Endogone. Statistical analysis of seasonal differences in animal diet as well as differences between animal’s species, age and sex has shown that in spring and autumn, M. glareolus and A. flavicollis eat the most common genera of hypogeous fungi, and in summer season both species consume significantly more fungi from a multitude of genera. The amount of found spores follows the patterns of high temperature and mild rainfall. The mean number of spores found in samples was higher in Spała than in Konewka. This may be due to more favourable microhabitat conditions in Spała, especially for hypogeous ascomycetes. Significantly more spores were found in samples from traps which were closer to the road. This corresponds to the fact that close proximity to trampled pathways limits plant vegetation and favours formation of sporocarps. M. glareolus is more mycophagous than A. flavicollis, as samples from voles were richer in fungal genera the those from mice. Young specimens of both species eat more hypogeous fungi than adults. The young are more likely to forage closer to the ground and due to their mobility, they play an important role in spore dispersion. Also females of A. flavicollis eat more hypogeous fungi than males. Females are more sedentary than males and forage in places suitable for fruiting of hypogeous fungi. Spores of genus Rhizopogon were observed to increase in size from spring through summer and autumn. This suggests that this genus is available to animals throughout the year unlike some genera which were found in samples only in one given season. The Author also presumes that the ornamentation on the surface of the spores may serve as a reservoir for nutritional material from the faeces.