Soil fauna community assembled in the abandoned nests of Japanese wood mice

The soil fauna found in the subterranean nests of forest mammals are expected to have a unique composition considering that the nests’ biotic and abiotic conditions differ from the surrounding soil conditions. In this study, we report the first record of the soil fauna community assembled in abandoned nests of the Japanese wood mouse species—Apodemus spp. Research was conducted at the Takizawa Research Forest of Iwate University, Morioka, Iwate, Japan (39°47′N, 141°09′E, approximately 200 m a.s.l.). The research site comprised a 0.54-ha plot (90 m × 60 m) that was established in the secondary forest where Quercus serrata was the dominant tree species (Shimada et al., 2015). Two mouse species, the large (A. speciosus) and small Japanese wood mice (A. argenteus), inhabited the research site. The former was much more abundant in population density than the latter (220.4 and 9.3 individuals/ha for A. speciosus and A. argenteus, respectively, in June 2020; T. Shimada, unpublished data). Thus, the nests we found were assumed to have been used mainly by A. speciosus, although the possibility of having been used by A. argenteus cannot be completely excluded. In June 2020, we investigated the soil mesofauna community of the abandoned mouse nests and compared it with the fauna community in the surrounding soils, which were used as controls in this study. We collected five nests and prepared 12 replications from the surrounding soil using soil cores of 100 cc. Based on hair and feces samples found in the nests, we determined that the nests had been used by wood mice in the nearest reproductive season (from mid-April to early May) or that before the nearest (October in the last year). These nests consisted of leaf litter and acorns collected by mice and were usually found beneath the coarse roots of trees. The collected mouse nests were nearly completely hidden in the soil and were randomly located throughout the plot (each point was approximately 10-20 m apart), but the control samples were collected from systematically determined soil points that were approximately 10–40 m apart. Soil fauna from the mouse nests and soil cores were extracted using a Tullgren funnel at 35°C for 10 days and sorted at the order or suborder level using a stereomicroscope. In case of mites, all astigmatids collected from the mouse nests were identified to the species level using a phase contrast microscope (400×), whereas the other mites