Diurnal detection of environmental DNA of the semi-aquatic water shrew Chimarrogale platycephala using 25-h water sampling in streams.

Whether environmental DNA (eDNA) testing methods are effective for semi-aquatic organisms that spend time both in rivers and on land remains unclear. We designed a species-specific primer–probe set for the semi-aquatic Japanese water shrew, Chimarrogale platycephala, an endangered top predator species for which limited ecological information is available. The designed primer–probe set was used to determine the effective sampling time for detecting eDNA from this species in running water. Hourly water sampling was conducted for 25 h in the autumn of 2020. Water sampling and camera trapping were conducted in the two streams in which feces had been observed on stream rocks. No C. platycephala activity was captured by the camera traps at any sampling point during the investigation. However, eDNA was mainly detected at night in both streams and twice during the daytime in one stream; the eDNA detection periods differed between streams (21:00–23:00 vs. 1:00–8:00 and daytime). These results demonstrate that eDNA testing methods are effective for detecting small semi-aquatic mammals. However, the sampling time affected the results, and eDNA was mostly detected at night, possibly because of the nocturnal activity of the species. Therefore, the sampling time should be adjusted to match the activity period of a species to improve the efficiency of eDNA testing for semi-aquatic organisms. [ABSTRACT FROM AUTHOR]