Seasonal changes in the diurnal behavior of Chimarrogale platycephalus evaluated using environmental DNA

The environmental DNA (eDNA) method is potentially useful to detect the diurnal activity of aquatic organisms. Seasonal changes in the diurnal activities of the endangered semiaquatic water shrew, Chimarrogale platycephalus, were investigated to evaluate the efficiency of the eDNA method in their tracking. We conducted hourly field surveys for a period of 25 consecutive hours in two streams quarterly, using a species-specific primer and camera trap observations. Using qPCR, we compared the frequency and concentration of eDNA detected between day and night, seasons, and streams. In both streams, eDNA was detected consistently with temporal fluctuations during all seasons for nighttime. However, during daytime, eDNA was detected in all seasons except autumn, in which it was detected only in one stream. This suggests that species activity occurs throughout both daytime and nighttime in winter, spring, and summer, and potentially less during the daytime in autumn, probably due to the lack of competition and energy constraints during that season, as most individuals were non-breeding in autumn and avoided the habitation of areas with high density after the dispersal of their offspring. The high eDNA concentration in summer may be attributable to the higher density of non-breeding individuals after the offspring left the nest and/or to the increased activity owing to the competition for food or space. The diurnal activities of species detected using eDNA sampling allow us to obtain detailed ecological information, which is beneficial for managing conservation in the future.