Toshiaki Jo, Sou Fukumoto, Toshifumi Minamoto, Yoh Yamashita, Reiji Masuda
Environmental DNA (eDNA) analysis has the potential for rapid and broad-scale assessment of time-series population and community dynamics. Although a number of studies have shown that seasonal changes in eDNA signals relate to the behavior of organisms, an understudied aspect is how diel changes in eDNA signals relate to this behavior. We conducted a literature analysis to summarize previous findings and identified behavioral factors potentially associated with diel changes in eDNA signals (activity changes, migration, and spawning). However, these effects were heterogeneous between the studies and behavioral factors, and it was unclear whether eDNA signals could reflect the diel changes in the activity and migratory behavior of any given organisms. We discussed the factors contributing to this uncertainty and emphasized the importance of sampling and statistical designs in detecting diel fluctuations in eDNA signals. To support the discussion, we introduced a case study that tracked the time-series changes in jack mackerel eDNA concentrations across multiple days, successfully demonstrating diel fluctuations and periodicity in the eDNA concentrations corresponding to the organism's diel activity and migratory behaviors in the field. Based on the findings, we discussed how the degree to which eDNA reflects the diel behavior of organisms could impact the design and interpretation of eDNA-based biomonitoring strategies. We recommend reporting the exact time of day for eDNA sampling and the time lags between sampling sites within a day. Although it is necessary to accumulate future studies in various taxonomic groups, environments, and seasons to generalize our results, this study contributes to identifying short-term temporal relationships between eDNA signals and the behavior of organisms in the field, and to understanding the ecology of aquatic populations and communities.