Integrating temperature-dependent production of environmental DNA into its relationship with organism abundance

Despite a consensus on the correlative relationship between environmental DNA (eDNA) concentration and organism abundance, precise and reliable abundance estimation using eDNA analysis is in its infancy. Previous studies suggested that water temperature could drive both eDNA degradation and production, but it remains unclarified how the eDNA-abundance relationship is influenced by water temperatures. To address the knowledge gap, numerical simulations considering temperature-dependent eDNA production and degradation were conducted by re-analyzing a previous dataset estimating fish eDNA production and decay rates at different water temperatures, followed by generating population-level eDNA concentrations depending on a given temperature, the number of individuals, and their mass distribution. Results showed that water temperatures had a positive, but relatively small, effect on the strength (R² value) of the eDNA-abundance relationship, regardless of eDNA production scenarios. In contrast, the sensitivity (regression slope) of the relationship was enhanced by warmer temperatures when temperature-dependent eDNA production was considered, but it decreased unless it was considered. Although further efforts should be required to integrate organism physiology into eDNA production, the present study implied the importance of linking the production mechanism of eDNA particles to organism physiology, offering a groundwork for theorizing the eDNA-abundance relationship depending on environmental conditions, including temperatures, for making eDNA signals more quantitative and reliable.