Estimation of Species Abundance Based on the Number of Segregating Sites Using Environmental DNA (eDNA)

The advance of environmental DNA (eDNA) has enabled rapid and non-invasive species detection in aquatic environments. While most studies focus on species detection, recent works explored using eDNA concentration to quantify species abundance. However, the differential individual DNA contribution to eDNA samples could easily obscure the eDNA concentration-species abundance relationship. We propose using the number of segregating sites as a proxy for estimating species abundance. Segregating sites reflect the genetic diversity of the population, which is less sensitive to differential individual DNA contribution than eDNA concentration. We examined the relationship between the number of segregating sites and species abundance in silico, in vitro, and in situ experiments, using two brackish goby species, Acanthogobius hasta and Tridentiger bifasciatus. Analyses of the simulated and in vitro data with DNA mixed from a known number of individuals showed a strong correlation between the number of segregating sites and species abundance (R² > 0.9; p < 0.01). In the in situ experiments, we analysed eDNA samples collected from mesocosm. The results further validated that the correlation (R² = 0.70, p < 0.01) was not affected by biotic factors, including body size and feeding behaviour (p > 0.05). The cross-validation test results also showed that the number of segregating sites predicted species abundance with less bias and variability than the eDNA concentration. Overall, the number of segregating sites is less affected by differential DNA contribution among individuals compared to eDNA concentration. This advancement can significantly enhance the proficiency of estimating species abundance using eDNA.