3. Re-analysis of the time-series changes in eDNA particle size
distribution
To assess the validity of the findings of the meta-analyses, we
re-analysed the dataset from a previous study investigating the particle
size distribution of eDNA derived from the mitochondria and nuclei of
Japanese jack mackerel (Trachurus japonicus ) and the time-series
changes therein, after fish removal from tanks (Jo et al., 2019b). In
the aforementioned study, mitochondrial and nuclear eDNA degradation was
examined under multiple size fractions, and both degradations tended to
be suppressed at smaller size fractions. We estimated the eDNA decay
rate constants at different size fractions using the dataset from the
said study, and assessed the variation in eDNA decay rates depending on
the eDNA particle size, target gene, and water temperature. Detailed
information on the experimental design, water sampling, and molecular
analyses can be found in Jo et al. (2019b).
We included all eDNA samples that could pass through sequential filters
with 10, 3, 0.8, and 0.2 μm pore sizes at 0, 6, 12, and 18 hours, which
yielded four eDNA size fractions, i.e. >10, 3-10, 0.8-3,
and 0.2-0.8 µm. Linear regressions were performed between eDNA
concentrations (original concentration + 1 followed by
log-transformation) and sampling time points for each size fraction,
target gene (mitochondrial or nuclear), and temperature level (13, 18,
23, or 28 °C), to estimate the slope (i.e. eDNA decay rate constant) and
the corresponding 95% CI, using lm and confint functions
in R, respectively. Here, the two fish biomass levels (Small and Large;
see Jo et al. (2019b)) were pooled to increase the sample size. We then
performed ANOVA to assess the relationship between eDNA degradation,
particle size, target gene, and temperature. We included the median of
the slope (eDNA decay rate) as the dependent variable, and the filter
pore size, target gene, water temperature, and their primary
interactions as the explanatory factors.