The relationship between eDNA particle concentration and organism abundance in nature is strengthened by allometric scaling

Abstract

Organism abundance is a critical parameter in ecology, but its estimation is often challenging.Approaches utilizing eDNA to indirectly estimate abundance have recently generated substantial interest. However, preliminary correlations observed between eDNA concentration and abundance in nature are typically moderate in strength with significant unexplained variation.Here we apply a novel approach to integrate allometric scaling coefficients into models of eDNA concentration and organism abundance. We hypothesize that eDNA particle production scales non-linearly with mass, with scaling coefficients < 1. Wild populations often exhibit substantial variation in individual body size distributions; we therefore predict that the distribution of mass across individuals within a population will influence population-level eDNA production rates. To test our hypothesis, we collected standardized body size distribution and mark-recapture abundance data using whole-lake experiments involving nine populations of brook trout. We correlated eDNA concentration with three metrics of abundance: density (individuals/ha), biomass (kg/ha), and allometrically scaled mass (ASM) (∑(individual mass 0.73 )/ha). Density and biomass were both significantly positively correlated with eDNA concentration (adj. R 2 = 0.59 and 0.63, respectively), but ASM exhibited improved model fit (adj. R 2 = 0.78). We also demonstrate how estimates of ASM derived from eDNA samples in 'unknown' systems can be converted to biomass or density estimates with additional size structure data. Future experiments should empirically validate allometric scaling coefficients for eDNA production, particularly where substantial intraspecific size distribution variation exists. Incorporating allometric scaling may improve predictive models to the extent that eDNA concentration may become a reliable

Lateral and longitudinal fish environmental DNA distribution in dynamic riverine habitats

“…Maruyama et al. (2014) detected elevated levels of eDNA release per gram bodyweight in juvenile fish, and recently, allometrically scaled fish mass was found to best describe the relationship between eDNA signals and brook trout populations in lakes (Yates et al., 2020). In the present study, several scenarios can explain the difference in detection probability and signal strength: The P. phoxinus individuals, although mostly not juvenile, could indeed have had higher metabolic rates (Vinberg, 1960), which are common for smaller fish species (Clarke & Johnston, 1999).…”

The Effect of Activity, Energy Use, and Species Identity on Environmental DNA Shedding of Freshwater Fish

“…For studies investigating eDNA shedding directly from live animals, biomass will always be an influential and potentially confounding variable and should thus be considered carefully already during experimental design. Recently, the allometrically scaled mass was found to be the best index variable for describing eDNA concentrations in lakes (Yates et al, 2020); since excretion rate, metabolic rate and surface area all scale allometrically too (Brown et al, 2004;O'Shea et al, 2006;Vanni and McIntyre, 2016), future experiments could greatly benefit from the incorporation of this concept. For activity measurements via videotaping, fish length had to be used as an index variable.…”

“…Under natural conditions, differences in fish physiology, diet, and behavior are likely to affect this process and confound the interpretation of eDNA-based results from a water body (Klymus et al, 2015). For perch and eel, Maruyama et al (2014) and Takeuchi et al (2019), respectively, found lower mass-specific eDNA shedding rates for adults in comparison to juveniles, which is likely caused by the scaling in metabolic rates, excretion rates, and surface area with body mass (discussed in Yates et al, 2020). However, these findings could not be confirmed in another experiment with a salmonid species (Mizumoto et al, 2018).…”

Vertical stratification of environmental DNA in the open ocean captures ecological patterns and behavior of deep-sea fishes

“…M. muelleri DNA appeared highly spread along the water column during both day and night, but exhibited remarkable abundance peaks during dark-time at 50 and 200 m depth. Although eDNA is to date not able to provide absolute biomass estimations, it is widely accepted that fish biomass and the amount of eDNA shed into the environment by fish are correlated (Klymus et al 2015;Salter et al 2019;Yates et al 2020). Also, it has been demonstrated that eDNA shedding rates are influenced by diet, feeding activity -being up to 10-fold times higher in fed fishes than in starving ones-and lifecycle stage of the individuals (Klymus et al 2015;Hansen et al 2018).…”