DOI: 10.5061/dryad.qz612jmhm
title: eDNA quantification to evaluate bullfrog management

description: Biological invasions contribute now more than ever to the global
 homogenization of fauna and flora. Large-scale monitoring programs are
 therefore needed to detect incipient invasions and to evaluate management
 interventions. As conventional monitoring methods are constrained by large
 costs, environmental DNA (eDNA)-based methods are increasingly recognized
 as valuable monitoring tools. However, accurately estimating species
 abundance from eDNA concentrations in natural systems remains challenging
 and consequently hinders their integration in management applications.
 Here, we used droplet digital PCR (ddPCR) in eDNA surveys to estimate the
 abundance of invasive American bullfrogs (Lithobates catesbeianus). We
 first introduced bullfrog tadpoles in natural ponds to assess the
 relationship between abundances and eDNA concentrations under field
 conditions. Next, we combined eDNA sampling with fyke netting in naturally
 colonized ponds to investigate whether bullfrog eDNA concentrations can
 estimate bullfrog capture success and conventional abundance measures
 obtained via depletion sampling. Finally, we evaluated eradication
 measures by comparing bullfrog eDNA concentrations before and after fyke
 netting. We found a strong linear relationship between the numbers of
 introduced tadpoles and eDNA concentrations (r2 = 0.988). Bullfrog eDNA
 concentrations were not only linearly related to the catch-per-unit-effort
 (r2 = 0.739), but also to conventional abundance estimates (r2 = 0.716),
 particularly when eDNA concentrations were standardized for pond area (r2
 = 0.834) and volume (r2 = 0.888). Bullfrog tadpoles were only captured
 when eDNA concentrations exceeded 1.5 copies µL-1, indicating that
 quantitative eDNA analyses enable the localization of breeding ponds. We
 found a significant reduction in eDNA concentrations after fyke netting
 proportional to the number of captured bullfrogs. These results
 demonstrate that eDNA quantification is a reliable tool that accurately
 estimates bullfrog abundance in natural lentic systems. We show that
 quantitative eDNA analyses can complement the toolbox of natural resource
 managers and facilitate the coordination of eradication campaigns
 targeting alien invasive species.
description: <strong>Overview of
 the collected data types:</strong> 
 <strong>Experimental ponds</strong> 
 Period of
 collected data: between the 30th of June and the 23rd of July
 2021 Types of
 collected data<br> Species-specific
 environmental DNA data Water quality variables
 pH Turbidity
 pH Pond
 volumes ..
 <strong>Management
 ponds</strong><br> Period of
 collected data: between June and September 2021 
 Types of
 collected data<br> Species-specific
 environmental DNA data Bullfrog depletion sampling
 data Water quality variables 
 pH Turbidity
 pH Pond
 volumes 
 <strong>Overview of the way the collected data
 types were acquired</strong> 
 <strong>Species-specific eDNA data</strong> 
 Primer/probe assay validated for western European usage in
 Everts et al. (2021). Droplet Digital PCR according
 to protocol described in Everts et al. (2021).
 Calculation of final eDNA concentrations according to formula in
 this article. 
 <strong>Water quality data</strong> pH
 and conducitivity were measured from the same volume of water as was
 filtered for eDNA sampling, using a WTW multiLine® Multi 3620 IDS SET KS1
 multimeter. Turbidity was measured from the same
 volume of water as was filtered for eDNA sampling that was deep-frozen and
 measured afterwards, using a 2100Q Portable Turbidity meter
 (Hach®) 
 <strong>Bullfrog catch data</strong> 
 Bullfrogs were caught using double fyke nets with a mesh size of
 8mm, consisting of two fykes interconnected with a seven meters long
 leader net, each with an initial hoop of 80 x 90 cm followed by three
 narrowing funnels in each fyke The number of fyke
 nets and period that they were used per pond were given in Table 1 in the
 Research Article. Catch-per-unit-effort was for all
 management ponds where bullfrogs were captured
 Conventional population size estiamtions were obtained via
 depletion sampling. Subsampling of the data was necessary to comply with
 the assumptions, which has been reported extensively in the Research
 Article. <strong>Pond
 volumes </strong>(a detailled description is given in the Appendix
 of the Research Article) Pond volumes were quantified
 using a 999 CXI HDSI multibeam (Humminbird®) sonar device and the
 associated software. Pond volumes of extremely
 shallow ponds (&lt; 50 cm deep) were quantified using a RTK satellite
 navigation technique using a Trimble® S6 total station with Trimble® R6
 receptors.