Utilizing environmental DNA for wide-range distributions of reproductive area of an invasive terrestrial toad in Ishikari river basin in Japan

Abstract

Understanding the distribution of invasive species and their reproductive area is crucial for their managements after invasion. While catch and observation surveys are still embraced, environmental DNA (eDNA) has been increasingly utilized as an efficient tool for identifying these species in the wild. In this study, we developed a Bufo-specific eDNA assay for detecting an invasive, toxic, and terrestrial toad species Bufo japonicus formosus in Hokkaido, Japan, and applied it to their reproductive area at watershed scale. The eDNA assay was field-validated in ponds where B. japonicus were observed, as well as in rivers downstream of the reproductive ponds. Thus, the assay provided us an opportunity to screen watersheds that include their reproductive area by collecting downstream water samples. Applying it to the Ishikari river basin, the largest river basin in Hokkaido (c.a., 14,330 km2), we detected toad eDNA at 32 out of 73 sampling sites. They are composed of eleven sites with species observation records nearby (all the sites with observation records within a 500 m radius) and 21 sites without such records. And those eDNA detections were from twelve out of 31 river systems in the entire river basin. A Bayesian, multiscale occupancy model supported high eDNA detectability among those sites. These results suggest that the eDNA assay can efficiently estimate the presence of reproductive area of the terrestrial toad even from a distant downstream of the watershed, and that it provides a powerful means of detecting new reproductive area and monitoring further spread of invasive species.

Environmental DNA methods for detecting two invasive alien species (American bullfrog and red swamp crayfish) in Japanese ponds

“…Among the ponds in which eDNA was detected, P. clarkia was captured in only two ponds with higher eDNA concentrations (Pond 4: 4159, Pond 8: 3973 copies L −1 ). In a previous study, eDNA was detected even at the point where the target species could not be visually confirmed (e.g., Doi et al, 2017; Mizumoto et al, 2022; Takahara et al, 2013). Thus, in the present study, even though P. clarkii inhabited the ponds, there is a possibility that it could not be caught.…”

“…In recent years, the methods involving environmental DNA (eDNA) have been developed and applied to the study of several species of macro‐organisms in various freshwater habitats (Minamoto et al, 2012; Takahara et al, 2012; Tsuji et al, 2019), including endangered species (Doi et al, 2017; Sigsgaard et al, 2015; Takahara et al, 2020; Thomsen et al, 2012) and alien species (Ficetola et al, 2008; Takahara et al, 2013). The latter comprises Burmese pythons (e.g., Python molurus bivittatus , P. sebae , Boa constrictor , Eunectes murinus , E. notaeus ) (Hunter et al, 2015), freshwater fishes (e.g., Leucaspius delineatus , Lepomis gibbosus , Pimephales promelas , Pseudorasbora parva ) (Davison et al, 2016), and crayfishes (e.g., Pacifastacus leniusculus , P. virginalis , Orconectes limosus , O. rusticus ) (Dougherty et al, 2016; Larson et al, 2017; Mauvisseau et al, 2018), as well as Japanese common toad ( Bufo japonicus formosus ) (Mizumoto et al, 2022). The eDNA methods rely on collecting and analyzing traces of cell debris and extracellular DNA in aquatic environments left behind by the inhabiting organisms.…”

Environmental DNA Reveals Patterns of Biological Invasion in an Inland Sea

“…Towards this goal, the sampling of environmental DNA (eDNA) has shown promise when applied to the detection of non-native species (17). Targeted quantitative Polymerase Chain Reaction (qPCR) methods have successfully revealed the presence of individual species of interest, including the terrestrial toad species Bufo japonicus formosus in Hokkaido, Japan and invasive crayfish in Baden-Württemberg, Germany (18,19). Data collected using qPCR has motivated management and legal action on invasive carp in the Great Lakes region of the United States (20).…”

Catchment-based sampling of river eDNA integrates terrestrial and aquatic biodiversity of alpine landscapes

“…eDNA metabarcoding of riverine samples can be used to retrieve information on aquatic, semi-aquatic and terrestrial species in the wider landscape (Broadhurst et al 2021 ; Deiner et al 2016 ; Mizumoto et al 2022 ; Ushio et al 2017 ). Rivers can therefore function as “conveyor belts” of biological information stored in eDNA (Deiner et al 2016 ; Sales et al 2020 ; Villacorta-Rath et al 2021 ), leading to an aggregated biodiversity signal downstream that captures the wider landscape biodiversity, i.e.…”