Introduction

Amphibians are vertebrates with life cycles that crucially depend on both aquatic and terrestrial habitats. They play an important intermediate position in food chains and ecosystems, and are important indicator taxa of environmental health (Li et al., 2017). Amphibians are not only an important component of biodiversity but are also a taxonomic group that has undergone significant changes in taxonomical organization in recent years and is experiencing rapid population declines and risks of extinction at a global scale (Gao et al., 2022). China is among the countries with the richest biodiversity in the world and specifically boasts the highest diversity of amphibian species(Xu et al.,2018). Monitoring the status of this diverse fauna is often challenging. According to the Technical Provisions on Survey and Assessment of Amphibian and Reptile Diversity in County Areas (Ministry of Ecology and Environment Announcement No. 84, 2017), traditional methods to investigate amphibian diversity include traditional line transect methods, trap-barrier systems, methods using artificial covers or shelters, mark-recapture, call counting, and others. Traditional investigation is often accurate and intuitive, but efficiency is frequently affected by species, life stages and environmental conditions (Ruppert et al., 2022). Moreover, a high level of taxonomic knowledge is required of the traditional investigator, especially for identification of eggs and larvae (Hopkins & Freckleton, 2002; S. Zhang et al., 2020). In recent years, there has been increasing use of the environmental DNA (eDNA) method, which allows the DNA of target organisms obtained from environmental samples (e.g. water, soil, excrement, ancient sediments, etc.) to be used for detection of presence or absence of the species, and even enables inferences about their numbers and biomass (Ficetola et al., 2019; Thomsen & Willerslev, 2015). Extensive use of eDNA technology has been made for biodiversity surveillance across diverse taxa, encompassing fish (Deiner et al., 2017; Jerde et al., 2011; P. F. Thomsen, J. Kielgast, L. L. Iversen, P. R. Moller, et al., 2012), amphibians (Goldberg et al., 2018; Pilliod et al., 2013; Strickler et al., 2015; Valentini et al., 2016), benthic fauna (Cowart et al., 2018; Laroche et al., 2018; Stoeck et al., 2018), plants (Johnson et al., 2019; Johnson et al., 2021; Kodama et al., 2022), bacteria (Laroche et al., 2018; Stoeck et al., 2018; Y. Zhang et al., 2020), and microorganisms (Handelsman, 2004; Rondon et al., 2000). Nonetheless, varied applications of eDNA technology among distinct biological cohorts elicit discernible disparities. This review provides an exposition of the applications of eDNA technology in amphibian monitoring and also discusses the multifaceted factors determining its efficacy and reliability. We also examine future research and questions that will need to be addressed for the further development of eDNA technology for amphibian population investigations.