Optimising the Detection of Southern Toadlets ( Pseudophryne semimarmorata ): A Comparative Study of eDNA and Conventional Survey Methods

ABSTRACT

Accurate and reliable monitoring of amphibians is essential for informing their conservation. Pseudophryne semimarmorata (southern toadlet) is a species of endangered brood frog with a largely terrestrial life history that has experienced widespread decline across southern Australia. This study sought to identify whether environmental DNA (eDNA) could be used as a non‐invasive method to detect the presence of southern toadlet during its breeding season alongside traditional call surveys. We collected 73 water samples for species‐specific analysis from 35 sites (waterbodies) in areas with recent records of southern toadlets throughout the breeding period. We also employed predictive models to reveal the environmental parameters associated with the presence of calling males. eDNA had limited in‐field success to accurately detect the species, with positive detections from three of the 73 samples, all taken from repeat samples from one site. In contrast, call surveys detected toadlets on 41 of the 73 occasions where water was concurrently sampled for eDNA. We found a greater presence of calling males at higher water temperatures, which was, in turn, more likely at the onset of the breeding period (early autumn). While eDNA sampling is a promising tool to monitor many amphibians and other aquatic taxa, our results demonstrate that it may have a limited ability to detect southern toadlets in their environment. A largely terrestrial life history, small population density and small biomass of individuals likely contribute to the low eDNA detection rate of southern toadlets.