Monitoring post-release survival of the northern corroboree frog, Pseudophryne pengilleyi, using environmental DNA

Context. Translocations are becoming an increasingly important conservation tool to combat rising levels of species extinction. Unfortunately, many translocation efforts fail; yet, the timing and cause of failure often remain unknown. Monitoring individuals in the days and weeks following release can provide valuable information on their capacity to survive this initial hurdle. In Australia, breeding programs have been established for the endangered northern corroboree frog, Pseudophryne pengilleyi, to enable reintroduction to the wild via captive-reared individuals, typically, early life stages such as eggs or juvenile frogs that cannot be monitored via traditional survey methods that target adult frogs (e.g. shout-response). Environmental DNA(eDNA) detects trace amounts of DNA that organisms release into their environment and could provide a means to infer population persistence for wildlife releases and translocations. Aims. In the present study, we aim to develop an eDNA assay capable of detecting both sexes of P. pengilleyi across multiple life stages, and use it to monitor their survival. Methods. An eDNA assay was developed to target the two corroboree frog species (P. pengilleyi and P. corroboree, the southern corroboree frog) and was tested for its sensitivity and specificity in silico and in vitro. Pseudophryne pengilleyi eggs were released into three naturally occurring ponds and water samples were, subsequently, collected from each pond on several occasions over a period of 78 days. Quantitative polymerase chain reaction was used to detect P. pengilleyi eDNA from water samples. Key Results. The developed assay was shown to be sensitive and specific to corroboree frogs. eDNA monitoring of reintroduced P. pengilleyi detected the species' DNA at three of three release ponds and DNA remained detectable until at least 78 days post-release at two of three ponds. Conclusions. We show how the development of a corroboree frog-specific assay allowed us to monitor the post-release survival of P. pengilleyi in naturally occurring pools.