Incidental invertebrate-derived DNA detection of invasive and threatened species in temperate dry Southeast Australian forest

Well-informed biodiversity conservation practice can often be precluded by poor species detectability. For example, populations being missed during surveys can lead to them being omitted from species lists or area management plans. iDNA (invertebrate-derived DNA) is a recently developed set of techniques for improving the detectability of elusive vertebrates by exploiting their associated invertebrates. Parasitic and scavenging invertebrates can be readily collected, and their gut contents DNA barcoded to detect local vertebrate diversity. However, most iDNA surveys have targeted mammals and have been carried out in tropical areas and/or rainforests. We carried out iDNA surveys targeting frogs in temperate dry sclerophyll forests in south-eastern Australia. We set mosquito traps broadcasting recorded frog calls with the aim of collecting frog-biting flies, which are attracted to frog calls. We collected 156 fly specimens, although none were of frog-biting species, and no frogs were detected via iDNA, despite many being observed in the field. However, two mammal and one reptile species were detected via iDNA: the feral cat (Felis catus: Felidae), domestic dog or dingo (Canis lupus: Canidae) and the threatened Rosenberg's monitor (Varanus rosenbergi: Varanidae). Vertebrate-sampling flies are likely highly abundant in the area since they were collected apparently incidentally in traps lacking appropriate attractants; a promising result for further surveys is different attractants are employed. This study is one of the few in which an invasive species has been detected through iDNA, and highlights its potential for improved detectability of threatened species outside of the tropics and early detection of invasive species.