RT Journal Article SR Electronic T1 A eDNA-qPCR combination assay to non-invasively detect the presence of the parasite Schistocephalus solidus inside its intermediate host, the threespine stickleback JF bioRxiv FD Cold Spring Harbor Laboratory SP 231670 DO 10.1101/231670 A1 Chloé Suzanne Berger A1 Nadia Aubin-Horth YR 2017 UL http://biorxiv.org/content/early/2017/12/09/231670.abstract AB To study parasite-host interactions, it is of major importance to detect the presence of the parasite during its development in the host. The Schistocephalus solidus-threespine stickleback pair has been used extensively to study host phenotypic alterations caused by a parasite with a complex life cycle. This cestode worm is localized inside the abdominal cavity of its intermediate fish host, which limits its detection to the time when it has grown substantially or to multiple infections. Here, we present a non-invasive species-specific quantitative real time PCR approach based on the detection of environmental DNA from the worm (eDNA), sampled directly in the abdominal cavity of the threespine stickleback. Using this approach on two fish populations (n=151), 98% of fish were correctly assigned to their S. solidus infection status. Among the 35 sticklebacks that harboured single or multiple infections, only 3 were not detected as infected. Furthermore, non-infected sticklebacks were never incorrectly identified as infected. There was a significant correlation between eDNA concentration and the total mass of parasites. We also assessed ventilation rates as a rapid and complimentary mean to detect infection (n=20). Ventilation rates were repeatable over 3 measurements, did not vary significantly between non-infected and infected fish, were not significantly correlated to the parasite index, and thus could not reliably be used to predict infection. Our eDNA approach could be used in this parasite-host system alone or in combination with morphological measurements to detect S. solidus.