A eDNA-qPCR assay to non-invasively detect the presence of the parasite Schistocephalus solidus inside its threespine stickleback host.

Abstract

Detecting the presence of a parasite within its host is crucial to the study of host-parasite interactions. The Schistocephalus solidus - threespine stickleback pair has been studied extensively to investigate host phenotypic alterations associated with a parasite with a complex life cycle. This cestode is localized inside the sticklebacks abdominal cavity and can be visually detected only once it passes a mass threshold. We present a non-invasive quantitative PCR approach based on detection of environmental DNA from the worm(eDNA),sampled in the fish abdominal cavity. Using this approach on two fish populations (n=151), 98% of fish were correctly assigned to their S. solidus infection status. There was a significant correlation between eDNA concentration and total parasitic mass. We also assessed ventilation rates as a complimentary mean to detect infection. Our eDNA detection method gives a reliable presence/absence response and its future use for quantitative assessment is promising.