Integrating eDNA, molecular cercariometry, and snail surveys enhances characterization of digenetic trematode diversity

Traditional methods for studying digenetic trematode populations involve collecting the snail first intermediate hosts and either shedding larval cercariae or dissecting the snails. Because larval trematodes can be difficult to identify based on morphology alone, these methods are often supplemented with DNA sequencing. This approach can be labour-intensive, and environmentally disruptive. Metabarcoding of environmental DNA (eDNA) or cercariometry (counting of cercariae in water) samples offers an alternative method to simplify this process without negatively affecting the trematode community through the removal of parasites and hosts from the environment. Through ongoing trematode research in central Alberta, Canada, we have documented 102 trematode species infecting multiple snail species and have developed a database of sequences using several DNA barcoding genes. To understand how the trematode community composition derived from metabarcoding compares to a snail infection baseline, we examined the trematode species richness detected by each method. We also established a 16 S rDNA database using representative sequences to align our metabarcoding datasets with others in the field. We found no significant difference between eDNA and cercariometry samples regarding the ability of either method to estimate pooled trematode species richness, but cercariometry detected more species than eDNA when trematode richness was compared between sites. However, snail collections predicted lower species richness than both molecular methods. These findings indicate that the combination of these methods result in enhanced characterization of the trematode community. As more researchers adopt 16 S rDNA for digenetic trematode studies, metabarcoding will become an increasingly valuable tool for trematode surveillance and diversity assessments.