An examination of composition and species richness in trematode communities using Stagnicola elodes

Abstract

Human-induced changes to the environment due to climate change, pollution, and loss of habitat have the potential to alter the community of parasites associated with a given host species. This is particularly true for parasites with complex life cycles, such as digenean trematodes, that involve free-living and parasitic stages, and have highly specific relationships with multiple hosts. Based on this, parasites can play a role as bioindicators, where loss of parasite diversity and changes in parasite assemblages can be indicative of degraded environments. In my study, I explored the diversity of digenean trematode parasites associated with a well-studied freshwater snail, Stagnicola elodes, in Blacketts Lake, Cape Breton, in relation to another more pristine Cape Breton lake (Lake Ainslie) and to previous studies in North America. S. elodes specimens were collected from Blacketts Lake and Lake Ainslie, and infected snails were identified by the emergence of cercarial larval stages. Cercariae were differentiated based on morphotype and behaviour and then preserved for molecular analyses. A DNA barcoding approach was used to assess species boundaries and to determine parasite identities, where possible, through comparisons to other parasite sequences on GenBank using BLAST. Following DNA extraction, a 750 base pair portion of the Cytochrome Oxidase Subunit I gene was amplified using PCR, and then sequenced at The Centre for Applied Genomics in Toronto. Data were also supplemented with results from previous sampling years in Blacketts Lake. My results indicate that a minimum of 13 distinct trematode species channel their life cycles through S. elodes in Blacketts Lake, spanning the families Plagiorchiidae, Diplostomidae, Strigeidae, Schistosomatidae, and Echinostomatidae. This assemblage of parasites overlappedwith those reported in previous studies that have focused on S. elodes, however, there were notable differences in the family composition between Blacketts Lake and Lake Ainslie. In terms of species richness, that of Blacketts Lake was low compared to the pristine habitats of Douglas and Burt Lakes, Michigan sampled in 1935-1936, but similar to the same habitat following 50 years of human development. Trematode diversity in Blacketts Lake falls within a broad range of values found across other studies in the literature. My study establishes a baseline of the trematode community present in Blacketts Lake that can be used to monitor trematode diversity across years. Having a baseline may be particularly useful for comparing the health of the same aquatic communities over time or for comparing local environments that share similar habitats and climate, but differ in potential human impacts. Further exploration of this trematode-S. elodes relationship within a given environmental context should therefore help to provide more insight into the faunal composition of aquatic communities and the integrity of these environments.