McPhail, B. A. | bioRxiv Science

bioRxiv2025

Snail-trematode dynamics in central Alberta wetlands: A longitudinal survey of infections and interactions

Previous research has shown that host diversity and heterogeneity promote parasite abundance and heterogeneity by creating additional niches for parasites to occupy. Central Alberta, Canada, sees a diverse array of native and migratory species each year. A previous snail-trematode survey conducted at six lakes in central Alberta from 2013-2015 uncovered 79 trematode species. However, analyses suggested that additional species remained to be uncovered. To build on this baseline, we conducted further snail-trematode collections from 2019 to 2022 at eight reclaimed wetland sites in various stages of reclamation, along with one established lake in Alberta. Across the nine sites, we collected 22,397 snails, of which 1,981 were infected with digenean trematodes. We also documented broader biodiversity at these sites using traditional survey techniques. Through DNA barcoding, we identified 74 trematode species infecting five snail species. Among these were 23 trematode species not previously reported in central Alberta and nine putative novel species. In addition, we observed several previously unreported snail-trematode interactions. While trematode richness did not vary significantly with the wetland reclamation stage, host identity did influence richness: Physa gyrina hosted significantly more trematode species than Planorbella trivolvis. When combined with data from the earlier survey, sample completeness analyses indicate that we captured 100% of the dominant species and 99% of the typical species, but only 63% of the overall species diversity in central Alberta. These findings underscore that trematode diversity in central Alberta remains underestimated and highlight the continued value of long-term and host-inclusive sampling efforts.

ecology↗

bioRxiv2021

Transient definitive host presence is sufficient to sustain avian schistosome populations

To control swimmers itch in northern Michigan inland lakes, one species of bird, the common merganser (Mergus merganser), has been relocated from several lakes since 2015. Relocation efforts are driven by a desire to reduce the prevalence of the swimmers itch-causing parasite Trichobilharzia stagnicolae. The intention of this state-sponsored control effort was to interrupt the life cycle of T. stagnicolae and reduce parasite egg contribution into the environment from summer resident mergansers such that infections of the intermediate snail host Stagnicola emarginata declined. Reduced snail infection prevalence was expected to greatly reduce abundance of the swimmers itch-causing cercarial stage of the parasite in water. With no official program in place to assess the success of this relocation effort, we sought to study the effectiveness and impact of the removal of a single definitive host from a location with high definitive host and parasite diversity. This was assessed through a comprehensive, lake-wide monitoring study measuring longitudinal changes in the abundance of three species of avian schistosome cercariae in four inland Michigan lakes. Environmental measurements were also taken at these lakes to understand how they can affect swimmers itch incidence. Results from this study demonstrate that the diversity of avian schistosomes at the study lakes would likely make targeting of a single species of swimmers itch-causing parasite meaningless from a swimmers itch control perspective. Our data also suggest that removal of the common merganser is not an effective control strategy for the T. stagnicolae parasite, likely due to parasite contributions of migratory birds in the fall and spring. This suggests that only minimal contact time between the definitive host and the lake ecosystem is required to contribute sufficient parasite numbers to maintain a thriving population of parasite species with a high host-specificity.

ecology↗