Relationships between nutrient enrichment, pleurocerid snail density and trematode infection rate in streams

Abstract

Summary Nutrient enrichment is a widespread environmental problem in freshwater ecosystems. Eutrophic conditions caused by nutrient enrichment may result in a higher prevalence of infection by trematode parasites in host populations, due to greater resource availability for the molluscan first intermediate hosts. This study examined relationships among land use, environmental variables indicating eutrophication, population density of the pleurocerid snail, Leptoxis carinata, and trematode infections. Fifteen study sites were located in streams within the Shenandoah River catchment (Virginia, U.S.A.), where widespread nutrient enrichment has occurred. Snail population density had a weak positive relationship with stream water nutrient concentration. Snail population density also increased as human activities within stream catchments increased, but density did not continue to increase in catchments where anthropogenic disturbance was greatest. Cercariae from five families of trematodes were identified in L. carinata, and infection rate was generally low (<10%). Neither total infection rate nor the infection rate of individual trematode types showed a positive relationship with snail population density, nutrients or land use. There were statistically significant but weak relationships between the prevalence of infection by two trematode families and physical and biological variables. The prevalence of Notocotylidae was positively related to water depth, which may be related to habitat use by definitive hosts. Prevalence of Opecoelidae had a negative relationship with orthophosphate concentration and a polynomial relationship with chlorophyll a concentration. Transmission of Opecoelid trematodes between hosts may be inhibited by eutrophic conditions. Leptoxis carinata appears to be a useful species for monitoring the biological effects of eutrophication and investigating trematode transmission dynamics in lotic systems.

Effects of Parasite Infection and Host Body Size on Habitat Associations of Invasive Aquatic Snails: Implications for Environmental Monitoring

“…Our results, despite the small sample sizes of infected snails, add to previous studies demonstrating that snails can occur in different habitats when parasitized (Williams and Esch ; Jokela and Lively ; Wetzel and Shreve ; Ciparis et al. ). Specifically, large, infected individuals of T. granifera were found in shallower locations than large, noninfected snails.…”

“…Nevertheless, our approach (similar to that of Ciparis et al. ) provided a unique opportunity to investigate the biotic interactions between invading snails and their trematode parasites in lotic systems. Furthermore, our results demonstrate that the spatial distributions and habitat associations of invasive thiarid snails are associated with body size and, to a lesser extent, parasite infection.…”

Effects of agrochemical pollution on schistosomiasis transmission: a systematic review and modelling analysis

“…By investigating both the component and net effects of agrochemicals, we found that the net effect of chlorpyrifos, profenofos, and atrazine is to amplify transmission through the dominance of indirect effects on snail predators and algal dynamics, which are longer lasting than direct effects on snails and schistosome larvae. 10 , 38 By contrast, snail predators appear to be more tolerant to the insecticide malathion, which has trivial net effects on transmission. Similarly, the widely used herbicide glyphosate decreases transmission owing to its reproductive toxicity to snails at environmentally relevant concentrations.…”

Molecular phylogeny of the Cyathocotylidae (Digenea, Diplostomoidea) necessitates systematic changes and reveals a history of host and environment switches

“…Other studies have generated DNA sequence data from other life cycle stages, mostly cercariae and metacercariae (Blasco‐Costa & Locke, ; Ciparis, Iwanowicz, & Voshell, ; Karamian et al, ; Locke et al, ; Locke, McLaughlin, & Marcogliese, ); however, the limited sequence data from adult forms prevent accurate species‐ or genus‐level diagnoses of the sequenced life cycle stages. While recent molecular phylogenetic studies (Blasco‐Costa & Locke, ; Hernández‐Mena et al, ; Locke et al, ) have indicated the general position of the Cyathocotylidae among other diplostomoidean families, the very limited number of taxa used in these analyses did not allow exploration of questions of evolution and systematics related to geographic distribution, host associations and environmental switches of the group.…”