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Further isolation may arise through site-specific co-evolution between the mussels and hosts; Douda et al. ([7]) demonstrated that there are often differences in the suite of fish hosts used by I U. crassus i , even across genetically and geographically close populations. Keywords: conservation; glochidia; host specificity; parasitism; reproduction EN conservation glochidia host specificity parasitism reproduction 1 5 5 05/03/23 20230501 NES 230501 Understanding the life-history characteristics of endangered species is crucial to their conservation, management, and predicting their responses to environmental change (Stark et al., [16]). Fishing for hosts: Larval spurting by the endangered thick-shelled river mussel, Uniocrassus Host specificity can increase vulnerability of mussels as survival is intrinsically linked to that of their hosts. [Extracted from the article]

Parasites can indirectly affect ecosystem function by altering host phenotype, but the trait‐mediated impacts of parasitism at an ecosystem level remain poorly characterised. However, understanding the influence of parasites is central to understanding the ecosystem services provided by host species, especially in an era of global environmental change.We examined the effect of native (the trematode Rhipidocotyle campanula) and invasive (the bitterling fish Rhodeus amarus) parasites, and their interaction, on the clearance rates of unionid mussels, a dominant ecosystem‐engineering group that modify freshwater ecosystems worldwide. We used a combination of field experiments, laboratory experiments and ecological simulations to demonstrate the phenotypic impact of parasites on the functional response of two mussel species across an environmental gradient (suspended particle concentration), and extended this with host and parasite community data to demonstrate the consequences for a real‐world ecosystem, the Old West River in Cambridgeshire, England.Both parasites altered the clearance rates of their hosts but in contrasting fashion: while R. campanula increased host clearance rates relative to uninfected conspecifics under all conditions, R. amarus supressed clearance rates at high suspended particle concentrations (eutrophic conditions) but elevated them otherwise. The parasites displayed different infection patterns in the two host species, and the invasive R. amarus rarely co‐infected mussels with R. campanula.Given their disparate effects, the parasites' distributions reversed the relative filtration capacity of the two host species under high vs. low concentrations of suspended particles, demonstrating how differences between the infection patterns of native and invasive parasites, as well as their individual effects, need to be considered. Overall, the proportion of daily river discharge filtered by the combined mussel community changed by up to 96% in the presence of parasites. By incorporating multiple host species and multiple parasite species, we provide ecologically relevant evidence for the trait‐mediated effects of parasites on ecosystem processes.Our study demonstrates that parasitism can significantly alter wider ecosystem processes through changing the phenotype of their host. Future work on ecosystem function should take parasitism into account, and consider both trait‐mediated and density‐mediated effects. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Parasites can negatively affect hosts at individual, population, and species‐level scales. However, the link between individual‐ and population‐level impacts is often poorly understood. In particular, the population‐level response to parasitism may alter wider ecosystem dynamics if animals with ecosystem engineering capabilities are infected.Here, we examine the effects of parasitism on a freshwater ecosystem engineer, the unionid mussel Anodonta anatina, at two different sites. We study three common parasites: the digenean trematode Rhipidocotyle campanula; the unionicolid mite Unionicola intermedia; and the ectoparasitic invasive zebra mussel Dreissena polymorpha. As well as demonstrating the individual‐level effects of parasitism on the native host mussel, we construct a simple model to estimate the reduction in population‐level reproductive output caused by parasites.We show that both infection prevalence and intensity were population‐specific, with one site having more than three times as many native mussels infected by trematodes and mites than the other, but more than four times fewer mussels afflicted by invasive zebra mussels. Negative reproductive consequences for individual host mussels were documented as a result of parasitism, with trematodes causing castration at both sites. Mites were also correlated with a reduction in the viability of larval offspring (glochidia) by more than 25%, but only at one site, suggesting some potential impacts of parasitism may be population specific. The population‐level model shows that parasitism alone reduces larval output of the two populations by 10% and 13%, respectively.Our study takes the important step of scaling individual‐level effects of parasitism to population‐level processes, and highlights the influence that parasites may have in the population dynamics of unionid mussels. Given the ecosystem engineering capabilities of A. anatina, such effects may have important impacts on the wider biota.Even at relatively low prevalences, the observed effects of parasites on native mussel populations suggests that parasitism must be considered in the conservation of freshwater mussels, one of the world's most globally imperilled faunal groups. Further, understanding how the effects of parasitism on individual hosts scales to the ecosystem level is a crucial and unaddressed question in freshwater biology. [ABSTRACT FROM AUTHOR]