Small snails, high productivity? Larval output of parasites from an abundant host

Abstract

How energy is transformed and distributed within ecosystems is a fundamental question in ecology. Parasites have been shown to play an essential role in these processes. In particular, the larval stages of trematodes, that is, cercariae, appear to contribute significantly to biomass and productivity in aquatic systems. Overall, ecosystem‐wide studies on parasite productivity remain scarce and have typically investigated systems with large hosts and high parasite infection rates. These studies may thus represent isolated cases of exceptionally high parasite contribution to ecosystem energetics, potentially overestimating the importance of parasite biomass. Here, we quantified the productivity of trematode cercariae from a small but hyper‐abundant snail intermediate host with only moderate trematode prevalence (i.e., proportion of infected individuals) in an entire lake ecosystem. We assessed individual larval output from snails and calculated the overall trematode productivity in the ecosystem. Average output of individual trematode species ranged from 3 to 62 cercariae per snail per day and correlated negatively with individual cercarial size. Cercarial productivity was not uniformly distributed across trematode taxa, but dominated by the most common species that accounted for more than 80% of the productivity. Total cercarial productivity amounted to 1.85 g m−2, which falls within the ranges of previous studies from freshwater systems. Small but abundant snail populations may thus support a considerable productivity of parasites. However, total annual cercarial productivity in the study system amounted to 5.9 kg, which constituted just 1.2% of the standing stock snail biomass, suggesting that intermediate host populations are potentially underexploited by their parasites. Moreover, comparisons with previous studies revealed contrasting patterns of parasite productivity and biomass contribution across different habitats, showing that impacts of parasites on ecosystem energetics can vary widely. Overall, we are still far away from having a complete picture of the dynamics of parasite productivity and biomass in many ecosystems. It therefore remains critical to quantify the contribution of parasites to the flow and distribution of energy and nutrients within and across habitats, to better understand their impacts on fundamental ecological principles, such as food‐web structure and ecosystem energetics.

Infection burdens and virulence under heat stress: ecological and evolutionary considerations

“…For example, in long-lived metazoan parasites, the adult parasite may stay within a host for many years, producing many broods of parasite larvae (e.g. [ 65 , 66 ]). In this case, the parasite burden might be measured as the number of adult parasites within the host, and parasite replication the number of larvae the host is able to produce over a lifetime of infection.…”

Consumption of trematode parasite infectious stages: from conceptual synthesis to future research agenda

“…The latter can be year-round in tropical regions (Cannon, 1979; Aeby, 2007), or confined to the warmer months in regions with more pronounced seasonality (Thieltges & Rick, 2006; Nikolaev et al , 2021). The resulting annual production values can be substantial (Kuris et al , 2008; Thieltges et al , 2008c; Preston et al , 2013; Soldánová et al , 2016; Rosenkranz et al , 2018), such that cercariae may constitute a relatively stable and constantly replenishing resource for consumers.…”

“…In addition, the high production of bottom-dwelling cercariae by many trematode species (e.g. Rosenkranz et al , 2018) might mean that their energy is primarily available to benthic consumers. This form of cercarial consumption is largely unstudied to date, but it is likely that the contribution of dead cercariae to energy flow through the detritivore and microbial compartments of food webs is substantial.…”

“…Morton et al , 2021). Of particular note is the substantial biomass reported for cercariae (Kuris et al , 2008; Preston et al , 2013, 2021; Soldánová et al , 2016; Rosenkranz et al , 2018), often collectively exceeding that of free-living taxa such as birds or aquatic insects. Consequently, cercariae represent a readily-available prey item in many habitats (Johnson & Thieltges, 2010; Johnson et al , 2010) and their consumption is well-studied relative to that of other parasite infectious stages given the number of trematode species with medical, economic and wildlife importance (Toledo & Fried, 2019).…”

Prospective enzymes for omega-3 PUFA biosynthesis found in endoparasitic classes within the phylum Platyhelminthes

“…Importantly, many macroparasites produce large numbers of their free-living infectious stages, particularly the aquatic cercariae of trematodes, thus contributing substantial biomass in certain ecosystems (e.g. Kuris et al , 2008; Preston et al , 2013; Rosenkranz et al , 2018). Consequently, better understanding the nutritional contributions and role(s) of macroparasite infectious stages within ecosystems is critical for explaining the nuances of food web structure and function (reviewed in Marcogliese & Cone, 1997; Marcogliese, 2005; Lafferty et al , 2008; Hatcher et al .,, 2012).…”