Parasite predators exhibit a rapid numerical response to increased parasite abundance and reduce transmission to hosts

Abstract

Predators of parasites have recently gained attention as important parts of food webs and ecosystems. In aquatic systems, many taxa consume free-living stages of parasites, and can thus reduce parasite transmission to hosts. However, the importance of the functional and numerical responses of parasite predators to disease dynamics is not well understood. We collected host–parasite–predator cooccurrence data from the field, and then experimentally manipulated predator abundance, parasite abundance, and the presence of alternative prey to determine the consequences for parasite transmission. The parasite predator of interest was a ubiquitous symbiotic oligochaete of mollusks, Chaetogaster limnaei limnaei, which inhabits host shells and consumes larval trematode parasites. Predators exhibited a rapid numerical response, where predator populations increased or decreased by as much as 60% in just 5 days, depending on the parasite:predator ratio. Furthermore, snail infection decreased substantially with increasing parasite predator densities, where the highest predator densities reduced infection by up to 89%. Predators of parasites can play an important role in regulating parasite transmission, even when infection risk is high, and especially when predators can rapidly respond numerically to resource pulses. We suggest that these types of interactions might have cascading effects on entire disease systems, and emphasize the importance of considering disease dynamics at the community level.

The invasive Chinese pond mussel Sinanodonta woodiana (Lea, 1834) as a host for native symbionts in European waters

“…The relationship between Ch. limnaei limnaei abundance and cercariae density was experimentally confirmed by Hopkins et al (2013). Some authors (Conn et al, 1996) indicate the seasonality of this annelid species in bivalve hosts and show a positive correlation of this phenomenon with water temperature changes.…”

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

“…Schistosome miracidia and cercariae may serve as prey for larval aquatic insects, crustaceans, oligochaetes, shrimps, and fish (271,(333)(334)(335)(336)(337)(338). In particular, the annelid Chaetogaster limnaei sensu lato, living commensally or parasitically on the shell surface or in the mantle and pulmonary cavities of freshwater snails, may act as an efficient predator and prevent penetration of miracidia (339,340) or feed on cercariae as they are released from the snail (341,342).…”

Host community composition and defensive symbionts determine trematode parasite abundance in host communities

“…Then, those snails and the frozen tadpoles were dissected to quantify Chaetogaster numbers for snail hosts and trematode infection for all hosts (e.g., Belden and Wojdak , Hopkins et al. ).…”

“…Chaetogaster directly influence snail susceptibility to echinostome infection by consuming cercariae, and higher Chaetogaster infestation intensities cause greater reductions in cercariae attack success (Sankurathri and Holmes , Hopkins et al. ). Also, observational evidence suggests that cercariae may abandon attempts to penetrate snails with Chaetogaster , causing cercariae to exhaust their energy stores and die before successfully infecting symbiont‐defended snails (Sankurathri and Holmes ).…”