Do behavioural defence mechanisms explain different levels of trematode infections in congeneric hosts?

Abstract

Susceptibility and tolerance to parasite infection vary greatly between host species. The congeneric isopod species Austridotea annectens and Austridotea lacustris often occur in sympatry and can both serve as intermediate hosts for the trematode Maritrema poulini. However, the intensity and prevalence of infections vary greatly in natural populations, with A. annectens often being heavily infected and A. lacustris rarely being infected. To shed light on the factors that may be involved in infection avoidance in A. lacustris, 100 isopods were collected and experimentally exposed to M. poulini cercariae. To examine for potential behavioural mechanisms, we used carbonated water as a paralysing agent to temporarily stop any movement by the isopods, and exposed paralysed isopods to cercariae. In the experiments, none of the individuals that were exposed to the parasite were found to be infected, although some cercariae seemed to have penetrated isopod hosts. Behavioural defence mechanisms do not seem to explain the different infection levels between A. lacustris and A. annectens, suggesting a physiological, possibly immunological, factor may be present. At the ecosystem level, this suggests a potential dilution effect caused by this low-competency host, and its effects on parasite transmission dynamics should be investigated.

Parasites shape community structure and dynamics in freshwater crustaceans

“…Zohar and Holmes, 1998; Bollache et al ., 2001), and may play a role in reduced pairing by P. fluviatilis . However, as A. lacustris is a very rare host (<1%; Goellner et al ., 2018), the difference in pairing success in this species may be due to indirect effects of infected competitors. Past studies have suggested that M. poulini in A. annectens affects the distribution of A. lacustris , and mediates the competition between these species (Friesen et al ., 2018).…”

Temperature and multiple parasites combine to alter host community structure

“…The isopod, A. annectens is also commonly infected by M. poulini . Maritrema poulini is also found in A. lacustris but at extremely low prevalence (Presswell et al 2014, Friesen et al 2018, 2020, Goellner et al 2018). As both M. poulini and C. parvum can successfully complete transmission between first and second intermediate hosts in a mesocosm setting and parasite exposure rate can be controlled, these trematodes were selected as focal parasites and used to create continuous exposure (infective larval stages of both species present in the mesocosm through infected first intermediate host snail) and arrested exposure (no additional exposure to infective parasite larval stages of either species in mesocosm) treatments.…”