Parasites shape community structure and dynamics in freshwater crustaceans

Abstract

Parasites directly and indirectly influence the important interactions among hosts such as competition and predation through modifications of behaviour, reproduction and survival. Such impacts can affect local biodiversity, relative abundance of host species and structuring of communities and ecosystems. Despite having a firm theoretical basis for the potential effects of parasites on ecosystems, there is a scarcity of experimental data to validate these hypotheses, making our inferences about this topic more circumstantial. To quantitatively test parasites' role in structuring host communities, we set up a controlled, multigenerational mesocosm experiment involving four sympatric freshwater crustacean species that share up to four parasite species. Mesocosms were assigned to either of two different treatments, low or high parasite exposure. We found that the trematode Maritrema poulini differentially influenced the population dynamics of these hosts. For example, survival and recruitment of the amphipod Paracalliope fluviatilis were dramatically reduced compared to other host species, suggesting that parasites may affect their long-term persistence in the community. Relative abundances of crustacean species were influenced by parasites, demonstrating their role in host community structure. As parasites are ubiquitous across all communities and ecosystems, we suggest that the asymmetrical effects we observed are likely widespread structuring forces.

The Ecological Importance of Amphipod–Parasite Associations for Aquatic Ecosystems

“…Parasitism should be taken into consideration when evaluating biodiversity, health and ecosystem function. Including parasites when studying the biology of amphipods is mandatory to have a complete picture of community dynamics and can be precious from an ecosystem perspective, especially in biological invasion contexts [112,137,197]. Parasites of amphipods play an important but often still overlooked role in aquatic ecosystems.…”

“…Moreover, the effects of parasites on host interactions have been studied mostly on smaller and less complex scales (generally two host species and one shared parasite) instead of natural ecosystems, therefore the real influence of parasitism within a community remains largely unexplored and difficult to predict. Recent papers (see for example [137,160]) attempted to tackle this problem by analyzing different parasite and host species in the same community. Most of the available knowledge on the ecological importance and implications of amphipod-parasite systems come from laboratory experimental studies but there is a need of field evidence and of quantitative data to draw solid conclusions.…”

“…In one of the few experimental studies available to date that focuses on the effects of parasites on communities of different crustacean species, Friesen et al [137] showed that a trematode parasite selectively reduced the survival of one of the tested amphipod species and that it influenced the overall abundances of the amphipod and isopod species used in this experiment. In another study, the parasite-induced mortality of acanthocephalan parasites was found to be different between "cryptic" amphipod lineages.…”

“…Birds that prey on infected amphipods are the final hosts. Several studies on the trematodes of amphipods include results on the ecological effects of the host-parasite relationship (e.g., [63,[135][136][137]).…”

Two parasites in one host: spatiotemporal dynamics and co-occurrence of Microsporidia and Rickettsia in an amphipod host

“…For instance, in an amphipod host, two vertically transmitted parasites, one microsporidian and one paramyxean, were shown to co-occur more frequently than expected by chance; since feminization of male hosts is necessary for successful vertical transmission of the parasites, this suggested that one parasite was hitchhiking with another capable of feminizing the host (Short et al, 2012), or that both can feminize their hosts (Arundell et al, 2015;Pickup and Ironside, 2018). Amphipods host diverse macroparasites (trematodes, acanthocephalans and nematodes) as well as diverse microparasites (viruses, bacteria and protists) (Bethel and Holmes, 1977;Poulin and Latham, 2002;Bojko and Ovcharenko, 2019;Friesen et al, 2019). Amphipods are used as intermediate hosts by many parasites (Dezfuli et al, 2000), and a single amphipod individual can be infected by several different groups of parasites at the same time (Haine et al, 2005;Short et al, 2012).…”