Parasite transmission in aquatic ecosystems under temperature change: effects of host activity and elimination of parasite larvae by filter-feeders

摘要

A moderate increase in temperature is likely to enhance the impact of parasites on aquatic ecosystems. Thus, under higher temperatures, poikilothermic animals (e.g. fish) increase their activity, which can result in a more frequent encounter with parasites and higher infection risk. However, temperature increase may also trigger counteracting processes in ambient communities decreasing the risk of parasitic infections. For instance, the removal of free-living stages of parasites by filter-feeding organisms can increase with temperature and potentially mitigate the disease risk in ecosystems under temperature shift. We examined whether an enhanced parasite transmission under higher temperatures can be compensated by the increased removal of parasitic larvae by filter-feeders. In addition, our study aimed to reveal the behavioral mechanism underlying the more successful transmission of the parasite at higher temperatures. We studied experimentally how temperature, behavior of fish hosts (rainbow trout), and presence of filter-feeding mussels in the environment influence the infection success of trematode larvae (Diplostomum pseudospathaceumcercariae). We found that heating increased while the presence of filter-feeding mussels in the environment decreased infection intensities in fish. However, the effect of mussel's presence was constant within the tested range of water temperatures (15-23 degrees C), which suggests that it cannot compensate for the observed increased transmission of parasites with temperature increase. Fish activity before the exposure to parasites was positively related to the host's vulnerability to infection. However, fish activity only weakly correlated with temperature, therefore, it is unlikely to be the only factor influencing the infection success under warmer conditions. In general, we showed that the elimination of trematode larvae by filter-feeders is unlikely to deter the potential effects of temperature increase on host-parasite interactions in temperate freshwater ecosystems.