Heat sensitivity of first host and cercariae may restrict parasite transmission in a warming sea

Abstract

To predict global warming impacts on parasitism, we should describe the thermal tolerance of all players in host–parasite systems. Complex life-cycle parasites such as trematodes are of particular interest since they can drive complex ecological changes. This study evaluates the net response to temperature of the infective larval stage of Himasthla elongata, a parasite inhabiting the southwestern Baltic Sea. The thermal sensitivity of (i) the infected and uninfected first intermediate host (Littorina littorea) and (ii) the cercarial emergence, survival, self-propelling, encystment, and infection capacity to the second intermediate host (Mytilus edulis sensu lato) were examined. We found that infection by the trematode rendered the gastropod more susceptible to elevated temperatures representing warm summer events in the region. At 22 °C, cercarial emergence and infectivity were at their optimum while cercarial survival was shortened, narrowing the time window for successful mussel infection. Faster out-of-host encystment occurred at increasing temperatures. After correcting the cercarial emergence and infectivity for the temperature-specific gastropod survival, we found that warming induces net adverse effects on the trematode transmission to the bivalve host. The findings suggest that gastropod and cercariae mortality, as a tradeoff for the emergence and infectivity, will hamper the possibility for trematodes to flourish in a warming ocean.

Combined effects of salinity and trematode infections on the filtration capacity, growth and condition of mussels

“…In addition to freshening, levels of parasitism may also increase as a consequence of climate change (Marcogliese 2001, Lafferty et al 2004. In particular, cercarial emergence and infection success of trematodes in the Baltic Sea appear to be enhanced by an increase in water temperature (Díaz-Morales et al 2022). However, this might not be the only possible scenario, since warming was found to be detrimental to the first intermediate gastropod host survival as well as the survival of cercariae and also because freshening reduces the in fectivity of cercariae (Bommarito et al 2020, Díaz-Morales et al 2022.…”

“…In particular, cercarial emergence and infection success of trematodes in the Baltic Sea appear to be enhanced by an increase in water temperature (Díaz-Morales et al 2022). However, this might not be the only possible scenario, since warming was found to be detrimental to the first intermediate gastropod host survival as well as the survival of cercariae and also because freshening reduces the in fectivity of cercariae (Bommarito et al 2020, Díaz-Morales et al 2022. Longer-term laboratory experiments including multiple abiotic factors followed by field experiments in more natural conditions and including all intermediate hosts involved in the trematode life cycle would be promising approaches to better understand the consequences for both the mussel host and the parasites.…”

Thermal optima of cercarial emergence in trematodes from a marine high-temperature ecosystem, the Persian Gulf

“…Since the effects of warming on parasite transmission dynamics can have far-reaching ecological and economic consequences for hosts and ecosystems 9,17 , it is important to understand the effects of temperature on parasite transmission as a pre-requisite for predicting climate change effects on the biosphere. Trematodes are an excellent example of parasites for which temperature effects are well known to affect crucial steps in the transmission process from one host to another 18,19 . Their life cycle usually involves three different hosts: a mollusc as rst intermediate host, invertebrates or vertebrates (depending on the species) as second intermediate host, and vertebrates as nal host 20 .…”

Thermal optima of cercarial emergence in trematodes from a marine high-temperature ecosystem, the Persian Gulf

“…Trematodes are an excellent example of parasites for which temperature effects are well known to affect crucial steps in the transmission process from one host to another 18 , 19 . Their life cycle usually involves three different hosts: a mollusc as first intermediate host, invertebrates or vertebrates (depending on the species) as second intermediate host, and vertebrates as final host 20 .…”

“…Since the effects of warming on parasite transmission dynamics can have far-reaching ecological and economic consequences for hosts and ecosystems 9,17 , it is important to understand the effects of temperature on parasite transmission as a pre-requisite for predicting climate change effects on the biosphere. Trematodes are an excellent example of parasites for which temperature effects are well known to affect crucial steps in the transmission process from one host to another 18,19 . Their life cycle usually involves three different hosts: a mollusc as first intermediate host, invertebrates or vertebrates (depending on the species) as second intermediate host, and vertebrates as final host 20 .…”