Virus

Littorina

Parasitism

Biology

Zoology

Infectivity

Host (biology)

World Wide Web

Helminths

Virology

Marine invertebrates

Ecology

Intermediate host

Mollusca

Trematoda

Mytilus

Computer science

Parasite hosting

Scientific Reports

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.

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