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.
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We would like to thank Maral Khosravi for her kind assistance in the field and trematode identification. We are also grateful to Björn Buchholz and Renate Schütt for their valuable technical and scientific input. We also extend our gratitude to Dr. Tim Staufenberger and Nikolai Nissen from the Kieler Meeresfarm for providing the mussels. This study was funded by BMBF/PTJ (Federal Ministry of Education and Research, Germany, grant 03F0821A, PI Wahl and grant 03F0821B, PI B Sures, and the BMBF/MOST grant 3-15216, PI G Rilov). Opinions, findings, conclusions and recommendations expressed in this publication are that of the authors, and the BMBF/ PTJ accepts no liability whatsoever in this regard.
© 2022, The Author(s).
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