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

Dakeishla M Díaz-Morales,Bernd Sures,Daniel S Grabner,Martin Wahl,Claudia Bommarito,Jahangir Vajedsamiei,Gil Rilov

doi:10.1038/s41598-022-05139-5

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.

Highlights

The present study illustrates that the first intermediate host and cercariae represent a fragile link in the life cycle of trematodes under current extremely warm events and projected end-of-century mean temperatures for temperate systems during s ummer[36]
The studied H. elongata host–parasite system is a good example of the complex dynamics between closely interacting species such as the trematodes and ecologically relevant benthic species under the influence of thermal stress
Our results conclusively showed that the optimal temperature range of parasite performance might be overestimated when looking at individual life cycle components

Summary

Results

Experiment 1a: General host infection status and survival. From the initial 125 snails, 82% survived the acclimation period. In the case of pre-mortem encystment, the model explained 78% of the variance Both gross and net infectivity significantly correlated with temperature in a bell-shaped curve (Fig. 5A,B). When considering cercarial emergence and the effect that temperature-specific gastropod survival has on cercarial emergence, the optimal temperature for net infective cercariae was reduced by 1.7 °C, with an estimated number of infective cercariae from surviving snails of 1933 (Fig. 5B). For this model, all terms (i.e., first-, second- and third-degree terms) were significant (p < 0.0001, GLMM z-statistic; see Supplementary Table S3). For the self-propelling capacity of cercariae, only the first eight hours are shown since, after this time, the larvae usually lose their self-propelling capacity

Discussion

Methods