Infection success of Echinoparyphium aconiatum (Trematoda) in its snail host under high temperature: role of host resistance

Abstract

BackgroundExtreme weather events such as summer heat waves become more frequent owing to global climate change and are predicted to alter disease dynamics. This is because high temperatures can reduce host immune function. Predicting the impact of climate change on host-parasite interactions is, however, difficult as temperature may also affect parasite infective stages and other host characteristics determining the outcome of interaction.MethodsTwo experiments were conducted to investigate these phenomena in a Lymnaea stagnalis–Echinoparyphium aconiatum (Trematoda) interaction. In the first experiment, the effects of exposure of snails to experimental heat waves [maintenance at 25°C vs. 15°C (control)] with different durations (3 days, 7 days) on the infection success of parasite cercariae was examined. In the second experiment, the infection success was examined under similar conditions, while controlling for the possible temperature effects on cercariae and at least partly also for host physiological changes that take place rapidly compared to alterations in immune function (exposure to cercariae at intermediate 20°C).ResultsIn the first experiment, increased infection success at 25°C was found independently of the duration of the heat wave. In the second experiment, increased infection success was found only in snails maintained at 25°C for 7 days, a treatment in which snail immune defence is known to be impaired.ConclusionsThese results suggest that the effects of host resistance in determining overall parasite infection success can be overridden by effects of temperature on parasite transmission stages and/or alterations in other host traits than immune defence.

How temperature shifts affect parasite production: testing the roles of thermal stress and acclimation

“…). Correspondingly, a recent comparison of the infection of Lymnaea stagnalis snails exposed to 15 °C or 25 °C for 7 days demonstrated that infection success with the trematode Echinoparyphium aconiatum was higher in snails exposed to the warmer temperature, even when the actual infection was performed at 20 °C (Leicht & Seppälä ). Additionally, the observed increase in snail mortality at higher temperatures in the present study is more consistent with host physiological stress than with improved immune function.…”

Diurnal variation around an optimum and near‐critically high temperature does not alter the performance of an ectothermic aquatic grazer

“…L. stagnalis is a hermaphroditic pulmonate gastropod (thus, no gender‐based differences), with a wide distribution in stagnant or slowly flowing water bodies in the Northern Hemisphere. It is extensively used as a model organism to investigate the effects of warming (e.g., Leicht, Jokela, & Seppälä, ; Salo, Räsänen, Stamm, Burdon, & Seppälä, ; Salo, Stamm, Burdon, Räsänen, & Seppälä, ; Seppälä & Jokela, ) and pollutants (e.g., Coutellec & Lagadic, ; Nyman, Schirmer, & Ashauer, ; Salo et al, ; Salo et al, ) on organisms, as well as host‐parasite interactions (e.g., Karvonen, Savolainen, Seppälä, & Valtonen, ; Leicht & Seppälä, ) and immunology (e.g., Dikkeboom, Knaap, Meuleman, & Sminia, ; Seppälä & Leicht, ). In this species, exposure to high temperatures increases several organismal process rates (Salo et al, ), which leads to increased growth rate and reproductive output with a temporal threshold (1 week), after which the reproductive rate is reduced (Leicht et al, ).…”

“…In this species, exposure to high temperatures increases several organismal process rates (Salo et al, ), which leads to increased growth rate and reproductive output with a temporal threshold (1 week), after which the reproductive rate is reduced (Leicht et al, ). High temperatures also reduce snail immune defense (Leicht et al, ; Salo et al, ; Seppälä & Jokela, ), which increases their susceptibility to trematode parasites (Leicht & Seppälä, ). However, these earlier studies on the effects of warming have all used experimental treatments with constant temperatures.…”

Quality attracts parasites: host condition‐dependent chemo‐orientation of trematode larvae

“…The observed effects can potentially have wide implications on infection dynamics also in relation to other environmental factors than resource availability. In our study system, for example, the effect of high temperature on parasite infection success does not fully reflect alterations observed in snail immune function (Leicht, Jokela & Seppälä ; Leicht & Seppälä ). Also such effects may at least partly reflect alterations in chemical host cues excreted to the environment by snails.…”