Effect of multiple parasitic infections on the tolerance to pollutant contamination

Abstract

The horizontally-transmitted acanthocephalan parasite Polymorphus minutus and the vertically-transmitted microsporidian parasite Dictyocoela roeselum have both been shown to influence on the antitoxic responses of mono-infected Gammarus roeseli exposed to cadmium. The present study investigates the effect of this co-infection on the antitoxic defence responses of naturally infected females exposed to cadmium stress. Our results revealed that, depending on the cadmium dose, bi-infection induced only slight, significant increased cell damage in G. roeseli as compared to non-infection. In addition, the antitoxic defence pattern of cadmium-exposed bi-infected hosts was similar to the pattern of cadmium-exposed D. roeselum-infected hosts. Reduced glutathione concentrations, carotenoid levels and γ-glutamylcystein ligase activity decreased, while metallothionein concentrations increased. This similar pattern indicates that host physiology can be controlled to some extent by microsporidia under stress conditions. It supports the hypothesis of a disruption of acanthocephalan effects in the presence of microsporidia. However, the global negative effects of bi-infection on host condition should be tested on more biological models, since competition between parasites depends on life history trade-off.

Figure 1. Influence of the presence of P. minutus and/or D. roeselum on energy and defences biomarkers of Gammarus roeseli females exposed to 2 and 8 µg Cd/L for 96 hrs.

Pm: P. minutus-infected females, Dr: D. roeselum-infected females, Pm/Dr: bi-infected females. Different letters above the bars indicate significantly different values (Tukey's HSD test, p-values<0.05).

Figure 2. Integrated Biomarker Responses measured in G. roeseli exposed to 2 and 8 µg Cd/L for 96 hrs.

Pm: P. minutus-infected females, Dr: D. roeselum-infected females, Pm/Dr: co-infected females. IBR values include defence responses (GSH, GCL, MT, carotenoids) and MDA responses.

Figure 3. Malondialdehyde levels measured in the acanthocephalan parasite P. minutus dissected from P. minutus-infected G. roeseli females (Pm) and from P. minutus/D. roeselum-bi-infected females (Pm/Dr) exposed to 2 and 8 µg Cd/L.

Different letters above the bars indicate significantly different values (Tukey's HSD test, p-values<0.05).