Pollution-induced heat shock protein expression in the amphipod Gammarus roeseli is affected by larvae of Polymorphus...

The relationship between the exposure of organisms to chemicals and subsequent alterations in various biochemical processes (commonly referred to as biomarkers) is of growing importance in environmental and ecotoxicological research. However, parasites which also affect the physiological homeostasis of their hosts, and thus may alter biomarker reactions, are usually ignored in environmental research. To address this deficit, we have used the host-parasite system Gammarus roeseli naturally infected with cystacanths of the acanthocephalan Polymorphus minutus to investigate whether infection of gammarids with parasites alters their heat shock protein response following exposure to palladium (Pd). After 24 days of metal exposure relative levels of heat shock protein hsp70 were analysed in the tissues of parasites and intermediate hosts. Simultaneously, the metal accumulation in gammarids and parasites was determined. As none of the infected gammarids showed hsp70 levels at the end of the Pd exposure (either exposed or not), infected and unparasitized G. roeseli were exposed to heat. Again, only uninfected gammarids showed a temperature-dependent increase in hsp70 levels. Interestingly, although the intermediate hosts showed no hsp70 response, exposure to Pd and heat results in increasing hsp70 in the parasites within in the haemocoel of G. roeseli. Heat experiments with isolated cystacanths also showed increasing hsp70 levels in P. minutus with temperature. Concerning uninfected G. roeseli, exposure to Pd and heat causes a hsp70 response. Pd concentrations were found to be higher in the larval parasites than in the gammarids. This result clearly contradicts previous results, as high metal accumulation was so far only described from adult acanthocephalans. Our findings provide experimental evidence that parasites alter the biomarker responses of their host and that the infection status of test animals is extremely important for ecotoxicological studies.