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Abstract: This study comparatively evaluated small heat shock proteins (sHSP) (related to α-crystallin) and antioxidant enzymes such as peroxidase (POD), catalase (CAT), glutathione S-transferase (GST) as anti-thermal stress response in two contrasting freshwater amphipods, the stenoecious Baikalean endemic Eulimnogammarus cyaneus and the Palearctic Gammarus lacustris. The thermal stress modulated the activity of antioxidant enzymes as well as the sHSP synthesis in both species. In both species, only the declining POD activity showed a clear dependency on exposure time. The most expressed response to elevated temperatures has been the activation of sHSP synthesis, with clear differences in the patterns: in G. lacustris, sHSP concentrations peaked after 12h with a subsequent decline, while they increased steadily in E. cyaneus. Hence, the stenoecious species did not acclimate to the thermal stress within the given exposure time as the euryecious did. [Copyright &y& Elsevier]

Abstract: The aim of this study was to clarify the significance of HSP70 and sHSP for thermotolerance in freshwater amphipods. We compared four amphipod species from different freshwater habitats and biogeographical regions (Central Europe vs. Lake Baikal). Test individuals were exposed to thermal stress generated by a water temperature of 25°C. The thermotolerance of the species, determined by median lethal time (LT50), followed in decreasing order by Gmelinoides fasciatus, Echinogammarus berilloni, Gammarus pulex, Eulimnogammarus verrucosus. HSP70 and sHSP base level concentrations for the species were determined at control (i.e. non-stress) conditions. For HSP70, the base levels were positively correlated to the species'' thermotolerances. For sHSP, however, only thermotolerant G. fasciatus showed a high level. Thermal stress at 25°C water temperature caused a deferred onset of HSP70 and sHSP expression followed by a subsequent offset, delineating a unimodal response curve. The time lag to the expression onset of HSP70 was shorter in the thermosensitive species, compared to thermotolerant ones. Conversely, the time span until the maximum level of HSP70 was variable, not showing a dependence on the thermotolerance properties of the species. The peak concentration in G. pulex was distinctly higher than in the other species, whereas E. verrucosus did not develop a well-defined response maximum at all. In sHSP, the temporal pattern of expression was even more variable than in HSP70. However, the thermosensitive species E. verrucosus showed a time lag of expression onset significantly shorter than the other species and thermotolerant G. fasciatus developed the most pronounced response maximum. Basing on these results, the cellular response to thermal stress in amphipods is more consistently reflected by HSP70, compared to sHSP. [Copyright &y& Elsevier]