Adaptations in a freshwater shrimp (Gammarus pulex) to increased salinity: Which responses boost survival?

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Abstract

Increased salinity of inland waters directly or indirectly has an effect on benthic communities, by influencing the behaviour as well as the physiology of the organisms. In a comparative study, we investigated traits and adaptations of the freshwater shrimp Gammarus pulex from two confluent streams with different salinity levels, situated in undulating lowland of northwest Germany - Central Europe (Saltwater Creek SWC: 6.0 to 7.5 g/L NaCl, Freshwater Creek FCW: approx. 0.3 g/L NaCl). In the SWC, G. pulex lives in the fringe range of physiological tolerance described for the species. The study targeted the mechanism that allows G. pulex, using with salinity as a case example, for extension of its distribution range along an environmental gradient and outlasting of extreme physiological conditions. Between 2012 and 2015, macrozoobenthic communities were sampled semi-quantitatively (based on area-time-reference), and abiotic environmental variables were recorded during each sampling campaign. In laboratory analyses, G pulex populations were tested for morphological parameters and age structure, physical performance, glycogen contents, and as a measure of stress response for hsp70-expression at a 27°C heat shock. G. pulex dominates in both benthic communities with SWC harbouring a significantly poorer and uneven taxa diversity compared to FWC. Contrarily thereto, G. pulex found in SWC represents a stable population. Morphological and experimental analyses revealed that G. pulex from the SWC showed a complex combination of ecological and physiological traits, with differences to FWC individuals being predominantly significant: females have a lower body weight, yet physical activity of both sexes is higher in saltwater gammarids, but also decreases faster during keeping time of one month. At the same time, mortality raises notably. Short-term energy storage, determined by glycogen content, is greater, and base level of hsp70 as well as intensity of expression following heat induced stress is markedly more intense. Based on these findings, we conclude that G. pulex tolerates elevated salinity levels by boosting metabolic turnover which apparently only can be maintained under natural conditions of relative system steadiness and availability of resources. Questions to what extent these mechanisms explain specific salinity tolerance of G. pulex, or whether the response pattern found mirrors a general potential of euryoeciousness and thus invasiveness, should motivate further specific investigations.

Speakers from the University of Münster

Meyer, Elisabeth Irmgard	Department of Limnology
Philipp, Berit Katrina	Professur für Molekulare Mikrobiologie und Biotechnologie (Prof. Philipp)
Riss, Hans-Wolfgang	Department of Limnology
Schmidt, Alexander	Department of Limnology