Salinity modulates thermotolerance, energy metabolism and stress response in amphipodsGammarus lacustris

Abstract

Temperature and salinity are important abiotic factors for aquatic invertebrates. We investigated the influence of different salinity regimes on thermotolerance, energy metabolism and cellular stress defense mechanisms in amphipods Gammarus lacustris Sars from two populations. We exposed amphipods to different thermal scenarios and determined their survival as well as activity of major antioxidant enzymes (peroxidase, catalase, glutathione S-transferase) and parameters of energy metabolism (content of glucose, glycogen, ATP, ADP, AMP and lactate). Amphipods from a freshwater population were more sensitive to the thermal challenge, showing higher mortality during acute and gradual temperature change compared to their counterparts from a saline lake. A more thermotolerant population from a saline lake had high activity of antioxidant enzymes. The energy limitations of the freshwater population (indicated by low baseline glucose levels, downward shift of the critical temperature of aerobic metabolism and inability to maintain steady-state ATP levels during warming) was observed, possibly reflecting a trade-off between the energy demands for osmoregulation under the hypo-osmotic condition of a freshwater environment and protection against temperature stress.

Nonspecific stress response to temperature increase in Gammarus lacustris Sars with respect to oxygen-limited thermal tolerance concept

“…Our previous study (Vereshchagina et al, 2016) found elevated levels of antioxidant enzyme activity for catalase and glutathione S-transferase in saltwater G. lacustris when compared to the freshwater population. These high levels suggest higher constitutive levels of NCSR in cells; however further research is required to confirm the causes of the observed differences.…”

“…In concentrations over 4 mM (Fregoso-Peñuñuri et al, 2017), pyruvate is capable of inhibiting the enzyme activity in crustaceans. In another study, we demonstrated the elevation of adenosine triphosphate (ATP) and the depletion of glucose content in the first phases of exposure to gradual temperature increase when starting from 13 °C (Vereshchagina et al, 2016). This also denotes the activation of glucose oxygen catabolism.…”

“…The time taken for 50% of individuals held at 30 °C to reach mortality (LT50) is 15.1 hours less in freshwater specimens than in those from saltwater populations (Vereshchagina et al, 2016). Additionally, the thermal tolerance of these saltwater populations is associated with a lower metabolic cost than in freshwater populations.…”

“…There is a lower energetic demand associated with sustaining osmotic pressure for G. lacustris individuals in a salt lake, as the water is isoosmotic to the hemolymph of saltwater amphipods. In contrast, the freshwater populations live in a hypoosmotic environment, which is costly on metabolic energy and affects their ability to provide energy for NCSR (Vereshchagina et al, 2016). …”

“…In our previous studies we investigated inter-populational differences of energy metabolism during gradual warming in two distant populations of the common Holarctic amphipod Gammarus lacustris Sars, 1863 (Vereshchagina et al, 2016) from freshwater and saline lakes, and NCSR capacity of this species from the freshwater reservoir (Axenov-Gribanov et al, 2016). …”