Thermal Preference Ranges Correlate with Stable Signals of Universal Stress Markers in Lake Baikal Endemic and Holarctic Amphipods

Abstract

Temperature is the most pervasive abiotic environmental factor for aquatic organisms. Fluctuations in temperature range lead to changes in metabolic performance. Here, we aimed to identify whether surpassing the thermal preference zones is correlated with shifts in universal cellular stress markers of protein integrity, responses to oxidative stress and lactate content, as indicators of anaerobic metabolism. Exposure of the Lake Baikal endemic amphipod species Eulimnogammarus verrucosus (Gerstfeldt, 1858), Ommatogammarus flavus (Dybowski, 1874) and of the Holarctic amphipod Gammarus lacustris Sars 1863 (Amphipoda, Crustacea) to increasing temperatures resulted in elevated heat shock protein 70 (Hsp70) and lactate content, elevated antioxidant enzyme activities (i.e., catalase and peroxidase), and reduced lactate dehydrogenase and glutathione S-transferase activities. Thus, the zone of stability (absence of any significant changes) of the studied molecular and biochemical markers correlated with the behaviorally preferred temperatures. We conclude that the thermal behavioral responses of the studied amphipods are directly related to metabolic processes at the cellular level. Thus, the determined thermal ranges may possibly correspond to the thermal optima. This relationship between species-specific behavioral reactions and stress response metabolism may have significant ecological consequences that result in a thermal zone-specific distribution (i.e., depths, feed spectrum, etc.) of species. As a consequence, by separating species with different temperature preferences, interspecific competition is reduced, which, in turn, increases a species' Darwinian fitness in its environment.

Fig 1. Distribution of E. verrucosus (n = 5), O. flavus (n = 4) and G. lacustris (n = 5) individuals in an experimental thermal gradient.

Additional information presented in S1 Table.

Fig 2. Mortality of E. verrucosus (n = 7), O. flavus (n = 11) and G. lacustris (n = 7) during exposure to a gradual temperature increase/decrease.

The figure includes data on gradually increasing hypothermia and hyperthermia experiments. Additional information presented in S2 Table.

Fig 3. Hsp70 levels in amphipod species during exposure to gradually changing temperatures.

The figure includes data on gradually increasing hypothermia and hyperthermia experiments. *Indicates a significant difference (p<0.05) from the control (O. flavus: 4°C; for E. verrucosus: 6°C and G. lacustris: 6°C). The dark grey columns and dotted line indicate the control level. Number of replicates: O. flavus (n_control = 4, n_exp. = 4); E. verrucosus (n_control = 8, n_exp. = 5) and G. lacustris (n_control = 5, n_exp. = 5). Additional information presented in S3 Table.

Fig 4. Peroxidase activity (in nKat/mg protein) in amphipod species during exposure to gradually changing temperatures.

The figure includes data on gradually increasing hypothermia and hyperthermia experiments. *Indicates significant difference (p<0.05) from the control (O. flavus: 4°C; for E. verrucosus: 6°C and G. lacustris: 6°C). The dark grey columns and dotted line indicate the control level. Number of replicates: O. flavus (n_control = 6, n_exp. = 4–5); E. verrucosus (n_control = 12, n_exp. = 5–8) and G. lacustris (n_control = 13, n_exp. = 5–8). Additional information presented in S4 Table.

Fig 5. Catalase activity (in nKat/mg protein) in amphipods species during exposure to gradual temperature changes.

The figure compilation includes gradual hypothermia and hyperthermia experiments. *Indicates significant difference (p<0.05) from the control (O. flavus: 4°C; for E. verrucosus: 6°C and G. lacustris: 6°C). The dark grey columns and dotted line indicate the control level. Number of replicates: O. flavus (n_control = 5, n_exp. = 4–5); E. verrucosus (n_control = 12, n_exp. = 5–7) and G. lacustris (n_control = 16, n_exp. = 5–9). Additional information presented in S5 Table.

Fig 6. Glutathione S-transferase activity (in nKat/ mg protein) in amphipod species during exposure to gradual temperature changes.

The figure includes data obtained during increasing hypothermia and hyperthermia. *Indicates a significant difference (p<0.05) from controls (O. flavus: 4°C; for E. verrucosus: 6°C and G. lacustris: 15°C). The dark grey columns and dotted line indicate the control level. *Indicates significant difference (p<0.05) from the control (O. flavus: 4°C; for E. verrucosus: 6°C and G. lacustris: 6°C). The dark grey columns and dotted line indicate the control level. Number of replicates: O. flavus (n_control = 6, n_exp. = 4–5); E. verrucosus (n_control = 12, n_exp. = 5–8) and G. lacustris (n_control = 16, n_exp. = 5–9). Additional information presented in S6 Table.

Fig 7. Lactate content (in μMol/g wet mass) in amphipods species during exposure to gradual temperature changes.

The figure includes data from hypothermia and hyperthermia experiments. *Indicates significant difference (p<0.05) from the control (O. flavus: 4°C; for E. verrucosus: 6°C and G. lacustris: 6°C). The dark grey columns and dotted line indicate the control level. Number of replicates: O. flavus (n_control = 11, n_exp. = 5–7); E. verrucosus (n_control = 13, n_exp. = 5–6) and G. lacustris (n_control = 16, n_exp. = 5–9). Additional information presented in S7 Table.

Fig 8. Lactate dehydrogenase activity (in nKat/ mg protein) in amphipods species during exposure to gradual temperature changes.

The figure includes data from hypothermia and hyperthermia experiments. *Indicates significant difference (p<0.05) from the control (O. flavus: 4°C; for E. verrucosus: 6°C and G. lacustris: 6°C). The dark grey columns and dotted line indicate the control level. Number of replicates: O. flavus (n_control = 6, n_exp. = 4–5); E. verrucosus (n_control = 13, n_exp. = 6–9) and G. lacustris (n_control = 10, n_exp. = 7–9). Additional information presented in S8 Table.