Thermal reaction norms of key metabolic enzymes reflect divergent physiological and behavioral adaptations of closely related amphipod species.

Lake Baikal is inhabited by more than 300 endemic amphipod species, which are narrowly adapted to certain thermal niches due to the high interspecific competition. In contrast, the surrounding freshwater fauna is commonly represented by species with large-scale distribution and high phenotypic thermal plasticity. Here, we investigated the thermal plasticity of the energy metabolism in two closely-related endemic amphipod species from Lake Baikal (Eulimnogammarus verrucosus; stenothermal and Eulimnogammarus cyaneus; eurythermal) and the ubiquitous Holarctic amphipod Gammarus lacustris (eurythermal) by exposure to a summer warming scenario (6-23.6 °C; 0.8 °C d-1). In concert with routine metabolic rates, activities of key metabolic enzymes increased strongly with temperature up to 15 °C in E. verrucosus, whereupon they leveled off (except for lactate dehydrogenase). In contrast, exponential increases were seen in E. cyaneus and G. lacustris throughout the thermal trial (Q10-values: 1.6-3.7). Cytochrome-c-oxidase, lactate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase activities were found to be higher in G. lacustris than in E. cyaneus, especially at the highest experimental temperature (23.6 °C). Decreasing gene expression levels revealed some thermal compensation in E. cyaneus but not in G. lacustris. In all species, shifts in enzyme activities favored glycolytic energy generation in the warmth. The congruent temperature-dependencies of enzyme activities and routine metabolism in E. verrucosus indicate a strong feedback-regulation of enzymatic activities by whole organism responses. The species-specific thermal reaction norms reflect the different ecological niches, including the spatial distribution, distinct thermal behavior such as temperature-dependent migration, movement activity, and mating season.

Uptake Kinetics and Subcellular Compartmentalization Explain Lethal but Not Sublethal Effects of Cadmium in Two Closely Related Amphipod Species.

Eulimnogammarus cyaneus and Eulimnogammarus verrucosus, closely related amphipod species endemic to Lake Baikal, differ with respect to body size (10- to 50-fold lower fresh weights of E. cyaneus) and cellular stress response (CSR) capacity, potentially causing species-related differences in uptake, internal sequestration, and toxic sensitivity to waterborne cadmium (Cd). We found that, compared to E. verrucosus, Cd uptake rates, related to a given exposure concentration, were higher, and lethal concentrations (50%; LC50) were 2.3-fold lower in E. cyaneus (4 weeks exposure; 6 °C). Upon exposures to species-specific subacutely toxic Cd concentrations (nominal LC1; E. cyaneus: 18 nM (2.0 µg L-1); E. verrucosus: 115 nM (12.9 µg L-1); 4 weeks exposure; 6 °C), Cd amounts in metal sensitive tissue fractions (MSF), in relation to fresh weight, were similar in both species (E. cyaneus: 0.25 ± 0.06 µg g-1; E. verrucosus: 0.26 ± 0.07 µg g-1), whereas relative Cd amounts in the biologically detoxified heat stable protein fraction were 35% higher in E. cyaneus. Despite different potencies in detoxifying Cd, body size appears to mainly explain species-related differences in Cd uptake and sensitivities. When exposed to Cd at LC1 over 4 weeks, only E. verrucosus continuously showed 15-36% reduced oxygen consumption rates indicating metabolic depression and pointing to particular sensitivity of E. verrucosus to persisting low-level toxicant pressure.

On Eulimnogammarus messerschmidtii, sp. n. (Amphipoda: Gammaridea) from Lake Baikal, Siberia, with redescription of E. cyanoides (Sowinsky) and remarks on taxonomy of the genus Eulimnogammarus.

A new amphipod species of the endemic fauna of Lake Baikal (East Siberia, Russia), Eulimnogammarus messerschmidtii sp. n., from the littoral zone of the northern part of the lake is described. The species is characterized by the presence of a group of spines with dense setae on the last 4 body segments. The basal peduncular segment of antenna 1 bears bunches of dense setae without spines, uropods 3 are covered by dense simple setae without plumose setae and the outer ramus has a second small article. The body length of sampled specimens ranges from 7.5 to 18 mm. Population analysis at one of the sampling points revealed a spring-summer reproduction period for this species. This species was previously erroneously identified as E. cyanoides. E. cyanoides is here redescribed in details based on the lectotype. The differences between E. messerschmidtii sp. n., E. cyanoides and other closely related Eulimnogammarus species are described. The taxonomy of the genus Eulimnogammarus is discussed.

A cellular and metabolic assessment of the thermal stress responses in the endemic gastropod Benedictia limnaeoides ongurensis from Lake Baikal.

Our objective was to determine if the Lake Baikal endemic gastropod Benedictia limnaeoides ongurensis, which inhabits in stable cold waters expresses a thermal stress response. We hypothesized that the evolution of this species in the stable cold waters of Lake Baikal resulted in a reduction of its thermal stress-response mechanisms at the biochemical and cellular levels. Contrary to our hypothesis, our results show that exposure to a thermal challenge activates the cellular and biochemical mechanisms of thermal resistance, such as heat shock proteins and antioxidative enzymes, and alters energetic metabolism in B. limnaeoides ongurensis. Thermal stress caused the elevation of heat shock protein 70 and the products of anaerobic glycolysis together with the depletion of glucose and phosphagens in the studied species. Thus, a temperature increase activates the complex biochemical system of stress response and alters the energetic metabolism in this endemic Baikal gastropod. It is concluded that the deepwater Lake Baikal endemic gastropod B. limnaeoides ongurensis retains the ability to activate well-developed biochemical stress-response mechanisms when exposed to a thermal challenge.

Optical diagnostic test of stress conditions of aquatic organisms.

Global climate change has become a dire reality and its impact is expected to rise dramatically in the near future. Combined with the day-to-day human activities the climatic changes heavily affect the environment. In particular, a global temperature increase accompanied by a number of anthropogenic chemicals falling within the freshwater ecosystem results in a dramatic enhancement of the overall stress for most aquatic organisms. This leads to a significant shift in the species inventory and potential breakdown of the water ecosystem with severe consequences for local economies and water supply. In order to understand and predict the influence of climatic changes on the physiological and biochemical processes that take place in living aquatic organisms we explore the application of optical spectroscopy for monitoring and quantitative assessment of antioxidant enzymes activity in benthic amphipods of Lake Baikal. We demonstrate that the changes of the enzymes activity in Baikal amphipods undergoing thermal and/or hypoxia stress can be observed and documented by UV and optical spectroscopy both in vivo and in vitro.