Thermal sensitivity of cell metabolism of different Antarctic fish species mirrors organism temperature tolerance

Despite cold adaptation, Antarctic fish show lower growth than expected from the van’t Hoff’s Q10 rule. Protein synthesis is one of the main energy-consuming processes, which is downregulated under energy deficiency. Considering the effect of temperature on growth performance, we tested if temperature-dependent cellular energy allocation to protein synthesis correlates with temperature-dependent whole-animal growth and thus thermal tolerance. Cell respiration and energy expenditure for protein synthesis were determined in hepatocytes of the circumpolar-distributed Antarctic eelpout Pachycara brachycephalum after warm acclimation (0 °C vs 5 °C) and, of two notothenioids the sub-Antarctic Lepidonotothen squamifrons and the high-Antarctic icefish Chionodraco hamatus. We used intermittent-flow respirometry to analyse cellular response to acute warming from 5 to 10 °C (P. brachycephalum) and from 1 to 5 °C (L. squamifrons, C. hamatus). Warming-induced rise in respiration was similar between 0- and 5 °C-acclimated P. brachycephalum and between L. squamifrons and C. hamatus. Irrespective of acclimation, warming decreased energy expenditure for protein synthesis in P. brachycephalum, which corresponds to reduced whole-animal growth at temperatures > 5 °C. Warming doubled energy expenditure for protein synthesis in L. squamifrons but had no effect on C. hamatus indicating that L. squamifrons might benefit from warmer waters. The species-specific temperature effect on energy expenditure for protein synthesis is discussed to mirror thermal sensitivity of whole-animal growth performance, thereby paralleling the degree of cold adaptation. Clearly more data are necessary including measurements at narrower temperature steps particularly for C. hamatus and an increased species’ number per ecotype to reinforce presented link between cellular and whole-animal thermal sensitivity

Naturally acidified habitat selects for ocean acidification–tolerant mussels

Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated Pco2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, Pco2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change

Intra-spezifische Unterschiede in Effekten von Ozeanversauerung auf marine Muscheln und Austern: integrative physiologische Studien am isolierten Gewebe und Gesamtorganismus

Ocean acidification (OA), caused by the oceanic uptake of anthropogenic CO2, is predicted to negatively affect marine mussels and oysters. In addition, the rapid rate at which OA occurs may outpace species’ ability to genetically adapt, leaving pre-existing genetic variation as a potential key to species resilience under OA. Against this backdrop, this thesis investigated the physiological mechanisms underlying intra-specific variation of OA sensitivity of Kiel Fjord blue mussels (Mytilus edulis) and Sydney rock oysters (Saccostrea glomerata). A long-term CO2 acclimation experiment with different family lines of blue mussel revealed that families whose offspring successfully settled at all experimental PCO2 levels (control, intermediate and high PCO2 level) were characterised by an inherently higher metabolic capacity at the whole animal and the cellular level compared to more sensitive family lines, whose offspring failed to survive at the highest experimental PCO2. This increased metabolic scope of tolerant family lines seems to cover elevated metabolic costs at the intermediate PCO2, however; at the highest PCO2, filtration rates and gill aerobic capacity declined, indicating an unfavourable shift in energy demand and supply. A second comparative CO2 acclimation study between a wild population of Sydney rock oysters and a more CO2 tolerant aquaculture line (selected for faster growth) showed that, in contrast to wild oysters, selected oysters were able to avoid a CO2-induced drop of extracellular pH, likely facilitated by an increased capacity for systemic CO2 release due to higher and more energetically efficient filtration rates. In conclusion, the observed pre-existing intra-specific variation in both species suggests potential adaptive capacities. However, as the physiology of marine bivalves is tightly linked with their functions within ecosystems, observed negative OA effects could have far reaching consequences at an ecosystem scale