Untersuchungen zur molekularen Anpassungsfähigkeit an den abiotischen Schlüsselfaktor Temperatur am Beispiel der antarktischen Aalmutter

Evolutionary adaptation and the connected acclimation capacity of species to changing environmental conditions represents one of the key factors in the composition and dynamics of any ecosystem. In marine environments temperature is one of the major factors defining the aquatic fauna. In respect to progressing climate change the question arises how individual species react to higher temperatures and how this affects the entire ecosystem. Species that are highly specialized on stable environmental conditions seem to be especially vulnerable. This thesis characterizes the Antarctic eelpout Pachycara brachycephalum (Pappenheim, 1912) in regards to its adaptation to low habitat temperatures as well as its capacity to acclimate to higher temperatures at the molecular level

Transcriptome sequencing of a keystone aquatic herbivore yields insights on the temperature-dependent metabolism of essential lipids

Abstract Background: Nutritional quality of phytoplankton is a major determinant of the trophic transfer efficiency at the plant-herbivore interface in freshwater food webs. In particular, the phytoplankton’s content of the essential polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA) has been repeatedly shown to limit secondary production in the major zooplankton herbivore genus Daphnia. Despite extensive research efforts on the biological model organism Daphnia, and the availability of several Daphnia genomes, little is known regarding the molecular mechanisms underlying the limitations in Daphnia related to dietary EPA availability. Results: We used RNA-seq to analyse the transcriptomic response of Daphnia magna which were fed with two different diets — each with or without supplementation of EPA — at two different temperature levels (15 and 20°C). The transcripts were mapped to the D. magna genome assembly version 2.4, containing 26,646 translations. When D. magna fed on green alga, changing the temperature provoked a differential expression of 2,001 transcripts, and in cyanobacteria-fed daphnia, 3,385 transcripts were affected. The supplementation of EPA affected 1,635 (on the green algal diet), or 175 transcripts (on the cyanobacterial diet), respectively. Combined effects for diet and temperature were also observed (669 for the green algal and 128 transcripts for the cyanobacterial diet). Searching for orthologous genes (COG-analysis) yielded a functional overview of the altered transcriptomes. Cross-matched transcript sets from both feed types were compiled to illuminate core responses to the factors temperature and EPA-supplementation. Conclusions: Our highly controlled eco-physiological experiments revealed an orchestrated response of genes involved in the transformation and signalling of essential fatty acids, including eicosanoid-signalling pathways with potential immune functions. We provide an overview of downstream-regulated genes, which contribute to enhance growth and reproductive output. We also identified numerous EPA-responsive candidate genes of yet unknown function, which constitute new targets for future studies on the molecular basis of EPA-dependent effects at the freshwater plant-herbivore interface.</jats:p

Transcriptome sequencing of a keystone aquatic herbivore yields insights on the temperature-dependent metabolism of essential lipids

Abstract Background: Phytoplankton dietary quality is the major determinant of the trophic transfer efficiency at the plant-herbivore interface in freshwater food webs. In particular, the phytoplankton’s content of the essential polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA) has repeatedly been shown to determine the secondary production in the major zooplankton herbivore genus Daphnia. Despite extensive research efforts on the biological model organism Daphnia and the availability of several Daphnia genomes, little is known on the molecular mechanisms underlying the limitation of Daphnia by dietary EPA availability. Results: Here, we used RNAseq to analyse the transcriptomic response of Daphnia magna fed with diets with or without EPA to specifically analyse gene-networks and pathways that are driven by dietary EPA availability. Since EPA is – among other functions – critical to the adaptation of poikilothermic organisms to low environmental temperatures, we ran our experiment at two temperature levels to investigate potentially constrained physiological responses to EPA availability at lower temperatures. Here, trade-offs between food quality and homeoviscous adjustments of biological membranes are expected through the incorporation of polyunsaturated fatty acids. Conclusions: Our highly controlled eco-physiological experiments revealed an orchestrated response of genes involved in transformation and signalling of the essential fatty acid, including eicosanoid-signalling pathways with potential immune functions. We provide an overview of downstream-regulated genes, which contribute to enhance growth and reproductive output. We also identified numerous EPA-responsive candidate genes of yet unknown function, which constitute new targets for future studies on the molecular basis of EPA-dependent effects at the freshwater plant-herbivore interface.</jats:p

Transcriptome sequencing of a keystone aquatic herbivore yields insights on the temperature-dependent metabolism of essential lipids

Abstract Background: Nutritional quality of phytoplankton is a major determinant of the trophic transfer efficiency at the plant-herbivore interface in freshwater food webs. In particular, the phytoplankton’s content of the essential polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA) has been repeatedly shown to limit secondary production in the major zooplankton herbivore genus Daphnia. Despite extensive research efforts on the biological model organism Daphnia, and the availability of several Daphnia genomes, little is known regarding the molecular mechanisms underlying the limitations in Daphnia related to dietary EPA availability. Results: We used RNA-seq to analyse the transcriptomic response of Daphnia magna which were fed with two different diets — each with or without supplementation of EPA — at two different temperature levels (15 and 20°C). The transcripts were mapped to the D. magna genome assembly version 2.4, containing 26,646 translations. When D. magna fed on green alga, changing the temperature provoked a differential expression of 2,001 transcripts, and in cyanobacteria-fed daphnia, 3,385 transcripts were affected. The supplementation of EPA affected 1,635 (on the green algal diet), or 175 transcripts (on the cyanobacterial diet), respectively. Combined effects for diet and temperature were also observed (669 for the green algal and 128 transcripts for the cyanobacterial diet). Searching for orthologous genes (COG-analysis) yielded a functional overview of the altered transcriptomes. Cross-matched transcript sets from both feed types were compiled to illuminate core responses to the factors temperature and EPA-supplementation. Conclusions: Our highly controlled eco-physiological experiments revealed an orchestrated response of genes involved in the transformation and signalling of essential fatty acids, including eicosanoid-signalling pathways with potential immune functions. We provide an overview of downstream-regulated genes, which contribute to enhance growth and reproductive output. We also identified numerous EPA-responsive candidate genes of yet unknown function, which constitute new targets for future studies on the molecular basis of EPA-dependent effects at the freshwater plant-herbivore interface.</jats:p

Transcriptome sequencing of a keystone aquatic herbivore yields insights on the temperature-dependent metabolism of essential lipids

Abstract Background: Nutritional quality of Phytoplankton is the major determinant of the trophic transfer efficiency at the plant-herbivore interface in freshwater food webs. In particular, the phytoplankton’s content of the essential polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA) has been repeatedly shown to limit secondary production in the major zooplankton herbivore genus Daphnia . Despite extensive research efforts on the biological model organism Daphni a, and the availability of several Daphnia genomes, little is known regarding the molecular mechanisms underlying the limitations in Daphnia relating to dietary EPA availability. Results: We used RNA-seq to analyse the transcriptomic response of Daphnia magna which were fed with two different diets — each with or without supplementation of EPA — at two different temperature levels (15 and 20°C). The transcripts were mapped to the D. magna genome assembly version 2.4, containing 26,646 translations. From the D. magna fed on green alga, changing the temperature provoked a differential expression of 2,001 transcripts, and in cyanobacteria-fed daphnia, 3,385 transcripts were affected. The supplementation of EPA affected 1,635 (green algal diet), or 175 transcripts (cyanobacterial diet) respectively. Combined effects were also observed (669 for green alga and 128 transcripts for cyanobacterial diet). Searching for orthologous genes (COG-analysis) yielded a functional overview of the altered transcriptomes. Cross matched transcript sets from both feed-types were compiled to illuminate core responses to the factors of temperature and EPA-supplementation. Conclusions: Our highly controlled eco-physiological experiments revealed an orchestrated response of genes involved in the transformation and signalling of essential fatty acids, including eicosanoid-signalling pathways with potential immune functions. We provide an overview of downstream-regulated genes, which contribute to enhance growth and reproductive output. We also identified numerous EPA-responsive candidate genes of yet unknown function, which constitute new targets for future studies on the molecular basis of EPA-dependent effects at the freshwater plant-herbivore interface.</jats:p

Monitoring a loss: Detection of the semi-aquatic crocodile lizard (Shinisaurus crocodilurus) in inaccessible habitats via environmental DNA

Assessing the conservation status of a species is strongly dependent upon data on species distribution and abundance. With the emergence of novel methods for species monitoring - such as the use of environmental DNA (eDNA) - monitoring success can be improved at reduced expenditure in the field, particularly in remote regions and terrains where access is difficult or dangerous. The highly endangered crocodile lizard (Shinisaurus crocodilurus Ahl, 1930) inhabits fragmented sites of the remaining evergreen forest with running water systems in a narrow distribution range in southern China and north-east Vietnam. Crocodile lizards spend most of the day within or above water bodies, which are commonly remote and inaccessible. To monitor recent spatial occurrences, and to confirm the persistence or extinction of previously reported populations (especially in heavily altered habitats), the suitability of using eDNA and quantitative polymerase chain reaction (qPCR) was tested as an alternative method for monitoring this semiaquatic lizard. To assess the accuracy and limitations of this method, eDNA results from the field were compared with eDNA data from mesocosms and census data on the actual abundance of this species in the field. Environmental DNA of the crocodile lizard was detected in all of the positive controls, and in four of six natural sites; thus, all data collected using traditional field surveys were confirmed with eDNA results. eDNA monitoring was found to be a reliable method for assessing the viability of populations; we suggest that it should be developed as a tool for efficient wildlife management, particularly under difficult field and funding conditions

Hepatic Transcriptomic Responsiveness of Polar Cod, <i>Boreogadus saida</i>, to Ocean Acidification and Warming

Background: This study was part of a larger comprehensive project (BIOACID) addressing the physiological resilience of Polar cod, Boreogadus saida, to ocean acidification and global warming and aimed to unravel underlying molecular mechanisms of the observed physiological responses. Methods: Fish were acclimated long-term to three CO2 concentrations comprising control conditions (390 ppm) and two projected climate scenarios (780 ppm and 1170 ppm). Each CO2 treatment was combined with four temperatures: 0, 3, 6, and 8 °C. Here, we focused on the hepatic transcriptomic profiles from these previously physiologically characterized fish. Results: Generally, we did not detect signs of a classical stress response. Consistent with functional observations, warming induced much stronger molecular responses compared to elevated PCO2, but an interaction between both factors existed to some extent. Gene ontology analysis revealed a strong response in lipid, amino acid, and protein metabolism. With increasing temperature, we observed a shift away from lipid metabolism, while carbohydrate metabolic pathways remained stable. Conclusions: Although we found Polar cod to be quite resilient to ocean acidification, temperature will remain a critical parameter for this valuable Arctic keystone species, and the question remains as to whether the observed acclimation strategies can be implemented in its natural habitat, especially when food supply is limited

Differences in neurochemical profiles of two gadid species under ocean warming and acidification

Abstract Background Exposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. So far, most studies investigated effects of ocean acidification on the behaviour of fish, either isolated or in combination with environmental temperature. However, only few physiological studies on this issue were conducted despite the putative neurophysiological origin of the CO2-induced behavioural changes. Here, we present the metabolic consequences of long-term exposure to projected ocean acidification (396–548 μatm PCO2 under control and 915–1272 μatm under treatment conditions) and parallel warming in the brain of two related fish species, polar cod (Boreogadus saida, exposed to 0 °C, 3 °C, 6 °C and 8 °C) and Atlantic cod (Gadus morhua, exposed to 3 °C, 8 °C, 12 °C and 16 °C). It has been shown that B. saida is behaviourally vulnerable to future ocean acidification scenarios, while G. morhua demonstrates behavioural resilience. Results We found that temperature alters brain osmolyte, amino acid, choline and neurotransmitter concentrations in both species indicating thermal responses particularly in osmoregulation and membrane structure. In B. saida, changes in amino acid and osmolyte metabolism at the highest temperature tested were also affected by CO2, possibly emphasizing energetic limitations. We did not observe changes in neurotransmitters, energy metabolites, membrane components or osmolytes that might serve as a compensatory mechanism against CO2 induced behavioural impairments. In contrast to B. saida, such temperature limitation was not detected in G. morhua; however, at 8 °C, CO2 induced an increase in the levels of metabolites of the glutamate/GABA-glutamine cycle potentially indicating greater GABAergic activity in G.morhua. Further, increased availability of energy-rich substrates was detected under these conditions. Conclusions Our results indicate a change of GABAergic metabolism in the nervous system of Gadus morhua close to the optimum of the temperature range. Since a former study showed that juvenile G. morhua might be slightly more behaviourally resilient to CO2 at this respective temperature, we conclude that the observed change of GABAergic metabolism could be involved in counteracting OA induced behavioural changes. This may serve as a fitness advantage of this respective species compared to B. saida in a future warmer, more acidified polar ocean

Thermal acclimation in Antarctic fish: Transcriptomic profiling of metabolic pathways

It is widely accepted that adaptation to the extreme cold has evolved at the expense of high thermal sensitivity. However, recent studies have demonstrated significant capacities for warm acclimation in Antarctic fishes. Here, we report on hepatic metabolic reorganisation and its putative molecular background in the Antarctic eelpout Pachycara brachycephalum during warm acclimation to 5°C over six weeks. Elevated capacities of cytochrome c oxidase suggest the use of warm acclimation pathways different from those in temperate fish. The capacity of this enzyme rose by 90%, while citrate synthase (CS) activity fell by 20% from the very beginning. The capacity of lipid oxidation by hydroxyacyl-CoA dehydrogenase remained constant, whereas phosphoenolpyruvate carboxykinase as a marker for gluconeogenesis displayed 40% higher activities. These capacities in relation to CS indicate a metabolic shift from lipid to carbohydrate metabolism. The finding was supported by large rearrangements of the related transcriptome, both functional genes and potential transcription factors. A multivariate analysis (canonical correspondence analyses) of various transcripts subdivided the incubated animals in three groups, one control group and two responding on short and long timescales, respectively. A strong dichotomy in the expression of PPAR1α and ~β receptors was most striking and has not previously been reported. Altogether, we identified a molecular network, which responds sensitively to warming beyond the realized ecological niche. The shift from lipid to carbohydrate stores and usage may support "warm-hardiness", as the latter sustain anaerobic metabolism and may prepare for hypoxemic conditions that would develop upon warming beyond the present acclimation temperature