Browsing by Author "Kunzmann, Andreas"
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- Acclimation capability inferred by metabolic performance in two sea cucumber species from different latitudesPublication . Kühnhold, Holger; Novais, Sara C.; Alves, Luís M. F.; Kamyab, Elham; Lemos, Marco F. L.; Slater, Matthew J.; Kunzmann, AndreasThe notion that thermal specialists from tropical regions live closer to their temperature limits than temperate eurytherms, seems too generalized. Species specific differences in physiological and biochemical stress reactions are linked to key components of organism fitness, like metabolic capacity, which indicates that acclimation potential across latitudes might be highly diverse rather than simplistic. In this study the exposure of a tropical (Holothuria scabra) and a temperate (Holothuria forskali) sea cucumber species to identical cold- and warmacclimation stress was compared using the key metabolic parameters, respiration rate, enzyme activity (ETS, LDH, IDH), and energy reserve fractions (lipid, carbohydrate and protein). Results show much broader respiratory adjustments, as response to temperature change, in H. scabra (2–30 μgO2*gww−1 *h−1) compared to H. forskali (1.5–6.6 μgO2*gww−1 *h−1). Moreover, the tropical species showed clearly pronounced up and down regulation of metabolic enzymes and shifts in energy reserves, due to thermal acclimation, while the same metabolic indicators remained consistent in the temperate species. In summary, these findings indicate enhanced metabolic plasticity in H. scabra at the cost of elevated energy expenditures, which seems to favor the tropical stenotherm in terms of thermal acclimation capacity. The comparison of such holistic metabolic analyses between conspecifics and congeners, may help to predict the heterogeneous effects of global temperature changes across latitudinal gradients.
- Chemical predator signals induce metabolic suppression in rock goby (Gobius paganellus)Publication . Paul, Nina; Novais, Sara C.; Lemos, Marco F. L.; Kunzmann, AndreasIn nature, a multitude of both abiotic and biotic stressors influence organisms with regard to their overall fitness. Stress responses that finally impair normal biological functions may ultimately result in consequences for whole populations. This study focused on the metabolic response of the intertidal rock pool fish Gobius paganellus towards simulated predation risk. Individuals were exposed to a mixture of skin extracts from conspecifics and chemical alarm cues from a top predator, Octopus vulgaris. Oxygen consumption rates of single fish were measured to establish standard (SMR) and routine metabolic rates (RMR) of G. paganellus, and to address the direct response towards simulated predation risk, compared to handling and light stress. The SMR of G. paganellus (0.0301 ± 0.0081 mg O2 h-1 g-1 WW) was significantly lower than the RMR (0.0409 ± 0.0078 mg O2 h-1 g-1 WW). In contrast to increased respiration due to handling and light stress, the exposure to chemical predation cues induced a significant reduction in oxygen consumption rates (0.0297 ± 0.0077 mg O2 h-1 g-1 WW). This metabolic suppression was interpreted as a result of the stereotypic freezing behaviour as antipredator response of gobiid fish. Results underline the importance of biotic interactions in environmental stress assessments and predation as a biotic factor that will provide more realistic scenarios when addressing stress impacts in tidal rock pool organisms.
- Global warming overrides physiological anti-predatory mechanisms in intertidal rock pool fish Gobius paganellusPublication . Paul, Nina; Novais, Sara C.; Silva, Cátia S. E.; Mendes, Susana; Kunzmann, Andreas; Lemos, Marco F.L.In nature, a multitude of factors influences the fitness of an organismat a given time,whichmakes single stressor assessments far from ecologically relevant scenarios. This study focused on the effects of water temperature and predation stress on the metabolismand bodymass gain of a common intertidal rock pool fish, Gobius paganellus, addressing the following hypotheses: (1) the energy metabolism of G. paganellus under predation stress is reduced; (2) G. paganellus shows thermal compensation under heat stress; and (3) thermal stress is the dominant stressor that may override predation stress responses. Individuals were exposed to simulated predation stress and temperature increase from 20 °C to 29 °C, and both stressors combined. Physiological effects were addressed using biochemical biomarkers related with energy metabolism (isocitrate dehydrogenase, lactate dehydrogenase, energy available, energy consumption rates), oxidative stress (superoxide dismutase, catalase, DNA damage, lipid peroxidation), and biotransformation (glutathione-S-transferase). The results of this study revealed that predation stress reduced the cellular metabolism of G. paganellus, and enhanced storage of protein reserves. As hypothesized, hyperthermia decreased the aerobic mitochondrial metabolism, indicating thermal compensationmechanisms to resist against unfavourable temperatures. Hyperthermia was the dominant stressor overriding the physiological responses to predation stress. Both stressors combined might further have synergistically activated detoxification pathways, even though not strong enough to counteract lipid peroxidation and DNA damage completely. The synergistic effect of combined thermal and predation stress thus may not only increase the risk of being preyed upon, but also may indicate extra energy trade-off for the basal metabolism,which in turnmay have ecologically relevant consequences for general body functions
- Thermal stress effects on energy resource allocation and oxygen consumption rate in the juvenile sea cucumber, Holothuria scabra (Jaeger, 1833)Publication . Kühnhold, Holger; Kamyab, Elham; Novais, Sara; Indriana, Lisa; Kunzmann, Andreas; Slater, Matthew; Lemos, MarcoWater temperature is a key factor in aquaculture production of the commercially valuable sea cucumber Holothuria scabra. Knowledge is scarce about actual energetic costs that can be associated with internal acclimatization processes as a response to thermal extremes. In the present study changes in cellular energy allocation, oxygen consumption rate and energy related enzymes' activity (IDH and LDH) were measured in juvenile H. scabra, held at different temperatures: 21, 27 and 33 °C. The results showed that the steady temperature change (1 °C/day) to both temperature treatments, until reaching the testing temperatures (day 0), clearly affected cellular energy consumption and available energy reserves, measured in the respiratory tree and muscle tissue, respectively. However, 15 and 30 days after acclimation, the initial differences in cellular energy allocation between treatments decreased. In contrast to the variations measured in cellular energy allocation, oxygen consumption was highest at 33 °C and lowest at 21 °C at all three measurement times. Moreover, a significant positive correlation between oxygen consumption rate and temperature was detected at day 15 and day 30. Likewise, a shift from anaerobic to aerobic energy metabolism, indicated by changes in LDH and IDH activities, was observed in the animals from the warm temperature treatment. Results imply that juvenile H. scabra were able to recover from initial disturbances in energy balance, caused by the incremental temperature change of ±6 °C. Over the experimental period of 30 days, elevated temperature did however, lead to a metabolic shift andmore efficient energy turnover, indicated by changes in oxygen consumption rate, LDH and IDH. The synergy of cellular energy allocation and oxygen consumption proved to be a viable indicator to assess the capability of sea cucumbers like H. scabra to cope with extreme temperature conditions. Surprisingly, juvenile H. scabra were able to sustain their energy balance and oxygen consumption rate within the homeostatic range, even at 33 °C. Thus, we assume that rearing temperatures of 33 °C might be possible, which could improve aquaculture production of H. scabra. However, further research is required to understand the mechanisms and effects of acclimation under aquaculture conditions. Statement of relevance: The sea cucumber H. scabra is considered a promising aquaculture candidate in the tropics. The commercial interest in H. scabra has led to a great number of attempts to culture this species e.g. in Madagascar, Tanzania, India and Indonesia, where the farming of this species also showed a great potential to increase the livelihood of the local community. Although, considerable research effort has been put into the advancement of the production cycle, fundamental knowledge, e.g. on physiological adjustments due to suboptimal rearing conditions, remains scarce for H. scabra.Water temperature has been identified as crucial factor, determining production efficiency. In our manuscriptwe introduce an innovative approach, for the assessment of shifts in the energy budget as well as in metabolic pathways, to detect thermal stress in juvenile H. scabra. Our results show that the combined application of cellular energy allocation (CEA) and measurement of the oxygen consumption rate (OCR) as well as the activity of two metabolic key enzymes: iso-citrate dehydrogenase (IDH) and lactate dehydrogenase (LDH), is a strong analytical tool to evaluatewhole animal homeostasis under thermal extremes. To our knowledge this is the first study inwhich the method of CEAwas optimized for the application on isolatedmuscle and respiratory tree tissue of a sea cucumber, like H. scabra.Hence, our results provide original insights into the thermal acclimation physiology of H. scabra, which provides crucial knowledge for setting up optimal culture conditions for this highly valuable aquaculture candidate. Moreover, our results show that juvenile H. scabra were strongly affected by rapid temperature changes, exhibiting distinct differences in metabolic adjustments as response to short-term cold and warm acclimation, but were able to restore homeostatic conditions at constant cold and warm temperature extremes. Concerning aquaculture practices, these findings imply that CEA might be a good condition indicator to evaluate the overall metabolic status in sea cucumbers. Moreover, rapid temperature fluctuations seem to provoke much higher energetic costs in juvenile H. scabra than constant extreme temperature conditions, which is important to consider in daily management practices. The OCR revealed an enhanced metabolism at warmer temperature conditions, throughout the entire experimental period. Likewise, the warm exposed animals were shifting their energy turnover from a more anaerobic to amore aerobic state, indicated by changes in LDH and IDH activities, and showed increased foraging activity at all times. The combined outcome of CEA, OCR and activities of energymetabolismrelated enzymes indicates, that the increased metabolic activity in juvenile H. scabra, as response to warmer temperature, was well within the homeostatic range. Thus, contrary to our expectations, a rearing temperature of up to 33 °C might presumably be favourable for the aquaculture of H. scabra.