Hans Poertner - Academia.edu (original) (raw)

Papers by Hans Poertner

Journal of Experimental Biology, 2010

The concept of oxygen-and capacity-dependent thermal tolerance in aquatic ectotherms has successf... more The concept of oxygen-and capacity-dependent thermal tolerance in aquatic ectotherms has successfully explained climateinduced effects of rising temperatures on species abundance in the field. Oxygen supply to tissues and the resulting aerobic performance characters thus form a primary link between organismal fitness and its role and functioning at the ecosystem level. The thermal window of performance in water breathers matches their window of aerobic scope. Loss of performance reflects the earliest level of thermal stress, caused by hypoxaemia and the progressive mismatch of oxygen supply and demand at the borders of the thermal envelope. Oxygen deficiency elicits the transition to passive tolerance and associated systemic and cellular stress signals like hormonal responses or oxidative stress as well as the use of protection mechanisms like heat shock proteins at thermal extremes. Thermal acclimatization between seasons or adaptation to a climate regime involves shifting thermal windows and adjusting window widths. The need to specialize on a limited temperature range results from temperaturedependent trade-offs at several hierarchical levels, from molecular structure to whole-organism functioning, and may also support maximized energy efficiency. Various environmental factors like CO 2 (ocean acidification) and hypoxia interact with these principal relationships. Existing knowledge suggests that these factors elicit metabolic depression supporting passive tolerance to thermal extremes. However, they also exacerbate hypoxaemia, causing a narrowing of thermal performance windows and prematurely leading the organism to the limits of its thermal acclimation capacity. The conceptual analysis suggests that the relationships between energy turnover, the capacities of activity and other functions and the width of thermal windows may lead to an integrative understanding of specialization on climate and, as a thermal matrix, of sensitivity to climate change and the factors involved. Such functional relationships might also relate to climate-induced changes in species interactions and, thus, community responses at the ecosystem level.

PLoS ONE, 2013

Antarctic notothenioid fish are characterized by their evolutionary adaptation to the cold, therm... more Antarctic notothenioid fish are characterized by their evolutionary adaptation to the cold, thermostable Southern Ocean, which is associated with unique physiological adaptations to withstand the cold and reduce energetic requirements but also entails limited compensation capacities to environmental change. This study compares the capacities of mitochondrial acclimation to ocean warming and acidification between the Antarctic nototheniid Notothenia rossii and the sub-Antarctic Lepidonotothen squamifrons, which share a similar ecology, but different habitat temperatures. After acclimation of L. squamifrons to 9uC and N. rossii to 7uC (normocapnic/hypercapnic, 0.2 kPa CO 2 /2000 ppm CO 2 ) for 4-6 weeks, we compared the capacities of their mitochondrial respiratory complexes I (CI) and II (CII), their P/O ratios (phosphorylation efficiency), proton leak capacities and mitochondrial membrane fatty acid compositions. Our results reveal reduced CII respiration rates in warm-acclimated L. squamifrons and cold hypercapnia-acclimated N. rossii. Generally, L. squamifrons displayed a greater ability to increase CI contribution during acute warming and after warm-acclimation than N. rossii. Membrane unsaturation was not altered by warm or hypercapnia-acclimation in both species, but membrane fatty acids of warm-acclimated L. squamifrons were less saturated than in warm normocapnia2/hypercapnia-acclimated N. rossii. Proton leak capacities were not affected by warm or hypercapnia-acclimation of N. rossii. We conclude that an acclimatory response of mitochondrial capacities may include higher thermal plasticity of CI supported by enhanced utilization of anaplerotic substrates (via oxidative decarboxylation reactions) feeding into the citrate cycle. L. squamifrons possesses higher relative CI plasticities than N. rossii, which may facilitate the usage of energy efficient NADH-related substrates under conditions of elevated energy demand, possibly induced by ocean warming and acidification. The observed adjustments of electron transport system complexes with a higher flux through CI under warming and acidification suggest a metabolic acclimation potential of the sub-Antarctic L. squamifrons, but only limited acclimation capacities for N. rossii. Citation: Strobel A, Graeve M, Poertner HO, Mark FC (2013) Mitochondrial Acclimation Capacities to Ocean Warming and Acidification Are Limited in the Antarctic Nototheniid Fish, Notothenia rossii and Lepidonotothen squamifrons. PLoS ONE 8(7): e68865.

COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY CTOXICOLOGY PHARMACOLOGY, 2011

The present study aims to examine whether the seasonal changes in the levels of heavy metals Cd a... more The present study aims to examine whether the seasonal changes in the levels of heavy metals Cd and Pb in the gills of sublittoral mussel Modiolus barbatus from populations distributed in Thermaikos Gulf are correlated to seasonal molecular (Heat Shock Response) and metabolic stress responses of this species. Our results indicate a season effect in the accumulation of heavy metals in the gills of bivalves in the area of Thermaikos Gulf, possibly implicating biological (reproductive cycle), natural (rivers' flow) and anthropogenic factors. Among the members of heat shock proteins (Hsps) examined, inducible Hsp70 seemed to play a major cytoprotective role against toxicity of metals. However, bivalves' tolerance against heavy metals may decrease during warming, arising further questions for their survival in context of global warming.

Marine Biology, 2013

Over the next century, elevated quantities of atmospheric CO 2 are expected to penetrate into the... more Over the next century, elevated quantities of atmospheric CO 2 are expected to penetrate into the oceans, causing a reduction in pH (-0.3/-0.4 pH unit in the surface ocean) and in the concentration of carbonate ions (so-called ocean acidification). Of growing concern are the impacts that this will have on marine and estuarine organisms and ecosystems. Marine shelled molluscs, which colonized a large latitudinal gradient and can be found from intertidal to deep-sea habitats, are economically and ecologically important species providing essential ecosystem services including habitat structure for benthic organisms, water purification and a food source for other organisms. The effects of ocean acidification on the growth and shell production by juvenile and adult shelled molluscs are variable among species and even within the same species, precluding the drawing of a general picture. This is, however, not the case for pteropods, with all species tested so far, being negatively impacted by ocean acidification. The blood of shelled molluscs may exhibit lower pH with consequences for several physiological processes (e.g. respiration, excretion, etc.) and, in some cases, increased mortality in the long term. While fertilization may remain unaffected by elevated pCO 2 , embryonic and larval development will be highly sensitive with important reductions in size and decreased survival of larvae, increases in the number of abnormal larvae and an increase in the developmental time. There are big gaps in the current understanding of the biological consequences of an Communicated by S. Dupont.

Frontiers in Marine Science, 2014

In order to assess the effects of ocean acidification and warming on the Mediterranean mussel (My... more In order to assess the effects of ocean acidification and warming on the Mediterranean mussel (Mytilus galloprovincialis), specimens were reared in aquarium tanks and exposed to elevated conditions of temperature (+3 • C) and acidity (−0.3 pH units) for a period of 10 months. The whole system comprised a factorial experimental design with 4 treatments (3 aquaria per treatment): control, lowered pH, elevated temperature, and lowered pH/elevated temperature. Mortality was estimated on a weekly basis and every 2 months, various biometrical parameters and physiological processes were measured: somatic and shell growth, metabolic rates and body fluid acid-base parameters. Mussels were highly sensitive to warming, with 100% mortality observed under elevated temperature at the end of our experiment in October. Mortality rates increased drastically in summer, when water temperature exceeded 25 • C. In contrast, our results suggest that survival of this species will not be affected by a pH decrease of ∼0.3 in the Mediterranean Sea. Somatic and shell growth did not appear very sensitive to ocean acidification and warming during most of the experiment, but were reduced, after summer, in the lowered pH treatment. This was consistent with measured shell net dissolution and observed loss of periostracum, as well as uncompensated extracellular acidosis in the lowered pH treatment indicating a progressive insufficiency in acid-base regulation capacity. However, based on the present dataset, we cannot elucidate if these decreases in growth and regulation capacities after summer are a consequence of lower pH levels during that period or a consequence of a combined effect of acidification and warming. To summarize, while ocean acidification will potentially contribute to lower growth rates, especially in summer when mussels are exposed to sub-optimal conditions, ocean warming will likely pose more serious threats to Mediterranean mussels in this region in the coming decades.

American Naturalist, 2009

Widespread recognition of the importance of biological studies at large spatial and temporal scal... more Widespread recognition of the importance of biological studies at large spatial and temporal scales, particularly in the face of many of the most pressing issues facing humanity, has fueled the argument that there is a need to reinvigorate such studies in physiological ecology through the establishment of a macrophysiology. Following a period when the fields of ecology and physiological ecology had been regarded as largely synonymous, studies of this kind were relatively commonplace in the first half of the twentieth century. However, such large-scale work subsequently became rather scarce as physiological studies concentrated on the biochemical and molecular mechanisms underlying the capacities and tolerances of species. In some sense, macrophysiology is thus an attempt at a conceptual reunification. In this article, we provide a conceptual framework for the continued development of macrophysiology. We subdivide this framework into three major components: the establishment of macrophysiological patterns, determining the form of those patterns (the very general ways in which they are shaped), and understanding the mechanisms that give rise to them. We suggest ways in which each of these components could be developed usefully.

Oecologia, 2007

Animal responses to changing environments are most commonly studied in relation to temperature ch... more Animal responses to changing environments are most commonly studied in relation to temperature change. The current paradigm for marine ectotherms is that temperature limits are set through oxygen limitation. Oxygen limitation leads to progressive reductions in capacity to perform work or activity, and these are more important and proximate measures of a population&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s ability to survive. Here we measured the ability of a large Antarctic clam to rebury when removed from sediment at temperatures between -1.5 and 7.5 degrees C and at three oxygen concentrations, 10.2, 20.5 and 27.7%. The proportion of the population capable of reburying declined rapidly and linearly with temperature from around 65% at 0 degrees C to 0% at 6 degrees C in normoxia (20.5% O2). Decreasing oxygen to 10.2% reduced temperature limits for successful burial by around 2 degrees C, and increasing oxygen to 27.7% raised the limits by 1-1.5 degrees C. There was an interactive effect of body size and temperature on burying: the temperature limits of larger individuals were lower than smaller animals. Similarly, these size limits were increased by increasing oxygen availability. Considering data for all temperatures and oxygen levels, the fastest burying rates occurred at 3 degrees C, which is 2 degrees C above the maximum summer temperature at this site.

Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology, 2009

Thermal acclimation is frequently cited as a means by which ectothermic animals improve their Dar... more Thermal acclimation is frequently cited as a means by which ectothermic animals improve their Darwinian fitness, i.e. the beneficial acclimation hypothesis. As the critical swimming speed (U crit ) test is often used as a proxy measure of fitness, we acclimated Atlantic cod (Gadus morhua) to 4 and 10°C and then assessed their U crit swimming performance at their respective acclimation temperatures and during acute temperature reversal. Because phenotypic differences exist between different populations of cod, we undertook these experiments in two different populations, North Sea cod and North East Arctic cod. Acclimation to 4 or 10°C had a minimal effect on swimming performance or U crit , however test temperature did, with all groups having a 10-17% higher U crit at 10°C. The swimming efficiency was significantly lower in all groups at 4°C arguably due to the compression of the muscle fibre recruitment order. This also led to a reduction in the duration of ''kick and glide'' swimming at 4°C. No significant differences were seen between the two populations in any of the measured parameters, due possibly to the extended acclimation period. Our data indicate that acclimation imparts little benefit on U crit swimming test in Atlantic cod. Further efforts need to identify the functional consequences of the long-term thermal acclimation process.

Marine Biology, 2010

Temperature and mitochondrial plasticity are well studied in Wshes, but little is known about thi... more Temperature and mitochondrial plasticity are well studied in Wshes, but little is known about this relationship in invertebrates. The eVects of habitat temperature on mitochondrial ultrastructure were examined in three confamilial limpets from the Antarctic (Nacella concinna), New Zealand (Cellana ornata), and Singapore (Cellana radiata). The eVects of seasonal changes in temperature were also examined in winter and summer C. ornata. Stereological methods showed that limpet pedal myocytes were 1-2 orders of magnitude smaller in diameter (t3.5 m) than in vertebrates, and that the diameter did not vary as a function of temperature. Mitochondrial volume density (Vv (mt,f) ) was approximately 2-4 times higher in N. concinna (0.024) than in the other species (0.01 and 0.006), which were not signiWcantly diVerent from each other. Mitochondrial cristae surface density (Sv (im,mt) ) was signiWcantly lower in summer C. ornata (24.1 § 0.50 m 2 m ¡3 ) than both winter C. ornata (32.3 § 0.95 m 2 m ¡3 ) and N. concinna (34.3 § 4.43 m 2 m ¡3 ). The surface area of mitochondrial cristae per unit Wbre volume was signiWcantly higher in N. concinna, due largely to the greater mitochondrial volume density. These results and previous studies indicate that mitochondrial proliferation in the cold is a common, but not universal response by diVerent species from diVerent thermal habitats. Seasonal temperature decreases on the other hand, leading preferentially to an increase in cristae surface density. Stereological measures also showed that energetic reserves, i.e. lipid droplets and glycogen in the pedal muscle changed greatly with season and species. This was most likely related to gametogenesis and spawning.

Physiological and Biochemical Zoology, 2006

Through functional analyses, integrative physiology is able to link molecular biology with ecolog... more Through functional analyses, integrative physiology is able to link molecular biology with ecology as well as evolutionary biology and is thereby expected to provide access to the evolution of molecular, cellular, and organismic functions; the genetic basis of adaptability; and the shaping of ecological patterns. This paper compiles several exemplary studies of thermal physiology and ecology, carried out at various levels of biological organization from single genes (proteins) to ecosystems. * This paper was prepared as an overview of a symposium session presented at "