Because temperature has a pervasive influence on all levels of biological organisation (Hochachka and Somero, 2002), research should address how mechanisms across these levels combine to shape the thermal limitations of an organism in the context of the ecosystem. The oxygen- and capacity-limitedthermaltolerance (OCLTT) concept (Box 1), developed over the last two decades, has been proposed to meet these challenges and to provide a framework explaining how physiological mechanisms co-define an animal ’ s fundamental and realised thermal niches (see Glossary), with a focus on critical life stages (for early summaries of OCLTT, see Pörtner, 2001, 2002; for thermal niches, see Pörtner et al., 2010; Deutsch et al., 2015; Payne et al., 2016). The basic idea underlying the OCLTT is that once temperatures approach limiting values, constraints on the capacity of an animal to supply oxygen to tissues to meet demand cause a progressive decline in performance (e.g. Pörtner and Giomi, 2013; Giomi et al., 2014), with consequences at the ecosystem level (e.g. Del Raye and Weng, 2015; Payne et al., 2016). OCLTT considers that most routine performances are fuelled sustainably by aerobic metabolism in excess of standard metabolic rate (SMR) and largely exclude anaerobic metabolism.
also hold in air breathers relying on convective oxygen transport. Oxygen- and capacity-limitedthermaltolerance (or, in other words, temperature-dependent oxygen limitation) has also been verified in larval stages of for example crustaceans (Storch et al., 2009) as well as in small zooplankton (Seidl et al., 2005). All of these observations match with a more general picture of how ambient oxygen levels shape and limit animal life through oxygen availability, be it in the limitedcapacity of adult specimens to ventilate their oxygen-limited egg masses (Cohen and Strathmann, 1996; Woods and Moran, 2008; Fernandez et al., 2000) or in the dependence of maximum body size of marine invertebrate phyla on temperature-dependent oxygen solubility and thus aquatic oxygen levels (Chapelle and Peck, 1999). These principles thus appear unifying in shaping (aquatic and possibly terrestrial) animal life, firstly referring to individual species. However, consideration of the physiology of species interacting at the ecosystem level (Pörtner and Farrell, 2008; Pörtner et al., 2010) is likely to improve the predictive power of presently insufficient physiological models of community dynamics (Davis et al., 1998). Starting from these observations one research direction is to deepen our understanding of climate specialization and sensitivity through mechanistic physiology including studies of the mechanisms of thermal adaptation and acclimatization at various levels: systemic, cellular to molecular (e.g. Guderley, 2004; Pörtner and Lannig, 2009; Dong and Somero, 2009) or of associated signalling pathways (e.g. Kassahn et al., 2009) and gene expression patterns (Hardewig et al., 1999; Lucassen et al., 2003; Lucassen et al., 2006; Podrabsky and Somero, 2004; McLelland et al., 2006). The other direction, less developed but equally important, is to establish firm links between physiological patterns and climate regimes or scenarios. This can be achieved through macrophysiology approaches, which use meta-analyses to firmly establish such patterns in relation to large scale variations in temperature or climate (e.g. Macpherson, 2002; Chown and Gaston, 2008; Gaston et al., 2009). Ideally, the two complementary directions would need to be equally developed for a comprehensive picture of climate specialization and sensitivity. However, the effort is so extensive that I am not aware of any example where such a comprehensive data set has been compiled for any one species or genus. This and the diversity of processes involved may also explain why a comprehensive or unifying concept, which brings together all the various aspects traditionally studied in evolutionary thermal biology and in thermalphysiology and ecology, is only emerging and is not widely established.
Previous comparisons between plastron breathers and aerial gas exchangers have shown the former to be especially vulnerable to warming and hypoxia, presumably because of their poor respiratory control (Verberk and Bilton, 2013). Here, this pattern is confirmed and extended to hyperoxia (Fig. 3). More importantly, our experimental manipulations enable us to isolate the effect of respiratory control within a single species. By denying the bimodal breather access to air, we reduce the respiratory control of I. cimicoides , and this resulted in a clear reduction of heat tolerance under hypoxia by as much as 4.6°C. This makes it very likely that respiratory control is the driving factor underlying the extent to which oxygen limits thermaltolerance, explaining the differences in support across a range of species (Verberk and Bilton, 2013). From our results, it is also unlikely that ontogenetic differences in thermal biology play a large role. Differences in thermaltolerance between life stages could be inherent, irrespective of differences in their gas exchange mechanism, arising because life stages may differ in their ability to thermoregulate (e.g. Bowler and Terblanche, 2008; Voorhees and Bradley, 2012). In holometabolous insects, larvae frequently differ from adults in their gas-exchange mechanisms, making it difficult to disentangle the potential effects of ontogenetic shifts in thermalphysiology and the effect of respiratory control. In the hemimetabolous bugs studied, comparing juveniles and adults and keeping the gas exchange mechanism constant, we showed very similar levels of heat tolerance for both life stages, suggesting that differences between instars may not result from ontogenetic differences in their thermalphysiology (Verberk and Bilton, 2011). A similar heat tolerance across life stages also implies that the capacity to increase oxygen consumption does not differ markedly with body size in these insects. For terrestrial insects, critical P O 2 (the oxygen tension
by Gibbs energy of mixing calculated as a function of composition at various temperatures. The Gibbs energy of fusion of pure FeO for the calculation of phase diagram is calculated from the heat capacity at constant pressure based on the temperature dependence of enthalpies calculated by MD simulation. The standard Gibbs energy of formation of solid Fe 2 SiO 4 from liquid FeO and SiO 2 , eq. (16), is
temperature (Mahapatra et al., 2004); however, no data are available to support this assumption. Available information is limited to field observations and a small number of laboratory studies (Mahapatra et al., 2003). Recently, from the annual catch data and discussion with local fishers, we observed that the population of these two fish has sharply declined in natural water bodies. We assume this phenomenal declining trend may be due to environmental changes like habitat loss, aquatic pollution and steadily increasing water temperature in the region. Considering the potential of these two fish species in ornamental fish industry, we investigated the thermaltolerance, stress response and rate of oxygen consumption in these fish species that were experimentally-acclimatized at four different temperatures (20, 25, 30 and 35°C).
Ventilation rate increased significantly during hypoxia both before and after reduction of haemoglobin oxygen-carrying capacity (Fig. 1). Ventilation rate in toads with normal capacity was 100±19 ml kg 21 min 21 (N=6) during normoxia and increased to 256±46 ml kg 21 min 21 (N=6) when F O ∑ was reduced to 0.05. Following reduction of
to 600 C; this process was repeated between 300 and 900 C 4 times. The thermal stability (weight and phase structural changes) of the as-prepared samples with temperature from room temperature to 1000 C under owing air was checked using a TGA/DTA technique carried out on a Stanton Redcro STA-780 series thermal analyser.
In aquatic environments, rising water temperatures reduce water oxygen content while increasing oxygen demand, leading several authors to propose cardiorespiratory oxygen transport capacity as the main determinant of aquatic animal fitness. It has also been argued that tropical species, compared with temperate species, live very close to their upper thermal limit and hence are vulnerable to even small elevations in temperature. Little, however, is known about physiological responses to high temperatures in tropical species. Here we report that the tropical giant freshwater shrimp (Macrobrachium rosenbergii) maintains normal growth when challenged by a temperature rise of 6°C above the present day average (from 27°C to 33°C). Further, by measuring heart rate, gill ventilation rate, resting and maximum oxygen uptake, and hemolymph lactate, we show that oxygen transport capacity is maintained up to the critical maximum temperature around 41°C. In M. rosenbergii heart rate and gill ventilation rate increases exponentially until immediately below critical temperatures and at 38°C animals still retained more than 76% of aerobic scope measured at 30°C, and there was no indication of anaerobic metabolism at the high temperatures. Our study shows that the oxygen transport capacity is maintained at high temperatures, and that other mechanisms, such as protein dysfunction, are responsible for the loss of ecological performance at elevated temperatures.
this context (Brijs et al., 2015; Devor et al., 2016; Ekström et al., 2016; Healy and Schulte, 2012a; Mark et al., 2002). While these studies indicate that factors other than tissue oxygen supply may also set absolute upper thermal limits, hyperoxia did slightly increase the critical thermal maximum (+0.9°C) of European perch (Ekström et al., 2016). Rock pools are expected to become hyperoxic during thermal ramping events that should approach upper thermal limits, and for this reason, the possibility of increased maximal thermaltolerance under hyperoxia in intertidal fish requires consideration. Given predicted increases in the severity of heat wave events due to climate change (Perkins et al., 2012), and the possibility that intertidal fish already live close to their upper thermal limits, resolving thermaltolerance limits of intertidal fish under environmentally relevant conditions is pertinent.
not necessarily the case. Poleward range limits are in part determined by the frequency and severity of low temperatures over winter, so increased winter survival may facilitate poleward expansion of species ranges (Crozier, 2003). Winter warming in temperate ecosystems may enhance fitness by lengthening the seasons of growth and reproduction, or reduce fitness through phenological shifts (Jeong et al., 2011). For example, extended periods of pre-winter dormancy in the spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricinae), and increases in post-winter thermal variability in Erynnis propertius (Lepidoptera: Hesperiidae), both reduce fitness by elevating metabolic rate and depleting energy stores required for summer development and reproduction (Han and Bauce, 1998; Williams et al., 2012). Animal distributions have already shifted in response to warming (Chen et al., 2011). In marine systems, distributions of several fish species in the North Sea have shifted northward with increased temperatures (Perry et al., 2005) while in terrestrial systems, shifts in range limits have been well documented in insects and are often directly attributed to warmer winters (Battisti et al., 2005; Chen et al., 2011; Crozier, 2003; Jepsen et al., 2008).
production increased when increasing the agitation rate (Figure 3 b and 3c). It is interesting to note that the OTR profile for the cultures at 700 rpm had two stages: in the first stage (0-9 h of cultivation) a linear increase in the OTR from 10 to 30 mmol L -1 h -1 was observed. Later, in a second stage, the OTR increased exponentially to reach a maximum of 70 mmol L -1 h -1 at 15 h of cultivation (Figure 3a). This behaviour seems to be typical of cultures non- limited by oxygen, such as it has been shown for other microbial cultures [20,21]. After 15 h of cultivation the OTR decreased to values close to 20 mmol L -1 h -1 . In con- trast to what was observed in the cultures at 5%, this drop in the OTR is not due to the depletion of the carbon source, as at this time the sucrose concentration was approximately 7 g L -1 (Figure 3 d). Analyzing the concen- tration of ammonium acetate used as nitrogen source, a total depletion of ammonium was observed at 15 h, which supports the fact that the culture could be limited by the nitrogen source after 15 h of fermentation. When A. vine- landii was cultured at 300 rpm, the OTR profile shows a characteristic plateau of the cultures with oxygen limita- tion, with a maximal OTR of 6 mmol L -1 h -1 (Figure 3a). This value of OTR remained constant from the 6 th to the 21 st h of cultivation.
Oxygen extraction is the proportion of oxygen unloaded from Hb into the tissue. Extraction is a dynamic process that is the end result of a changing oxygen gradient, tissue blood flow, and Hb-oxygen affinity. Thus, increases in oxygen extraction can buffer, or compensate for, decreased oxygen delivery and/ or increased oxygen consumption. Mathematically, extraction is calculated as the ratio between oxygen consumption and delivery (Table 1). Because extraction is dependent on the establishment of an oxygen gradient from the alveolar– pulmonary capillary interface to the cell, its key determinants are factors that influence the oxygen gradient, including Hb affinity and capillary transit time. Accordingly, extraction is a summary measure of all the endogenous and exogenous influences on the oxygenphysiology in an individual.
facile, while experiments indicated little or no dissociation. More recently the consensus of most theoretical calculations is that no dissociation occurs. New results presented here, based on analysis of scanned-energy mode photoelectron diffraction data from the OH component of O 1s photoemission, show the coexistence of molecular water and OH species in both atop (OH t ) and bridging (OH br ) sites. OH br can arise from reaction with oxygen vacancy defect
water loss and metabolic rate typical of many birds, using panting and lingual flutter (analogous to gular flutter in other taxa) to augment rates of evaporative water loss (Dawson and Fisher, 1982; Greenwald et al., 1967; Weathers and Caccamise, 1975; Weathers and Schoenbaechler, 1976). However, it is not clear whether these studies elicited maximum heat tolerance and evaporative cooling capacities in the study individuals used, or whether greater heat tolerance is possible under different experimental conditions. In Dawson and Fisher ’ s (1982) study of galahs, for instance, the dewpoint of air in chambers varied between 14 and 18°C, potentially impeding evaporative heat loss from birds exposed to high T a (Gerson
showed the most reduced VC, and their respiratory function was more affected than in hemiplegic children. Also, during the feeding of persons with severe disabilities who also suffer from gastrointestinal reflux, aspiration could happen and lead to aspira- tion pneumonia. 4 The oxygen saturation (OS) level, as measured by pulse oximetry,
Holistic and reductionist microbial ecology thus operate at opposing and extreme ends of the control-complexity spectrum, with a largely uncharted territory between the two. Can we bridge this divide? Will this help to achieve a better understanding of microbial community formation, structure, functioning, and evolution? Similar ques- tions permeate through nearly every scientiﬁc ﬁeld, and theoretical and experimental approaches have been developed to connect levels of complexity in other disciplines, e.g., in chemical engineering. Arguably, an analogous breakthrough in microbial ecol- ogy poses speciﬁc challenges and likely requires its own inventive approaches. Here, we propose a possible roadmap forward that integrates conceptual, experimental, and methodological developments in microbial ecology to address its unique complexity scaling challenges.
factor controlling ecological processes at all levels of organization (Brown et al., 2004). Although the generality of this claim has rightly been questioned (Harte, 2004), the predicted exponential increase in standard metabolic rate (SMR) of ectotherms as temperature increases (Brown et al., 2004; Gillooly et al., 2001) may play a pivotal role in determining an organism ’ s thermaltolerance and future geographical distribution. Moreover, aerobic scope (AS), defined as the difference between SMR and maximum metabolic rate (MMR), has been reported to gradually decline at temperatures exceeding the optimal thermal range in several fishes (Brett, 1971; Fry, 1947). The loss of AS at the upper critical temperature has been suggested to be the fundamental factor in determining the upper thermal limits of fish, as survival is proposed to be time limited beyond this point as a result of a transition to anaerobic metabolism (Lannig et al., 2004; Pörtner, 2002; Sartoris et al., 2003; Zakhartsev et al., 2003). One suggested explanation for the reported loss of AS at high temperatures, formalized as the ‘ oxygen- and capacity-limitedthermaltolerance (OCLTT) hypothesis ’ , is that the cardiorespiratory system progressively fails to maintain the necessary oxygen supply to active tissues (Pörtner and Farrell, 2008).
selection-driven bottleneck in the past. Phenotypically, the PFRC H-strain has been shown to tolerate the extreme temperature of 27°C for twice as long as the wild-type S-strain from Serpentine Dam (Molony et al., 2004). More broadly, an earlier study showed the longer survival time at high temperatures (25 – 29°C) of PFRC rainbow trout than their counterparts from New South Wales and Victoria, where the PFRC rainbow trout directly originated (Morrissy, 1973). These results suggest the possibility that poorly adapted individuals have been eliminated during hatchery rearing because the water temperature cannot be operationally maintained below 25°C (Fig. 1), whereas similar selection pressures were avoided by wild fish in the dam that had access to cool water at depth (<20°C). Therefore, to better elucidate the underlying physiological changes of PFRC H-strain rainbow trout that renders them more heat tolerant, we undertook a comprehensive physiological phenotypic assessment of their upper thermal performance. Specifically, the ability of PFRC H-strain rainbow trout to tolerate acute warming was characterized by measuring critical thermal maximum (CT max ),