Oxygen supply capacity breathes new life into critical oxygen partial pressure (Pcrit)

Author Posting. © Company of Biologists, 2021. This article is posted here by permission of Company of Biologists for personal use, not for redistribution. The definitive version was published in Journal of Experimental Biology 224(8), (2021): jeb242210, https://doi.org/10.1242/jeb.242210.The critical oxygen partial pressure (Pcrit), typically defined as the PO2 below which an animal's metabolic rate (MR) is unsustainable, is widely interpreted as a measure of hypoxia tolerance. Here, Pcrit is defined as the PO2 at which physiological oxygen supply (α0) reaches its maximum capacity (α; µmol O2 g−1 h−1 kPa−1). α is a species- and temperature-specific constant describing the oxygen dependency of the maximum metabolic rate (MMR=PO2×α) or, equivalently, the MR dependence of Pcrit (Pcrit=MR/α). We describe the α-method, in which the MR is monitored as oxygen declines and, for each measurement period, is divided by the corresponding PO2 to provide the concurrent oxygen supply (α0=MR/PO2). The highest α0 value (or, more conservatively, the mean of the three highest values) is designated as α. The same value of α is reached at Pcrit for any MR regardless of previous or subsequent metabolic activity. The MR need not be constant (regulated), standardized or exhibit a clear breakpoint at Pcrit for accurate determination of α. The α-method has several advantages over Pcrit determination and non-linear analyses, including: (1) less ambiguity and greater accuracy, (2) fewer constraints in respirometry methodology and analysis, and (3) greater predictive power and ecological and physiological insight. Across the species evaluated here, α values are correlated with MR, but not Pcrit. Rather than an index of hypoxia tolerance, Pcrit is a reflection of α, which evolves to support maximum energy demands and aerobic scope at the prevailing temperature and oxygen level.This project was supported by National Oceanic and Atmospheric Administration grants NA18NOS4780167 and NA17OAR4310081 and National Science Foundation grant OCE-1459243 to B.A.S., the Jack and Katharine Ann Lake Fellowship to A.A., the Anne and Werner Von Rosenstiel Fellowship and Garrels Memorial Endowed Fellowship to A.W.T., the Hogarth Fellowship to C.J.W., the Southern Kingfish Association Fellowship to A.L.B., and a National Science Foundation postdoctoral fellowship (DBI-1907197) to M.A.B.2022-04-3

Use of observing system simulation experiments in the United States

Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 101(8), (2020): E1427-E1438, https://doi.org/10.1175/BAMS-D-19-0155.1.The NOAA Science Advisory Board appointed a task force to prepare a white paper on the use of observing system simulation experiments (OSSEs). Considering the importance and timeliness of this topic and based on this white paper, here we briefly review the use of OSSEs in the United States, discuss their values and limitations, and develop five recommendations for moving forward: national coordination of relevant research efforts, acceleration of OSSE development for Earth system models, consideration of the potential impact on OSSEs of deficiencies in the current data assimilation and prediction system, innovative and new applications of OSSEs, and extension of OSSEs to societal impacts. OSSEs can be complemented by calculations of forecast sensitivity to observations, which simultaneously evaluate the impact of different observation types in a forecast model system

The case for strategic international alliances to harness nutritional genomics for public and personal health

Nutrigenomics is the study of how constituents of the diet interact with genes, and their products, to alter phenotype and, conversely, how genes and their products metabolise these constituents into nutrients, antinutrients, and bioactive compounds. Results from molecular and genetic epidemiological studies indicate that dietary unbalance can alter gene-nutrient interactions in ways that increase the risk of developing chronic disease. The interplay of human genetic variation and environmental factors will make identifying causative genes and nutrients a formidable, but not intractable, challenge. We provide specific recommendations for how to best meet this challenge and discuss the need for new methodologies and the use of comprehensive analyses of nutrient-genotype interactions involving large and diverse populations. The objective of the present paper is to stimulate discourse and collaboration among nutrigenomic researchers and stakeholders, a process that will lead to an increase in global health and wellness by reducing health disparities in developed and developing countrie

Plants in aquatic ecosystems: current trends and future directions

Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper we present an overview of current trends and future directions in aquatic plant research in the early 21st century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrate the global relevance of aquatic plant research in the early 21st century but also the many challenges that this burgeoning scientific discipline must address

Ecophysiology of Oxygen Supply in Cephalopods

Cephalopods are an important component of many marine ecosystems and support large fisheries. Their active lifestyles and complex behaviors are thought to be driven in large part by competition with fishes. Although cephalopods appear to compete successfully with fishes, a number of their important physiological traits are arguably inferior, such as an inefficient mode of locomotion via jet propulsion and a phylogenetically limited means of blood-borne gas transport. In active shallow-water cephalopods, these traits result in an interesting combination of very high oxygen demand and limited oxygen supply. The ability to maintain active lifestyles despite these metabolic constraints makes cephalopods a fascinating subject for metabolic physiology. This dissertation focuses on the physiological adaptations that allow coleoid cephalopods to maintain a balance of oxygen supply and demand in a variety of environmental conditions. A critical component of understanding oxygen supply in any animal is knowing the means of oxygen delivery from the environment to the mitochondria. Squids are thought to obtain a fairly large portion of their oxygen via simple diffusion across the skin in addition to uptake at the gills. Although this hypothesis has support from indirect evidence and is widely accepted, no empirical examinations have been conducted to assess the validity of this hypothesis. In Chapter 2, I examined cutaneous respiration in two squid species, Doryteuthis pealeii and Lolliguncula brevis, by using a divided chamber to physically separate the mantle cavity and gills from the outer mantle surface. I measured the oxygen consumption rate in the two compartments and found that, at rest, squids only obtain enough oxygen cutaneously to meet demand of the skin tissue locally (12% of total). The majority of oxygen is obtained via the traditional branchial pathway. In light of these findings, I re-examine and discuss the indirect evidence that has supported the cutaneous respiration hypothesis. Ocean acidification is believed to limit the performance of squids due to their exceptional oxygen demand and pH-sensitivity of blood-oxygen binding, which may reduce oxygen supply in acidified waters. The critical oxygen partial pressure (Pcrit), defined as the PO2 below which oxygen supply cannot match basal demand, is a commonly reported index of hypoxia tolerance. Any CO2-induced reduction in oxygen supply should be apparent as an increase in Pcrit. In Chapter 3, I assessed the effects of CO2 (40 to 140 Pa) on the metabolic rate and Pcrit of two squid species: Dosidicus gigas and Doryteuthis pealeii. Carbon dioxide had no effect on metabolic rate or hypoxia tolerance in either species. Furthermore, considering oxygen transport parameters (e.g. Bohr coefficient, blood P50) and blood PCO2 values from the literature, I estimated an increase in seawater PCO2 to 100 Pa (≈1000 μatm/ppmv) would result in a maximum drop in hemocyanin-O2 saturation by 6% at normoxia and a Pcrit increase of ≈1 kPa (≈5% air saturation) in the absence of active extracellular pH compensation. Such changes are unlikely given the capacity for acid-base regulation in many cephalopods. Moreover, this estimated change is within the 95% confidence intervals of the Pcrit measurements reported here. Squid blood-O2 binding is more sensitive to pH than most other marine animals measured to date. Therefore, the lack of effect in squids suggests that ocean acidification is unlikely to have a limiting effect on blood-O2 supply in most marine animals. The pelagic octopod, Japetella diaphana, is known to inhabit meso- and bathypelagic depths worldwide. Across its range, individuals encounter oxygen levels ranging from nearly air-saturated to nearly anoxic. In Chapter 4, we assessed the physiological adaptations of individuals from the eastern tropical Pacific (ETP) where oxygen is extremely low. Ship-board measurements of metabolic rate and hypoxia tolerance were conducted and a metabolic index was constructed to model suitable habitat for aerobic metabolism. I found that animals from the ETP had a higher metabolic rate than animals from more oxygen-rich habitats. Despite their higher oxygen demand, they maintained better hypoxia tolerance than conspecifics from oxygen-rich Hawaiian waters. Furthermore, I found that hypoxia tolerance in Japetella has a reverse temperature dependence from most marine ectotherms, a characteristic that uniquely suits the physical characteristics of its oxygen-poor environment. Even with their high tolerance to hypoxia, the OMZ core likely has insufficient oxygen supply to meet the basal oxygen demand of Japetella. Despite the limited aerobic habitat in this region, species abundance was comparable to more oxygenated ocean regions, suggesting that physiological or behavioral plasticity such as altered hypoxia tolerance or hypoxic avoidance in this globally-distributed species is sufficient to maintain species fitness in this extreme environment. These findings contribute towards our understanding of the impacts of climate change on cephalopod physiology and biogeography. The study of environmental physiology provides a mechanistic basis for the understanding and prediction of ecological responses to climate change

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Unique thermal sensitivity imposes a cold-water energetic barrier for vertical migrators

Alterations of marine species’ ranges with climate change are often attributed to oxygen limitation in warming oceans. Here we report unique metabolic temperature sensitivities for the myriad of vertically migrating oceanic species that daily cross depth-related gradients in temperature and oxygen. In these taxa, selection favours high metabolic activity for predator–prey interactions in warm shallow water and hypoxia tolerance in the cold at depth. These diverging selective pressures result in thermal insensitivity of oxygen supply capacity and enhanced thermal sensitivity of active metabolic rate. Aerobic scope is diminished in the cold, well beyond thermodynamic influences and regardless of ambient oxygen levels, explaining the native distributions of tropical migrators and their recent range expansions following warming events. Cold waters currently constitute an energetic barrier to latitudinal range expansion in vertical migrators. As warming due to climate change approaches, and eventually surpasses, temperatures seen during past warming events, this energetic barrier will be relieved

Unique thermal sensitivity imposes a cold-water energetic barrier for vertical migrators

Alterations of marine species’ ranges with climate change are often attributed to oxygen limitation in warming oceans. Here we report unique metabolic temperature sensitivities for the myriad of vertically migrating oceanic species that daily cross depth-related gradients in temperature and oxygen. In these taxa, selection favours high metabolic activity for predator–prey interactions in warm shallow water and hypoxia tolerance in the cold at depth. These diverging selective pressures result in thermal insensitivity of oxygen supply capacity and enhanced thermal sensitivity of active metabolic rate. Aerobic scope is diminished in the cold, well beyond thermodynamic influences and regardless of ambient oxygen levels, explaining the native distributions of tropical migrators and their recent range expansions following warming events. Cold waters currently constitute an energetic barrier to latitudinal range expansion in vertical migrators. As warming due to climate change approaches, and eventually surpasses, temperatures seen during past warming events, this energetic barrier will be relieved

Seawater carbonate chemistry and metabolic rate, ventilation rate and critical oxygen partial pressure of Dosidicus gigas and Doryteuthis pealeii

Ocean acidification is hypothesized to limit the performance of squid owing to their exceptional oxygen demand and pH sensitivity of blood–oxygen binding, which may reduce oxygen supply in acidified waters. The critical oxygen partial pressure (Pcrit), the PO2 below which oxygen supply cannot match basal demand, is a commonly reported index of hypoxia tolerance. Any CO2-induced reduction in oxygen supply should be apparent as an increase in Pcrit. In this study, we assessed the effects of CO2 (46–143 Pa; 455–1410 μatm) on the metabolic rate and Pcrit of two squid species - Dosidicus gigas and Doryteuthis pealeii – through manipulative experiments. We also developed a model, with inputs for hemocyanin pH sensitivity, blood PCO2 and buffering capacity, that simulates blood oxygen supply under varying seawater CO2 partial pressures. We compare model outputs with measured Pcrit in squid. Using blood–O2 parameters from the literature for model inputs, we estimated that, in the absence of blood acid–base regulation, an increase in seawater PCO2 to 100 Pa (1000 μatm) would result in a maximum drop in arterial hemocyanin–O2 saturation by 1.6% at normoxia and a Pcrit increase of 0.5 kPa. Our live-animal experiments support this supposition, as CO2 had no effect on measured metabolic rate or Pcrit in either squid species