Shining new light on mammalian diving physiology using wearable near-infrared spectroscopy

Cardiorespiratory adaptations in small cetaceans and marine mammals

The dive response, or the 'master switch of life', is probably the most studied physiological trait in marine mammals and is thought to conserve the available O2 for the heart and brain. Although generally thought to be an autonomic reflex, several studies indicate that the cardiovascular changes during diving are anticipatory and can be conditioned. The respiratory adaptations, where the aquatic breathing pattern resembles intermittent breathing in land mammals, with expiratory flow exceeding 160 litres s-1 has been measured in cetaceans, and where exposure to extreme pressures results in alveolar collapse (atelectasis) and recruitment upon ascent. Cardiorespiratory coupling, where breathing results in changes in heart rate, has been proposed to improve gas exchange. Cardiorespiratory coupling has also been reported in marine mammals, and in the bottlenose dolphin, where it alters both heart rate and stroke volume. When accounting for this respiratory dependence on cardiac function, several studies have reported an absence of a diving-related bradycardia except during dives that exceed the duration that is fuelled by aerobic metabolism. This review summarizes what is known about the respiratory physiology in marine mammals, with a special focus on cetaceans. The cardiorespiratory coupling is reviewed, and the selective gas exchange hypothesis is summarized, which provides a testable mechanism for how breath-hold diving vertebrates may actively prevent uptake of N2 during routine dives, and how stress results in failure of this mechanism, which results in diving-related gas emboli.

Adaptive strategies of aquatic mammals: Exploring the role of the HIF pathway and hypoxia tolerance

Aquatic mammals (marine and freshwater species) share significant and similar adaptations, enabling them to tolerate hypoxia during regular breath-hold diving. Despite the established importance of HIF1A, a master regulator in the molecular mechanism of hypoxia response, and other associated genes, their role in the evolutionary adaptation of aquatic mammals is not fully understood. In this study, we investigated this topic by employing a candidate gene approach to analyze 11 critical genes involved in the HIF1A signaling pathway in aquatic mammals. Our gene analyses included evaluating positive and negative selection, relaxation or constriction of selection, and molecular convergence compared to other terrestrial mammals, including subterranean mammals. Evidence of selection suggested a significant role of negative selection, as well as relaxation of the selective regime in cetaceans for most of these genes. We found that the glutamine 68 variant in the HIF3α protein is unique to cetaceans and initial evaluations indicated a destabilizing effect on protein structure. However, further analyses are necessary to evaluate its functional impact and adaptive relevance in this taxon.

Biologging and Biotelemetry: Tools for Understanding the Lives and Environments of Marine Animals

Addressing important questions in animal ecology, physiology, and environmental science often requires in situ information from wild animals. This difficulty is being overcome by biologging and biotelemetry, or the use of miniaturized animal-borne sensors. Although early studies recorded only simple parameters of animal movement, advanced devices and analytical methods can now provide rich information on individual and group behavior, internal states, and the surrounding environment of free-ranging animals, especially those in marine systems. We summarize the history of technologies used to track marine animals. We then identify seven major research categories of marine biologging and biotelemetry and explain significant achievements, as well as future opportunities. Big data approaches via international collaborations will be key to tackling global environmental issues (e.g., climate change impacts), and curiosity about the secret lives of marine animals will also remain a major driver of biologging and biotelemetry studies.

A sampling, exposure and receptor framework for identifying factors that modulate behavioural responses to disturbance in cetaceans

The assessment of behavioural disturbance in cetacean species (e.g. resulting from exposure to anthropogenic sources such as military sonar, seismic surveys, or pile driving) is important for effective conservation and management. Disturbance effects can be informed by Behavioural Response Studies (BRSs), involving either controlled exposure experiments (CEEs) where noise exposure conditions are presented deliberately to meet experimental objectives or in opportunistic contexts where ongoing activities are monitored in a strategic manner. In either context, animal-borne sensors or in situ observations can provide information on individual exposure and disturbance responses. The past 15 years of research have greatly expanded our understanding of behavioural responses to noise, including hundreds of experiments in nearly a dozen cetacean species. Many papers note limited sample sizes, required knowledge of baseline behaviour prior to exposure and the importance of contextual factors modulating behavioural responses, all of which in combination can lead to sampling biases, even for well-designed research programs. It is critical to understand these biases to robustly identify responses. This ensures outcomes of BRSs help inform predictions of how anthropogenic disturbance impacts individuals and populations. Our approach leverages concepts from the animal behaviour literature focused on helping to avoid sampling bias by considering what shapes an animal's response. These factors include social, experience, genetic and natural changes in responsiveness. We developed and applied a modified version of this framework to synthesise current knowledge on cetacean response in the context of effects observed across marine and terrestrial taxa. This new 'Sampling, Exposure, Receptor' framework (SERF) identifies 43 modulating factors, highlights potential biases, and assesses how these vary across selected focal species. In contrast to studies that identified variation in 'Exposure' factors as a key concern, our analysis indicated that factors relating to 'Sampling' (e.g. deploying tags on less evasive individuals, which biases selection of subjects), and 'Receptor' (e.g. health status or coping style) have the greatest potential for weakening the desired broad representativeness of BRSs. Our assessment also highlights how potential biases could be addressed with existing datasets or future developments.

A global meta-analysis of animal manure application and soil microbial ecology based on random control treatments

The processes involved in soil domestication have altered the soil microbial ecology. We examined the question of whether animal manure application affects the soil microbial ecology of farmlands. The effects of global animal manure application on soil microorganisms were subjected to a meta-analysis based on randomized controlled treatments. A total of 2303 studies conducted in the last 30 years were incorporated into the analysis, and an additional 45 soil samples were collected and sequenced to obtain 16S rRNA and 18S rRNA data. The results revealed that manure application increased soil microbial biomass. Manure application alone increased bacterial diversity (M-Z: 7.546 and M-I: 8.68) and inhibited and reduced fungal diversity (M-Z: -1.15 and M-I: -1.03). Inorganic fertilizer replaced cattle and swine manure and provided nutrients to soil microorganisms. The soil samples of the experimental base were analyzed, and the relative abundances of bacteria and fungi were altered compared with no manure application. Manure increased bacterial diversity and reduced fungal diversity. Mrakia frigida and Betaproteobacteriales, which inhibit other microorganisms, increased significantly in the domesticated soil. Moreover, farm sewage treatments resulted in a bottleneck in the manure recovery rate that should be the focus of future research. Our results suggest that the potential risks of restructuring the microbial ecology of cultivated land must be considered.

Near-Infrared Spectroscopy as a Tool for Marine Mammal Research and Care

Developments in wearable human medical and sports health trackers has offered new solutions to challenges encountered by eco-physiologists attempting to measure physiological attributes in freely moving animals. Near-infrared spectroscopy (NIRS) is one such solution that has potential as a powerful physio-logging tool to assess physiology in freely moving animals. NIRS is a non-invasive optics-based technology, that uses non-ionizing radiation to illuminate biological tissue and measures changes in oxygenated and deoxygenated hemoglobin concentrations inside tissues such as skin, muscle, and the brain. The overall footprint of the device is small enough to be deployed in wearable physio-logging devices. We show that changes in hemoglobin concentration can be recorded from bottlenose dolphins and gray seals with signal quality comparable to that achieved in human recordings. We further discuss functionality, benefits, and limitations of NIRS as a standard tool for animal care and wildlife tracking for the marine mammal research community.

Handgrip exercise induces sex-specific mean arterial pressure and oxygenation responses but similar performance fatigability

Women exhibit an attenuated exercise pressor reflex (EPR) when compared to men. The influence of sex-specific mechanisms related to the EPR and performance fatigability remain to be fully elucidated. The purpose was to determine the impact of oxygenation and metabolic efficiency on sex-specific performance fatigability and increases in mean arterial pressure (MAP) resulting from a fatiguing isometric handgrip (IHG). Twenty-four adults volunteered to perform an IHG at 25% at maximal voluntary isometric contractions (MVICs). Pre- and posttest MVICs were conducted to quantify performance fatigability. MAP was collected at 3 timepoints. A near-infrared spectroscopy device was attached to the forearm to derive the following signals: oxy[haem], deoxy[haem], total[haem], and diff[haem]. These values were normalized and examined across time in 5% segments of time-to-task-failure. Metabolic efficiency was defined as the ratio force:deoxy[haem]. During the IHG, there was a decline in oxy[haem] for the men (b = -0.075), whereas the women demonstrated an increase (b = 0.117). For the men, the diff[haem] tracked the mean oxy[haem] response, but there was no change for the women. The men exhibited greater declines in metabolic efficiency, yet there were no sex differences in PF (46.6 ± 9.7% vs. 45.5 ± 14.2%). For relative MAP, the men (24.5 ± 15.1%) exhibited a greater (p = .03) increase than the women (11.0 ± 17.6%). These results indicated the EPR was more prominent for the men, perhaps due to differences in mechanical stimuli and a lack of ability to maintain metabolic efficiency. However, these physiological differences did not induce a sex difference in performance fatigability.

A Physio-Logging Journey: Heart Rates of the Emperor Penguin and Blue Whale

Physio-logging has the potential to explore the processes that underlie the dive behavior and ecology of marine mammals and seabirds, as well as evaluate their adaptability to environmental change and other stressors. Regulation of heart rate lies at the core of the physiological processes that determine dive capacity and performance. The bio-logging of heart rate in unrestrained animals diving at sea was infeasible, even unimaginable in the mid-1970s. To provide a historical perspective, I review my 40-year experience in the development of heart rate physio-loggers and the evolution of a digital electrocardiogram (ECG) recorder that is still in use today. I highlight documentation of the ECG and the interpretation of heart rate profiles in the largest of avian and mammalian divers, the emperor penguin and blue whale.

Future trends in measuring physiology in free-living animals

Thus far, ecophysiology research has predominantly been conducted within controlled laboratory-based environments, owing to a mismatch between the recording technologies available for physiological monitoring in wild animals and the suite of behaviours and environments they need to withstand, without unduly affecting subjects. While it is possible to record some physiological variables for free-living animals using animal-attached logging devices, including inertial-measurement, heart-rate and temperature loggers, the field is still in its infancy. In this opinion piece, we review the most important future research directions for advancing the field of 'physiologging' in wild animals, including the technological development that we anticipate will be required, and the fiscal and ethical challenges that must be overcome. Non-invasive, multi-sensor miniature devices are ubiquitous in the world of human health and fitness monitoring, creating invaluable opportunities for animal and human physiologging to drive synergistic advances. We argue that by capitalizing on the research efforts and advancements made in the development of human wearables, it will be possible to design the non-invasive loggers needed by ecophysiologists to collect accurate physiological data from free-ranging animals ethically and with an absolute minimum of impact. In turn, findings have the capacity to foster transformative advances in human health monitoring. Thus, we invite biomedical engineers and researchers to collaborate with the animal-tagging community to drive forward the advancements necessary to realize the full potential of both fields. This article is part of the theme issue 'Measuring physiology in free-living animals (Part II)'.

What is physiologging? Introduction to the theme issue, part 2

The physiological mechanisms by which animals regulate energy expenditure, respond to stimuli and stressors, and maintain homeostasis at the tissue, organ and whole organism levels can be described by 'physiologging'-that is, the use of onboard miniature electronic devices to record physiological metrics of animals in captivity or free-living in the wild. Despite its origins in the 1960s, physiologging has evolved more slowly than its umbrella field of biologging. However, the recording of physiological metrics in free-living animals will be key to solving some of the greatest challenges in biodiversity conservation, issues pertaining to animal health and welfare, and for inspiring future therapeutic strategies for human health. Current physiologging technologies encompass the measurement of physiological variables such as heart rate, brain activity, body temperature, muscle stimulation and dynamic movement, yet future developments will allow for onboard logging of metrics relating to organelle, molecular and genetic function. This article is part of the theme issue 'Measuring physiology in free-living animals (Part II)'.

Diving physiology of marine mammals and birds: the development of biologging techniques

In the 1940s, Scholander and Irving revealed fundamental physiological responses to forced diving of marine mammals and birds, setting the stage for the study of diving physiology. Since then, diving physiology research has moved from the laboratory to the field. Modern biologging, with the development of microprocessor technology, recorder memory capacity and battery life, has advanced and expanded investigations of the diving physiology of marine mammals and birds. This review describes a brief history of the start of field diving physiology investigations, including the invention of the time depth recorder, and then tracks the use of biologging studies in four key diving physiology topics: heart rate, blood flow, body temperature and oxygen store management. Investigations of diving heart rates in cetaceans and O2 store management in diving emperor penguins are highlighted to emphasize the value of diving physiology biologging research. The review concludes with current challenges, remaining diving physiology questions and what technologies are needed to advance the field. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Fur seals do, but sea lions don't - cross taxa insights into exhalation during ascent from dives

Management of gases during diving is not well understood across marine mammal species. Prior to diving, phocid (true) seals generally exhale, a behaviour thought to assist with the prevention of decompression sickness. Otariid seals (fur seals and sea lions) have a greater reliance on their lung oxygen stores, and inhale prior to diving. One otariid, the Antarctic fur seal (Arctocephalus gazella), then exhales during the final 50-85% of the return to the surface, which may prevent another gas management issue: shallow-water blackout. Here, we compare data collected from animal-attached tags (video cameras, hydrophones and conductivity sensors) deployed on a suite of otariid seal species to examine the ubiquity of ascent exhalations for this group. We find evidence for ascent exhalations across four fur seal species, but that such exhalations are absent for three sea lion species. Fur seals and sea lions are no longer genetically separated into distinct subfamilies, but are morphologically distinguished by the thick underfur layer of fur seals. Together with their smaller size and energetic dives, we suggest their air-filled fur might underlie the need to perform these exhalations, although whether to reduce buoyancy and ascent speed, for the avoidance of shallow-water blackout or to prevent other cardiovascular management issues in their diving remains unclear. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Shining new light on sensory brain activation and physiological measurement in seals using wearable optical technology

Sensory ecology and physiology of free-ranging animals is challenging to study but underpins our understanding of decision-making in the wild. Existing non-invasive human biomedical technology offers tools that could be harnessed to address these challenges. Functional near-infrared spectroscopy (fNIRS), a wearable, non-invasive biomedical imaging technique measures oxy- and deoxyhaemoglobin concentration changes that can be used to detect localized neural activation in the brain. We tested the efficacy of fNIRS to detect cortical activation in grey seals (Halichoerus grypus) and identify regions of the cortex associated with different senses (vision, hearing and touch). The activation of specific cerebral areas in seals was detected by fNIRS in responses to light (vision), sound (hearing) and whisker stimulation (touch). Physiological parameters, including heart and breathing rate, were also extracted from the fNIRS signal, which allowed neural and physiological responses to be monitored simultaneously. This is, to our knowledge, the first time fNIRS has been used to detect cortical activation in a non-domesticated or laboratory animal. Because fNIRS is non-invasive and wearable, this study demonstrates its potential as a tool to quantitatively investigate sensory perception and brain function while simultaneously recording heart rate, tissue and arterial oxygen saturation of haemoglobin, perfusion changes and breathing rate in free-ranging animals. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Introduction to the theme issue: Measuring physiology in free-living animals

By describing where animals go, biologging technologies (i.e. animal attached logging of biological variables with small electronic devices) have been used to document the remarkable athletic feats of wild animals since the 1940s. The rapid development and miniaturization of physiologging (i.e. logging of physiological variables such as heart rate, blood oxygen content, lactate, breathing frequency and tidal volume on devices attached to animals) technologies in recent times (e.g. devices that weigh less than 2 g mass that can measure electrical biopotentials for days to weeks) has provided astonishing insights into the physiology of free-living animals to document how and why wild animals undertake these extreme feats. Now, physiologging, which was traditionally hindered by technological limitations, device size, ethics and logistics, is poised to benefit enormously from the on-going developments in biomedical and sports wearables technologies. Such technologies are already improving animal welfare and yield in agriculture and aquaculture, but may also reveal future pathways for therapeutic interventions in human health by shedding light on the physiological mechanisms with which free-living animals undertake some of the most extreme and impressive performances on earth. This article is part of the theme issue 'Measuring physiology in free-living animals (Part I)'.

Partial pressure of oxygen in adipose tissue and its relationship with fatness in a natural animal model of extreme fat deposition, the grey seal

Excessive adiposity is associated with altered oxygen tension and comorbidities in humans. In contrast, marine mammals have high adiposity with no apparent detrimental effects. However, partial pressure of oxygen (Po2 ) in their subcutaneous adipose tissue (blubber) and its relationship with fatness have not been reported. We measured Po2 and temperature at different blubber depths in 12 healthy juvenile grey seals. Fatness was estimated from blubber thickness and morphometric parameters. Simultaneously, we monitored breathing pattern; heart rate and arterial blood saturation with a pulse oximeter; and relative changes in total hemoglobin, deoxyhemoglobin, and oxyhemoglobin in blubber capillaries using near-infrared spectroscopy (NIRS) as proxies for local oxygenation changes. Blubber Po2 ranged from 14.5 to 71.4 mmHg (39.2 ± 14.1 mmHg), which is similar to values reported in other species. Blubber Po2 was strongly and negatively associated with fatness (LME: p < 0.0001, R2marginal = 0.53, R2conditional = 0.64, n = 10), but not with blubber depth. No other parameters explained variability in Po2 , suggesting arterial blood and local oxygen delivery did not vary within and between measurements. The fall in blubber Po2 with increased fatness in seals is consistent with other animal models of rapid fat deposition. However, the Po2  levels at which blubber becomes hypoxic and consequences of low blubber Po2 for its health and function, particularly in very fat individuals, remain unknown. How seals avoid detrimental effects of low oxygen tension in adipose tissue, despite their high and fluctuating adiposity, is a fruitful avenue to explore.

Demographic History, Adaptation, and NRAP Convergent Evolution at Amino Acid Residue 100 in the World Northernmost Cattle from Siberia

Native cattle breeds represent an important cultural heritage. They are a reservoir of genetic variation useful for properly responding to agriculture needs in the light of ongoing climate changes. Evolutionary processes that occur in response to extreme environmental conditions could also be better understood using adapted local populations. Herein, different evolutionary histories of the world northernmost native cattle breeds from Russia were investigated. They highlighted Kholmogory as a typical taurine cattle, whereas Yakut cattle separated from European taurines approximately 5,000 years ago and contain numerous ancestral and some novel genetic variants allowing their adaptation to harsh conditions of living above the Polar Circle. Scans for selection signatures pointed to several common gene pathways related to adaptation to harsh climates in both breeds. But genes affected by selection from these pathways were mostly different. A Yakut cattle breed-specific missense mutation in a highly conserved NRAP gene represents a unique example of a young amino acid residue convergent change shared with at least 16 species of hibernating/cold-adapted mammals from six distinct phylogenetic orders. This suggests a convergent evolution event along the mammalian phylogenetic tree and fast fixation in a single isolated cattle population exposed to a harsh climate.

Too big to study? The biologging approach to understanding the behavioural energetics of ocean giants

Wild animals are under selective pressure to optimise energy budgets; therefore, quantifying energy expenditure, intake and allocation to specific activities is important if we are to understand how animals survive in their environment. One approach toward estimating energy budgets has involved measuring oxygen consumption rates under controlled conditions and constructing allometric relationships across species. However, studying 'giant' marine vertebrates (e.g. pelagic sharks, whales) in this way is logistically difficult or impossible. An alternative approach involves the use of increasingly sophisticated electronic tags that have allowed recordings of behaviour, internal states and the surrounding environment of marine animals. This Review outlines how we could study the energy expenditure and intake of free-living ocean giants using this 'biologging' technology. There are kinematic, physiological and theoretical approaches for estimating energy expenditure, each of which has merits and limitations. Importantly, tag-derived energy proxies can hardly be validated against oxygen consumption rates for giant species. The proxies are thus qualitative, rather than quantitative, estimates of energy expenditure, and have more limited utilities. Despite this limitation, these proxies allow us to study the energetics of ocean giants in their behavioural context, providing insight into how these animals optimise their energy budgets under natural conditions. We also outline how information on energy intake and foraging behaviour can be gained from tag data. These methods are becoming increasingly important owing to the natural and anthropogenic environmental changes faced by ocean giants that can alter their energy budgets, fitness and, ultimately, population sizes.

Field Physiology: Studying Organismal Function in the Natural Environment

Continuous physiological measurements collected in field settings are essential to understand baseline, free-ranging physiology, physiological range and variability, and the physiological responses of organisms to disturbances. This article presents a current summary of the available technologies to continuously measure the direct physiological parameters in the field at high-resolution/instantaneous timescales from freely behaving animals. There is a particular focus on advantages versus disadvantages of available methods as well as emerging technologies "on the horizon" that may have been validated in captive or laboratory-based scenarios but have yet to be applied in the wild. Systems to record physiological variables from free-ranging animals are reviewed, including radio (VHF/UFH) telemetry, acoustic telemetry, and dataloggers. Physiological parameters that have been continuously measured in the field are addressed in seven sections including heart rate and electrocardiography (ECG); electromyography (EMG); electroencephalography (EEG); body temperature; respiratory, blood, and muscle oxygen; gastric pH and motility; and blood pressure and flow. The primary focal sections are heart rate and temperature as these can be, and have been, extensively studied in free-ranging organisms. Predicted aspects of future innovation in physiological monitoring are also discussed. The article concludes with an overview of best practices and points to consider regarding experimental designs, cautions, and effects on animals. © 2021 American Physiological Society. Compr Physiol 11:1979-2015, 2021.

When the human brain goes diving: using near-infrared spectroscopy to measure cerebral and systemic cardiovascular responses to deep, breath-hold diving in elite freedivers

Continuous measurements of haemodynamic and oxygenation changes in free living animals remain elusive. However, developments in biomedical technologies may help to fill this knowledge gap. One such technology is continuous-wave near-infrared spectroscopy (CW-NIRS)-a wearable and non-invasive optical technology. Here, we develop a marinized CW-NIRS system and deploy it on elite competition freedivers to test its capacity to function during deep freediving to 107 m depth. We use the oxyhaemoglobin and deoxyhaemoglobin concentration changes measured with CW-NIRS to monitor cerebral haemodynamic changes and oxygenation, arterial saturation and heart rate. Furthermore, using concentration changes in oxyhaemoglobin engendered by cardiac pulsation, we demonstrate the ability to conduct additional feature exploration of cardiac-dependent haemodynamic changes. Freedivers showed cerebral haemodynamic changes characteristic of apnoeic diving, while some divers also showed considerable elevations in venous blood volumes close to the end of diving. Some freedivers also showed pronounced arterial deoxygenation, the most extreme of which resulted in an arterial saturation of 25%. Freedivers also displayed heart rate changes that were comparable to diving mammals both in magnitude and patterns of change. Finally, changes in cardiac waveform associated with heart rates less than 40 bpm were associated with changes indicative of a reduction in vascular compliance. The success here of CW-NIRS to non-invasively measure a suite of physiological phenomenon in a deep-diving mammal highlights its efficacy as a future physiological monitoring tool for human freedivers as well as free living animals. This article is part of the theme issue 'Measuring physiology in free-living animals (Part II)'.

Marine mammal conservation: over the horizon

Marine mammals can play important ecological roles in aquatic ecosystems, and their presence can be key to community structure and function. Consequently, marine mammals are often considered indicators of ecosystem health and flagship species. Yet, historical population declines caused by exploitation, and additional current threats, such as climate change, fisheries bycatch, pollution and maritime development, continue to impact many marine mammal species, and at least 25% are classified as threatened (Critically Endangered, Endangered or Vulnerable) on the IUCN Red List. Conversely, some species have experienced population increases/recoveries in recent decades, reflecting management interventions, and are heralded as conservation successes. To continue these successes and reverse the downward trajectories of at-risk species, it is necessary to evaluate the threats faced by marine mammals and the conservation mechanisms available to address them. Additionally, there is a need to identify evidence-based priorities of both research and conservation needs across a range of settings and taxa. To that effect we: (1) outline the key threats to marine mammals and their impacts, identify the associated knowledge gaps and recommend actions needed; (2) discuss the merits and downfalls of established and emerging conservation mechanisms; (3) outline the application of research and monitoring techniques; and (4) highlight particular taxa/populations that are in urgent need of focus.

An integrated comparative physiology and molecular approach pinpoints mediators of breath-hold capacity in dolphins

Background and objectives

Ischemic events, such as ischemic heart disease and stroke, are the number one cause of death globally. Ischemia prevents blood, carrying essential nutrients and oxygen, from reaching tissues, leading to cell and tissue death, and eventual organ failure. While humans are relatively intolerant to ischemic events, other species, such as marine mammals, have evolved a unique tolerance to chronic ischemia/reperfusion during apneic diving. To identify possible molecular features of an increased tolerance for apnea, we examined changes in gene expression in breath-holding dolphins.

Methodology

Here, we capitalized on the adaptations possesed by bottlenose dolphins (Tursiops truncatus) for diving as a comparative model of ischemic stress and hypoxia tolerance to identify molecular features associated with breath holding. Given that signals in the blood may influence physiological changes during diving, we used RNA-Seq and enzyme assays to examine time-dependent changes in gene expression in the blood of breath-holding dolphins.

Results

We observed time-dependent upregulation of the arachidonate 5-lipoxygenase (ALOX5) gene and increased lipoxygenase activity during breath holding. ALOX5 has been shown to be activated during hypoxia in rodent models, and its metabolites, leukotrienes, induce vasoconstriction.

Conclusions and implications

The upregulation of ALOX5 mRNA occurred within the calculated aerobic dive limit of the species, suggesting that ALOX5 may play a role in the dolphin’s physiological response to diving, particularly in a pro-inflammatory response to ischemia and in promoting vasoconstriction. These observations pinpoint a potential molecular mechanism by which dolphins, and perhaps other marine mammals, respond to the prolonged breath holds associated with diving.

Collision risk modelling for tidal energy devices: A flexible simulation-based approach

The marine renewable energy industry is expanding as countries strive to reach climate targets as set out in the Paris Agreement. For tidal energy devices, the potential risk for animals to collide with a device, particularly its moving parts such as rotor blades, is often a major barrier in the consenting process. Theoretical work surrounding collision risk has commonly made use of a formulaic modelling approach. However, whilst providing a platform to assess conventional horizontal axis tidal turbines, the frameworks applied lack the flexibility to incorporate novel device designs or more complex animal movement parameters (e.g. dive trajectories). To demonstrate the novel simulation-based approach to estimating collision probabilities a hypothetical case study was used to demonstrated how the approach can assess the influence that variations in ecological and behavioural data had on collision probabilities. To do this, a tidal kite moving in a 3D figure-of-eight trajectory and a seal-shaped object were modelled and variations to angle of approach, speed and size of the animal were made. To further improve the collision risk estimates, results of the simulations were post-processed by integrating a hypothetical dive profile. The simulations showed how variation in the input parameters and additional post-processing influence collision probabilities. Our results demonstrate the potential for using this simulation-based approach for assessing collision risk, highlighting the flexibility it offers by way of incorporating empirical data or expert elicitation to better inform the modelling process. This framework, where device type, configuration and animal-related parameters can be varied with relative simplicity, on a case-by-case basis, provides a more tailored tool for assessing a diverse range of interactions between marine renewable energy developments and receptors. In providing a robust and transparent quantitative approach to addressing collision risk this flexible approach can better inform the decision-making process and aid progress with respect to developing a renewable energy industry in a sustainable manner. Therefore, the approach outlined has clear applications that are relevant to many stakeholders and can contribute to our ability to ensure we achieve sustainable growth in the marine renewable energy industry as part of a global strategy to combat climate change.

Physiological resiliency in diving mammals: Insights on hypoxia protection using the Krogh principle to understand COVID-19 symptoms

Sequential diving by wild marine mammals results in a lifetime of rapid physiological transitions between lung collapse-reinflation, bradycardia-tachycardia, vasoconstriction-vasodilation, and oxygen store depletion-restoration. The result is a cycle of normoxia and hypoxia in which blood oxygen partial pressures can decline to <20–30 mmHg during a dive, a level considered injurious to oxygen-dependent human tissues (i.e., brain, heart). Safeguards in the form of enhanced on-board oxygen stores, selective oxygen transport, and unique tissue buffering capacities enable marine-adapted mammals to maintain physiological homeostasis and energy metabolism even when breathing and pulmonary gas exchange cease. This stands in stark contrast to the vulnerability of oxygen-sensitive tissues in humans that may undergo irreversible damage within minutes of ischemia and tissue hypoxia. Recently, these differences in protection against hypoxic injury have become evident in the systemic, multi-organ physiological failure during COVID-19 infection in humans. Prolonged recoveries in some patients have led to delays in the return to normal exercise levels and cognitive function even months later. Rather than a single solution to this problem, we find that marine mammals rely on a unique, integrative assemblage of protections to avoid the deleterious impacts of hypoxia on tissues. Built across evolutionary time, these solutions provide a natural template for identifying the potential for tissue damage when oxygen is lacking, and for guiding management decisions to support oxygen-deprived tissues in other mammalian species, including humans, challenged by hypoxia.

Extreme diving in mammals: first estimates of behavioural aerobic dive limits in Cuvier's beaked whales

We analysed 3680 dives from 23 satellite-linked tags deployed on Cuvier's beaked whales to assess the relationship between long duration dives and inter-deep dive intervals and to estimate aerobic dive limit (ADL). The median duration of presumed foraging dives was 59 min and 5% of dives exceeded 77.7 min. We found no relationship between the longest 5% of dive durations and the following inter-deep dive interval nor any relationship with the ventilation period immediately prior to or following a long dive. We suggest that Cuvier's beaked whales have low metabolic rates, high oxygen storage capacities and a high acid-buffering capacity to deal with the by-products of both aerobic and anaerobic metabolism, which enables them to extend dive durations and exploit their bathypelagic foraging habitats.

Physiological correlates of cognitive load in laparoscopic surgery

Laparoscopic surgery can be exhausting and frustrating, and the cognitive load experienced by surgeons may have a major impact on patient safety as well as healthcare economics. As cognitive load decreases with increasing proficiency, its robust assessment through physiological data can help to develop more effective training and certification procedures in this area. We measured data from 31 novices during laparoscopic exercises to extract features based on cardiac and ocular variables. These were compared with traditional behavioural and subjective measures in a dual-task setting. We found significant correlations between the features and the traditional measures. The subjective task difficulty, reaction time, and completion time were well predicted by the physiology features. Reaction times to randomly timed auditory stimuli were correlated with the mean of the heart rate (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$r = - 0.29$$\end{document}r=-0.29) and heart rate variability (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$r = 0.4$$\end{document}r=0.4). Completion times were correlated with the physiologically predicted values with a correlation coefficient of 0.84. We found that the multi-modal set of physiology features was a better predictor than any individual feature and artificial neural networks performed better than linear regression. The physiological correlates studied in this paper, translated into technological products, could help develop standardised and more easily regulated frameworks for training and certification.

The Mammalian Diving Response: Inroads to Its Neural Control

The mammalian diving response (DR) is a remarkable behavior that was first formally studied by Laurence Irving and Per Scholander in the late 1930s. The DR is called such because it is most prominent in marine mammals such as seals, whales, and dolphins, but nevertheless is found in all mammals studied. It consists generally of breathing cessation (apnea), a dramatic slowing of heart rate (bradycardia), and an increase in peripheral vasoconstriction. The DR is thought to conserve vital oxygen stores and thus maintain life by directing perfusion to the two organs most essential for life-the heart and the brain. The DR is important, not only for its dramatic power over autonomic function, but also because it alters normal homeostatic reflexes such as the baroreceptor reflex and respiratory chemoreceptor reflex. The neurons driving the reflex circuits for the DR are contained within the medulla and spinal cord since the response remains after the brainstem transection at the pontomedullary junction. Neuroanatomical and physiological data suggesting brainstem areas important for the apnea, bradycardia, and peripheral vasoconstriction induced by underwater submersion are reviewed. Defining the brainstem circuit for the DR may open broad avenues for understanding the mechanisms of suprabulbar control of autonomic function in general, as well as implicate its role in some clinical states. Knowledge of the proposed diving circuit should facilitate studies on elite human divers performing breath-holding dives as well as investigations on sudden infant death syndrome (SIDS), stroke, migraine headache, and arrhythmias. We have speculated that the DR is the most powerful autonomic reflex known.

microRNA profiling in the Weddell seal suggests novel regulatory mechanisms contributing to diving adaptation

Background

The Weddell Seal (Leptonychotes weddelli) represents a remarkable example of adaptation to diving among marine mammals. This species is capable of diving > 900 m deep and remaining underwater for more than 60 min. A number of key physiological specializations have been identified, including the low levels of aerobic, lipid-based metabolism under hypoxia, significant increase in oxygen storage in blood and muscle; high blood volume and extreme cardiovascular control. These adaptations have been linked to increased abundance of key proteins, suggesting an important, yet still understudied role for gene reprogramming.

In this study, we investigate the possibility that post-transcriptional gene regulation by microRNAs (miRNAs) has contributed to the adaptive evolution of diving capacities in the Weddell Seal.

Results

Using small RNA data across 4 tissues (brain, heart, muscle and plasma), in 3 biological replicates, we generate the first miRNA annotation in this species, consisting of 559 high confidence, manually curated miRNA loci. Evolutionary analyses of miRNA gain and loss highlight a high number of Weddell seal specific miRNAs.

Four hundred sixteen miRNAs were differentially expressed (DE) among tissues, whereas 80 miRNAs were differentially expressed (DE) across all tissues between pups and adults and age differences for specific tissues were detected in 188 miRNAs. mRNA targets of these altered miRNAs identify possible protective mechanisms in individual tissues, particularly relevant to hypoxia tolerance, anti-apoptotic pathways, and nitric oxide signal transduction. Novel, lineage-specific miRNAs associated with developmental changes target genes with roles in angiogenesis and vasoregulatory signaling.

Conclusions

Altogether, we provide an overview of miRNA composition and evolution in the Weddell seal, and the first insights into their possible role in the specialization to diving.

Deiminated proteins and extracellular vesicles as novel biomarkers in pinnipeds: Grey seal (Halichoerus gryptus) and harbour seal (Phoca vitulina)

Peptidylarginine deiminases (PADs) are phylogenetically conserved calcium-dependent enzymes which post-translationally convert arginine into citrulline in target proteins in an irreversible manner, leading to functional and structural changes in target proteins. Protein deimination can cause the generation of neo-epitopes, affect gene regulation and also allow for protein moonlighting and therefore facilitate multifaceted functions of the same protein. PADs are furthermore a key regulator of cellular release of extracellular vesicle (EVs), which are found in most body fluids and participate in cellular communication via transfer of cargo proteins and genetic material. In this study, post-translationally deiminated proteins and EVs were assessed in sera of two seal species, grey seal and harbour seal. We report a poly-dispersed population of serum-EVs, which were positive for phylogenetically conserved EV-specific markers and characterised by transmission electron microscopy. A number of deiminated proteins critical for immune and metabolic functions were identified in the seal sera and varied somewhat between the two species under study, while some targets were in common. EV profiles of the seal sera further revealed that key microRNAs for inflammation, immunity and hypoxia also vary between the two species. Protein deimination and EVs profiles may be useful biomarkers for assessing health status of sea mammals, which face environmental challenges, including opportunistic infection, pollution and shifting habitat due to global warming.

Natural Tolerance to Ischemia and Hypoxemia in Diving Mammals: A Review

Reperfusion injury follows ischemia/reperfusion events occurring during myocardial infarction, stroke, embolism, and other peripheral vascular diseases. Decreased blood flow and reduced oxygen tension during ischemic episodes activate cellular pathways that upregulate pro-inflammatory signaling and promote oxidant generation. Reperfusion after ischemia recruits inflammatory cells to the vascular wall, further exacerbating oxidant production and ultimately resulting in cell death, tissue injury, and organ dysfunction. Diving mammals tolerate repetitive episodes of peripheral ischemia/reperfusion as part of the cardiovascular adjustments supporting long duration dives. These adjustments allow marine mammals to optimize the use of their body oxygen stores while diving but can result in selectively reduced perfusion to peripheral tissues. Remarkably, diving mammals show no apparent detrimental effects associated with these ischemia/reperfusion events. Here, we review the current knowledge regarding the strategies marine mammals use to suppress inflammation and cope with oxidant generation potentially derived from diving-induced ischemia/reperfusion.