Physiological and Genetic Adaptations to Diving in Sea Nomads

High-altitude hypoxia promotes BRD4-mediated activation of the Wnt/β-catenin pathway and disruption of intestinal barrier

Hypobaric hypoxia, commonly experienced at elevated altitudes, presents significant physiological challenges. Our investigation is centered on the impact of the bromodomain protein 4 (BRD4) under these conditions, especially its interaction with the Wnt/β-Catenin pathway and resultant effects on glycolytic inflammation and intestinal barrier stability. By combining transcriptome sequencing with bioinformatics, we identified BRD4's key role in hypoxia-related intestinal anomalies. Clinical parameters of altitude sickness patients, including serum BRD4 levels, inflammatory markers, and barrier integrity metrics, were scrutinized. In vitro studies using CCD 841 CoN cells depicted expression changes in BRD4, Interleukin (IL)-1β, IL-6, and β-Catenin. Transepithelial electrical resistance (TEER) and FD4 analyses assessed barrier resilience. Hypoxia-induced mouse models, analyzed via H&E staining and Western blot, provided insights into barrier and protein alterations. Under hypoxic conditions, marked BRD4 expression variations emerged. Elevated serum BRD4 in patients coincided with intensified Wnt signaling, inflammation, and barrier deterioration. In vitro, findings showed hypoxia-induced upregulation of BRD4 and inflammatory markers but a decline in Occludin and ZO1, affecting barrier strength-effects mitigated by BRD4 inhibition. Mouse models echoed these patterns, linking BRD4 upregulation in hypoxia to barrier perturbations. Hypobaric hypoxia-induced BRD4 upregulation disrupts the Wnt/β-Catenin signaling, sparking glycolysis-fueled inflammation and weakening intestinal tight junctions and barrier degradation.

Protective alleles and precision healthcare in crewed spaceflight

Common and rare alleles are now being annotated across millions of human genomes, and omics technologies are increasingly being used to develop health and treatment recommendations. However, these alleles have not yet been systematically characterized relative to aerospace medicine. Here, we review published alleles naturally found in human cohorts that have a likely protective effect, which is linked to decreased cancer risk and improved bone, muscular, and cardiovascular health. Although some technical and ethical challenges remain, research into these protective mechanisms could translate into improved nutrition, exercise, and health recommendations for crew members during deep space missions.

Apnoea as a novel method to improve exercise performance: A current state of the literature

Acute breath-holding (apnoea) induces a spleen contraction leading to a transient increase in haemoglobin concentration. Additionally, the apnoea-induced hypoxia has been shown to lead to an increase in erythropoietin concentration up to 5 h after acute breath-holding, suggesting long-term haemoglobin enhancement. Given its potential to improve haemoglobin content, an important determinant for oxygen transport, apnoea has been suggested as a novel training method to improve aerobic performance. This review aims to provide an update on the current state of the literature on this topic. Although the apnoea-induced spleen contraction appears to be effective in improving oxygen uptake kinetics, this does not seem to transfer into immediately improved aerobic performance when apnoea is integrated into a warm-up. Furthermore, only long and intense apnoea protocols in individuals who are experienced in breath-holding show increased erythropoietin and reticulocytes. So far, studies on inexperienced individuals have failed to induce acute changes in erythropoietin concentration following apnoea. As such, apnoea training protocols fail to demonstrate longitudinal changes in haemoglobin mass and aerobic performance. The low hypoxic dose, as evidenced by minor oxygen desaturation, is likely insufficient to elicit a strong erythropoietic response. Apnoea therefore does not seem to be useful for improving aerobic performance. However, variations in apnoea, such as hypoventilation training at low lung volume and repeated-sprint training in hypoxia through short end-expiratory breath-holds, have been shown to induce metabolic adaptations and improve several physical qualities. This shows promise for application of dynamic apnoea in order to improve exercise performance. HIGHLIGHTS: What is the topic of this review? Apnoea is considered as an innovative method to improve performance. This review discusses the effectiveness of apnoea (training) on performance. What advances does it highlight? Although the apnoea-induced spleen contraction and the increase in EPO observed in freedivers seem promising to improve haematological variables both acutely and on the long term, they do not improve exercise performance in an athletic population. However, performing repeated sprints on end-expiratory breath-holds seems promising to improve repeated-sprint capacity.

Acute moderate normobaric hypoxia does not modify circulating thyroid hormone concentrations induced by 1 h of head-out cold-water immersion

This study tested the hypothesis that acute moderate normobaric hypoxia augments circulating thyroid hormone concentrations during and following 1 h of cold head-out water immersion (HOWI), compared with when cold HOWI is completed during normobaric normoxia. In a randomized crossover single-blind design, 12 healthy adults (27 ± 2 yr, 2 women) completed 1 h of cold (22.0 ± 0.1°C) HOWI breathing either normobaric normoxia ([Formula: see text] = 0.21) or normobaric hypoxia ([Formula: see text] = 0.14). Free and total thyroxine (T3) and triiodothyronine (T4), and thyroid-stimulating hormone (TSH) concentrations were measured in venous blood samples obtained before (baseline), during (15-, 30-, and 60 min), and 15 min following HOWI (post-), and were corrected for changes in plasma volume. Arterial oxyhemoglobin saturation and core (rectal) temperature were measured continuously. Arterial oxyhemoglobin saturation was lower during hypoxia (90 ± 3%) compared with normoxia (98 ± 1%, P < 0.001). Core temperature fell from baseline (normoxia: 37.2 ± 0.4°C, hypoxia: 37.2 ± 0.4°C) to post-cold HOWI (normoxia: 36.4 ± 0.5°C, hypoxia: 36.3 ± 0.5°C, P < 0.001) in both conditions but did not change differently between conditions (condition × time: P = 0.552). Circulating TSH, total T3, free T4, total T3, and free T4 concentrations demonstrated significant main effects of time (all P ≤ 0.024), but these changes did not differ between normoxic and hypoxic conditions (condition × time: all P ≥ 0.163). These data indicate that acute moderate normobaric hypoxia does not modify the circulating thyroid hormone response during 1 h of cold HOWI.NEW & NOTEWORTHY Acute head-out cold (22°C) water immersion (HOWI) decreased core temperature and increased thermogenesis. This thermogenic response was paralleled by the activation of the hypothalamic-pituitary-thyroid axis, as evidenced by changes in thyroid hormones. However, cold HOWI in combination with moderate normobaric hypoxia did not modify the thermogenic nor the circulating thyroid hormone response. This finding suggests that hypoxia-induced alterations in thyroid hormone concentrations are unlikely to acutely contribute to adaptations resulting from repeated cold-water exposures.

Larger spleens and greater splenic contraction during exercise may be an adaptive characteristic of Nepali Sherpa at high-altitude

OBJECTIVES

The Sherpa ethnic group living at altitude in Nepal may have experienced natural selection in response to chronic hypoxia. We have previously shown that Sherpa in Kathmandu (1400 m) possess larger spleens and a greater apnea-induced splenic contraction compared to lowland Nepalis. This may be significant for exercise capacity at altitude as the human spleen responds to stress-induced catecholamine secretion by an immediate contraction, which results in transiently elevated hemoglobin concentration ([Hb]).

METHODS

To investigate splenic contraction in response to exercise at high-altitude (4300 m; Pb = ~450 Torr), we recruited 63 acclimatized Sherpa (29F) and 14 Nepali non-Sherpa (7F). Spleen volume was measured before and after maximal exercise on a cycle ergometer by ultrasonography, along with [Hb] and oxygen saturation (SpO2).

RESULTS

Resting spleen volume was larger in the Sherpa compared with Nepali non-Sherpa (237 ± 62 vs. 165 ± 34 mL, p < .001), as was the exercise-induced splenic contraction (Δspleen volume, 91 ± 40 vs. 38 ± 32 mL, p < .001). From rest to exercise, [Hb] increased (1.2 to 1.4 g.dl-1), SpO2 decreased (~9%) and calculated arterial oxygen content (CaO2) remained stable, but there were no significant differences between groups. In Sherpa, both resting spleen volume and the Δspleen volume were modest positive predictors of the change (Δ) in [Hb] and CaO2 with exercise (p-values from .026 to .037 and R2 values from 0.059 to 0.067 for the predictor variable).

CONCLUSIONS

Larger spleens and greater splenic contraction may be an adaptive characteristic of Nepali Sherpa to increase CaO2 during exercise at altitude, but the direct link between spleen size/function and hypoxia tolerance remains unclear.

Hemoglobin concentration and blood shift during dry static apnea in elite breath hold divers

Introduction

Elite breath-hold divers (BHD) enduring apneas of more than 5 min are characterized by tolerance to arterial blood oxygen levels of 4.3 kPa and low oxygen-consumption in their hearts and skeletal muscles, similar to adult seals. Adult seals possess an adaptive higher hemoglobin-concentration and Bohr effect than pups, and when sedated, adult seals demonstrate a blood shift from the spleen towards the brain, lungs, and heart during apnea. We hypothesized these observations to be similar in human BHD. Therefore, we measured hemoglobin- and 2,3-biphosphoglycerate-concentrations in BHD (n = 11) and matched controls (n = 11) at rest, while myocardial mass, spleen and lower extremity volumes were assessed at rest and during apnea in BHD.

Methods and results

After 4 min of apnea, left ventricular myocardial mass (LVMM) determined by 15O-H2O-PET/CT (n = 6) and cardiac MRI (n = 6), was unaltered compared to rest. During maximum apnea (∼6 min), lower extremity volume assessed by DXA-scan revealed a ∼268 mL decrease, and spleen volume, assessed by ultrasonography, decreased ∼102 mL. Compared to age, BMI and VO2max matched controls (n = 11), BHD had similar spleen sizes and 2,3- biphosphoglycerate-concentrations, but higher total hemoglobin-concentrations.

Conclusion

Our results indicate: 1) Apnea training in BHD may increase hemoglobin concentration as an oxygen conserving adaptation similar to adult diving mammals. 2) The blood shift during dry apnea in BHD is 162% more from the lower extremities than from the spleen. 3) In contrast to the previous theory of the blood shift demonstrated in sedated adult seals, blood shift is not towards the heart during dry apnea in humans.

Differential splenic responses to hyperoxic breathing at high altitude in Sherpa and lowlanders

The human spleen contracts in response to stress-induced catecholamine secretion, resulting in a temporary rise in haemoglobin concentration ([Hb]). Recent findings highlighted enhanced splenic response to exercise at high altitude in Sherpa, possibly due to a blunted splenic response to hypoxia. To explore the potential blunted splenic contraction in Sherpas at high altitude, we examined changes in spleen volume during hyperoxic breathing, comparing acclimatized Sherpa with acclimatized individuals of lowland ancestry. Our study included 14 non-Sherpa (7 female) residing at altitude for a mean continuous duration of 3 months and 46 Sherpa (24 female) with an average of 4 years altitude exposure. Participants underwent a hyperoxic breathing test at altitude (4300 m; barrometric pressure = ∼430 torr;P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$  = ∼90 torr). Throughout the test, we measured spleen volume using ultrasonography and monitored oxygen saturation (S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ). During rest, Sherpa exhibited larger spleens (226 ± 70 mL) compared to non-Sherpa (165 ± 34 mL; P < 0.001; effect size (ES) = 0.95, 95% CI: 0.3-1.6). In response to hyperoxia, non-Sherpa demonstrated 22 ± 12% increase in spleen size (35 ± 17 mL, 95% CI: 20.7-48.9; P < 0.001; ES = 1.8, 95% CI: 0.93-2.66), while spleen size remained unchanged in Sherpa (-2 ± 13 mL, 95% CI: -2.4 to 7.3; P = 0.640; ES = 0.18, 95% CI: -0.10 to 0.47). Our findings suggest that Sherpa and non-Sherpas of lowland ancestry exhibit distinct variations in spleen volume during hyperoxia at high altitude, potentially indicating two distinct splenic functions. In Sherpa, this phenomenon may signify a diminished splenic response to altitude-related hypoxia at rest, potentially contributing to enhanced splenic contractions during physical stress. Conversely, non-Sherpa experienced a transient increase in spleen size during hyperoxia, indicating an active tonic contraction, which may influence early altitude acclimatization in lowlanders by raising [Hb].

Molecular genetic association of rs8099917 and rs1800795 polymorphisms in the progression of hepatitis Delta virus liver disease

Background

The relationship between viral infections and host factors holds high hopes for identifying the role of Interferon Lambda 3 (IFNL3) and Interleukin 6 (IL-6) polymorphisms in the development of Chronic Liver Disease (CLD) in patients infected with hepatitis Delta virus (HDV) in the Western Brazilian Amazon.

Methods

Cross-sectional study conducted with a cohort of 40 chronic HDV patients, 27 with CLD and 13 without evident liver damage. Biological samples from the participants were analyzed using the polymerase chain reaction (PCR) technique, followed by sequencing by the automated Sanger method.

Results

The rs8099917 T allele, from the IFNL3 gene, showed a higher frequency in both groups; however, it was not possible to establish an association with HDV infection [OR = 1.42 (0.42 - 4.75; p = 0.556 (95% CI). For IL-6, the rs1800795 G allele was superior to rs1800795 C. Analyzing both distributions in the studied groups, any association with HDV was absent (p > 0.05).

Conclusion

The results suggest that the rs8099917 T/G (IFNL3) and rs1800795 G/C (IL-6) polymorphisms are not associated with the evolution of HDV in the studied population.

Earliest known funerary rites in Wallacea after the last glacial maximum

The insular region of Wallacea has become a focal point for studying Pleistocene human ecological and cultural adaptations in island environments, however, little is understood about early burial traditions during the Pleistocene. Here we investigate maritime interactions and burial practices at Ratu Mali 2, an elevated coastal cave site on the small island of Kisar in the Lesser Sunda Islands of eastern Indonesia dated to 15,500-3700 cal. BP. This multidisciplinary study demonstrates extreme marine dietary adaptations, engagement with an extensive exchange network across open seas, and early mortuary practices. A flexed male and a female, interred in a single grave with abundant shellfish and obsidian at Ratu Mali 2 by 14.7 ka are the oldest known human burials in Wallacea with established funerary rites. These findings highlight the impressive flexibility of our species in marginal environments and provide insight into the earliest known ritualised treatment of the dead in Wallacea.

Splenic stromal niches in homeostasis and immunity

The spleen is a gatekeeper of systemic immunity where immune responses against blood-borne pathogens are initiated and sustained. Non-haematopoietic stromal cells construct microanatomical niches in the spleen that make diverse contributions to physiological spleen functions and regulate the homeostasis of immune cells. Additional signals from spleen autonomic nerves also modify immune responses. Recent insight into the diversity of the splenic fibroblastic stromal cells has revised our understanding of how these cells help to orchestrate splenic responses to infection and contribute to immune responses. In this Review, we examine our current understanding of how stromal niches and neuroimmune circuits direct the immunological functions of the spleen, with a focus on T cell immunity.

Tissue Perfusion and Diffusion and Cellular Respiration: Transport and Utilization of Oxygen

This article provides an overview of the journey of inspired oxygen after its uptake across the alveolar-capillary interface, and the interplay among tissue perfusion, diffusion, and cellular respiration in the transport and utilization of oxygen. The critical interactions between oxygen and its facilitative carriers (hemoglobin in red blood cells and myoglobin in muscle cells), and with other respiratory and vasoactive molecules (carbon dioxide, nitric oxide, and carbon monoxide), are emphasized to illustrate how this versatile system dynamically optimizes regional convective transport and diffusive gas exchange. The rates of reciprocal gas exchange in the lung and the periphery must be well-matched and sufficient for meeting the range of energy demands from rest to maximal stress but not excessive as to become toxic. The mobile red blood cells play a vital role in matching tissue perfusion and gas exchange by dynamically regulating the controlled uptake of oxygen and communicating regional metabolic signals across different organs. Intracellular oxygen diffusion and facilitation via myoglobin into the mitochondria, and utilization via electron transport chain and oxidative phosphorylation, are summarized. Physiological and pathophysiological adaptations are briefly described. Dysfunction of any component across this integrated system affects all other components and elicits corresponding structural and functional adaptation aimed at matching the capacities across the entire system and restoring equilibrium under normal and pathological conditions.

Deep phenotyping of 11,880 highlanders reveals novel adaptive traits in native Tibetans

Tibetans are the ideal population to study genetic adaptation in extreme environments. Here, we performed systematic phenotyping of 11,880 highlanders, covering 133 quantitative traits of 13 organ systems. We provided a comprehensive phenotypic atlas by comparing altitude adaptation and altitude acclimatization. We found the differences between adaptation and acclimatization are quantitative rather than qualitative, with a whole-system "blunted effect" seen in the adapted Tibetans. We characterized twelve different functional changes between adaptation and acclimatization. More importantly, we established a landscape of adaptive phenotypes of indigenous Tibetans, including 45 newly identified Tibetan adaptation-nominated traits, involving specific changes of Tibetans in internal organ state, metabolism, eye morphology, and skin pigmentation. In addition, we observed a sex-biased pattern between altitude acclimatization and adaptation. The generated atlas of phenotypic landscape provides new insights into understanding of human adaptation to high-altitude environments, and it serves as a valuable blueprint for future medical and physiological studies.

North African fox genomes show signatures of repeated introgression and adaptation to life in deserts

Elucidating the evolutionary process of animal adaptation to deserts is key to understanding adaptive responses to climate change. Here we generated 82 individual whole genomes of four fox species (genus Vulpes) inhabiting the Sahara Desert at different evolutionary times. We show that adaptation of new colonizing species to a hot arid environment has probably been facilitated by introgression and trans-species polymorphisms shared with older desert resident species, including a putatively adaptive 25 Mb genomic region. Scans for signatures of selection implicated genes affecting temperature perception, non-renal water loss and heat production in the recent adaptation of North African red foxes (Vulpes vulpes), after divergence from Eurasian populations approximately 78 thousand years ago. In the extreme desert specialists, Rueppell's fox (V. rueppellii) and fennec (V. zerda), we identified repeated signatures of selection in genes affecting renal water homeostasis supported by gene expression and physiological differences. Our study provides insights into the mechanisms and genetic underpinnings of a natural experiment of repeated adaptation to extreme conditions.

Comparative physiological anthropogeny: exploring molecular underpinnings of distinctly human phenotypes

Anthropogeny is a classic term encompassing transdisciplinary investigations of the origins of the human species. Comparative anthropogeny is a systematic comparison of humans and other living nonhuman hominids (so-called "great apes"), aiming to identify distinctly human features in health and disease, with the overall goal of explaining human origins. We begin with a historical perspective, briefly describing how the field progressed from the earliest evolutionary insights to the current emphasis on in-depth molecular and genomic investigations of "human-specific" biology and an increased appreciation for cultural impacts on human biology. While many such genetic differences between humans and other hominids have been revealed over the last two decades, this information remains insufficient to explain the most distinctive phenotypic traits distinguishing humans from other living hominids. Here we undertake a complementary approach of "comparative physiological anthropogeny," along the lines of the preclinical medical curriculum, i.e., beginning with anatomy and considering each physiological system and in each case considering genetic and molecular components that are relevant. What is ultimately needed is a systematic comparative approach at all levels from molecular to physiological to sociocultural, building networks of related information, drawing inferences, and generating testable hypotheses. The concluding section will touch on distinctive considerations in the study of human evolution, including the importance of gene-culture interactions.

A gene-level test for directional selection on gene expression

Most variants identified in human genome-wide association studies and scans for selection are noncoding. Interpretation of their effects and the way in which they contribute to phenotypic variation and adaptation in human populations is therefore limited by our understanding of gene regulation and the difficulty of confidently linking noncoding variants to genes. To overcome this, we developed a gene-wise test for population-specific selection based on combinations of regulatory variants. Specifically, we use the QX statistic to test for polygenic selection on cis-regulatory variants based on whether the variance across populations in the predicted expression of a particular gene is higher than expected under neutrality. We then applied this approach to human data, testing for selection on 17,388 protein-coding genes in 26 populations from the Thousand Genomes Project. We identified 45 genes with significant evidence (FDR<0.1) for selection, including FADS1, KHK, SULT1A2, ITGAM, and several genes in the HLA region. We further confirm that these signals correspond to plausible population-level differences in predicted expression. While the small number of significant genes (0.2%) is consistent with most cis-regulatory variation evolving under genetic drift or stabilizing selection, it remains possible that there are effects not captured in this study. Our gene-level QX score is independent of standard genomic tests for selection, and may therefore be useful in combination with traditional selection scans to specifically identify selection on regulatory variation. Overall, our results demonstrate the utility of combining population-level genomic data with functional data to understand the evolution of gene expression.

Training methods for maximal static apnea performance: a systematic review and meta-analysis

INTRODUCTION

Currently, there is an increase in people practicing freediving (FD) both in competition and leisure. As a sports practice, its modalities are grouped into static, dynamic, and constant weight apnea. The aim of this systematic review and meta-analysis (PROSPERO-CRD42021230322) was to identify the training methods used to improve the static apnea time (AT) performance.

EVIDENCE ACQUISITION

Ten training protocols were analyzed from eight studies published until March 09, 2022. The effect size (Hedge's g) and its confidence interval (CI<inf>95%</inf>) were calculated from the AT measured pre- and post-training.

EVIDENCE SYNTHESIS

Three different apnea training methods were verified, the breath-hold (BH) that uses BH exercises, physical training with strength and cardiorespiratory exercises, and cross training that combines BH exercises with physical training. These training methods were applied to 138 participants of both sexes with or without experience in apnea episode or diving practice. In general, the AT improvement showed a large effect after the interventions (g=1.30, CI<inf>95%</inf>=0.85-1.76, P<0.01).

CONCLUSIONS

All three methods were effective in improving static AT, however from the existing protocols is not possible to recommend an ideal to improve AT and therefore FD performance.

Increased spleen volume provoked by temperate head-out-of-water immersion

This study tested the hypotheses that 1) spleen volume increases during head-out-of-water immersion (HOWI) and returns to pre-HOWI values postdiuresis, and 2) the magnitude of apnea-induced spleen contraction increases when preapnea spleen volume is elevated. Spleen volume was measured before and after a set of five apneas in 12 healthy adults (28 ± 5 yr, 3 females) before, during (at 30 and 150 min), and 20 min after temperate temperature (36 ± 1°C) HOWI. At each time point, spleen length, width, and thickness were measured via ultrasound, and spleen volume was calculated using the Pilström equation. Compared with pre-HOWI (276 ± 88 mL), spleen volume was elevated at 30 (353 ± 94 mL, P < 0.01) and 150 (322 ± 87 mL, P < 0.01) min of HOWI but returned to pre-HOWI volume at post-HOWI (281 ± 90 mL, P = 0.58). Spleen volume decreased from pre- to postapnea bouts at each time point (P < 0.01). The magnitude of reduction in spleen volume from pre- to postapneas was elevated at 30 min of HOWI (-69 ± 24 mL) compared with pre-HOWI (-52 ± 20 mL, P = 0.04) but did not differ from pre-HOWI at 150 min of HOWI (-54 ± 16 mL, P = 0.99) and post-HOWI (-50 ± 18 mL, P = 0.87). Thus, spleen volume is increased throughout 180 min of HOWI, and whereas apnea-induced spleen contraction is augmented after 30 min of HOWI, the magnitude of spleen contraction is unaffected by HOWI thereafter.

Eight weeks of dry dynamic breath-hold training results in larger spleen volume but does not increase haemoglobin concentration

Purpose: It has previously been reported that repeated exposure to hypoxia increases spleen size and haemoglobin (HGB) level and recent reports on the effect apnoea has on spleen size and haematological parameters are contradictory. Therefore, this study aims to evaluate the effect apnoea training has on spleen size and haematological parameters.

Methods: The breath-holding (BH) group was comprised of 12 local student-athletes with no BH exercise experience who performed BH jogging and BH jumping rope dynamic apnoea protocols, five times weekly for 8 weeks. The BH event duration was progressively increased as the apnoea tolerance of the athletes improved (20 to 35 s). The same training task was performed by the control group (n = 10) without BH. Spleen sizes were measured with an ultrasound system and a complete blood cell analysis was performed on the median cubital venous blood.

Results: Spleen volume in the BH group increased from 109 ± 13 ml to 136 ± 13 ml (p < 0.001), and bulky platelets decreased from 70.50 ± 5.83 to 65.17 ± 5.87 (p = 0.034), but no changes were recorded for erythrocytes (p = 0.914), HGB (p = 0.637), PLTs (p = 0.346) and WBC (p = 0.532). No changes were recorded for the control group regarding spleen size or haematological parameters.

Conclusion: Eight weeks of dry dynamic apnoea training increased spleen size and decreased the number of circulating bulky platelets in the athletes who were assessed in this study. However, the baseline RBC counts and HGB levels of the athletes were not altered by the training programme.

Handling Ethics Dumping and Neo-Colonial Research: From the Laboratory to the Academic Literature

This paper explores that the topic of ethics dumping (ED), its causes and potential remedies. In ED, the weaknesses or gaps in ethics policies and systems of lower income countries are intentionally exploited for intellectual or financial gains through research and publishing by higher income countries with a more stringent or complex ethical infrastructure in which such research and publishing practices would not be permitted. Several examples are provided. Possible ED needs to be evaluated before research takes place, and detected prior to publication as an academic paper, because it might lead to a collaborative effort between a wealthier country with restrictive ethical policies and a less wealthy country with more permissive policies. Consequently, if that collaboration ultimately results in an academic paper, there are ethical ramifications of ED to scholarly communication. Institutional review board approval is central to avoid ED-based collaborations. Blind trust and goodwill alone cannot eliminate the exploitation of indigenous or "vulnerable" populations' intellect and resources. Combining community-based participatory research using clear codes of research conduct and a simple but robust verification system in academic publishing may reduce the risks of ED-based research from being published.

Time Domains of Hypoxia Responses and -Omics Insights

The ability to respond rapidly to changes in oxygen tension is critical for many forms of life. Challenges to oxygen homeostasis, specifically in the contexts of evolutionary biology and biomedicine, provide important insights into mechanisms of hypoxia adaptation and tolerance. Here we synthesize findings across varying time domains of hypoxia in terms of oxygen delivery, ranging from early animal to modern human evolution and examine the potential impacts of environmental and clinical challenges through emerging multi-omics approaches. We discuss how diverse animal species have adapted to hypoxic environments, how humans vary in their responses to hypoxia (i.e., in the context of high-altitude exposure, cardiopulmonary disease, and sleep apnea), and how findings from each of these fields inform the other and lead to promising new directions in basic and clinical hypoxia research.

Chemoreflex Control as the Cornerstone in Immersion Water Sports: Possible Role on Breath-Hold

Immersion water sports involve long-term apneas; therefore, athletes must physiologically adapt to maintain muscle oxygenation, despite not performing pulmonary ventilation. Breath-holding (i.e., apnea) is common in water sports, and it involves a decrease and increases PaO₂ and PaCO₂, respectively, as the primary signals that trigger the end of apnea. The principal physiological O₂ sensors are the carotid bodies, which are able to detect arterial gases and metabolic alterations before reaching the brain, which aids in adjusting the cardiorespiratory system. Moreover, the principal H⁺/CO₂ sensor is the retrotrapezoid nucleus, which is located at the brainstem level; this mechanism contributes to detecting respiratory and metabolic acidosis. Although these sensors have been characterized in pathophysiological states, current evidence shows a possible role for these mechanisms as physiological sensors during voluntary apnea. Divers and swimmer athletes have been found to displayed longer apnea times than land sports athletes, as well as decreased peripheral O₂ and central CO₂ chemoreflex control. However, although chemosensitivity at rest could be decreased, we recently found marked sympathoexcitation during maximum voluntary apnea in young swimmers, which could activate the spleen (which is a reservoir organ for oxygenated blood). Therefore, it is possible that the chemoreflex, autonomic function, and storage/delivery oxygen organ(s) are linked to apnea in immersion water sports. In this review, we summarized the available evidence related to chemoreflex control in immersion water sports. Subsequently, we propose a possible physiological mechanistic model that could contribute to providing new avenues for understanding the respiratory physiology of water sports.

The cardiosplenic axis: the prognostic role of the spleen in heart failure

Despite the number of available methods to predict prognosis in patients with heart failure, prognosis remains poor, likely because of marked patient heterogeneity and varied heart failure etiologies. Thus, identification of novel prognostic indicators to stratify risk in patients with heart failure is of paramount importance. The spleen is emerging as a potential novel prognostic indicator for heart failure. In this article, we provide an overview of the current prognostic tools used for heart failure. We then introduce the spleen as a potential novel prognostic indicator, before outlining the structure and function of the spleen and introducing the concept of the cardiosplenic axis. This is followed by a focused discussion on the function of the spleen in the immune response and in hemodynamics, as well as a review of what is known about the usefulness of the spleen as an indicator of heart failure. Expert insight into the most effective spleen-related measurement indices for the prognostication of patients with heart failure is provided, and suggestions on how these could be measured in clinical practice are considered. In future, studies in humans will be required to draw definitive links between specific splenic measurements and different heart failure manifestations, as well as to determine whether splenic prognostic measurements differ between heart failure classes and etiologies. These contributions will provide a step forward in our understanding of the usefulness of the spleen as a prognostic predictor in heart failure.

Genomic signatures of high-altitude adaptation and chromosomal polymorphism in geladas

Primates have adapted to numerous environments and lifestyles, but very few species are native to high elevations. Here, we investigated high-altitude adaptations in the gelada (Theropithecus gelada), a monkey endemic to the Ethiopian Plateau. We examined genome-wide variation in conjunction with measurements of hematological and morphological traits. Our new gelada reference genome is highly intact and assembled at chromosome-length levels. Unexpectedly, we identified a chromosomal polymorphism in geladas that could potentially contribute to reproductive barriers between populations. Compared to baboons at low altitude, we found that high-altitude geladas exhibit significantly expanded chest circumferences, potentially allowing for greater lung surface area for increased oxygen diffusion. We identified gelada-specific amino acid substitutions in the alpha-chain subunit of adult hemoglobin but found that gelada hemoglobin does not exhibit markedly altered oxygenation properties compared to lowland primates. We also found that geladas at high altitude do not exhibit elevated blood hemoglobin concentrations, in contrast to the normal acclimatization response to hypoxia in lowland primates. The absence of altitude-related polycythemia suggests that geladas are able to sustain adequate tissue-oxygen delivery despite environmental hypoxia. Finally, we identified numerous genes and genomic regions exhibiting accelerated rates of evolution, as well as gene families exhibiting expansions in the gelada lineage, potentially reflecting altitude-related selection. Our findings lend insight into putative mechanisms of high-altitude adaptation while suggesting promising avenues for functional hypoxia research.

A complete reference genome improves analysis of human genetic variation

Compared to its predecessors, the Telomere-to-Telomere CHM13 genome adds nearly 200 million base pairs of sequence, corrects thousands of structural errors, and unlocks the most complex regions of the human genome for clinical and functional study. We show how this reference universally improves read mapping and variant calling for 3202 and 17 globally diverse samples sequenced with short and long reads, respectively. We identify hundreds of thousands of variants per sample in previously unresolved regions, showcasing the promise of the T2T-CHM13 reference for evolutionary and biomedical discovery. Simultaneously, this reference eliminates tens of thousands of spurious variants per sample, including reduction of false positives in 269 medically relevant genes by up to a factor of 12. Because of these improvements in variant discovery coupled with population and functional genomic resources, T2T-CHM13 is positioned to replace GRCh38 as the prevailing reference for human genetics.

The evolution of larger size in high-altitude Drosophila melanogaster has a variable genetic architecture

Important uncertainties persist regarding the genetic architecture of adaptive trait evolution in natural populations, including the number of genetic variants involved, whether they are drawn from standing genetic variation, and whether directional selection drives them to complete fixation. Here, we take advantage of a unique natural population of Drosophila melanogaster from the Ethiopian highlands, which has evolved larger body size than any other known population of this species. We apply a bulk segregant quantitative trait locus mapping approach to 4 unique crosses between highland Ethiopian and lowland Zambian populations for both thorax length and wing length. Results indicated a persistently variable genetic basis for these evolved traits (with largely distinct sets of quantitative trait loci for each cross), and at least a moderately polygenic architecture with relatively strong effects present. We complemented these mapping experiments with population genetic analyses of quantitative trait locus regions and gene ontology enrichment analysis, generating strong hypotheses for specific genes and functional processes that may have contributed to these adaptive trait changes. Finally, we find that the genetic architectures indicated by our quantitative trait locus mapping results for size traits mirror those from similar experiments on other recently evolved traits in this species. Collectively, these studies suggest a recurring pattern of polygenic adaptation in this species, in which causative variants do not approach fixation and moderately strong effect loci are present.

The Antarctic Weddell seal genome reveals evidence of selection on cardiovascular phenotype and lipid handling

The Weddell seal (Leptonychotes weddellii) thrives in its extreme Antarctic environment. We generated the Weddell seal genome assembly and a high-quality annotation to investigate genome-wide evolutionary pressures that underlie its phenotype and to study genes implicated in hypoxia tolerance and a lipid-based metabolism. Genome-wide analyses included gene family expansion/contraction, positive selection, and diverged sequence (acceleration) compared to other placental mammals, identifying selection in coding and non-coding sequence in five pathways that may shape cardiovascular phenotype. Lipid metabolism as well as hypoxia genes contained more accelerated regions in the Weddell seal compared to genomic background. Top-significant genes were SUMO2 and EP300; both regulate hypoxia inducible factor signaling. Liver expression of four genes with the strongest acceleration signals differ between Weddell seals and a terrestrial mammal, sheep. We also report a high-density lipoprotein-like particle in Weddell seal serum not present in other mammals, including the shallow-diving harbor seal.

Exponential Relationship Between Maximal Apnea Duration and Exercise Intensity in Non-apnea Trained Individuals

It is well known that the duration of apnea is longer in static than in dynamic conditions, but the impact of exercise intensity on the apnea duration needs to be investigated. The aim of this study was to determine the relationship between apnea duration and exercise intensity, and the associated metabolic parameters. Ten healthy active young non-apnea trained (NAT) men participated in this study. During the first visit, they carried out a maximum static apnea (SA) and a maximal progressive cycle exercise to evaluate the power output achieved at peak oxygen uptake (PVO₂peak). During the second visit, they performed four randomized dynamic apneas (DAs) at 20, 30, 40, and 50% of PVO₂peak (P20, P30, P40, and P50) preceded by 4 min of exercise without apnea. Duration of apnea, heart rate (HR), arterial oxygen saturation (SpO₂), blood lactate concentration [La], rating of perceived exertion (RPE), and subjective feeling were recorded. Apnea duration was significantly higher during SA (68.1 ± 23.6 s) compared with DA. Apnea duration at P20 (35.6 ± 11.7 s) was higher compared with P30 (25.6 ± 6.3 s), P40 (19.2 ± 6.7 s), and P50 (16.9 ± 2.5 s). The relationship between apnea duration and exercise intensity followed an exponential function (y = 56.388e^{-0.025 x} ). SA as DA performed at P20 and P30 induces a bradycardia. Apnea induces an SpO₂ decrease which is higher during DA (-10%) compared with SA (-4.4%). The decreases of SPO₂ recorded during DA do not differ despite the increase in exercise intensity. An increase of [La] was observed in P30 and P40 conditions. RPE and subjective feeling remained unchanged whatever the apnea conditions might be. These results suggest that the DA performed at 30% of VO₂peak could be the best compromise between apnea duration and exercise intensity. Then, DA training at low intensity could be added to aerobic training since, despite the moderate hypoxia, it is sufficient to induce and increase [La] generally observed during high-intensity training.

Relationship between spleen size and exercise tolerance in advanced heart failure patients with a left ventricular assist device

OBJECTIVE

Spleen volume increases in patients with advanced heart failure (HF) after left ventricular assist device (LVAD) implantation. However, the relationship between spleen volume and exercise tolerance (peak oxygen consumption [VO₂]) in these patients remains unknown. In this exploratory study, we enrolled 27 patients with HF using a LVAD (median age: 46 years). Patients underwent blood testing, echocardiography, right heart catheterization, computed tomography (CT), and cardiopulmonary exercise testing. Spleen size was measured using CT volumetry, and the correlations/causal relationships of factors affecting peak VO₂ were identified using structural equation modeling.

RESULTS

The median spleen volume was 190.0 mL, and peak VO₂ was 13.2 mL/kg/min. The factors affecting peak VO₂ were peak heart rate (HR; β = 0.402, P = .015), pulmonary capillary wedge pressure (PCWP; β =  - 0.698, P = .014), right ventricular stroke work index (β = 0.533, P = .001), blood hemoglobin concentration (β = 0.359, P = .007), and spleen volume (β = 0.215, P = .041). Spleen volume correlated with peak HR, PCWP, and hemoglobin concentration, reflecting sympathetic activity, cardiac preload, and oxygen-carrying capacity, respectively, and was thus related to peak VO₂. These results suggest an association between spleen volume and exercise tolerance in advanced HF.

An Erythropoietin-Independent Mechanism of Erythrocytic Precursor Proliferation Underlies Hypoxia Tolerance in Sea Nomads

The Bajau Sea Nomads were recently demonstrated to have evolved larger spleens as an adaptation to millennia of a marine foraging lifestyle. The large-spleen phenotype appears to derive from increases in thyroid hormone (TH) production as a result of reduced expression of phosphodiesterase 10A (PDE10A), though the exact mechanism remains unknown. Through pharmacological inhibition of PDE10A using the selective inhibitor MP-10 in mice, we were able to mimic the Bajau adaptation and show that treated mice had significantly larger spleens than control animals. This difference appears connected to an excess of early stage erythrocytes and an apparent increase in red blood cell (RBC) precursor proliferation in response to increased TH. However, we determined that the stimulation of RBC production in the mouse model via TH is Erythropoietin (EPO)-independent, unlike in the altitude (chronic hypoxemia) response. We confirmed this using human GWAS data; although the Bajau PDE10A variants are significantly associated with increased TH levels and RBC count, they are not associated with EPO levels, nor are other strongly thyroid-associated SNPs. We therefore suggest that an EPO-independent mechanism of stimulating RBC precursor proliferation via TH upregulation underlies the increase in spleen size observed in Sea Nomad populations.

No differences in splenic emptying during on-transient supine cycling between aerobically trained and untrained participants

Purpose

The role of splenic emptying in O₂ transport during aerobic exercise still remains a matter of debate. Our study compared the differences in spleen volume changes between aerobically trained and untrained individuals during step-transition supine cycling exercise at moderate-intensity. We also examined the relationship between spleen volume changes, erythrocyte release, and O₂ uptake parameters.

Methods

Fourteen healthy men completed all study procedures, including a detailed medical examination, supine maximal O₂ uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{2}$$\end{document}V˙O2 max.) test, and three step-transitions from 20 W to a moderate-intensity power output, equivalent to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{2}$$\end{document}V˙O2 uptake at 90% gas exchange threshold. During these step-transitions pulmonary \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{{2{\text{p}}}}$$\end{document}V˙O2p, near-infrared spectroscopy of the vastus lateralis, and cardiovascular responses were continuously measured. In parallel, minute-by-minute ultrasonic measurements of the spleen were performed. Blood samples were taken before and immediately after step-transition cycling.

Results

On average, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{2}$$\end{document}V˙O2 max. was 10 mL kg min⁻¹ (p = 0.001) higher in trained compared to their aerobically untrained peers. In response to supine step-transition cycling, the splenic volume was significantly reduced, and the largest reduction (~ 106 to 115 mL, ~ 38%, p = 0.001) was similar in both aerobically trained and untrained individuals. Erythrocyte concentration and platelet count transiently increased after exercise cessation, with no differences observed between groups. However, the vastus lateralis deoxygenation amplitude was 30% (p = 0.001) greater in trained compared to untrained individuals. No associations existed between: (i) spleen volumes at rest (ii) spleen volume changes (%), (iii) resting hematocrit and oxygen uptake parameters.

Conclusion

Greater splenic emptying and subsequent erythrocyte release do not lead to a slower \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau {\dot{\text{V}}\text{O}}_{{2{\text{p}}}}$$\end{document}τV˙O2p, regardless of individual \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}\text{O}}_{2}$$\end{document}V˙O2 max. readings.

Evolution of polygenic traits under global vs local adaptation

Observations about the number, frequency, effect size, and genomic distribution of alleles associated with complex traits must be interpreted in light of evolutionary process. These characteristics, which constitute a trait's genetic architecture, can dramatically affect evolutionary outcomes in applications from agriculture to medicine, and can provide a window into how evolution works. Here, I review theoretical predictions about the evolution of genetic architecture under spatially homogeneous, global adaptation as compared with spatially heterogeneous, local adaptation. Due to the tension between divergent selection and migration, local adaptation can favor "concentrated" genetic architectures that are enriched for alleles of larger effect, clustered in a smaller number of genomic regions, relative to expectations under global adaptation. However, the evolution of such architectures may be limited by many factors, including the genotypic redundancy of the trait, mutation rate, and temporal variability of environment. I review the circumstances in which predictions differ for global vs local adaptation and discuss where progress can be made in testing hypotheses using data from natural populations and lab experiments. As the field of comparative population genomics expands in scope, differences in architecture among traits and species will provide insights into how evolution works, and such differences must be interpreted in light of which kind of selection has been operating.

A Dual Role for Behavior in Evolution and Shaping Organismal Selective Environments

The hypothesis that evolved behaviors play a determining role in facilitating and impeding the evolution of other traits has been discussed for more than 100 years with little consensus beyond an agreement that the ideas are theoretically plausible in accord with the Modern Synthesis. Many recent reviews of the genomic, epigenetic, and developmental mechanisms underpinning major behavioral transitions show how facultative expression of novel behaviors can lead to the evolution of obligate behaviors and structures that enhance behavioral function. Phylogenetic and genomic studies indicate that behavioral traits are generally evolutionarily more labile than other traits and that they help shape selective environments on the latter traits. Adaptive decision-making to encounter resources and avoid stress sources requires specific sensory inputs, which behaviorally shape selective environments by determining those features of the external world that are biologically relevant. These recent findings support the hypothesis of a dual role for behavior in evolution and are consistent with current evolutionary theory.

Local adaptation and archaic introgression shape global diversity at human structural variant loci

Large genomic insertions and deletions are a potent source of functional variation, but are challenging to resolve with short-read sequencing, limiting knowledge of the role of such structural variants (SVs) in human evolution. Here, we used a graph-based method to genotype long-read-discovered SVs in short-read data from diverse human genomes. We then applied an admixture-aware method to identify 220 SVs exhibiting extreme patterns of frequency differentiation - a signature of local adaptation. The top two variants traced to the immunoglobulin heavy chain locus, tagging a haplotype that swept to near fixation in certain southeast Asian populations, but is rare in other global populations. Further investigation revealed evidence that the haplotype traces to gene flow from Neanderthals, corroborating the role of immune-related genes as prominent targets of adaptive introgression. Our study demonstrates how recent technical advances can help resolve signatures of key evolutionary events that remained obscured within technically challenging regions of the genome.

The hazards of genotype imputation in chromosomal regions under selection: A case study using the Lactase gene region

Although imputation of missing SNP results has been widely used in genetic studies, claims about the quality and usefulness of imputation have outnumbered the few studies that have questioned its limitations. But it is becoming clear that these limitations are real-for example, disease association signals can be missed in regions of LD breakdown. Here, as a case study, using the chromosomal region of the well-known lactase gene, LCT, we address the issue of imputation in the context of variants that have become frequent in a limited number of modern population groups only recently, due to selection. We study SNPs in a 500 bp region covering the enhancer of LCT, and compare imputed genotypes with directly genotyped data. We examine the haplotype pairs of all individuals with discrepant and missing genotypes. We highlight the nonrandom nature of the allelic errors and show that most incorrect imputations and missing data result from long haplotypes that are evolutionarily closely related to those carrying the derived alleles, while some relate to rare and recombinant haplotypes. We conclude that bias of incorrectly imputed and missing genotypes can decrease the accuracy of imputed results substantially.

Relationship between rice farming and polygenic scores potentially linked to agriculture in China

Following domestication in the lower Yangtze River valley 9400 years ago, rice farming spread throughout China and changed lifestyle patterns among Neolithic populations. Here, we report evidence that the advent of rice domestication and cultivation may have shaped humans not only culturally but also genetically. Leveraging recent findings from molecular genetics, we construct a number of polygenic scores (PGSs) of behavioural traits and examine their associations with rice cultivation based on a sample of 4101 individuals recently collected from mainland China. A total of nine polygenic traits and genotypes are investigated in this study, including PGSs of height, body mass index, depression, time discounting, reproduction, educational attainment, risk preference, ADH1B rs1229984 and ALDH2 rs671. Two-stage least-squares estimates of the county-level percentage of cultivated land devoted to paddy rice on the PGS of age at first birth (b = -0.029, p = 0.021) and ALDH2 rs671 (b = 0.182, p < 0.001) are both statistically significant and robust to a wide range of potential confounds and alternative explanations. These findings imply that rice farming may influence human evolution in relatively recent human history.

Nasopharyngeal carriage rate, serotype distribution, and antimicrobial susceptibility profile of Streptococcus pneumoniae isolated from children under five years old in Kotabaru, South Kalimantan, Indonesia

BACKGROUND

Streptococcus pneumoniae is a bacterial pathogen that colonizes the human nasopharynx. Colonization is frequently reported to be high in young children. In this study, we investigated the nasopharyngeal (NP) carriage rate, serotype distribution, and antibiotic susceptibility of S. pneumoniae in children under five years of age in Kotabaru, South Kalimantan, Indonesia.

METHODS

NP swab specimens were collected from 399 young children (mean age: 30 months) who participated in the Rampa Village Community Health Center, with 74% of the participants being Bajau children. S. pneumoniae was identified using optochin susceptibility and bile solubility tests. Serotyping was performed by sequential multiplex PCR, and antimicrobial susceptibility profiling was performed by disk diffusion and microdilution methods.

RESULTS

The NP carriage rate of S. pneumoniae was 45% (180/399). The most commonly serotypes were 6A/6B (18%), followed by 15B/15C (17%), 19F (16%), 34 (8%), and 23F (5%); 46% of them were identified as strains of the PCV13 vaccine type. Additionally, almost half of the pneumococcal isolates were non-susceptible to penicillin (40%), whereas non-susceptibility to tetracycline (36.8%), trimethoprim/sulfamethoxazole (29.7%), erythromycin (16.8%), chloramphenicol (9.7%), and clindamycin (8.6%) was also found. We identified 18% (n = 34) of S. pneumoniae isolates as multidrug-resistant (MDR) strains, and serotype 19F was the most common (74%) among them.

CONCLUSIONS

MDR S. pneumoniae vaccine type strains were dominated by serotype 19F. The implementation of a pneumococcal conjugate vaccine program in Indonesia might reduce MDR strains circulating in the community in the future.

Enhanced splenic volume and contraction in elite endurance athletes

Splenic contraction, which leads to ejection of stored erythrocytes, is greater in athletes involved in regular freediving or high-altitude activities. As this response facilitates oxygen-carrying capacity, similar characteristics may be expected of elite endurance athletes. Therefore, our aims were to compare resting and apnea-induced splenic volume in endurance athletes and untrained individuals, and to assess the athletes' exercise-induced splenic volume. Twelve elite biathletes (7 women) and 12 controls (6 women) performed a maximal effort apnea in a seated position. In addition, the biathletes completed a maximal roller-skiing time trial. Splenic dimensions were measured by ultrasonic imaging for subsequent volume calculations, whereas Hb was analyzed from capillary blood samples and cardiorespiratory variables were monitored continuously. Baseline splenic volume was larger in the biathletes (214 ± 56 mL) compared with controls (157 ± 39 mL, P = 0.008) and apnea-induced splenic contraction was also greater in the biathletes (46 ± 20 mL vs. 30 ± 16 mL, P = 0.035). Hb increased immediately after apnea in the biathletes (4.5 ± 4.8%, P = 0.029) but not in the controls (-0.7 ± 3.1%, P = 0.999). Increases in exercise-induced splenic contraction (P = 0.008) and Hb (P = 0.001) were greater compared with the apnea-induced responses among the athletes. Baseline splenic volume tended to be correlated with V̇o_2max (r = 0.584, P = 0.059). We conclude that elite biathletes have greater splenic volume with a greater ability to contract and elevate Hb compared with untrained individuals. These characteristics may transiently enhance O₂-carrying capacity and possibly increase O₂ uptake, thereby helping biathletes to cope with high intermittent O₂ demands and severe O₂ deficits that occur during biathlon training and competition.NEW & NOTEWORTHY This study demonstrates that elite biathletes have larger splenic volume, apnea-induced splenic contraction, and Hb elevation compared with untrained individuals, which is likely functional to cope with high O₂ demands and substantial O₂ deficits. We believe that enhanced splenic contraction may be of importance during competitions involving cross-country skiing, to regulate circulating Hb and enhance O₂-carrying capacity, which may protect [Formula: see text] and increase O₂ uptake.

Breath-Hold Diving - The Physiology of Diving Deep and Returning

Breath-hold diving involves highly integrative physiology and extreme responses to both exercise and asphyxia during progressive elevations in hydrostatic pressure. With astonishing depth records exceeding 100 m, and up to 214 m on a single breath, the human capacity for deep breath-hold diving continues to refute expectations. The physiological challenges and responses occurring during a deep dive highlight the coordinated interplay of oxygen conservation, exercise economy, and hyperbaric management. In this review, the physiology of deep diving is portrayed as it occurs across the phases of a dive: the first 20 m; passive descent; maximal depth; ascent; last 10 m, and surfacing. The acute risks of diving (i.e., pulmonary barotrauma, nitrogen narcosis, and decompression sickness) and the potential long-term medical consequences to breath-hold diving are summarized, and an emphasis on future areas of research of this unique field of physiological adaptation are provided.

Spleen Volume and Contraction During Apnea in Mt. Everest Climbers and Everest Base Camp Trekkers

The human spleen can contract and transiently boost the blood with stored erythrocytes. We measured spleen volume and contraction during apneas in two groups, each containing 12 Caucasian participants (each 3 women): one group planning to summit Mt. Everest (8848 m; "Climbers") and another trekking to Everest Base Camp (5300 m; "Trekkers"). Tests were done in Kathmandu (1370 m) 1-3 days after arrival, before the Climb/Trek. Age, height, weight, vital capacity, resting heart rate, and arterial oxygen saturation were similar between groups (not significant). After 15 minutes of sitting rest, all participants performed a 1-minute apnea and, after 2 minutes of rest, 1 maximal duration apnea was performed. Six of the climbers did a third apnea and hemoglobin concentration (Hb) was measured. Three axial spleen diameters were measured by ultrasonic imaging before and after the apneas for spleen volume calculation. Mean (standard deviation) baseline spleen volume was larger in Climbers [367 (181) mL] than in Trekkers [228 (70) mL; p = 0.022]. Spleen contraction occurred during apneas in both groups, with about twice the magnitude in Climbers. Three apneas in six of the Climbers resulted in a spleen volume reduction from 348 (145) to 202 (91) mL (p = 0.005) and an Hb elevation from 147.9 (13.1) to 153.3 (11.3) g/L (p = 0.024). Maximal apneic duration was longer in Climbers [88 (23) seconds vs. 67 (18) seconds in Trekkers; p = 0.023]. We concluded that a large spleen characterizes Climbers, suggesting that spleen function may be important for high-altitude climbing performance.

Using seasonal genomic changes to understand historical adaptation to new environments: Parallel selection on stickleback in highly-variable estuaries

Parallel evolution is considered strong evidence for natural selection. However, few studies have investigated the process of parallel selection as it plays out in real time. The common approach is to study historical signatures of selection in populations already well adapted to different environments. Here, to document selection under natural conditions, we study six populations of threespine stickleback (Gasterosteus aculeatus) inhabiting bar-built estuaries that undergo seasonal cycles of environmental changes. Estuaries are periodically isolated from the ocean due to sandbar formation during dry summer months, with concurrent environmental shifts that resemble the long-term changes associated with postglacial colonization of freshwater habitats by marine populations. We used pooled whole-genome sequencing to track seasonal allele frequency changes in six of these populations and search for signatures of natural selection. We found consistent changes in allele frequency across estuaries, suggesting a potential role for parallel selection. Functional enrichment among candidate genes included transmembrane ion transport and calcium binding, which are important for osmoregulation and ion balance. The genomic changes that occur in threespine stickleback from bar-built estuaries could provide a glimpse into the early stages of adaptation that have occurred in many historical marine to freshwater transitions.

Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review

Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity.

Genomic Mechanisms of Physiological and Morphological Adaptations of Limestone Langurs to Karst Habitats

Knowledge of the physiological and morphological evolution and adaptation of nonhuman primates is critical to understand hominin origins, physiological ecology, morphological evolution, and applications in biomedicine. Particularly, limestone langurs represent a direct example of adaptations to the challenges of exploiting a high calcium and harsh environment. Here, we report a de novo genome assembly (Tfra_2.0) of a male François's langur (Trachypithecus francoisi) with contig N50 of 16.3 Mb and resequencing data of 23 individuals representing five limestone and four forest langur species. Comparative genomics reveals evidence for functional evolution in genes and gene families related to calcium signaling in the limestone langur genome, probably as an adaptation to naturally occurring high calcium levels present in water and plant resources in karst habitats. The genomic and functional analyses suggest that a single point mutation (Lys1905Arg) in the α1c subunit of the L-type voltage-gated calcium channel Cav1.2 (CACNA1C) attenuates the inward calcium current into the cells in vitro. Population genomic analyses and RNA-sequencing indicate that EDNRB is less expressed in white tail hair follicles of the white-headed langur (T. leucocephalus) compared with the black-colored François's langur and hence might be responsible for species-specific differences in body coloration. Our findings contribute to a new understanding of gene-environment interactions and physiomorphological adaptative mechanisms in ecologically specialized primate taxa.

The Counteracting Effects of Demography on Functional Genomic Variation: The Roma Paradigm

Demographic history plays a major role in shaping the distribution of genomic variation. Yet the interaction between different demographic forces and their effects in the genomes is not fully resolved in human populations. Here, we focus on the Roma population, the largest transnational ethnic minority in Europe. They have a South Asian origin and their demographic history is characterized by recent dispersals, multiple founder events, and extensive gene flow from non-Roma groups. Through the analyses of new high-coverage whole exome sequences and genome-wide array data for 89 Iberian Roma individuals together with forward simulations, we show that founder effects have reduced their genetic diversity and proportion of rare variants, gene flow has counteracted the increase in mutational load, runs of homozygosity show ancestry-specific patterns of accumulation of deleterious homozygotes, and selection signals primarily derive from preadmixture adaptation in the Roma population sources. The present study shows how two demographic forces, bottlenecks and admixture, act in opposite directions and have long-term balancing effects on the Roma genomes. Understanding how demography and gene flow shape the genome of an admixed population provides an opportunity to elucidate how genomic variation is modeled in human populations.

Understanding the Adaptive Evolutionary Histories of South American Ancient and Present-Day Populations via Genomics

The South American continent is remarkably diverse in its ecological zones, spanning the Amazon rainforest, the high-altitude Andes, and Tierra del Fuego. Yet the original human populations of the continent successfully inhabited all these zones, well before the buffering effects of modern technology. Therefore, it is likely that the various cultures were successful, in part, due to positive natural selection that allowed them to successfully establish populations for thousands of years. Detecting positive selection in these populations is still in its infancy, as the ongoing effects of European contact have decimated many of these populations and introduced gene flow from outside of the continent. In this review, we explore hypotheses of possible human biological adaptation, methods to identify positive selection, the utilization of ancient DNA, and the integration of modern genomes through the identification of genomic tracts that reflect the ancestry of the first populations of the Americas.

Resting Energy Expenditure: From Cellular to Whole-Body Level, a Mechanistic Historical Perspective

The basis of heat generated by the human body has been a source of speculation and research for more than 2,000 years. Basal heat production, now usually referred to as resting energy expenditure (REE), is currently recognized as deriving from biochemical reactions at subcellular and cellular levels that are expressed in the energy expended by the body's 78 organs and tissues. These organs and tissues, and the 11 systems to which they belong, influence body size and shape. Connecting these subcellular-/cellular-level reactions to organs and tissues, and then on to body size and shape, provides a comprehensive understanding of individual differences in REE, a contemporary topic of interest in obesity research and clinical practice. This review critically examines these linkages, their association with widely used statistical and physiological REE prediction formulas, and often-unappreciated aspects of measuring basal heat production in humans.

Scanning the human genome for "signatures" of positive selection: Transformative opportunities and ethical obligations

The relationship history of evolutionary anthropology and genetics is complex. At best, genetics is a beautifully integrative part of the discipline. Yet this integration has also been fraught, with punctuated, disruptive challenges to dogma, periodic reluctance by some members of the field to embrace results from analyses of genetic data, and occasional over-assertions of genetic definitiveness by geneticists. At worst, evolutionary genetics has been a tool for reinforcing racism and colonialism. While a number of genetics/genomics papers have disproportionately impacted evolutionary anthropology, here we highlight the 2002 presentation of an elegantly powerful approach for identifying "signatures" of past positive selection from haplotype-based patterns of genetic variation. Together with technological advances in genotyping methods, this article transformed our field by facilitating genome-wide "scans" for signatures of past positive selection in human populations. This approach helped researchers test longstanding evolutionary anthropology hypotheses while simultaneously providing opportunities to develop entirely new ones. Genome-wide scans for signatures of positive selection have since been conducted in diverse worldwide populations, with striking findings of local adaptation and convergent evolution. Yet there are ethical considerations with respect to the ubiquity of these studies and the cross-application of the genome-wide scan approach to existing datasets, which we also discuss.

Hypoxic Respiratory Chemoreflex Control in Young Trained Swimmers

During an apnea, changes in PaO₂ activate peripheral chemoreceptors to increase respiratory drive. Athletes with continuous apnea, such as breath-hold divers, have shown a decrease in hypoxic ventilatory response (HVR), which could explain the long apnea times; however, this has not been studied in swimmers. We hypothesize that the long periods of voluntary apnea in swimmers is related to a decreased HVR. Therefore, we sought to determine the HVR and cardiovascular adjustments during a maximum voluntary apnea in young-trained swimmers. In fifteen trained swimmers and twenty-seven controls we studied minute ventilation (V_E), arterial saturation (SpO₂), heart rate (HR), and autonomic response [through heart rate variability (HRV) analysis], during acute chemoreflex activation (five inhalations of pure N₂) and maximum voluntary apnea test. In apnea tests, the maximum voluntary apnea time and the end-apnea HR were higher in swimmers than in controls (p < 0.05), as well as a higher low frequency component of HRV (p < 0.05), than controls. Swimmers showed lower HVR than controls (p < 0.01) without differences in cardiac hypoxic response (CHR). We conclude that swimmers had a reduced HVR response and greater maximal voluntary apnea duration, probably due to decreased HVR.

Six weeks of dynamic apnoeic training stimulates erythropoiesis but does not increase splenic volume

Purpose

This study examined the influence of dynamic apnoea training on splenic volume and haematological responses in non-breath-hold divers (BHD).

Methods

Eight non-BHD performed ten maximal dynamic apnoeas, four times a week for  six weeks. Splenic volumes were assessed ultrasonically, and blood samples were drawn for full blood count analysis, erythropoietin, iron, ferritin, albumin, protein and osmolality at baseline, 24 h post the completion of each week’s training sessions and seven days post the completion of the training programme. Additionally, blood samples were drawn for haematology at 30, 90, and 180 min post session one, twelve and twenty-four.

Results

Erythropoietin was only higher than baseline (6.62 ± 3.03 mlU/mL) post session one, at 90 (9.20 ± 1.88 mlU/mL, p = 0.048) and 180 min (9.04 ± 2.35 mlU/mL, p = 0.046). Iron increased from baseline (18 ± 3 µmol/L) post week five (23 ± 2 µmol/L, p = 0.033) and six (21 ± 6 µmol/L; p = 0.041), whereas ferritin was observed to be lower than baseline (111 ± 82 µg/L) post week five (95 ± 75 µg/L; p = 0.016), six (84 ± 74 µg/L; p = 0.012) and one week post-training (81 ± 63 µg/L; p = 0.008). Reticulocytes increased from baseline (57 ± 12 × 10⁹/L) post week one (72 ± 17 × 10⁹/L, p = 0.037) and six (71 ± 17 × 10⁹/L, p = 0.021) while no changes were recorded in erythrocytes (p = 0.336), haemoglobin (p = 0.124) and splenic volumes (p = 0.357).

Conclusions

Six weeks of dynamic apnoeic training increase reticulocytes without altering mature erythrocyte concentration and splenic volume.