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1. Differential resistance and acclimation of two coral species to chronic nutrient enrichment reflect life‐history traits

   https://doi.org/10.1111/1365-2435.13780  

   Fox, Michael D. ; Nelson, Craig E. ; Oliver, Thomas A. ; Quinlan, Zachary A. ; Remple, Kristina ; Glanz, Jess ; Smith, Jennifer E. ; Putnam, Hollie M. ; Fox, ed., Charles ( March 2021 , Functional Ecology)

   The effects of nutrient pollution on coral reef ecosystems are multifaceted. Numerous experiments have sought to identify the physiological effects of nutrient enrichment on reef‐building corals, but the results have been variable and sensitive to choices of nutrient quantity, chemical composition and exposure duration.

   To test the effects of chronic, ecologically relevant nutrient enrichment on coral growth and photophysiology, we conducted a 5‐week continuous dosing experiment on two Hawaiian coral species,Porites compressaandPocillopora acuta. We acclimated coral fragments to five nutrient concentrations (0.1–7 µMand 0.06–2.24 µM) with constant stoichiometry 2.5:1 nitrate to phosphate) bracketing in situ observations from reefs throughout the Pacific.

   Nutrient enrichment linearly increased photophysiological performance of both species within 3 weeks. The effect of nutrients onP. acutaphotochemical efficiency increased through time while a consistent response inP. compressaindicated acclimation to elevated nutrients within 5 weeks. Endosymbiont densities and total chlorophyll concentrations also increased proportionally with nutrient enrichment inP. acuta, but not inP. compressa, revealing contrasting patterns of host–symbiont acclimatization.

   The two species also exhibited contrasting effects of nutrient enrichment on skeletal growth. Calcification was enhanced at low nutrient enrichment (1 µM) inP. acuta, but comparable to the control at higher concentrations, whereas calcification was reduced inP. compressa(30%–35%) above 3 µM.

   Stable isotope analysis revealed species‐specific nitrogen uptake dynamics in the coral–algal symbiosis. The endosymbionts ofP. acutaexhibited increased nitrogen uptake (decreased δ¹⁵N) and incorporation (19%–31% decrease in C:N ratios) across treatments. In contrast,P. compressaendosymbionts maintained constant δ¹⁵N values and low levels of nitrogen incorporation (9%–11% decrease in C:N ratios). The inability ofP. acutato regulate endosymbiont nutrient uptake may indicate an emerging destabilization in the coral–algal symbiosis under nutrient enrichment that could compromise resistance to additional environmental stressors.

   Our results highlight species‐specific differences in the coral–algal symbiosis, which influence responses to chronic nutrient enrichment. These findings showcase how symbioses can vary among closely related taxa and underscore the importance of considering how life‐history traits modify species response to environmental change.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Modelling the relationships between haemoglobin oxygen affinity and the oxygen cascade in humans

   https://doi.org/10.1113/JP277591  

   Shepherd, John R. A. ; Dominelli, Paolo B. ; Roy, Tuhin K. ; Secomb, Timothy W. ; Hoyer, James D. ; Oliveira, Jennifer L. ; Joyner, Michael J. ( July 2019 , The Journal of Physiology)

   Haemoglobin affinity is an integral concept in exercise physiology that impacts oxygen uptake, delivery and consumption.

   How chronic alterations in haemoglobin affinity impact physiology is unknown.

   Using human haemoglobin variants, we demonstrate that the affinity of haemoglobin for oxygen is highly correlated with haemoglobin concentration.

   Using the Fick equation, we model how altered haemoglobin affinity and the associated haemoglobin concentration influences oxygen consumption at rest and during exercise via alterations in cardiac output and mixed‐venous.

   The combination of low oxygen affinity haemoglobin and reduced haemoglobin concentration seenin vivomay be unable to support oxygen uptake during moderate or heavy exercise.

   The physiological implications, with regard to exercise, of altered haemoglobin affinity for oxygen are not fully understood. Data from the Mayo Clinic Laboratories database of rare human haemoglobin variants reveal a strong inverse correlation (r = −0.82) between blood haemoglobin concentration andP₅₀, an index of oxygen affinity [Hb = −0.3135(P₅₀) + 23.636]. In the present study, observedP₅₀values for high, normal and low oxygen‐affinity haemoglobin variants (13, 26 and 39 mmHg) and corresponding haemoglobin concentrations (19.5, 15.5 and 11.4 g dL⁻¹respectively) are used to model oxygen consumption as a fraction of delivery at rest ( = 0.25 L min⁻¹, cardiac output = 5.70 L min⁻¹) and during exercise ( = 2.75 L min⁻¹, cardiac output = 18.9 l min⁻¹). With high‐affinity haemoglobin, the model shows that normal levels of oxygen consumption can be achieved at rest and during exercise at the assumed cardiac output levels, with reduced oxygen extraction both at rest (16.8% high affinityvs. 21.7% normal) and during exercise (55.8% high affinityvs. 72.2% normal). With low‐affinity haemoglobin, which predicts low haemoglobin concentration, oxygen consumption at rest can be sustained with the assumed cardiac output, with increased oxygen extraction (31.1% low affinityvs. 21.7% normal). However, exercise at 2.75 l min⁻¹cannot be achieved with the assumed cardiac output, even with 100% oxygen extraction. In conclusion, the model indicates chronic alterations inP₅₀associate directly with Hb concentration, highlighting that human Hb variants can serve as ‘experiments of nature’ to address fundamental hypotheses on oxygen transport and exercise.

    

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3. The effect of lifelong endurance exercise on cardiovascular structure and exercise function in women

   https://doi.org/10.1113/JP278503  

   Carrick‐Ranson, Graeme ; Sloane, Nikita M. ; Howden, Erin J. ; Bhella, Paul S. ; Sarma, Satyam ; Shibata, Shigeki ; Fujimoto, Naoki ; Hastings, Jeffrey L. ; Levine, Benjamin D. ( May 2020 , The Journal of Physiology)

   The beneficial effects of sustained or lifelong (>25 years) endurance exercise on cardiovascular structure and exercise function have been largely established in men.

   The current findings indicate that committed (≥4 weekly exercise sessions) lifelong exercise results in substantial benefits in exercise capacity (), cardiovascular function at submaximal and maximal exercise, left ventricular mass and compliance, and blood volume compared to similarly aged or even younger (middle‐age) untrained women.

   Endurance exercise training should be considered a key strategy to prevent cardiovascular disease with ageing in women as well as men.

   This study was a retrospective, cross‐sectional analysis of exercise performance and left ventricular (LV) morphology in 70 women to examine whether women who have performed regular, lifelong endurance exercise acquire the same beneficial adaptations in cardiovascular structure and function and exercise performance that have been reported previously in men. Three groups of women were examined: (1) 35 older (>60 years) untrained women (older untrained, OU), (2) 13 older women who had consistently performed four or more endurance exercise sessions weekly for at least 25 years (older trained, OT), and (3) 22 middle‐aged (range 35–59 years) untrained women (middle‐aged untrained, MU) as a reference control for the appropriate age‐related changes. Oxygen uptake () and cardiovascular function (cardiac output (); stroke volume (SV) acetylene rebreathing) were examined at rest, steady‐state submaximal exercise and maximal exercise (maximal oxygen uptake,). Blood volume (CO rebreathing) and LV mass (cardiac magnetic resonance imaging), plus invasive measures of static and dynamic chamber compliance were also examined.(p < 0.001) and maximal exerciseand SV were larger in older trained women compared to the two untrained groups (∼17% and ∼27% forand SV, respectively,versusMU; ∼40% and ∼38%versusOU, allp < 0.001). Blood volume (mL kg⁻¹) and LV mass index (g m⁻²) were larger in OTversusOU (∼11% and ∼16%, respectively, bothP ≤ 0.015) Static LV chamber compliance was greater in OT compared to both untrained groups (median (25–75%): MU: 0.065 (0.049–0.080); OU: 0.085 (0.061–0.138); OT: 0.047 (0.031–0.054),P ≤ 0.053). Collectively, these findings indicate that lifetime endurance exercise appears to be extremely effective at preserving or even enhancing cardiovascular structure and function with advanced age in women.

    

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4. Effect of spontaneous movement on respiration in preterm infants

   https://doi.org/10.1113/EP089143  

   Zuzarte, Ian ; Paydarfar, David ; Sternad, Dagmar ( March 2021 , Experimental Physiology)

   What is the central question of this study?

   The respiratory centres in the brainstem that control respiration receive inputs from various sources, including proprioceptors in muscles and joints and suprapontine centres, which all affect limb movements. What is the effect of spontaneous movement on respiration in preterm infants?

   What is the main finding and its importance?

   Apnoeic events tend to be preceded by movements. These activity bursts can cause respiratory instability that leads to an apnoeic event. These findings show promise that infant movements might serve as potential predictors of life‐threatening apnoeic episodes, but more research is required.

   A common condition in preterm infants (<37 weeks’ gestational age) is apnoea resulting from immaturity and instability of the respiratory system. As apnoeas are implicated in several acute and long‐term complications, prediction of apnoeas may preempt their onset and subsequent complications. This study tests the hypothesis that infant movements are a predictive marker for apnoeic episodes and examines the relation between movement and respiration. Movement was detected using a wavelet algorithm applied to the photoplethysmographic signal. Respiratory activity was measured in nine infants using respiratory inductance plethysmography; in an additional eight infants, respiration and partial pressure of airway carbon dioxide () were measured by a nasal cannula with side‐stream capnometry. In the first cohort, the distribution of movements before and after the onset of 370 apnoeic events was compared. Results showed that apnoeic events were associated with longer movement duration occurring before apnoea onsets compared to after. In the second cohort, respiration was analysed in relation to movement, comparing standard deviation of inter‐breath intervals (IBI) before and after apnoeas. Poincaré maps of the respiratory activity quantified variability of airwayin phase space. Movement significantly increased the variability of IBI and. Moreover, destabilization of respiration was dependent on the duration of movement. These findings support that bodily movements of the infants precede respiratory instability. Further research is warranted to explore the predictive value of movement for life‐threatening events, useful for clinical management and risk stratification.

    

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5. Positive interactions between an exotic invader and moss biocrusts vary across life stage and correspond with the effect of water pulses on soil nitrogen

   https://doi.org/10.1111/1365-2435.13831  

   Slate, Mandy L. ; McLeod, Morgan Luce ; Callaway, Ragan M. ( June 2021 , Functional Ecology)

   The size and frequency of resource pulses can affect plant interactions and increase the abundance of invasive species relative to native species. We examined resource pulses generated during the desiccation and rehydration of communities of native biological soil crust (biocrust)‐forming mosses, in the context of positive associations between biocrusts and the invasive forb,Centaurea stoebe.

   We surveyedCentaureaand biocrust cover and evaluated how interactions amongCentaurea, biocrusts and water pulses influenced plant biomass and soil nitrogen in a field experiment.Centaureaseedling and biocrust interactions were also compared in a greenhouse experiment to evaluate differences related to life stage.

   In field surveys,Centaureaand biocrusts were positively associated. Across water pulse treatments, biocrust biomass decreased whenCentaureawas removed, indicating thatCentaureafacilitated biocrusts. Biocrusts did not affect adultCentaureain the field, butCentaureaseedling biomass was greater when grown with biocrusts in the greenhouse. Water pulses did not affect plant biomass, but interactions betweenCentaureaand biocrusts corresponded with variation in the effect of water pulses on soil nitrogen which were not evident whenCentaureaor biocrusts were grown alone. Twenty‐four hours after large water pulses were added, soilwas nine times higher in plots where biocrusts andCentaureaco‐occurred compared with small water pulse plots. In these same plots, soiltended to be lower at the end of the experiment.

   These results highlight positive interactions between an invasive exotic forb and native moss biocrust. Water pulses influenced soil nitrogen availability when both plants co‐occurred, but did not affect plant biomass, suggesting that resource pulses and species interactions can interact to affect ecosystem processes.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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