Physiological Drivers Research Articles

Structural basis for membrane-proximal proteolysis of substrates by ADAM10

The endopeptidase ADAM10 is a critical catalyst for the regulated proteolysis of key drivers of mammalian development, physiology, and non-amyloidogenic cleavage of APP as the primary α-secretase. ADAM10 function requires the formation of a complex with a C8-tetraspanin protein, but how tetraspanin binding enables positioning of the enzyme active site for membrane-proximal cleavage remains unknown. We present here a cryo-EM structure of a vFab-ADAM10-Tspan15 complex, which shows that Tspan15 binding relieves ADAM10 autoinhibition and acts as a molecular measuring stick to position the enzyme active site about 20Å from the plasma membrane for membrane-proximal substrate cleavage. Cell-based assays of N-cadherin shedding establish that the positioning of the active site by the interface between the ADAM10 catalytic domain and the bound tetraspanin influences selection of the preferred cleavage site. Together, these studies reveal the molecular mechanism underlying ADAM10 proteolysis at membrane-proximal sites and offer a roadmap for its modulation in disease.

Physiological protection against weight gain: evidence from overfeeding studies and future directions.

Body weight is under physiological regulation. When body fat mass decreases, a series of responses are triggered to promote weight regain by increasing food intake and decreasing energy expenditure. Analogous, in response to experimental overfeeding, excessive weight gain is counteracted by a reduction in food intake and possibly by an increase in energy expenditure. While low blood leptin and other hormones defend against weight loss, the signals that oppose overfeeding-induced fat mass expansion are still unknown. In this article, we discuss insights gained from overfeeding interventions in humans and intragastric overfeeding studies in rodents. We summarize the knowledge on the relative contributions of energy intake, energy expenditure and energy excretion to the physiological defence against overfeeding-induced weight gain. Furthermore, we explore literature supporting the existence of unidentified endocrine and non-endocrine pathways that defend against weight gain. Finally, we discuss the physiological drivers of constitutional thinness and suggest that overfeeding of individuals with constitutional thinness represents a gateway to understand the physiology of weight gain resistance in humans. Experimental overfeeding, combined with modern multi-omics techniques, has the potential to unveil the long-sought signalling pathways that protect against weight gain. Discovering these mechanisms could give rise to new treatments for obesity. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

Carbon isotope composition of respired CO2 in woody stems and leafy shoots of three tree species along the growing season: physiological drivers for respiratory fractionation.

The carbon isotope composition of respired CO2 (δ13CR) and bulk organic matter (δ13CB) of various plant compartments informs about isotopic fractionation and substrate of respiratory processes, crucial to advance understanding of carbon allocation in plants. Nevertheless, its variation across organs, species, and seasons remains poorly understood. Cavity ring-down laser spectroscopy was applied to measure δ13CR in leafy shoots and woody stems of maple, oak, and cedar trees during spring and late summer. Photosynthesis, respiration, growth, and non-structural carbohydrates were measured in parallel to evaluate potential drivers for respiratory fractionation. CO2 respired by maple and oak shoots was 13C-enriched relative to δ13CB during spring but not late summer or in the stem. In cedar, δ13CR did not vary significantly throughout organs and seasons, with respired CO2 being 13C-depleted relative to δ13CB. Shoot δ13CR was positively related to leaf starch concentration in maple, while stem δ13CR was inversely related to stem growth. These relations were not significant for oak or cedar. The variability in δ13CR suggests (i) different contributions of respiratory pathways between organs and (ii) seasonality in the respiratory substrate and constitutive compounds for wood formation in deciduous species, less apparent in evergreen cedar, whose respiratory metabolism might be less variable.

Seasonal trends in leaf-level photosynthetic capacity and water use efficiency in a North American Eastern deciduous forest and their impact on canopy-scale gas exchange.

Vegetative transpiration (E) and photosynthetic carbon assimilation (A) are known to be seasonally dynamic, with changes in their ratio determining the marginal water use efficiency (WUE). Despite an understanding that stomata play a mechanistic role in regulating WUE, it is still unclear how stomatal and nonstomatal processes influence change in WUE over the course of the growing season. As a result, limited understanding of the primary physiological drivers of seasonal dynamics of canopy WUE remains one of the largest uncertainties in earth system model projections of carbon and water exchange in temperate deciduous forest ecosystems. We investigated seasonal patterns in leaf-level physiological, hydraulic, and anatomical properties, including the seasonal progress of the stomatal slope parameter (g1 ; inversely proportional to WUE) and the maximum carboxylation rate (Vcmax ). Vcmax and g1 were seasonally variable; however, their patterns were not temporally synchronized. g1 generally showed an increasing trend until late in the season, while Vcmax peaked during the midsummer months. Seasonal progression of Vcmax was primarily driven by changes in leaf structural, and anatomical characteristics, while seasonal changes in g1 were most strongly related to changes in Vcmax and leaf hydraulics. Using a seasonally variable Vcmax and g1 to parameterize a canopy-scale gas exchange model increased seasonally aggregated A and E by 3% and 16%, respectively.

Exploring environmental and physiological drivers of the annual carbon budget of biocrusts from various climatic zones with a mechanistic data-driven model

Abstract. Biocrusts are a worldwide phenomenon, contributing substantially to ecosystem functioning. Their growth and survival depend on multiple environmental factors, including climatic ones, and the relations of these factors to physiological processes. Responses of biocrusts to individual environmental factors have been examined in a large number of field and laboratory experiments. These observational data, however, have rarely been assembled into a comprehensive, consistent framework that allows quantitative exploration of the roles of multiple environmental factors and physiological properties for the performance of biocrusts, in particular across climatic regions. Here we used a data-driven mechanistic modelling framework to simulate the carbon balance of biocrusts, a key measure of their growth and survival. We thereby assessed the relative importance of physiological and environmental factors for the carbon balance at six study sites that differ in climatic conditions. Moreover, we examined the role of seasonal acclimation of physiological properties using our framework, since the effects of this process on the carbon balance of biocrusts are poorly constrained so far. We found substantial effects of air temperature, CO2 concentration, and physiological parameters that are related to respiration on biocrust carbon balance, which differ, however, in their patterns across regions. The ambient CO2 concentration is the most important factor for biocrusts from drylands, while air temperature has the strongest impact at alpine and temperate sites. Metabolic respiration cost plays a more important role than optimum temperature for gross photosynthesis at the alpine site; this is not the case, however, in drylands and temperate regions. Moreover, we estimated a small annual carbon gain of 1.5 gm-2yr-1 by lichen-dominated biocrust and 1.9 gm-2yr-1 by moss-dominated biocrust at a dryland site, while the biocrusts lost a large amount of carbon at some of the temperate sites (e.g. −92.1 for lichen-dominated and −74.7 gm-2yr-1 for moss-dominated biocrust). These strongly negative values contradict the observed survival of the organisms at the sites and may be caused by the uncertainty in environmental conditions and physiological parameters, which we assessed in a sensitivity analysis. Another potential explanation for this result may be the lack of acclimation in the modelling approach, since the carbon balance can increase substantially when testing for seasonally varying parameters in the sensitivity analysis. We conclude that the uncertainties in air temperature, CO2 concentration, respiration-related physiological parameters, and the absence of seasonal acclimation in the model for humid temperate and alpine regions may be a relevant source of error and should be taken into account in future approaches that aim at estimating the long-term biocrust carbon balance based on ecophysiological data.

Elevated cfDNA after exercise is derived primarily from mature polymorphonuclear neutrophils, with a minor contribution of cardiomyocytes

Strenuous physical exercise causes a massive elevation in the concentration of circulating cell-free DNA (cfDNA), which correlates with effort intensity and duration. The cellular sources and physiological drivers of this phenomenon are unknown. Using methylation patterns of cfDNA and associated histones, we show that cfDNA in exercise originates mostly in extramedullary polymorphonuclear neutrophils. Strikingly, cardiomyocyte cfDNA concentration increases after a marathon, consistent with elevated troponin levels and indicating low-level, delayed cardiac cell death. Physical impact, low oxygen levels, and elevated core body temperature contribute to neutrophil cfDNA release, while muscle contraction, increased heart rate, β-adrenergic signaling, or steroid treatment fail to cause elevation of cfDNA. Physical training reduces neutrophil cfDNA release after a standard exercise, revealing an inverse relationship between exercise-induced cfDNA release and training level. We speculate that the release of cfDNA from neutrophils in exercise relates to the activation of neutrophils in the context of exercise-induced muscle damage.

Biogeochemical‐Argo floats show that chlorophyll increases before carbon in the high‐latitude Southern Ocean spring bloom

AbstractIn the Southern Ocean, phytoplankton blooms are an annually recurring prominent feature that play a significant role in ocean CO2 uptake. Understanding the timing of the phytoplankton bloom is necessary to provide insights into the underlying physiological drivers, for the study of ecosystem dynamics and consequent patterns in downward carbon export. Previous studies have used chlorophyll (chl) and particulate organic carbon, from either satellites or biogeochemical‐Argo (BGC‐Argo) floats, to investigate bloom phenology, but provide inconsistent findings regarding bloom timing. Here, we compare bloom dynamics based on three diagnostics from 7114 BGC‐Argo float profiles, south of 60°S. Bloom onset consistently occurs earlier when calculated using chl than when based on phytoplankton carbon or nitrate uptake, and the decoupling increases with latitude. This suggests that phytoplankton synthesize increased chl to acclimate to low‐light conditions, before increasing their biomass. These results highlight the importance of considering phytoplankton physiology when choosing proxies for phytoplankton growth.

Do marine planktonic ciliates follow Bergmann's rule?

Body size is a fundamental trait determining individual fitness and ecological processes. Reduction in body size with increasing temperature has been widely observed in most ectotherms and endotherms, known as Bergmann's rule. However, we lack data to assess if ciliates, the major consumers of marine primary production, follow Bergmann's rule and what drives the distributions of their cell size. Here, we examined a data set (287 samples) collected across the global oceans to investigate biogeographic patterns in the mean cell‐size of ciliate communities. By measuring the sizes of every ciliate cell (< 10 to > 300 per sample), we found that community cell‐size increased with increasing latitude, conforming to Bergmann's rule. We then addressed the cause. Temperature was a main driver of the trend. Ciliate community mean cell‐size decreased 34% when temperature increased from 3.5 to 31°C, implying that temperature may be a direct physiological driver. In addition, prey (phytoplankton) size also influenced the trend, with ciliate size increasing by 35% across the gradient of phytoplankton size (0.6–15.5 μm). Generally, these findings emphasized the importance of how both biotic and abiotic factors affect size distribution of marine ciliates, a key component of pelagic ecosystems. Our novel, extensive dataset and the predictive trends arising from them contribute to understanding how climate change will influence pelagic ecosystem functions.

Functional interactions between potassium-chloride cotransporter (KCC) and inward rectifier potassium (Kir) channels in the insect central nervous system

The K+/Cl− cotransporter (KCC) is the primary mechanism by which mature neurons maintain low intracellular chloride (Cl−) concentration and has been shown to be functionally coupled to the GABA-gated chloride channels (GGCC) in Drosophila central neurons. Further, pharmacological inhibition of KCC has been shown to lead to acute toxicity of mosquitoes that highlights the toxicological relevance of insect KCC. Yet, gaps in knowledge remain regarding physiological drivers of KCC function and interactions of ion flux mechanisms upstream of GGCC in insects. Considering this, we employed electrophysiological and fluorescent microscopy techniques to further characterize KCC in the insect nervous system. Fluorescent microscopy indicated insect KCC2 is expressed in rdl neurons, which is the neuron type responsible for GABA-mediated neurotransmission, and are coexpressed with inward rectifier potassium (Kir) 2 channels. Coexpression of Kir2 and KCC2 suggested the possibility of functional coupling between these two K+ flux pathways. Indeed, extracellular recordings of Drosophila CNS showed pre-block of Kir channels prior to block of KCC led to a significant (P < 0.001) increase in CNS firing rates over baseline that when taken together, supports functional coupling of Kir to KCC function. Additionally, we documented a synergistic increase to toxicity of VU0463271, an established KCC inhibitor, above the expected additive toxicity after co-treatment with the Kir inhibitor, VU041. These data expand current knowledge regarding the physiological roles of KCC and Kir channels in the insect nervous system by defining additional pathways that facilitate inhibitory neurotransmission through GGCC.

Relationship between aerobic scope and upper thermal limits of Pacific white shrimp (Litopenaeus vannamei) in low-salinity culture systems

Aquaculture of the Pacific white shrimp Litopenaeus vannamei in low-salinity water is a viable industry and production strategy in the southeastern United States. A major challenge facing this industry is a phenomenon called late-term mortality which is thought to be driven by thermal stress at the end of the growing season when water temperatures can reach or exceed 36 °C in shrimp production ponds. To investigate the physiological mechanisms behind upper lethal limits in shrimp, we evaluated linkages between empirically measured thermal limits and absolute aerobic scope (AAS), or ability to provide energy above that needed for basic maintenance. In this study, we tested whether thermal tolerance decreases with increasing shrimp age/size and whether AAS is a useful concept for understanding the physiological basis of thermal tolerance in shrimp. We exposed two size classes (small: 2.07 ± 0.86 and large: 24.64 ± 2.55 g) of shrimp to increasing temperature at a rate of 1 °C/h from 28 to 42 °C. At each temperature, we used intermittent respirometry to estimate resting metabolic rate and we directly measured lethal thermal tolerance by evaluating critical thermal maximum (CTmax). Additionally, we used the electron transport system assay to estimate maximum metabolic rate (RMR) at temperatures from 9 to 45 °C. Small shrimp had a higher CTmax than large shrimp, with upper lethal limits of 40.6 and 39.0 °C, respectively. For both size-classes, AAS reached its minimum (AASmin) at temperatures near the peak RMR (RMRpeak) and within 2 °C of CTmax. Large shrimp exhibited a lower temperature at AASmin than that of the smaller shrimp. Reductions in AAS appear to be one of the underlying physiological drivers of thermal tolerance in L. vannamei and an indicator of increasing thermal stress. Changes in the temperature at which AAS reaches its minimum may be a useful predictor of shifts in thermal tolerance among shrimp size-classes.

Low Antioxidant Glutathione Levels Lead to Longer Telomeres: A Sex-Specific Link to Longevity?

Telomeres are repetitive DNA sequences at the end of chromosomes that protect them from degradation. They have been the focus of intense research because short telomeres would predict accelerated ageing and reduced longevity in vertebrates. Oxidative stress is considered a physiological driver of the telomere shortening and, consequently, short lifespan. Among molecules fighting against oxidative stress, glutathione is involved in many antioxidant pathways. Literature supports that oxidative stress may trigger a compensatory "hormetic" response increasing glutathione levels and telomere length. Here, we tested the link between total glutathione concentration and telomere length in captive birds (zebra finches; Taeniopygia guttata). Total glutathione levels were experimentally decreased during birds' growth using a specific inhibitor of glutathione synthesis (buthionine sulfoximine; BSO). We monitored the birds' reproductive performance in an outdoor aviary during the first month of life, and their longevity for almost 9 years. Among control individuals, erythrocyte glutathione levels during development positively predicted erythrocyte telomere length in adulthood. However, BSO-treated females, but not males, showed longer telomeres than control females in adulthood. This counterintuitive finding suggests that females mounted a compensatory response. Such compensation agrees with precedent findings in the same population where the BSO treatment increased growth and adult body mass in females but not males. BSO did not influence longevity or reproductive output in any sex. However, early glutathione levels and adult telomere length interactively predicted longevity only among control females. Those females with "naturally" low (non-manipulated) glutathione levels at the nestling age but capable of producing longer telomeres in adulthood seem to live longer. The results suggest that the capability to mount a hormetic response triggered by low early glutathione levels can improve fitness via telomere length. Overall, the results may indicate a sex-specific link between glutathione and telomere values. Telomerase activity and sexual steroids (estrogens) are good candidates to explain the sex-biased mechanism underlying the early-life impact of oxidative stress on adult telomere length.

Aerobic methane emissions from the shoots of Scots pine

Plants are recognized sources of methane (CH4) but plant-mediated CH4 emissions have mostly been studied on herbaceous species, although also trees are known to emit CH4. Emissions from tree canopies likely mostly derive from an aerobic, abiotic process. Aerobic CH4 production from trees has not been thoroughly studied, leaving uncertainties to the global source strength estimates, which vary from 0 to 240 Tg yr-1. Even less is known about how aerobic emissions affect the CH4 cycles in boreal forest ecosystems, as the environmental and physiological drivers are not fully understood. In this study, shoot-level CH4 fluxes of boreal conifer trees were measured outdoors and in the greenhouse, to investigate the environmental and physiological drivers and regulators of shoot-level CH4 fluxes. Most of the measurements were done from saplings of Pinus sylvestris L. (Scots pine), one of the most important tree species of the boreal region of the Eurasian continent, by using chamber enclosure methods with spectral, online greenhouse gas analysers. The measurements were conducted either manually, or with an automated measurement system, developed to overcome issues related to manual measurement techniques. The shoots of Scots pine showed small but significant emissions of CH4 in all experimental setups, the emissions were driven by light, enhanced by elevated temperature, and occurred independently from drought and photosynthesis. Solar radiation was a more significant driver of these CH4 emissions than artificial light with UV-A. These results show that Scots pine canopies have the potential to produce CH4 in a similar process that has been described before for the foliage of herbaceous plants, but these emissions are smaller than the initial estimates of the aerobic CH4 source from vegetation. The boreal forest canopies are sources of CH4 and have the capacity to decrease the CH4 sink strength of boreal upland forests by ~ 5 %.

Late-season nitrogen application increases grain protein concentration and is neutral for yield in wheat. A global meta-analysis

Late-season nitrogen (N) application has been proposed to boost grain yield and grain protein concentration (GPC) in cereals; however, its effects on bread and durum wheat have been inconsistent in field experiments. We performed a meta-analysis to (i) assess the effect of N applications to wheat after flag leaf visible (GS 37) on grain yield and GPC; and to assess the variation in these responses with (ii) N fertiliser management, (iii) environmental factors, and (iv) physiological traits. We searched ‘ Agronomy Journal ’, ‘ Crop Science ’, ‘ European Journal of Agronomy ’, and ‘ Field Crops Research ’ for articles published between 1980 and 2021 that allowed for a direct comparison of wheat yield and GPC between N application after GS 37 to an otherwise equally managed crop that received basal N fertilisation. We also collected other traits such as stover biomass and N uptake at plant maturity, and dough rheological properties, when available. The search resulted in 38 articles that, in addition to one unpublished trial from our group, evaluated 542 pairwise comparisons in 127 environments. Across studies, grain yield ranged from 1.15 to 10.63 Mg ha −1 and showed a negative relation with GPC, which ranged from 65 to 189 g kg −1 . Late-season N fertilisation was consistently neutral for grain yield (I 2 , proportion of the overall variance due to variation in real effects rather than chance, 26.2 %) and increased GPC with a pooled estimate of 3.96 %. The response of GPC was heterogeneous (I 2 = 84 %), suggesting the need for exploration of potential moderators of the response. Meta-regression suggested that increasing the proportion of late N relative to the total available N positively associated to increases in GPC, and the residuals of this analysis suggested that later applications increased GPC response, with no effect of N fertiliser source or placement. Environments with low temperature, high photothermal quotient, and long duration of the critical period associated with greater GPC response to late-season N applications. The relative response of GPC to late fertilisation correlated with the relative response of both stover N uptake and nitrogen concentration in stover at maturity, but not with stover biomass at maturity. Alveogram index and dough extensibility increased when late-season N increased GPC. Enhancing GPC through late N applications should consider associations between management, environmental, and physiological factors. Future research should focus on forecasting GPC response to late N, based on GPC response drivers identified in the current research. • Meta-analysis highlighted physiological drivers of wheat response to late N • Grain yield was unaffected by late N across a broad range of environments • Late N increased protein by 3.96% and its effects were heterogeneous • Protein increased linearly with the proportion of late N and with later applications • Higher protein response to late N associated to favourable growing conditions

Macrophage Phenotypes and Gene Expression Patterns Are Unique in Naturally Occurring Metabolically Healthy Obesity.

Obesity impacts 650 million individuals globally, often co-occurring with metabolic syndrome. Though many obese individuals experience metabolic abnormalities (metabolically unhealthy obese [MUO]), ~30% do not (metabolically healthy obese [MHO]). Conversely, >10% of lean individuals are metabolically unhealthy (MUL). To evaluate the physiologic drivers of these phenotypes, a 44-animal African green monkey cohort was selected using metabolic syndrome risk criteria to represent these four clinically defined health groups. Body composition imaging and subcutaneous adipose tissue (SQ AT) biopsies were collected. Differences in adipocyte size, macrophage subtype distribution, gene expression, vascularity and fibrosis were analyzed using digital immunohistopathology, unbiased RNA-seq, endothelial CD31, and Masson’s trichrome staining, respectively. MHO AT demonstrated significant increases in M2 macrophages (p = 0.02) and upregulation of fatty acid oxidation-related terms and transcripts, including FABP7 (p = 0.01). MUO AT demonstrated downregulation of these factors and co-occurring upregulation of immune responses. These changes occurred without differences in AT distributions, adipocyte size, AT endothelial cells, collagen I deposition, or circulating cytokine levels. Without unhealthy diet consumption, healthy obesity is defined by an increased SQ AT M2/M1 macrophage ratio and lipid handling gene expression. We highlight M2 macrophages and fatty acid oxidation as targets for improving metabolic health with obesity.

Reproductive senescence in polar bears in a variable environment

Reproductive senescence is ubiquitous in mammals. However, patterns of senescence vary across reproductive traits, even within populations, perhaps because of differences in selection pressures, physiological constraints, and responses to environmental conditions. We investigated reproductive senescence in wild female polar bears (Ursus maritimus), using 31 years of capture-recapture data from the Svalbard area. We studied the influence of environmental conditions on age-specific litter production and litter size using generalized linear mixed models. Further, using a capture-recapture model that handles the dependency between vital rates of individuals belonging to the same family unit, we assessed maternal-age-related changes in first year cub and litter survival. We provide clear evidence for reproductive senescence in female polar bears. Litter production and litter size peaked in middle-aged females and declined sharply afterward. By contrast cub and litter survival did not decline after prime age. We found no evidence of terminal investment. The reproductive output of all females was affected by sea-ice conditions during the previous year and the Arctic Oscillation, with some effects differing greatly between age groups. Old females were affected the most by environmental conditions. Our results suggest that the decline in reproductive output is a combination of fertility and body-condition senescence, with a weak contribution of maternal-effect senescence, possibly due to benefits of experience. Further, as predicted by evolutionary theory, senescence appears to be a consequence of failures in early stages of the reproductive cycle rather than in late stages, and environmental variation affected old females more than prime-aged females. Our study emphasizes the need to study several reproductive traits and account for environmental variation when investigating reproductive senescence. Differences in senescence patterns across reproductive traits should be interpreted in light of evolutionary theory and while considering underlying physiological drivers.

Interannual variability of ozone fluxes in a broadleaf deciduous forest in Italy

Multiannual measurements of ozone (O3) fluxes were performed from 2012 to 2020 in a broadleaf deciduous forest of the Po Valley, Italy. Fluxes were measured with the eddy covariance technique on a 41-m high tower, 15 m above the forest canopy. Different partition methodologies, based on concomitant water and carbon dioxide measurements, were compared for the calculation of the stomatal and non-stomatal components of the O3 fluxes. Total O3 fluxes revealed a marked interannual variability that was mainly driven by the stomatal activity in summer. Therefore, those factors that influence stomatal conductance were responsible for the flux variability, with soil water content being the main physiological driver. Despite the variability of the total O3 fluxes, the annual mean of the stomatal fraction was similar in the different years, around 42% on a 24-h basis, with an average summer value of 52% and a maximum around 60% during the summer daylight hours. The non-stomatal deposition was mainly driven by air humidity, surface wetness, and chemical sinks such as reaction of O3 with nitric oxide. Wind speed, turbulence intensity, and surface temperature showed a negative relationship with the non-stomatal fraction, but this was probably the result of a temporal misalignment between the daily cycles of non-stomatal conductance and those of temperature, turbulence, and wind speed. During the 7 years of measurements, the forest experienced a phytotoxic O3 dose of 10.55 mmolO3 m−2, as annual average, with an estimated reduction of the forest growth rate around 3% yr−1 according to the dose–effect relationships of the United Nations Economic Commission for Europe for broadleaf deciduous forests. Besides their implication for the O3 risk assessment for vegetation, these long-term measurements could be useful to test the deposition models used to correctly assess the O3 budget in troposphere on a multiannual time span.

Modulating disease phenotype in a songbird: A role for inflammation in disease tolerance?

Individual animals vary greatly in their responses to infection, either killing off the invading pathogen (resistance) or minimizing the per-pathogen costs of infection on host fitness (tolerance). Though we understand little about the physiological drivers of tolerance in wild animals, phenotypically, it manifests as milder clinical signs of disease. Here, we use a well-described disease system, finch mycoplasmosis, to evaluate the role of inflammation in disease tolerance. House finches (Haemorhous mexicanus) infected with the bacterial pathogen Mycoplasma gallisepticum (MG) develop conjunctival pathology that satisfies the cardinal signs of inflammation. We report on a captive trial performed in 2016 and replicated in 2018 that tested whether chemotherapeutics, specifically nonsteroidal anti-inflammatory drugs (NSAIDs), can reduce lesion severity, thus pushing individuals toward more tolerant phenotypes. Though birds treated with NSAIDs in the first trial developed milder pathology per unit pathogen load, we found no effect of treatment in the second trial, perhaps due to natural variation in baseline tolerance within the source population across years. Second-trial control birds developed markedly milder pathology than first-year controls, suggesting that the effect of trial swamped the effect of treatment in this study. Moving forward, using birds from a population in which the disease is absent or only recently emerged-and so tolerance has not yet been selected for-may better elucidate the role of pro-inflammatory mediators in disease tolerance.

Phenological, morphological and physiological drivers of cereal grain yield in Mediterranean agroforestry systems

Climate change will pose a major threat to food supply worldwide. Agroforestry has been proposed as an effective approach to minimize its effects on crops. However, to design sustainable and productive agroforestry systems, net responses of crops to trees need to be clarified, particularly in regions where competitive interactions will outweigh facilitative ones. The study of plant traits has become a useful approach to select best-adapted plants, yet the sensitivity of yield components to agroforestry and their relationship with plant traits needs investigation. In this experiment, we assess the phenological, morphological and physiological responses of shade-adapted cultivars of winter wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), growing in an agroforestry system (AF) with walnut trees (Juglans x intermedia Mj209xRa), as compared to cereal monocrops (MC). Agroforestry reduced the light intercepted by crops by 58 %, buffered extreme temperatures at the crop canopy level and increased air relative humidity, advancing plant development for wheat and barley. Major tree effects on crops were observed after walnut budburst. Under trees, crops increased the relative water content (RWC), Photochemical Reflectance Index (PRI) and P content of both wheat and barley leaves, increased Normalized Difference Vegetation Index (NDVI) of barley leaves, and reduced leaf mass area (LMA) in wheat and cell membrane damage in both species. In agroforestry, crops also reduced plant growth, leaf area (LA), leaf area index (LAI) and grain yield in both wheat and barley. Drivers of grain yield differed among agroforestry and open conditions in both species, showing for the first time that the selection of cereal cultivars for specific conditions could be based on plant traits, along with the shade tolerance, to establish successful agroforestry systems.

Physiological drivers of responses of grains per m2 to environmental and genetic factors in wheat

Most of the required increases in food production over the next decades are expected to be achieved through increases in crop yield. As wheat is essential for food security it is worrying that its yield gains over the last two decades were small. To achieve further yield increases it is critical to continue increasing number of grains per unit area (GN m -2 ), the trait best related to yield. In this context, it is relevant to identify the main determinants of GN m -2 in response to genetic and environmental factors as well as the trade-offs between them. In the present study we compiled a large database across the literature to analyse the relative importance of components when affected by genetic or environmental factors, producing small or large changes in GN m -2 and its components, either numerical (the number of spikes per m 2 , SN m -2 ; and the number of grains per spike, GN spike -1 ) or physiological (spike dry weight at anthesis, SDWa; and fruiting efficiency, FE) determinants. The database included 367 papers published in: (i) Field Crop Research (FCR), (ii) European Journal of Agronomy (EJA), (iii) Crop Science (CS) and (iv) Crop and Pasture Science (CPS, formerly Australian Journal of Agricultural Research) between 1990 and 2020. The complete dataset was split into classes, depending on the source of experimental variation, environment or genotype and was normalised to remove the differences between experiments and determine the environmental and genotypic effects within each experiment. Normalised data showed that the responsiveness of GN m -2 was similarly explained by changes in both SN m -2 and GN spike -1 , but in terms of physiological components SDWa was more relevant than FE for explaining the variations in GN m -2 . Considering the numerical components of GN m -2 genotypic and environmental factors modified more GN spike -1 than in SN m -2 . On the other hand, physiological components were differently modified by genotype and environment: for genotypic effects FE was more critical than SDWa and the other way around for environmental factors. A trade-off between numerical and physiological components was observed although was greater between physiological than between numerical components. • We quantified physiological/numerical components (and trade-offs) of grains/m -2 in wheat. • We recognised differences depending on magnitude and source of variation (genetic/environmental). • Grains/spike -1 explained better grains/m -2 than spikes/m -2 , particularly for genotypes. • Genotypes affected more fruiting efficiency than spike-dry-weight-at-anthesis, environments the opposite. • Trade-offs seemed more relevant for physiological than for numerical components.

Diminished carbon and nitrate assimilation drive changes in diatom elemental stoichiometry independent of silicification in an iron-limited assemblage

In the California Current Ecosystem, upwelled water low in dissolved iron (Fe) can limit phytoplankton growth, altering the elemental stoichiometry of the particulate matter and dissolved macronutrients. Iron-limited diatoms can increase biogenic silica (bSi) content >2-fold relative to that of particulate organic carbon (C) and nitrogen (N), which has implications for carbon export efficiency given the ballasted nature of the silica-based diatom cell wall. Understanding the molecular and physiological drivers of this altered cellular stoichiometry would foster a predictive understanding of how low Fe affects diatom carbon export. In an artificial upwelling experiment, water from 96 m depth was incubated shipboard and left untreated or amended with dissolved Fe or the Fe-binding siderophore desferrioxamine-B (+DFB) to induce Fe-limitation. After 120 h, diatoms dominated the communities in all treatments and displayed hallmark signatures of Fe-limitation in the +DFB treatment, including elevated particulate Si:C and Si:N ratios. Single-cell, taxon-resolved measurements revealed no increase in bSi content during Fe-limitation despite higher transcript abundance of silicon transporters and silicanin-1. Based on these findings we posit that the observed increase in bSi relative to C and N was primarily due to reductions in C fixation and N assimilation, driven by lower transcript expression of key Fe-dependent genes.