Burning questions for a warming and changing world: 15 unknowns in plant abiotic stress.

We present unresolved questions in plant abiotic stress biology as posed by 15 research groups with expertise spanning eco-physiology to cell and molecular biology. Common themes of these questions include the need to better understand how plants detect water availability, temperature, salinity, and rising carbon dioxide (CO2) levels; how environmental signals interface with endogenous signaling and development (e.g. circadian clock and flowering time); and how this integrated signaling controls downstream responses (e.g. stomatal regulation, proline metabolism, and growth versus defense balance). The plasma membrane comes up frequently as a site of key signaling and transport events (e.g. mechanosensing and lipid-derived signaling, aquaporins). Adaptation to water extremes and rising CO2 affects hydraulic architecture and transpiration, as well as root and shoot growth and morphology, in ways not fully understood. Environmental adaptation involves tradeoffs that limit ecological distribution and crop resilience in the face of changing and increasingly unpredictable environments. Exploration of plant diversity within and among species can help us know which of these tradeoffs represent fundamental limits and which ones can be circumvented by bringing new trait combinations together. Better defining what constitutes beneficial stress resistance in different contexts and making connections between genes and phenotypes, and between laboratory and field observations, are overarching challenges.

The tuatara genome reveals ancient features of amniote evolution.

The tuatara (Sphenodon punctatus)-the only living member of the reptilian order Rhynchocephalia (Sphenodontia), once widespread across Gondwana1,2-is an iconic species that is endemic to New Zealand2,3. A key link to the now-extinct stem reptiles (from which dinosaurs, modern reptiles, birds and mammals evolved), the tuatara provides key insights into the ancestral amniotes2,4. Here we analyse the genome of the tuatara, which-at approximately 5 Gb-is among the largest of the vertebrate genomes yet assembled. Our analyses of this genome, along with comparisons with other vertebrate genomes, reinforce the uniqueness of the tuatara. Phylogenetic analyses indicate that the tuatara lineage diverged from that of snakes and lizards around 250 million years ago. This lineage also shows moderate rates of molecular evolution, with instances of punctuated evolution. Our genome sequence analysis identifies expansions of proteins, non-protein-coding RNA families and repeat elements, the latter of which show an amalgam of reptilian and mammalian features. The sequencing of the tuatara genome provides a valuable resource for deep comparative analyses of tetrapods, as well as for tuatara biology and conservation. Our study also provides important insights into both the technical challenges and the cultural obligations that are associated with genome sequencing.

Publisher Correction: The tuatara genome reveals ancient features of amniote evolution.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Pinpointing the causal influences of stomatal anatomy and behavior on minimum, operational, and maximum leaf surface conductance.

Leaf surface conductance to water vapor and CO2 across the epidermis (gleaf) strongly determines rates of gas exchange. Thus, clarifying the drivers of gleaf has important implications for resolving mechanisms of photosynthetic productivity and leaf and plant responses and tolerance to drought. It is well recognized that gleaf is a function of the conductances of the stomata (gs) and of the epidermis + cuticle (gec). Yet, controversies have arisen around the relative roles of stomatal density (d) and size (s), fractional stomatal opening (α; aperture relative to maximum) and gec in determining gleaf. Resolving the importance of these drivers is critical across the range of leaf surface conductances, from strong stomatal closure under drought (gleaf, min), to typical opening for photosynthesis (gleaf, op), to maximum achievable opening (gleaf, max). We derived equations and analyzed a compiled database of published and measured data for approximately 200 species and genotypes. On average, within and across species, higher gleaf, min was determined ten times more strongly by α and gec than by d, and negligibly by s; higher gleaf, op was determined approximately equally by α (47%) than by stomatal anatomy (45% by d, and 8% by s), and negligibly by gec; and higher gleaf, max was determined entirely by d. These findings clarify how diversity in stomatal functioning arises from multiple structural and physiological causes with importance shifting with context. The rising importance of d relative to α, from gleaf, min to gleaf, op, enables even species with low gleaf, min, which can retain leaves through drought, to possess high d and thereby achieve rapid gas exchange in periods of high water availability.

Multiple hybridization events and repeated evolution of homoeologue expression bias in parthenogenetic, polyploid New Zealand stick insects.

During hybrid speciation, homoeologues combine in a single genome. Homoeologue expression bias (HEB) occurs when one homoeologue has higher gene expression than another. HEB has been well characterized in plants but rarely investigated in animals, especially invertebrates. Consequently, we have little idea as to the role that HEB plays in allopolyploid invertebrate genomes. If HEB is constrained by features of the parental genomes, then we predict repeated evolution of similar HEB patterns among hybrid genomes formed from the same parental lineages. To address this, we reconstructed the history of hybridization between the New Zealand stick insect genera Acanthoxyla and Clitarchus using a high-quality genome assembly from Clitarchus hookeri to call variants and phase alleles. These analyses revealed the formation of three independent diploid and triploid hybrid lineages between these genera. RNA sequencing revealed a similar magnitude and direction of HEB among these hybrid lineages, and we observed that many enriched functions and pathways were also shared among lineages, consistent with repeated evolution due to parental genome constraints. In most hybrid lineages, a slight majority of the genes involved in mitochondrial function showed HEB towards the maternal homoeologues, consistent with only weak effects of mitonuclear incompatibility. We also observed a proteasome functional enrichment in most lineages and hypothesize this may result from the need to maintain proteostasis in hybrid genomes. Reference bias was a pervasive problem, and we caution against relying on HEB estimates from a single parental reference genome.

The poorly-explored stomatal response to temperature at constant evaporative demand.

Changes in leaf temperature are known to drive stomatal responses, because the leaf-to-air water vapour gradient (Δw) increases with temperature if ambient vapour pressure is held constant, and stomata respond to changes in Δw. However, the direct response of stomata to temperature (DRST; the response when Δw is held constant by adjusting ambient humidity) has been examined far less extensively. Though the meagre available data suggest the response is usually positive, results differ widely and defy broad generalisation. As a result, little is known about the DRST. This review discusses the current state of knowledge about the DRST, including numerous hypothesised biophysical mechanisms, potential implications of the response for plant adaptation, and possible impacts of the DRST on plant-atmosphere carbon and water exchange in a changing climate.

Amphistomy increases leaf photosynthesis more in coastal than montane plants of Hawaiian 'ilima (Sida fallax).

PREMISE: The adaptive significance of amphistomy (stomata on both upper and lower leaf surfaces) is unresolved. A widespread association between amphistomy and open, sunny habitats suggests the adaptive benefit of amphistomy may be greatest in these contexts, but this hypothesis has not been tested experimentally. Understanding amphistomy informs its potential as a target for crop improvement and paleoenvironment reconstruction. METHODS: We developed a method to quantify "amphistomy advantage" ( AA $\text{AA}$ ) as the log-ratio of photosynthesis in an amphistomatous leaf to that of the same leaf but with gas exchange blocked through the upper surface (pseudohypostomy). Humidity modulated stomatal conductance and thus enabled comparing photosynthesis at the same total stomatal conductance. We estimated AA $\text{AA}$ and leaf traits in six coastal (open, sunny) and six montane (closed, shaded) populations of the indigenous Hawaiian species 'ilima (Sida fallax). RESULTS: Coastal 'ilima leaves benefit 4.04 times more from amphistomy than montane leaves. Evidence was equivocal with respect to two hypotheses: (1) that coastal leaves benefit more because they are thicker and have lower CO2 conductance through the internal airspace and (2) that they benefit more because they have similar conductance on each surface, as opposed to most conductance being through the lower surface. CONCLUSIONS: This is the first direct experimental evidence that amphistomy increases photosynthesis, consistent with the hypothesis that parallel pathways through upper and lower mesophyll increase CO2 supply to chloroplasts. The prevalence of amphistomatous leaves in open, sunny habitats can partially be explained by the increased benefit of amphistomy in "sun" leaves, but the mechanistic basis remains uncertain.

How and why do species break a developmental trade-off? Elucidating the association of trichomes and stomata across species.

PREMISE: Previous studies have suggested a trade-off between trichome density (Dt) and stomatal density (Ds) due to shared cell precursors. We clarified how, when, and why this developmental trade-off may be overcome across species. METHODS: We derived equations to determine the developmental basis for Dt and Ds in trichome and stomatal indices (it and is) and the sizes of epidermal pavement cells (e), trichome bases (t), and stomata (s) and quantified the importance of these determinants of Dt and Ds for 78 California species. We compiled 17 previous studies of Dt-Ds relationships to determine the commonness of Dt-Ds associations. We modeled the consequences of different Dt-Ds associations for plant carbon balance. RESULTS: Our analyses showed that higher Dt was determined by higher it and lower e, and higher Ds by higher is and lower e. Across California species, positive Dt-Ds coordination arose due to it-is coordination and impacts of the variation in e. A Dt-Ds trade-off was found in only 30% of studies. Heuristic modeling showed that species sets would have the highest carbon balance with a positive or negative relationship or decoupling of Dt and Ds, depending on environmental conditions. CONCLUSIONS: Shared precursor cells of trichomes and stomata do not limit higher numbers of both cell types or drive a general Dt-Ds trade-off across species. This developmental flexibility across diverse species enables different Dt-Ds associations according to environmental pressures. Developmental trait analysis can clarify how contrasting trait associations would arise within and across species.

Collegiate student-athletes concussion knowledge and attitudes: what a difference a decade Makes.

OBJECTIVE: The purpose of this study was to assess changes in concussion knowledge and attitudes amongst incoming intercollegiate student-athletes over the course of a decade (2010-2012 vs 2021-2023). METHODS: There were 592 student-athletes from 2 cohorts (2010-2012, 2021-2023) who completed the Rosenbaum Concussion Knowledge and Attitudes Survey (ROCKaS) questionnaire which is comprised of a concussion knowledge index (CKI, 0-24) and attitude index (CAI, 15-75) with higher scores reflecting better performance. A three factor ANOVA (Group, Sex, Concussion History) compared performance on the CKI and CAI. Individual questions were compared between groups with a Chi-Square analysis. RESULTS: For the CKI, there was a significant main effect for Group (2010-2012: 18.5 ± 2.6, 2021-2023: 19.4 ± 2.5, p < 0.001, η2=0.032). For the CAI, there was also a significant main effect for group (2010-2012: 52.9 ± 6.0, 2021-2023: 62.2 ± 6.5, p < 0.001, η2=0.359). CONCLUSIONS: The results of this study show a modest increase in concussion knowledge; however, large improvements in concussion attitudes were observed between groups. These results suggest a continued improvement in student-athlete concussion awareness and provide specific areas to continue addressing persistent misconceptions.

The experiences and challenges of nurses who become patients in a hospital setting: A scoping review of the literature.

AIM: This scoping review aimed to identify and describe evidence regarding the experiences of nurses when they become patients or when nurses care for other health professional-patients in a hospital setting. DESIGN: A scoping review of internationally published peer-reviewed literature. DATA SOURCES: A systematic search of peer-reviewed evidence was conducted in electronic databases: CINAHL, Medline, Scopus, ProQuest and PsycINFO. METHODS: Critical appraisal, data extraction and summary were performed independently by two reviewers according to the scoping review framework developed by Arksey and O'Malley. Twenty-three publications from 1999 to 2021 were included in this scoping review. RESULTS: This scoping review highlighted seven key themes as follows: (1) the challenges for nurse-patients and caregivers; (2) role ambiguity when a nurse becomes a patient; (3) the need for personalized care to consider the nurse's professional experience; (4) the requirement to not make assumptions about the registered nurse's knowledge; (5) loss of control and vulnerabilities of being a patient; (6) the impact of the valuable small things that carers did and (7) the impact of being a nurse-patient on their future practice. CONCLUSION: While some aspects of nurse-patients' experiences are common to non-healthcare professional-patients, this review highlights there are unique challenges when nurses become patients themselves. Future research should focus on exploring nurses' experience of caring for other healthcare professional-patients and strive to better understand how to meet nurses' unique needs when they become patients themselves. IMPACT: This review advances knowledge on an under-explored topic, highlighting the unique and challenging experience when nurses become patients in a hospital setting. Nurses should be aware of the unique needs of nurse-patients to provide person-centred quality care. PATIENT OR PUBLIC CONTRIBUTION: There was no direct patient or public contribution to this scoping review, although one of the authors did have experience as a nurse-patient in the last 3 years.

Nurse practitioners' use of diagnostic imaging: A scoping review.

AIM: To explore the nature and extent of peer-reviewed literature related to the use of diagnostic imaging by nurse practitioners (NPs) to inform future practice and research. BACKGROUND: Nurse practitioners undertake advanced assessment, diagnosis, and management of patients, including requesting and interpretation of diagnostic imaging. It is unclear what evidence exists related to the quality use of radiological investigations by NPs in recent years. DESIGN: A scoping review based on the steps suggested by the Joanna Briggs Institute. METHODS: A structured review of the databases Medline, CINAHL and Embase was undertaken using the keywords and MESH terms 'nurse practitioner', 'medical imaging', 'diagnostic imaging', 'scan' and 'radiography'. Only English language articles were included, and no date limit was applied. Database review was completed on 30 May 2021. RESULTS: Eight themes were identified-country and clinical context, requesting diagnostic imaging, performing diagnostic imaging, image-guided interventions, interpreting diagnostic imaging, training education and knowledge, impact on resource usage and comparison with medical practitioners. There were more studies across a greater breadth of clinical specialties and imaging modalities in the United States than in other countries. Nurse practitioner practice is frequently benchmarked against that of medical colleagues. There is a paucity of studies focusing on educational preparation and the lack of relevant university curricula for NPs around diagnostic imaging. CONCLUSION: There are significant gaps in the evidence outside of the United States across several of the identified themes. Further studies are needed to explore NP access to and use of diagnostic imaging and to understand the barriers and facilitators to this. RELEVANCE TO CLINICAL PRACTICE: Studies from four countries were included in this review. The evidence suggests that, where studied, nurse practitioners (NPs) can safely and appropriately request and interpret plain x-rays in the emergency and minor injuries setting. Further research is needed to evaluate the educational needs of NPs in relation to diagnostic imaging and their use of advanced imaging techniques, particularly outside of the United States. PATIENT OR PUBLIC CONTRIBUTION: No patient or public contribution.

Family's preferences for and experiences of writing practices in adult intensive care and its use in early bereavement: A descriptive qualitative study.

BACKGROUND: Family partaking in writing practices, such as writing intensive care unit (ICU) patient diaries, personal diaries/journaling, social media, or instant messaging services, during ICU admission may allow the family to unintentionally participate in a form of expressive writing. These writing practices could provide structure for the family authors to explore emotions and manage significant life events, including death of a loved one. Limited studies have explored the family's postmortem experiences and perceived value of writing practices maintained during an ICU admission. OBJECTIVES: The objective of this study was to explore the family member's preferences for and experiences of writing practices in the adult ICU and its use in early bereavement. METHODS: descriptive qualitative design using inductive reflexive thematic analysis from a purposeful, convenience sample of 16 bereaved participants from a tertiary referral, adult ICU in Australia who discussed their experiences of and preferences in writing practices. Reporting adheres to the consolidated criteria for reporting qualitative research checklist. FINDINGS: Six participants maintained writing practices during the ICU admission and 10 did not. Three themes were generated from the data: the decision to maintain writing practices was shaped by past behaviours and perceived utility; moments captured were influenced by the loved ones' clinical status and their ability to access the writing medium; and writing practices have limited utility as a memory making object in early bereavement. CONCLUSIONS: Based on the generated findings, participants who did not maintain writing practices did not later regret this decision during early bereavement. Participants who did maintain writing practices predominately used a personal diary/journal that they carried with them. As the loved one approached death, the written entries became shorter, then ceased. Most of the written entries were not read during early bereavement, suggesting the writing practices' psychological value might have been predominately gained at the time of writing, rather than during early bereavement.

Genome-wide association identifies candidate genes for drought tolerance in coast redwood and giant sequoia.

Drought is a major limitation for survival and growth in plants. With more frequent and severe drought episodes occurring due to climate change, it is imperative to understand the genomic and physiological basis of drought tolerance to be able to predict how species will respond in the future. In this study, univariate and multitrait multivariate genome-wide association study methods were used to identify candidate genes in two iconic and ecosystem-dominating species of the western USA, coast redwood and giant sequoia, using 10 drought-related physiological and anatomical traits and genome-wide sequence-capture single nucleotide polymorphisms. Population-level phenotypic variation was found in carbon isotope discrimination, osmotic pressure at full turgor, xylem hydraulic diameter, and total area of transporting fibers in both species. Our study identified new 78 new marker × trait associations in coast redwood and six in giant sequoia, with genes involved in a range of metabolic, stress, and signaling pathways, among other functions. This study contributes to a better understanding of the genomic basis of drought tolerance in long-generation conifers and helps guide current and future conservation efforts in the species.

Kinetic factors of physiology and the dynamic light environment influence the economic landscape of short-term hydraulic risk.

Optimality-based models of stomatal conductance unify biophysical and evolutionary constraints and can improve predictions of land-atmosphere carbon and water exchange. Recent models incorporate hydraulic constraints by penalizing excessive stomatal opening in relation to hydraulic damage caused by low water potentials. We used simulation models to test whether penalties based solely on vulnerability curves adequately represent the optimality hypothesis, given that they exclude the effects of kinetic factors on stomatal behavior and integrated carbon balance. To quantify the effects of nonsteady-state phenomena on the landscape of short-term hydraulic risk, we simulated diurnal dynamics of leaf physiology for 10 000 patches of leaf in a canopy and used a ray-tracing model, Helios, to simulate realistic variation in sunfleck dynamics. Our simulations demonstrated that kinetic parameters of leaf physiology and sunfleck properties influence the economic landscape of short-term hydraulic risk, as characterized by the effect of stomatal strategy (gauged by the water potential causing a 50% hydraulic penalty) on both aggregated carbon gain and the aggregated carbon cost of short-term hydraulic risk. Hydraulic penalties in optimization models should be generalized to allow their parameters to account for kinetic factors, in addition to parameters of hydraulic vulnerability.

The dynamic multi-functionality of leaf water transport outside the xylem.

A surge of papers have reported low leaf vulnerability to xylem embolism during drought. Here, we focus on the less studied, and more sensitive, outside-xylem leaf hydraulic responses to multiple internal and external conditions. Studies of 34 species have resolved substantial vulnerability to dehydration of the outside-xylem pathways, and studies of leaf hydraulic responses to light also implicate dynamic outside-xylem responses. Detailed experiments suggest these dynamic responses arise at least in part from strong control of radial water movement across the vein bundle sheath. While leaf xylem vulnerability may influence leaf and plant survival during extreme drought, outside-xylem dynamic responses are important for the control and resilience of water transport and leaf water status for gas exchange and growth.

Thermal sensitivity across forest vertical profiles: patterns, mechanisms, and ecological implications.

Rising temperatures are influencing forests on many scales, with potentially strong variation vertically across forest strata. Using published research and new analyses, we evaluate how microclimate and leaf temperatures, traits, and gas exchange vary vertically in forests, shaping tree, and ecosystem ecology. In closed-canopy forests, upper canopy leaves are exposed to the highest solar radiation and evaporative demand, which can elevate leaf temperature (Tleaf ), particularly when transpirational cooling is curtailed by limited stomatal conductance. However, foliar traits also vary across height or light gradients, partially mitigating and protecting against the elevation of upper canopy Tleaf . Leaf metabolism generally increases with height across the vertical gradient, yet differences in thermal sensitivity across the gradient appear modest. Scaling from leaves to trees, canopy trees have higher absolute metabolic capacity and growth, yet are more vulnerable to drought and damaging Tleaf than their smaller counterparts, particularly under climate change. By contrast, understory trees experience fewer extreme high Tleaf 's but have fewer cooling mechanisms and thus may be strongly impacted by warming under some conditions, particularly when exposed to a harsher microenvironment through canopy disturbance. As the climate changes, integrating the patterns and mechanisms reviewed here into models will be critical to forecasting forest-climate feedback.

Leaf relative water content at 50% stomatal conductance measured by noninvasive NMR is linked to climate of origin in nine species of eucalypt.

Stomata are the gatekeepers of plant water use and must quickly respond to changes in plant water status to ensure plant survival under fluctuating environmental conditions. The mechanism for their closure is highly sensitive to disturbances in leaf water status, which makes isolating their response to declining water content difficult to characterise and to compare responses among species. Using a small-scale non-destructive nuclear magnetic resonance spectrometer as a leaf water content sensor, we measure the stomatal response to rapid induction of water deficit in the leaves of nine species of eucalypt from contrasting climates. We found a strong linear correlation between relative water content at 50% stomatal conductance (RWCgs50 ) and mean annual temperature at the climate of origin of each species. We also show evidence for stomata to maintain control over water loss well below turgor loss point in species adapted to warmer climates and secondary increases in stomatal conductance despite declining water content. We propose that RWCgs50 is a promising trait to guide future investigations comparing stomatal responses to water deficit. It may provide a useful phenotyping trait to delineate tolerance and adaption to hot temperatures and high leaf-to-air vapour pressure deficits.

Secondary analysis of a randomized trial testing community health educator interventions for diabetes prevention among refugees with depression: effects on nutrition, physical activity and sleep.

BACKGROUND: Refugees have high levels of psychological distress that hamper lifestyle change efforts. We previously reported that community health educator (CHE) diabetes prevention interventions decreased HbA1c and depressive symptoms among Cambodian-American refugees with depression; this paper reports health behavior outcomes of those interventions. METHODS: Participants were aged 35-75, Khmer speaking, at risk for diabetes, and met study criteria for likely depression by either a) antidepressant medication and/or b) prolonged elevated depressive symptoms. Participants were randomized to one of three CHE interventions: 1) lifestyle intervention called Eat, Walk, Sleep (EWS), 2) EWS plus medication therapy management with a pharmacist/CHE team (EWS + MTM), or, 3) social services (SS; control). Physical activity and sleep were measured with 7 days of actigraphy. Nutrition was measured as carbohydrates as reported in a culturally tailored food frequency questionnaire. Assessments were at baseline, end point (12 months), and follow-up (15 months). RESULTS: The n = 188 participants were 78% female, average age of 55 years, half had a household income < $20,000, and modal education was 7.0 years. Individuals in the two treatment groups that received the EWS intervention significantly increased their brown rice consumption (p < .001, Cohen's d = 0.76) and their moderate-to-vigorous activity (p = .039, d = 0.32). No intervention changed sleep duration, timing, efficiency or wake after sleep onset. Across groups, individuals who increased brown rice consumption, increased vigorous activity and decreased total sleep time variability showed decreased HbA1c, with small effect sizes. CONCLUSIONS: CHEs may improve nutrition and physical activity in refugees with depression but more intensive interventions may be required to impact sleep. Improvements in all three behaviors appear to be associated with HbA1c lowering TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT02502929.

Exposure to Starvation: Associations with HbA1c, Anthropometrics, and Trauma Symptoms Four Decades Later Among Cambodians Resettled in the USA.

BACKGROUND: Epidemiological data suggest that populations exposed to starvation show increased incidence of type 2 diabetes but these studies are limited by lack of person-level data. Cambodians resettled in the USA survived severe malnutrition during distinct historical eras. We examined the relationship of individual exposure to starvation with current HbA1c, anthropometrics, and trauma symptoms among Cambodian Americans. METHODS: Participants were excluded for extant diabetes but all had elevated risk factors for type 2 diabetes and depression. Participants identified images on a 5-point scale that best depicted their body size during four distinct periods: before 1970 (peacetime), 1970-1975 (USA bombing campaign, widespread hunger), 1975-1979 (Pol Pot regime, mass starvation), and "now" (2016-2019, resettled in the USA). They reported trauma symptoms and provided anthropometrics and a blood sample. RESULTS: The n = 189 participants were mean = 55 years old and had glycosylated hemoglobin (HbA1c) mean = 5.5%. Self-reported body size showed excellent validity by strong correlations between body thinness "now" and objectively measured waist circumference (r = -0.35), weight (r = -0.50), and body mass index (r = -0.50). Whereas there was some variability, modal self-reported body size started as normal during peacetime, became thinner during the USA bombing campaign, became emaciated during the Pol Pot regime, and rebounded to normal/slightly heavy "now." Body size during Pol Pot showed the strongest associations with long-term outcomes; thinner body size (greater starvation) was associated with higher trauma symptoms and higher HbA1c even after controlling for age, current waist circumference, and current body mass index. CONCLUSION: Greater degree of starvation was associated with higher HbA1c and trauma symptoms four decades later.

Test-Retest Reliability and Efficacy of Individual Symptoms in Concussion Management.

OBJECTIVE: (1) To determine test-retest reliability of individual Sport Concussion Assessment Tool-Third Edition (SCAT-3) symptom scores and symptom severity scores, (2) to examine the specificity/sensitivity of individual SCAT-3 symptom severity scores acutely (24-48 hours) postconcussion, and (3) to develop a model of symptoms best able to differentiate concussed from nonconcussed student athletes and cadets. DESIGN: Prospective, longitudinal, and cross-sectional. SETTING: Twenty-six civilian schools and 3 US service academies. PARTICIPANTS: Collegiate student athletes (n = 5519) and cadets (n = 5359) from the National Collegiate Athletic Association-Department of Defense Grand Alliance: Concussion Assessment, Research and Education Consortium, including 290 student athletes and 205 cadets, assessed 24 to 48 hours postconcussion. INDEPENDENT VARIABLES: Concussed and nonconcussed student athlete and cadet groups. MAIN OUTCOME MEASURES: Sport Concussion Assessment Tool-Third Edition individual symptom severity scores, total symptom scores, and symptom severity scores. RESULTS: Results indicated poor test-retest reliability across all symptom scores (intraclass correlation coefficient = 0.029-0.331), but several individual symptoms had excellent predictive capability in discriminating concussed from nonconcussed participants (eg, headache, pressure in the head, and don't feel right had area under the curve >0.8, sensitivity >70%, and specificity >85%) regardless of baseline testing. These symptoms were consistent with Chi-square Automatic Interaction Detector classification trees with the highest mean probability. CONCLUSIONS: Findings support the excellent diagnostic accuracy of honest symptom reporting, notwithstanding the known limitations in symptom underreporting, and suggest that there may be added value in examining individual symptoms rather than total symptom scores and symptom severity scores alone. Finally, findings suggest that baseline testing is not necessary for interpreting postconcussion symptom scores.