Prioritization of Randomized Clinical Trial Questions for Children Hospitalized With Common Conditions: A Consensus Statement.

Importance: There is a lack of randomized clinical trial (RCT) data to guide many routine decisions in the care of children hospitalized for common conditions. A first step in addressing the shortage of RCTs for this population is to identify the most pressing RCT questions for children hospitalized with common conditions. Objective: To identify the most important and feasible RCT questions for children hospitalized with common conditions. Design, Setting, and Participants: For this consensus statement, a 3-stage modified Delphi process was used in a virtual conference series spanning January 1 to September 29, 2022. Forty-six individuals from 30 different institutions participated in the process. Stage 1 involved construction of RCT questions for the 10 most common pediatric conditions leading to hospitalization. Participants used condition-specific guidelines and reviews from a structured literature search to inform their development of RCT questions. During stage 2, RCT questions were refined and scored according to importance. Stage 3 incorporated public comment and feasibility with the prioritization of RCT questions. Main Outcomes and Measures: The main outcome was RCT questions framed in a PICO (population, intervention, control, and outcome) format and ranked according to importance and feasibility; score choices ranged from 1 to 9, with higher scores indicating greater importance and feasibility. Results: Forty-six individuals (38 who shared demographic data; 24 women [63%]) from 30 different institutions participated in our modified Delphi process. Participants included children's hospital (n = 14) and community hospital (n = 13) pediatricians, parents of hospitalized children (n = 4), other clinicians (n = 2), biostatisticians (n = 2), and other researchers (n = 11). The process yielded 62 unique RCT questions, most of which are pragmatic, comparing interventions in widespread use for which definitive effectiveness data are lacking. Overall scores for importance and feasibility of the RCT questions ranged from 1 to 9, with a median of 5 (IQR, 4-7). Six of the top 10 selected questions focused on determining optimal antibiotic regimens for 3 common infections (pneumonia, urinary tract infection, and cellulitis). Conclusions and Relevance: This consensus statementhas identified the most important and feasible RCT questions for children hospitalized with common conditions. This list of RCT questions can guide investigators and funders in conducting impactful trials to improve care and outcomes for hospitalized children.

Exposure to E-Cigarette Marketing and Susceptibility to Future Vaping among Black and Latino Adolescents in the United States.

Evidence suggests an association between exposure to electronic cigarette (e-cigarette) marketing and e-cigarette use (vaping) among adolescents. However, there is limited evidence on exposure to e-cigarette marketing and susceptibility to future vaping, especially among Black and Latino adolescents. This study aimed to examine associations between exposure to e-cigarette marketing and susceptibility to future vaping among Black and Latino adolescents in the United States (US). Participants (N = 362; equal representation between Black and Latino adolescents) completed a baseline assessment (available in English and Spanish) including sociodemographic characteristics (e.g., racial/ethnic group, age, gender, sexual orientation, etc.), exposure to e-cigarette marketing, and susceptibility to future vaping. Exposure to e-cigarette marketing was recoded and organized into two categories (high exposure = 2 to 3; low exposure = 0 to 1). Cochran-Mantel-Haenszel tests were used to evaluate the association between exposure to e-cigarette marketing and susceptibility to future vaping, stratified by racial/ethnic group. Multiple logistic regressions assessed the association between exposure to e-cigarette marketing and susceptibility to future vaping, controlling for gender, sexual orientation, grade, and academic performance within each racial/ethnic group. Black adolescents reported significantly higher frequencies of exposure to e-cigarette marketing (p = 0.005). A significant interaction was found between exposure to e-cigarette marketing and racial/ethnic group (X2 (1) = 6.294, p = 0.012). Among Black adolescents, high exposure to e-cigarette marketing (vs. low exposure) was associated with a higher probability of susceptibility to future vaping (OR: 2.399, 95% CI 1.147-5.021, p = 0.020). For Latino adolescents, exposure to e-cigarette marketing was not associated with susceptibility to future vaping (OR: 0.503, 95% CI 0.245-1.03, p = 0.062). Future studies should evaluate how and where adolescents are exposed to e-cigarette marketing. Prevention efforts must include the implementation of effective counter-marketing campaigns and the reduction of exposure to e-cigarette marketing among Black and Latino adolescents.

Human epididymis protein 4: Analysis of national health and nutrition examination survey data.

BACKGROUND: Human epididymis protein 4 (HE4) is a tumor marker overexpressed in ovarian cancer and is commonly utilized to aid with diagnosis of an adnexal mass. HE4 levels vary based on pregnancy, age, menopausal status, and tobacco use. OBJECTIVE(S): The objective of this study was to evaluate population-based data to examine factors that affect HE4 among adult women in the United States and stratify levels of HE4 by demographic and gynecologic factors. STUDY DESIGN: A retrospective analysis was conducted using data from 2,480 women aged 20 + who participated in the National Health and Nutrition Examination Survey (2001-2002). From these cross-sectional data, serum HE4 and cotinine, a marker of tobacco exposure, were combined with demographic and interview data. Estimated glomerular filtration rates (eGFR) were based on serum creatinine, age, sex, and race. Other variables of interest included menopausal status, pregnancy, and various gynecologic factors. Summary HE4 data are provided as geometric means with associated 95 % confidence intervals. RESULTS: HE4 levels were independently associated with age, renal function, and nicotine use, all p < 0.001. Pre-menopausal women with a history of endometriosis were found to have elevated HE4 levels compared to those without, p < 0.01; however, we found no such difference among post-menopausal women. Adjusting for age, no differences in HE4 were found based on race/ethnicity, p = 0.29. HE4 levels showed statistically significant associations with income level; however, these were small and clinically irrelevant. CONCLUSION: This study provides evaluation of HE4 levels among a data set representative of 98.5 million non-institutionalized women in the United States and gives insight into extraneous factors that may influence these levels.

Cu and Zn promoted Al-fumarate metal organic frameworks for electrocatalytic CO2 reduction.

Metal organic frameworks (MOFs) are attractive materials to generate multifunctional catalysts for the electrocatalytic reduction of CO2 to hydrocarbons. Here we report the synthesis of Cu and Zn modified Al-fumarate (Al-fum) MOFs, in which Zn promotes the selective reduction of CO2 to CO and Cu promotes CO reduction to oxygenates and hydrocarbons in an electrocatalytic cascade. Cu and Zn nanoparticles (NPs) were introduced to the Al-fum MOF by a double solvent method to promote in-pore metal deposition, and the resulting reduced Cu-Zn@Al-fum drop-cast on a hydrophobic gas diffusion electrode for electrochemical study. Cu-Zn@Al-fum is active for CO2 electroreduction, with the Cu and Zn loading influencing the product yields. The highest faradaic efficiency (FE) of 62% is achieved at -1.0 V vs. RHE for the conversion of CO2 into CO, HCOOH, CH4, C2H4 and C2H5OH, with a FE of 28% to CH4, C2H4 and C2H5OH at pH 6.8. Al-fum MOF is a chemically robust matrix to disperse Cu and Zn NPs, improving electrocatalyst lifetime during CO2 reduction by minimizing transition metal aggregation during electrode operation.

Global analysis of Poales diversification - parallel evolution in space and time into open and closed habitats.

Poales are one of the most species-rich, ecologically and economically important orders of plants and often characterise open habitats, enabled by unique suites of traits. We test six hypotheses regarding the evolution and assembly of Poales in open and closed habitats throughout the world, and examine whether diversification patterns demonstrate parallel evolution. We sampled 42% of Poales species and obtained taxonomic and biogeographic data from the World Checklist of Vascular Plants database, which was combined with open/closed habitat data scored by taxonomic experts. A dated supertree of Poales was constructed. We integrated spatial phylogenetics with regionalisation analyses, historical biogeography and ancestral state estimations. Diversification in Poales and assembly of open and closed habitats result from dynamic evolutionary processes that vary across lineages, time and space, most prominently in tropical and southern latitudes. Our results reveal parallel and recurrent patterns of habitat and trait transitions in the species-rich families Poaceae and Cyperaceae. Smaller families display unique and often divergent evolutionary trajectories. The Poales have achieved global dominance via parallel evolution in open habitats, with notable, spatially and phylogenetically restricted divergences into strictly closed habitats.

Development of Scholarship Core Competencies for Pediatric Hospital Medicine Fellowship Programs.

The Pediatric Hospital Medicine (PHM) Fellowship Directors, recent fellowship graduates, and senior leaders in PHM have long identified training in scholarly activities as a key educational priority for fellowship training programs. We led a 2-day conference funded by the Agency for Healthcare Research and Quality to develop scholarship core competencies for PHM fellows. Participants included fellowship directors, national experts in PHM research, and representatives from key stakeholder organizations. Through engagement in large group presentations and small group iterative feedback and editing, participants created and refined a set of scholarship core competencies. After the conference, goals and objectives were edited and harmonized by conference leaders incorporating feedback from conference participants. Core competency development included 7 domains: (1) study design and execution, (2) data management, (3) principles of analytics, (4) critical appraisal of the medical literature, (5) ethics and responsible conduct of research, (6) peer review, dissemination, and funding, and (7) professionalism and leadership. Specific objectives for each goal were further organized into 3 levels to indicate core skills for all fellowship trainees (level 1), specialized and specific skills determined by fellow scholarly focus (level 2), and advanced skills for fellows interested in a clinical investigator career path (level 3). These newly developed scholarship core competencies provide a foundation for curricular development and implementation to ensure that the field continues to expand academically, given the 2-year training period and variable infrastructure across programs.

Are Black and Latino adolescents being asked if they use electronic cigarettes and advised not to use them? Results from a community-based survey.

Objective: This study aimed to explore whether African American/Black and Hispanic/Latino adolescents are being asked about electronic cigarette (e-cigarette) use (vaping) and advised not to use them. Methods: In 2021, adolescents (N = 362) with no vaping history, self-identified as African American/Black and/or Hispanic/Latino, and able to read and speak English and/or Spanish were recruited through partner schools and community-based organizations. Participants completed a survey reporting sociodemographic characteristics (e.g., race/ethnicity, gender, and language of preference) and they were asked about e-cigarette use and/or were advised not to use them by a health professional. Results: In total, 12% of African American/Black and 5% of Hispanic/Latino participants reported not seeing a health professional in the year prior to enrollment. Of the participants who reported visiting a health professional, 50.8% reported being asked and advised about vaping. Over one-quarter (28.4%) of participants were neither asked nor advised regarding vaping. Compared to English-speaking participants, Spanish-speaking participants were significantly less likely to be asked about e-cigarette use (45.2 vs. 63.9%, p = 0.009) and advised not to use them (40.3 vs. 66.9%, p < 0.001). Moreover, compared to African American/Black participants, Hispanic/Latino participants were significantly less likely to be advised not to use e-cigarettes (52.9 vs. 68.6%, p = 0.018). Furthermore, compared to male participants, female participants were significantly less likely to be advised not to use e-cigarettes (51.3 vs. 68.2%, p = 0.003). Conclusion: Compared to English-speaking participants, Spanish-speaking participants were significantly less likely to self-report being asked about e-cigarette use and advised not to use them. Moreover, Hispanic/Latino and female adolescents were significantly less likely to self-report being advised not to use e-cigarettes compared to their Black/African American and male counterparts. Future research is needed to improve health professional attention toward asking about and advising against vaping among adolescents.

Expedited transfer to a cardiac arrest centre for non-ST-elevation out-of-hospital cardiac arrest (ARREST): a UK prospective, multicentre, parallel, randomised clinical trial.

BACKGROUND: The International Liaison Committee on Resuscitation has called for a randomised trial of delivery to a cardiac arrest centre. We aimed to assess whether expedited delivery to a cardiac arrest centre compared with current standard of care following resuscitated cardiac arrest reduces deaths. METHODS: ARREST is a prospective, parallel, multicentre, open-label, randomised superiority trial. Patients (aged ≥18 years) with return of spontaneous circulation following out-of-hospital cardiac arrest without ST elevation were randomly assigned (1:1) at the scene of their cardiac arrest by London Ambulance Service staff using a secure online randomisation system to expedited delivery to the cardiac catheter laboratory at one of seven cardiac arrest centres or standard of care with delivery to the geographically closest emergency department at one of 32 hospitals in London, UK. Masking of the ambulance staff who delivered the interventions and those reporting treatment outcomes in hospital was not possible. The primary outcome was all-cause mortality at 30 days, analysed in the intention-to-treat (ITT) population excluding those with unknown mortality status. Safety outcomes were analysed in the ITT population. The trial was prospectively registered with the International Standard Randomised Controlled Trials Registry, 96585404. FINDINGS: Between Jan 15, 2018, and Dec 1, 2022, 862 patients were enrolled, of whom 431 (50%) were randomly assigned to a cardiac arrest centre and 431 (50%) to standard care. 20 participants withdrew from the cardiac arrest centre group and 19 from the standard care group, due to lack of consent or unknown mortality status, leaving 411 participants in the cardiac arrest centre group and 412 in the standard care group for the primary analysis. Of 822 participants for whom data were available, 560 (68%) were male and 262 (32%) were female. The primary endpoint of 30-day mortality occurred in 258 (63%) of 411 participants in the cardiac arrest centre group and in 258 (63%) of 412 in the standard care group (unadjusted risk ratio for survival 1·00, 95% CI 0·90-1·11; p=0·96). Eight (2%) of 414 patients in the cardiac arrest centre group and three (1%) of 413 in the standard care group had serious adverse events, none of which were deemed related to the trial intervention. INTERPRETATION: In adult patients without ST elevation, transfer to a cardiac arrest centre following resuscitated cardiac arrest in the community did not reduce deaths. FUNDING: British Heart Foundation.

Longitudinal Assessment of Association Between Tobacco Use and Tobacco Dependence Among Adults: Latent Class Analysis of the Population Assessment of Tobacco and Health Study Waves 1-4.

INTRODUCTION: With increasing tobacco product varieties, understanding tobacco use (TU) profiles and their associations with tobacco dependence (TD) has also become increasingly challenging. AIMS AND METHODS: We aimed to identify TU profiles and their associations with TD over time, and to identify subgroups with high risk of TD. We included 3463 adult recent tobacco users who had complete TU and TD data across waves 1-4 of the Population Assessment of Tobacco and Health (PATH) study. We used a composite index of TD and a summed TD score from an established 16-item TD measure. We applied a latent class analysis to identify TU profiles based on participants' usage of eight common tobacco product groups at each survey wave and to check the stability of the TU profiles over time. We then used generalized estimating equations regressions to evaluate the longitudinal TU-TD association, adjusting for potential confounders. RESULTS: We identified three distinct TU profiles that remained consistent across four survey waves: Dominant cigarette users (62%-68%), poly users with high propensity of using traditional cigarettes, e-cigarettes, and cigars (24%-31%), and dominant smokeless product users (7%-9%). Covariate-adjusted models showed that TD was significantly lower among the poly users and the dominant smokeless users, compared to that among the dominant cigarette users. CONCLUSIONS: Both TU profiles and their associations with TD were stable over time at the population level. Poly users and smokeless product users were consistently associated with lower TD than cigarette-dominant users, suggesting the need for tailored tobacco cessation interventions for users with different TU profiles. IMPLICATIONS: The finding of consistent TU profiles across four survey waves extends the current literature in capturing TU patterns in an evolving tobacco product landscape. The finding of the overall higher level of TD among the cigarette-dominant users compared to the other TU latent profiles (the Cig+eCig+Cigar dominant poly users and the dominant smokeless product users) can help identify high-risk groups for potential interventions. Our application of innovative statistical methods to high-quality longitudinal data from the PATH study helps improve the understanding of the dynamic TU-TD relationship over time.

Comfort levels in discussing tobacco smoking among hospital staff in a children's hospital.

INTRODUCTION: Hospital staff discussing smoking with children and their families can impact tobacco control, which is crucial in reducing the harmful effects of tobacco smoke exposure. Our study aims to assess staff comfort level in discussing smoking with patients or their families, and coworkers, after the implementation of a hospital-wide tobacco control policy. METHODS: This cross-sectional study included 2340 staff members who completed an anonymous online survey in a large urban children's hospital in 2019. The main outcomes of interest were the comfort level in discussing smoking with patients or their families, and co-workers. We used multivariable logistic regression to identify whether the comfort level varied by sex, age, job type, and smoking status. RESULTS: Most of the respondents (83.8%) were female, 41.2% were aged 18-35 years, 57.6% worked as clinical staff, and 15.5% were ever smokers. Compared to males, females were less likely to feel very comfortable in asking patients or their families about their smoking tobacco (adjusted odds ratio, AOR=0.72; 95% CI: 0.56-0.92) or talking to co-workers about the health risks associated with their smoking (AOR=0.71; 95% CI: 0.54-0.93). Staff who were non-smokers were less likely to feel very comfortable in talking to co-workers about the health risks associated with their smoking (AOR=0.60; 95% CI: 0.45-0.78). The odds of feeling very comfortable in discussing smoking were consistently lower among those aged 18-35 years than their older counterparts. Clinical staff were more likely than non-clinical staff to feel very comfortable in discussing with patients and their parents about smoking, but there was no difference when talking to co-workers. CONCLUSIONS: We found differences in staff comfort level in discussing smoking with patients or their families, and coworkers, by sex, age, job type, and smoking status. These results can guide training and identify potential barriers and improve tailored tobacco control training programs and policies for hospital staff.

Substrate Morphology Directs (001) Sb2 Se3 Thin Film Growth by Crystallographic Orientation Filtering.

Antimony chalcogenide, Sb2 X3 (X = S, Se), applications greatly benefit from efficient charge transport along covalently bonded (001) oriented (Sb4 X6 )n ribbons, making thin film orientation control highly desirable - although particularly hard to achieve experimentally. Here, it is shown for the first time that substrate nanostructure plays a key role in driving the growth of (001) oriented antimony chalcogenide thin films. Vapor Transport Deposition of Sb2 Se3 thin films is conducted on ZnO substrates whose morphology is tuned between highly nanostructured and flat. The extent of Sb2 Se3 (001) orientation is directly correlated to the degree of substrate nanostructure. These data showcase that nanostructuring a substrate is an effective tool to control the orientation and morphology of Sb2 Se3 films. The optimized samples demonstrate high (001) crystallographic orientation. A growth mechanism for these films is proposed, wherein the substrate physically restricts the development of undesirable crystallographic orientations. It is shown that the surface chemistry of the nanostructured substrates can be altered and still drive the growth of (001) Sb2 Se3 thin films - not limiting this phenomenon to a particular substrate type. Insights from this work are expected to guide the rational design of Sb2 X3 thin film devices and other low-dimensional crystal-structured materials wherein performance is intrinsically linked to morphology and orientation.

Improving the Quality of Written Discharge Instructions: A Multisite Collaborative Project.

BACKGROUND AND OBJECTIVES: Written discharge instructions help to bridge hospital-to-home transitions for patients and families, though substantial variation in discharge instruction quality exists. We aimed to assess the association between participation in an Institute for Healthcare Improvement Virtual Breakthrough Series collaborative and the quality of pediatric written discharge instructions across 8 US hospitals. METHODS: We conducted a multicenter, interrupted time-series analysis of a medical records-based quality measure focused on written discharge instruction content (0-100 scale, higher scores reflect better quality). Data were from random samples of pediatric patients (N = 5739) discharged from participating hospitals between September 2015 and August 2016, and between December 2017 and January 2020. These periods consisted of 3 phases: 1. a 14-month precollaborative phase; 2. a 12-month quality improvement collaborative phase when hospitals implemented multiple rapid cycle tests of change and shared improvement strategies; and 3. a 12-month postcollaborative phase. Interrupted time-series models assessed the association between study phase and measure performance over time, stratified by baseline hospital performance, adjusting for seasonality and hospital fixed effects. RESULTS: Among hospitals with high baseline performance, measure scores increased during the quality improvement collaborative phase beyond the expected precollaborative trend (+0.7 points/month; 95% confidence interval, 0.4-1.0; P < .001). Among hospitals with low baseline performance, measure scores increased but at a lower rate than the expected precollaborative trend (-0.5 points/month; 95% confidence interval, -0.8 to -0.2; P < .01). CONCLUSIONS: Participation in this 8-hospital Institute for Healthcare Improvement Virtual Breakthrough Series collaborative was associated with improvement in the quality of written discharge instructions beyond precollaborative trends only for hospitals with high baseline performance.

Staff Time in the Community: An Enduring Critical Component of Individual Placement and Support in the Digital Age.

OBJECTIVE: This study examined the relationship between individual placement and support (IPS) employment specialists' time spent in the community and employment outcomes in the current digital age, featuring increased technology use and online hiring practices. METHODS: The authors examined the relationship between employment outcomes and IPS employment specialists' time spent in the community at 78 sites in 2018 and 84 sites in 2019. RESULTS: The amount of time staff spent in the community was significantly and positively associated with better employment outcomes. CONCLUSIONS: These data support the continued importance of employment specialists' spending time in the community with employers and IPS recipients to achieve optimal outcomes for recipients.

Relations of Current and Past Cancer with Severe Outcomes among 104,590 Hospitalized COVID-19 Patients: The COVID EHR Cohort at the University of Wisconsin.

BACKGROUND: There is mixed evidence about the relations of current versus past cancer with severe COVID-19 outcomes and how they vary by patient and cancer characteristics. METHODS: Electronic health record data of 104,590 adult hospitalized patients with COVID-19 were obtained from 21 United States health systems from February 2020 through September 2021. In-hospital mortality and ICU admission were predicted from current and past cancer diagnoses. Moderation by patient characteristics, vaccination status, cancer type, and year of the pandemic was examined. RESULTS: 6.8% of the patients had current (n = 7,141) and 6.5% had past (n = 6,749) cancer diagnoses. Current cancer predicted both severe outcomes but past cancer did not; adjusted odds ratios (aOR) for mortality were 1.58 [95% confidence interval (CI), 1.46-1.70] and 1.04 (95% CI, 0.96-1.13), respectively. Mortality rates decreased over the pandemic but the incremental risk of current cancer persisted, with the increment being larger among younger vs. older patients. Prior COVID-19 vaccination reduced mortality generally and among those with current cancer (aOR, 0.69; 95% CI, 0.53-0.90). CONCLUSIONS: Current cancer, especially among younger patients, posed a substantially increased risk for death and ICU admission among patients with COVID-19; prior COVID-19 vaccination mitigated the risk associated with current cancer. Past history of cancer was not associated with higher risks for severe COVID-19 outcomes for most cancer types. IMPACT: This study clarifies the characteristics that modify the risk associated with cancer on severe COVID-19 outcomes across the first 20 months of the COVID-19 pandemic. See related commentary by Egan et al., p. 3.

Smoking Status, Nicotine Medication, Vaccination, and COVID-19 Hospital Outcomes: Findings from the COVID EHR Cohort at the University of Wisconsin (CEC-UW) Study.

INTRODUCTION: Available evidence is mixed concerning associations between smoking status and COVID-19 clinical outcomes. Effects of nicotine replacement therapy (NRT) and vaccination status on COVID-19 outcomes in smokers are unknown. METHODS: Electronic health record data from 104 590 COVID-19 patients hospitalized February 1, 2020 to September 30, 2021 in 21 U.S. health systems were analyzed to assess associations of smoking status, in-hospital NRT prescription, and vaccination status with in-hospital death and ICU admission. RESULTS: Current (n = 7764) and never smokers (n = 57 454) did not differ on outcomes after adjustment for age, sex, race, ethnicity, insurance, body mass index, and comorbidities. Former (vs never) smokers (n = 33 101) had higher adjusted odds of death (aOR, 1.11; 95% CI, 1.06-1.17) and ICU admission (aOR, 1.07; 95% CI, 1.04-1.11). Among current smokers, NRT prescription was associated with reduced mortality (aOR, 0.64; 95% CI, 0.50-0.82). Vaccination effects were significantly moderated by smoking status; vaccination was more strongly associated with reduced mortality among current (aOR, 0.29; 95% CI, 0.16-0.66) and former smokers (aOR, 0.47; 95% CI, 0.39-0.57) than for never smokers (aOR, 0.67; 95% CI, 0.57, 0.79). Vaccination was associated with reduced ICU admission more strongly among former (aOR, 0.74; 95% CI, 0.66-0.83) than never smokers (aOR, 0.87; 95% CI, 0.79-0.97). CONCLUSIONS: Former but not current smokers hospitalized with COVID-19 are at higher risk for severe outcomes. SARS-CoV-2 vaccination is associated with better hospital outcomes in COVID-19 patients, especially current and former smokers. NRT during COVID-19 hospitalization may reduce mortality for current smokers. IMPLICATIONS: Prior findings regarding associations between smoking and severe COVID-19 disease outcomes have been inconsistent. This large cohort study suggests potential beneficial effects of nicotine replacement therapy on COVID-19 outcomes in current smokers and outsized benefits of SARS-CoV-2 vaccination in current and former smokers. Such findings may influence clinical practice and prevention efforts and motivate additional research that explores mechanisms for these effects.

Chromosome size matters: genome evolution in the cyperid clade.

BACKGROUND AND AIMS: While variation in genome size and chromosome numbers and their consequences are often investigated in plants, the biological relevance of variation in chromosome size remains poorly known. Here, we examine genome and mean chromosome size in the cyperid clade (families Cyperaceae, Juncaceae and Thurniaceae), which is the largest vascular plant lineage with predominantly holocentric chromosomes. METHODS: We measured genome size in 436 species of cyperids using flow cytometry, and augment these data with previously published datasets. We then separately compared genome and mean chromosome sizes (2C/2n) amongst the major lineages of cyperids and analysed how these two genomic traits are associated with various environmental factors using phylogenetically informed methods. KEY RESULTS: We show that cyperids have the smallest mean chromosome sizes recorded in seed plants, with a large divergence between the smallest and largest values. We found that cyperid species with smaller chromosomes have larger geographical distributions and that there is a strong inverse association between mean chromosome size and number across this lineage. CONCLUSIONS: The distinct patterns in genome size and mean chromosome size across the cyperids might be explained by holokinetic drive. The numerous small chromosomes might function to increase genetic diversity in this lineage where crossovers are limited during meiosis.