Biology subjects

Dixon, P.

Publications and source records attributed to Dixon, P..

3 recordsLinked to original sources

bioRxiv2025

Trends in stomatal density and size in maize hybrids representing 100 years of long-term breeding for yield

Maize hybrid breeding started over 100 years ago, has increased yield and vigor through improved genetics in conjunction with increased fertilizer and pesticide use, planting density, and agricultural mechanization. Stomata are expected to change in response to rising atmospheric CO2 concentration and average temperature anomalies ({degrees}C). Yet, the impact of long-term maize breeding over the past century on stomatal traits and their responses to climate factors remains poorly understood. We evaluated stomatal traits at the seedling stage in 27 maize hybrids released from 1920 to 2022, grown under controlled conditions. Modern hybrids (2013 - 2022) had a smaller total stomatal pore area (9.17 x 108 m2) than (1920 - 2012) historical ERA hybrids (9.94 x 108 m2; p[≤] 0.001), a higher stomatal density (47.2 per mm-2) vs. historical ERA hybrids (44.5), and a smaller leaf area (17.9 cm2 vs. 20.5 cm2). No significant differences were found in the size (m2), length (m), or width (m) of stomata between the two groups. Stomatal density increased, while all other traits decreased in modern hybrids. Stomatal density was negatively correlated with stomatal size (r = -0.62), length (r = -0.57), width (r = - 0.54), and leaf area (r = -0.54). Stomatal size had a negative correlation with atmospheric CO2 concentration (r = -0.22) and average temperature anomalies ({degrees}C) (r = -0.35) in the hybrids year of release and climate proxies. In contrast, stomatal density had a positive correlation with both atmospheric CO2 concentration and average temperature anomalies ({degrees}C) (r = 0.44) in year of release. Total stomatal pore area negatively correlated with atmospheric CO2 concentration (r = -0.45) and average temperature anomalies ({degrees}C) (r = -0.36). Our study indicates that maize stomatal traits suggest inadvertent selection for key stomatal traits (density and size), total stomatal pore area (per year decline of about 0.02%) associated with yield stability and environmental adaptation. HighlightsMaize stomatal traits changed through environmental (CO2 and {degrees}C) adaptation but total stomatal pore area, effects indirectly by decreased leaf area in maize hybrids representing 100 years of long-term breeding for yield. A negative correlation was observed across 27 ERA hybrids between stomatal density and stomatal size, length, width and leaf area. Stomatal density increases while stomata size, length width and leaf area decrease per se. Over the past 100 years, the total stomatal pore area on leaves decreased, while stomatal density increased as leaf area declined, revealing a connection between these two patterns. A negative correlation was found between total stomatal pore area and atmospheric CO2 concentrations, and temperature over the past century.

genetics↗

bioRxiv2019

The causal effect of adiposity on hospital costs: Mendelian Randomization analysis of over 300,000 individuals from the UK Biobank

Estimates of the marginal effect of measures of adiposity such as body mass index (BMI) on healthcare costs are important for the formulation and evaluation of policies targeting adverse weight profiles. Many existing estimates of this association are affected by endogeneity bias caused by simultaneity, measurement error and omitted variables. The contribution of this study is to avoid this bias by using a novel identification strategy - random germline genetic variation in an instrumental variable analysis - to identify the presence and magnitude of the causal effect of BMI on inpatient hospital costs. We also use data on genetic variants to undertake much richer testing of the sensitivity of results to potential violations of the instrumental variable assumptions than is possible with existing approaches. Using data on over 300,000 individuals, we found effect sizes for the marginal unit of BMI more than 50% larger than multivariable effect sizes. These effects attenuated under sensitivity analyses, but remained larger than multivariable estimates for all but one estimator. There was little evidence for non-linear effects of BMI on hospital costs. Within-family estimates, intended to address dynastic biases, were null but suffered from low power. This paper is the first to use genetic variants in a Mendelian Randomization framework to estimate the causal effect of BMI (or any other disease/trait) on healthcare costs. This type of analysis can be used to inform the cost-effectiveness of interventions and policies targeting the prevention and treatment of overweight and obesity, and for setting research priorities.

epidemiology↗

bioRxiv2018

The association between adiposity and inpatient hospital costs in the UK Biobank cohort

BackgroundHigh adiposity is associated with higher risks for a variety of adverse health outcomes, including higher rates of age-adjusted mortality and increased morbidity. This has important implications for the management of healthcare systems, since the endocrinal, cardiometabolic and other changes associated with increased adiposity may be associated with substantial healthcare costs.\n\nMethodsWe studied the association between various measures of adiposity and inpatient hospital costs through record linkage between UK Biobank and records of inpatient care in England and Wales. UK Biobank is a large prospective cohort study that aimed to recruit men and women aged between 40 and 69 from 2006 to 2010. We applied generalised linear models to cost per person year to estimate the marginal effect and averaged adjusted predicted cost of adiposity on inpatient costs.\n\nResultsValid cost and body mass index (BMI) data from 457,689 participants were available for inferential analysis. Some 54.4% of individuals included in the analysis sample had positive inpatient healthcare costs over the period of follow-up. Median hospital costs per person year of follow-up were {pound}89, compared to mean costs of {pound}481. Mean BMI overall was 27.4 kg/m2 (standard deviation 4.8). The marginal effect of a unit increase in BMI was {pound}13.61 (99% confidence interval: {pound}12.60 to {pound}14.63) per person year of follow up. The marginal effect of a standard deviation increase in BMI was {pound}69.20 (99% confidence interval: {pound}64.98 to {pound}73.42). The marginal effect of becoming obese was {pound}136.35 (99% confidence interval: {pound}124.62 to {pound}148.08). Average adjusted predicted inpatient hospital costs increased almost linearly when modelled using continuous measure of adiposity. Sensitivity analysis of different scenarios did not substantially change these conclusions, although there was some evidence of attenuation of the effects of adiposity when controlling for waist-hip ratios, and when individuals who self-reported any pre-existing conditions were excluded from analysis.\n\nConclusionsHigher adiposity is associated with higher inpatient hospital costs. Further scrutiny using causal inferential methods is warranted to establish if further public health investments are required to manage the large healthcare costs observationally associated with overweight and obesity.

epidemiology↗