Ecological factors influence balancing selection on leaf chemical profiles of a wildflower.

Balancing selection is frequently invoked as a mechanism that maintains variation within and across populations. However, there are few examples of balancing selection operating on loci underpinning complex traits, which frequently display high levels of variation. We investigated mechanisms that may maintain variation in a focal polymorphism-leaf chemical profiles of a perennial wildflower (Boechera stricta, Brassicaceae)-explicitly interrogating multiple ecological and genetic processes including spatial variation in selection, antagonistic pleiotropy and frequency-dependent selection. A suite of common garden and greenhouse experiments showed that the alleles underlying variation in chemical profile have contrasting fitness effects across environments, implicating two ecological drivers of selection on chemical profile: herbivory and drought. Phenotype-environment associations and molecular genetic analyses revealed additional evidence of past selection by these drivers. Together, these data are consistent with balancing selection on chemical profile, probably caused by pleiotropic effects of secondary chemical biosynthesis genes on herbivore defence and drought response.

Clinical and laboratory evaluation of patients with SARS-CoV-2 pneumonia treated with high-titer convalescent plasma: a prospective study

OBJECTIVESTo determine the rate of intubation, overall survival, viral clearance, and the development of endogenous antibodies in patients with COVID-19 pneumonia treated with convalescent plasma containing high levels of neutralizing anti-SARS-CoV-2 antibodies. We also aimed to describe the laboratory parameters of the plasma products. DESIGNThis was a phase IIa, single institution, prospective study in adults hospitalized with SARS-CoV-2 pneumonia. SETTINGHackensack University Medical Center, a 770-bed research and teaching hospital located in Bergen County NJ, 11 km from New York City. The study was conducted between April 15 and June 18, 2020. PARTICIPANTS47 hospitalized adult patients were treated: 32 in the non-mechanically ventilated group and 15 in the mechanically ventilated group. All patients had confirmed SARS-CoV-2 pneumonia by radiographic and laboratory evaluation. INTERVENTIONFresh or frozen convalescent plasma from donors with high titers of viral neutralizing antibodies was administered. MAIN OUTCOME MEASURESIncidence of intubation, overall survival, and discharge rate of patients divided in cohorts based on severity of disease. Description of infused plasma characteristics. Evaluation of recipients pre-treatment viral immunity, immunity transfer from convalescent plasma administration, and late immunity 30 and 60 days after treatment. Rates of viral clearance by nasopharyngeal PCR at 10 and 30 days. Outcomes of patients with no pre-treatment immunity. Survival comparison with institutional data for each cohort. RESULTSAnalysis for the non-mechanically ventilated patients showed an intubation rate of 15.6% (95% CI: 5.3%-32.8%) and a day-30 survival rate of 87.5% (28/32; 95% CI:70.2%-96.4%). The overall survival for a comparative group based on institutional data was 66% (675/1023; p=0.012). The rates of negative nasopharyngeal swab by PR-PCR on day+10 and +30 post treatment were 42.9% (95% CI: 24%-63%) and 78% (95% CI: 56%-93%) respectively. Patients mechanically ventilated had a day-30 mortality of 46.7% (95% CI:21.3%-73.4%); the mortality for a comparative group based on institutional data was 68.5% (217/317; p=0.093). The rates of negative nasopharyngeal swab by PR-PCR at day+10 and +30 was 85.7% (95% CI: 42-100%; n=7) and 100% (95% CI: 63-100%; n=8). Seven patients (15%) had no pre-infusion immunity, and all were found to have anti-SARS-CoV-2 neutralizing titers three days post infusion. All evaluable patients were found to have neutralizing antibodies on day+30 (n=30) and on day+60 (n=12) post treatment. There was no difference in outcomes within the ranges of high antiviral neutralizing titers used, mostly greater than 1:1000. There was also no difference between fresh or frozen plasma. The only adverse event was a mild rash in one patient. CONCLUSIONIn this study of adult patients hospitalized with SARS-CoV-2 pneumonia, convalescent plasma was safe and conferred effective transfer of immunity while preserving endogenous immune response. Intubation rates, survival rates compared with institutional data, and viral clearance rates, support the continued evaluation of this antiviral modality. STUDY REGISTRATIONClinicalTrials.gov NTC04343755

Antagonistic selection and pleiotropy constrain the evolution of plant chemical defenses.

When pleiotropy is present, genetic correlations may constrain the evolution of ecologically important traits. We used a quantitative genetics approach to investigate constraints on the evolution of secondary metabolites in a wild mustard, Boechera stricta. Much of the genetic variation in chemical composition of glucosinolates in B. stricta is controlled by a single locus, BCMA1/3. In a large-scale common garden experiment under natural conditions, we quantified fitness and glucosinolate profile in two leaf types and in fruits. We estimated genetic variances and covariances (the G-matrix) and selection on chemical profile in each tissue. Chemical composition of defenses was strongly genetically correlated between tissues. We found antagonistic selection between defense composition in leaves and fruits: compounds that were favored in leaves were disadvantageous in fruits. The positive genetic correlations and antagonistic selection led to strong constraints on the evolution of defenses in leaves and fruits. In a hypothetical population with no genetic variation at BCMA1/3, we found no evidence for genetic constraints, indicating that pleiotropy affecting chemical profile in multiple tissues drives constraints on the evolution of secondary metabolites.

Ecological differentiation facilitates fine-scale coexistence of sexual and asexual Boechera.

PREMISE OF THE STUDY: Ecological differentiation (ED) between sexual and asexual organisms may permit the maintenance of reproductive polymorphism. Several studies of sexual/asexual ED in plants have shown that the geographic ranges of asexuals extend beyond those of sexuals, often in areas of higher latitude or elevation. But very little is known about ED at fine scales, wherein coexistence of sexuals and asexuals may be permitted by differential niche occupation. METHODS: We used 149 populations of sexual and apomictic lineages in the genus Boechera (rock cress) collected across a portion of this mustard's vast range. We characterized reproductive mode, ploidy, and species identity or hybrid parentage of each individual, and then used a multipronged statistical approach to (1) identify ED between sexuals and asexuals; (2) investigate the impacts of two confounding factors, polyploidy and hybridization, on ED; and (3) determine the environmental variables underlying ED. KEY RESULTS: We found that sexuals and asexuals are significantly ecologically differentiated across the landscape, despite fine-scale interdigitation of these two reproductive forms. Asexual reproduction was strongly associated with greater disturbance, reduced slope, and greater environmental variability. Although ploidy had little effect on the patterns observed, hybridization has a unique impact on the relationships between asexual reproduction and specific environmental variables. CONCLUSIONS: Ecological differentiation along the axes of disturbance, slope, and climatic variability, as well as the effects of heterozygosity, may contribute to the maintenance of sexuality and asexuality across the landscape, ultimately impacting the establishment and spread of asexual lineages.

Testing the optimal defense hypothesis in nature: Variation for glucosinolate profiles within plants.

Plants employ highly variable chemical defenses against a broad community of herbivores, which vary in their susceptibilities to specific compounds. Variation in chemical defenses within the plant has been found in many species; the ecological and evolutionary influences on this variation, however, are less well-understood. One central theory describing the allocation of defenses in the plant is the Optimal Defense Hypothesis (ODH), which predicts that defenses will be concentrated in tissues that are of high fitness value to the plant. Although the ODH has been repeatedly supported within vegetative tissues, few studies have compared vegetative and reproductive tissues, and the results have not been conclusive. We quantified variation in glucosinolate profile and tissue value between vegetative and reproductive tissues in Boechera stricta, a close relative of Arabidopsis. B. stricta manufactures glucosinolates, a set of defensive compounds that vary genetically and are straightforward to quantify. Genetic diversity in glucosinolate profile has been previously demonstrated to be important to both herbivory and fitness in B. stricta; however, the importance of glucosinolate variation among tissues has not. Here, we investigate whether allocation of glucosinolates within the plant is consistent with the ODH. We used both clipping experiments on endogenous plants and ambient herbivory in a large-scale transplant experiment at three sites to quantify fitness effects of loss of rosette leaves, cauline leaves, and flowers and fruits. We measured glucosinolate concentration in leaves and fruits in the transplant experiment, and asked whether more valuable tissues were more defended. We also investigated within-plant variation in other aspects of the glucosinolate profile. Our results indicated that damage to fruits had a significantly larger effect on overall fitness than damage to leaves, and that fruits had much higher concentrations of glucosinolates, supporting the ODH. This is, to the best of our knowledge, the first study to explicitly compare both tissue value and chemical defense concentrations between vegetative and reproductive tissues under natural conditions.

Natural selection drives clinal life history patterns in the perennial sunflower species, Helianthus maximiliani.

In plants, ecologically important life history traits often display clinal patterns of population divergence. Such patterns can provide strong evidence for spatially varying selection across environmental gradients but also may result from nonselective processes, such as genetic drift, population bottlenecks and spatially restricted gene flow. Comparison of population differentiation in quantitative traits (measured as Q(ST) ) with neutral molecular markers (measured as F(ST) ) provides a useful tool for understanding the relative importance of adaptive and nonadaptive processes in the formation and maintenance of clinal variation. Here, we demonstrate the existence of geographic variation in key life history traits in the diploid perennial sunflower species Helianthus maximiliani across a broad latitudinal transect in North America. Strong population differentiation was found for days to flowering, growth rate and multiple size-related traits. Differentiation in these traits greatly exceeds neutral predictions, as determined both by partial Mantel tests and by comparisons of global Q(ST) values with theoretical F(ST) distributions. These findings indicate that clinal variation in these life history traits likely results from local adaptation driven by spatially heterogeneous environments.