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Shaping global water and carbon cycles, plants lift water from roots to leaves through xylem conduits. The importance of xylem water conduction makes it crucial to understand how natural selection deploys conduit diameters within and across plants. Wider conduits transport more water but are likely more vulnerable to conduction-blocking gas embolisms and cost more for a plant to build, a tension necessarily shaping xylem conduit diameters along plant stems. We build on this expectation to present the Widened Pipe Model (WPM) of plant hydraulic evolution, testing it against a global dataset. The WPM predicts that xylem conduits should be narrowest at the stem tips, widening quickly before plateauing toward the stem base. This universal profile emerges from Pareto modeling of a trade-off between just two competing vectors of natural selection: one favoring rapid widening of conduits tip to base, minimizing hydraulic resistance, and another favoring slow widening of conduits, minimizing carbon cost and embolism risk. Our data spanning terrestrial plant orders, life forms, habitats, and sizes conform closely to WPM predictions. The WPM highlights carbon economy as a powerful vector of natural selection shaping plant function. It further implies that factors that cause resistance in plant conductive systems, such as conduit pit membrane resistance, should scale in exact harmony with tip-to-base conduit widening. Furthermore, the WPM implies that alterations in the environments of individual plants should lead to changes in plant height, for example, shedding terminal branches and resprouting at lower height under drier climates, thus achieving narrower and potentially more embolism-resistant conduits.

Practice is an essential component in learning any new skill. For learning the quantitative disciplines at the university level, web-based homework management systems provide the means for extensive practice with immediate feedback, which research suggests should lead to increased student learning (Palocsay & Stevens, 2008; Titard, DeFranceschi, & Knight, 2014). Do web-based homework management systems improve student learning, as measured by exam scores, for adult learners in an online course? Does the use of simple Microsoft Excel-based homework templates relate to improved student exam scores? This natural experiment divided a sample of 2431 online students in an entry level university economics course into three treatment groups to look at the relationship between homework support and exam scores. Results suggest that practice provided by a web-based homework management system is correlated with increased student learning as evidenced by increased exam scores.

Mosquito-borne viruses are emerging or re-emerging globally, afflicting millions of people around the world. Aedes aegypti, the yellow fever mosquito, is the principal vector of dengue, Zika, and chikungunya viruses, and has well-established populations across tropical and subtropical urban areas of the Americas, including the southern United States. While intense arboviral epidemics have occurred in Mexico and further south in the Americas, local transmission in the United States has been minimal. Here, we study Ae. aegypti and Culex quinquefasciatus host feeding patterns and vertebrate host communities in residential environments of South Texas to identify host-utilization relative to availability. Only 31% of Ae. aegypti blood meals were derived from humans, while 50% were from dogs and 19% from other wild and domestic animals. In Cx. quinquefasciatus, 67% of blood meals were derived from chicken, 22% came from dogs, 9% from various wild avian species, and 2% from other mammals including one human, one cat, and one pig. We developed a model for the reproductive number, R0, for Zika virus (ZIKV) in South Texas relative to northern Mexico using human disease data from Tamaulipas, Mexico. We show that ZIKV R0 in South Texas communities could be greater than one if the risk of human exposure to Ae. aegypti bites in these communities is at least 60% that of Northern Mexico communities. The high utilization of non-human vertebrates and low risk of human exposure in South Texas diminishes the outbreak potential for human-amplified urban arboviruses transmitted by Ae. aegypti.

Climate change is affecting mountain ecosystems by increasing vegetation coverage and altering meteorological conditions. These changes are likely to impact the timing and magnitude of dissolved organic matter (DOM) inputs to lakes from the surrounding catchment. We examined temporal dynamics of DOM using in situ optical sensors that measured DOM fluorescence (fDOM) through the ice-free season in five lakes with differing catchment characteristics. We also measured changes in lake level and compiled daily meteorological data from nearby weather stations. At a seasonal time scale, fDOM dynamics occurred in two phases. fDOM declined in the first phase, which lasted until late July--mid-August, and corresponded to a decline in lake level following spring snowmelt. This decline was more pronounced in lakes with more vegetated catchments. At a shorter time scale, fDOM increased following precipitation events with a 0- to 1-day lag. Rates of fDOM increase per centmetre change in lake level were greater in lakes with vegetated catchments. As climate change increases vegetation coverage, DOM will likely become more dynamic at daily and seasonal time scales and impact water transparency and productivity of mountain lakes. Les changements climatiques ont une incidence sur les ecosystemes de montagnes en accroissant le couvert vegetal et en modifiant les conditions meteorologiques. Ces changements auront vraisemblablement un impact sur la chronologie et l'ampleur des apports de matiere organique dissoute (MOD) dans les lacs en provenance des bassins versants qui les entourent. Nous avons examine la dynamique temporelle de la MOD en utilisant des capteurs optiques in situ pour mesurer la fluorescence de la MOD (fMOD) durant la periode d'eaux libres dans cinq lacs dont les bassins versants presentent des caracteristiques differentes. Nous avons aussi mesure les variations des niveaux des lacs et compile des donnees meteorologiques quotidiennes issues de stations meteorologiques situees a proximite. A l'echelle saisonniere, la dynamique de la fMOD s'est deroulee en deux phases. La fMOD a diminue durant la premiere phase, qui a dure jusqu'a la fin juillet--mi-aout et correspondait a une baisse du niveau des lacs suivant la fonte printaniere de la neige. Cette baisse etait plus prononcee dans les lacs aux bassins versants plus vegetalises. A une echelle de temps plus courte, la fMOD augmentait apres des episodes de precipitation, avec un decalage de 0 a 1 jour. Les taux d'augmentation de la fDOM par centimetre de variation du niveau du lac etaient plus eleves pour les lacs aux bassins versants vegetalises. Avec l'accroissement du couvert vegetal decoulant des changements climatiques, la MOD deviendra probablement plus dynamique aux echelles quotidienne et saisonniere et aura un impact sur la transparence et la productivite des lacs de montagnes. [Traduit par la Redaction], Introduction Dissolved organic matter (DOM) is a complex of substances that play a critical role in structuring lake ecosystems (Williamson et al. 1999; Solomon et al. 2015). Both autochthonous and [...]

Moringa oleifera is widely grown throughout the tropics and increasingly used for its therapeutic and nutraceutical properties. These properties are attributed to potent antioxidant and metabolism regulators, including glucosinolates/isothiocyanates as well as flavonoids, polyphenols, and phenolic acids. Research to date largely consists of geographically limited studies that only examine material available locally. These practices make it unclear as to whether moringa samples from one area are superior to another, which would require identifying superior variants and distributing them globally. Alternatively, the finding that globally cultivated moringa material is essentially functionally equivalent means that users can easily sample material available locally. We brought together accessions of Moringa oleifera from four continents and nine countries and grew them together in a common garden. We performed a metabolomic analysis of leaf extracts (MOLE) using an LC-MSMS ZenoTOF 7600 mass spectrometry system. The antioxidant capacity of leaf samples evaluated using the Total Antioxidant Capacity assay did not show any significant difference between extracts. MOLE samples were then tested for their antioxidant activity on C2C12 myotubes challenged with an oxidative insult. Hydrogen peroxide (H2O2) was added to the myotubes after pretreatment with different extracts. H2O2 exposure caused an increase in cell death that was diminished in all samples pretreated with moringa extracts. Our results show that Moringa oleifera leaf extract is effective in reducing the damaging effect of H2O2 in C2C12 myotubes irrespective of geographical origin. These results are encouraging because they suggest that the use of moringa for its therapeutic benefits can proceed without the need for the lengthy and complex global exchange of materials between regions. [ABSTRACT FROM AUTHOR]

Hypoallometric (slope<1) scaling between metabolic rate and body mass is often regarded as near-universal across organisms. However, there are compelling reasons to question hypoallometric scaling in woody plants, where metabolic rate is directly proportional to leaf area. This leaf area must provide carbon to the volume of the metabolically active sapwood (V MASW). Within populations of a species, variants in which V MASW increases per unit leaf area with height growth (e.g. ⅔ or ¾ scaling) would have proportionally less carbon for growth and reproduction as they grow taller. Therefore, selection should favor individuals in which, as they grow taller, leaf area scales isometrically with shoot V MASW (slope=1). Using tetrazolium staining, we measured total V MASW and total leaf area (LAtot) across 22 individuals of Ricinus communis and confirmed that leaf area scales isometrically with V MASW, and that V MASW is much smaller than total sapwood volume. With the potential of the LAtot– V MASW relationship to shape factors as diverse as the crown area–stem diameter relationship, conduit diameter scaling, reproductive output, and drought-induced mortality, our work indicates that the notion that sapwood increases per unit leaf area with height growth requires revision. [ABSTRACT FROM AUTHOR]

Background The mechanisms leading to dieback and death of trees under drought remain unclear. To gain an understanding of these mechanisms, addressing major empirical gaps regarding tree structure–function relations remains essential. Scope We give reasons to think that a central factor shaping plant form and function is selection simultaneously favouring constant leaf-specific conductance with height growth and isometric (1:1) scaling between leaf area and the volume of metabolically active sink tissues ('sapwood'). Sapwood volume–leaf area isometry implies that per-leaf area sapwood volumes become transversely narrower with height growth; we call this 'stretching'. Stretching means that selection must favour increases in permeability above and beyond that afforded by tip-to-base conduit widening ("ultra-widening permeability"), via fewer and wider vessels or tracheids with larger pits or larger margo openings. Leaf area–metabolically active sink tissue isometry would mean that it is unlikely that larger trees die during drought because of carbon starvation due to greater sink–source relationships as compared to shorter plants. Instead, an increase in permeability is most plausibly associated with greater risk of embolism, and this seems a more probable explanation of the preferential vulnerability of larger trees to climate change-induced drought. Other implications of selection favouring constant per-leaf area sapwood construction and maintenance costs are departure from the da Vinci rule expectation of similar sapwood areas across branching orders, and that extensive conduit furcation in the stem seems unlikely. Conclusions Because all these considerations impact the likelihood of vulnerability to hydraulic failure versus carbon starvation, both implicated as key suspects in forest mortality, we suggest that these predictions represent essential priorities for empirical testing. [ABSTRACT FROM AUTHOR]

Understanding how plants survive drought and cold is increasingly important as plants worldwide experience dieback with drought in moist places and grow taller with warming in cold ones. Crucial in plant climate adaptation are the diameters of water-transporting conduits. Sampling 537 species across climate zones dominated by angiosperms, we find that plant size is unambiguously the main driver of conduit diameter variation. And because taller plants have wider conduits, and wider conduits within species are more vulnerable to conduction-blocking embolisms, taller conspecifics should be more vulnerable than shorter ones, a prediction we confirm with a plantation experiment. As a result, maximum plant size should be short under drought and cold, which cause embolism, or increase if these pressures relax. That conduit diameter and embolism vulnerability are inseparably related to plant size helps explain why factors that interact with conduit diameter, such as drought or warming, are altering plant heights worldwide.

Glucosinolates (GS) are metabolized to isothiocyanates that may enhance human healthspan by protecting against a variety of chronic diseases. Moringa oleifera, the drumstick tree, produces unique GS but little is known about GS variation within M. oleifera, and even less in the 12 other Moringa species, some of which are very rare. We assess leaf, seed, stem, and leaf gland exudate GS content of 12 of the 13 known Moringa species. We describe 2 previously unidentified GS as major components of 6 species, reporting on the presence of simple alkyl GS in 4 species, which are dominant in M. longituba. We document potent chemoprotective potential in 11 of 12 species, and measure the cytoprotective activity of 6 purified GS in several cell lines. Some of the unique GS rank with the most powerful known inducers of the phase 2 cytoprotective response. Although extracts of most species induced a robust phase 2 cytoprotective response in cultured cells, one was very low (M. longituba), and by far the highest was M. arborea, a very rare and poorly known species. Our results underscore the importance of Moringa as a chemoprotective resource and the need to survey and conserve its interspecific diversity.

Taste drives consumption of foods. The tropical tree Moringa oleifera is grown worldwide as a protein-rich leafy vegetable and for the medicinal value of its phytochemicals, in particular its glucosinolates, which can lead to a pronounced harsh taste. All studies to date have examined only cultivated, domestic variants, meaning that potentially useful variation in wild type plants has been overlooked. We examine whether domesticated and wild type M. oleifera differ in myrosinase or glucosinolate levels, and whether these different levels impact taste in ways that could affect consumption. We assessed taste and measured levels of protein, glucosinolate, myrosinase content, and direct antioxidant activity of the leaves of 36 M. oleifera accessions grown in a common garden. Taste tests readily highlighted differences between wild type and domesticated M. oleifera. There were differences in direct antioxidant potential, but not in myrosinase activity or protein quantity. However, these two populations were readily separated based solely upon their proportions of the two predominant glucosinolates (glucomoringin and glucosoonjnain). This study demonstrates substantial variation in glucosinolate composition within M. oleifera. The domestication of M. oleifera appears to have involved increases in levels of glucomoringin and substantial reduction of glucosoonjnain, with marked changes in taste.

A pilot study depicting a collaborative learning experience involving students in the helping professions (i.e., social work and paramedic) is presented, whereby students put discipline-specific practice behaviors into action in a training exercise using standardized clients (SCs). Real world scenarios commonly encountered in emergency response situations were replicated, providing students with opportunities to utilize assessment, intervention and referral skills in a carefully controlled, technologically enhanced learning environment. Simulations were observed and reviewed by faculty and classmates in debriefing sessions following student-SC interactions. Emergent themes, lessons learned and recommendations for further study are presented.

This article describes how a secondary teacher education program at a midsized university made the turn toward a practice-based program in teacher education. The authors argue that efforts to recenter the program around practices have not only improved opportunities for novice teachers, but also have provided teacher educators a programmatic framework for making substantive progress toward three attributes of quality teacher education: increased collaboration between teacher educators, greater coherence between courses and experiences, and improved legitimacy of university-based teacher education. The authors detail specific components of this program reform and explain how such efforts have resulted in valuable gains across each attribute. The authors also explain how they implemented these programmatic changes largely within existing course and field-experience structures, and without substantive new infusions of personnel or funding.

Greater diversity in functional morphology should be associated with the evolution of greater ontogenetic diversity, an expectation difficult to test in most long-lived wild organisms. In the cells derived from the wood meristem (vascular cambium), plants provide extraordinary systems for reconstructing ontogenies in often long-lived organisms. The vascular cambium produces files of cells from the stem center to the periphery, with each cambial derivative "deciding" which of four cell types it differentiates into. Wood cell files remain in place, allowing tracing of the ontogenetic "decisions" taken throughout the life of a stem. We compared cell files from the Pedilanthus clade (genus Euphorbia), which span a range of growth forms from small trees and shrubs of tropical habitats to desert succulents. Using language theory, we represented wood cell types as "letters" and combinations of cell types in cell files as "words," allowing us to measure the diversity of decisions based on word frequency matrices. We also used information content metrics to compare levels of predictability in "decision-making." Our analyses identified a wider array of developmental decisions in woody trees as compared to succulent shrubs, illustrating ways that woody plants provide unparalleled systems for studying the evolution of ontogeny in long-lived, non-model species. [ABSTRACT FROM AUTHOR]