The evolution of reproductive isolation in a simultaneous hermaphrodite, the freshwater snail Physa

<p>Abstract</p> <p>Background</p> <p>The cosmopolitan freshwater snail <it>Physa acuta </it>has recently found widespread use as a model organism for the study of mating systems and reproductive allocation. Mitochondrial DNA phylogenies suggest that <it>Physa carolinae</it>, recently described from the American southeast, is a sister species of <it>P. acuta</it>. The divergence of the <it>acuta/carolinae </it>ancestor from the more widespread <it>P. pomilia </it>appears to be somewhat older, and the split between a hypothetical <it>acuta/carolinae/pomilia </it>ancestor and <it>P. gyrina </it>appears older still.</p> <p>Results</p> <p>Here we report the results of no-choice mating experiments yielding no evidence of hybridization between <it>gyrina </it>and any of four other populations (<it>pomilia, carolinae</it>, Philadelphia <it>acuta</it>, or Charleston <it>acuta</it>), nor between <it>pomilia </it>and <it>carolinae</it>. Crosses between <it>pomilia </it>and both <it>acuta </it>populations yielded sterile F1 progeny with reduced viability, while crosses between <it>carolinae </it>and both <it>acuta </it>populations yielded sterile F1 hybrids of normal viability. A set of mate-choice tests also revealed significant sexual isolation between <it>gyrina </it>and all four of our other <it>Physa </it>populations, between <it>pomilia </it>and <it>carolinae</it>, and between <it>pomilia </it>and Charleston <it>acuta</it>, but not between <it>pomilia </it>and the <it>acuta </it>population from Philadelphia, nor between <it>carolinae </it>and either <it>acuta </it>population. These observations are consistent with the origin of hybrid sterility prior to hybrid inviability, and a hypothesis that speciation between <it>pomilia </it>and <it>acuta </it>may have been reinforced by selection for prezygotic reproductive isolation in sympatry.</p> <p>Conclusions</p> <p>We propose a two-factor model for the evolution of postzygotic reproductive incompatibility in this set of five <it>Physa </it>populations consistent with the Dobzhansky-Muller model of speciation, and a second two-factor model for the evolution of sexual incompatibility. Under these models, species trees may be said to correspond with gene trees in American populations of the freshwater snail, <it>Physa</it>.</p

Selective scattering between Floquet-Bloch and Volkov states in a topological insulator

The coherent optical manipulation of solids is emerging as a promising way to engineer novel quantum states of matter. The strong time periodic potential of intense laser light can be used to generate hybrid photon-electron states. Interaction of light with Bloch states leads to Floquet-Bloch states which are essential in realizing new photo-induced quantum phases. Similarly, dressing of free electron states near the surface of a solid generates Volkov states which are used to study non-linear optics in atoms and semiconductors. The interaction of these two dynamic states with each other remains an open experimental problem. Here we use Time and Angle Resolved Photoemission Spectroscopy (Tr-ARPES) to selectively study the transition between these two states on the surface of the topological insulator Bi2Se3. We find that the coupling between the two strongly depends on the electron momentum, providing a route to enhance or inhibit it. Moreover, by controlling the light polarization we can negate Volkov states in order to generate pure Floquet-Bloch states. This work establishes a systematic path for the coherent manipulation of solids via light-matter interaction.Comment: 21 pages, 6 figures, final version to appear in Nature Physic

Recommendations for a core outcome set for measuring standing balance in adult populations: a consensus-based approach

Standing balance is imperative for mobility and avoiding falls. Use of an excessive number of standing balance measures has limited the synthesis of balance intervention data and hampered consistent clinical practice.To develop recommendations for a core outcome set (COS) of standing balance measures for research and practice among adults.A combination of scoping reviews, literature appraisal, anonymous voting and face-to-face meetings with fourteen invited experts from a range of disciplines with international recognition in balance measurement and falls prevention. Consensus was sought over three rounds using pre-established criteria.The scoping review identified 56 existing standing balance measures validated in adult populations with evidence of use in the past five years, and these were considered for inclusion in the COS.Fifteen measures were excluded after the first round of scoring and a further 36 after round two. Five measures were considered in round three. Two measures reached consensus for recommendation, and the expert panel recommended that at a minimum, either the Berg Balance Scale or Mini Balance Evaluation Systems Test be used when measuring standing balance in adult populations.Inclusion of two measures in the COS may increase the feasibility of potential uptake, but poses challenges for data synthesis. Adoption of the standing balance COS does not constitute a comprehensive balance assessment for any population, and users should include additional validated measures as appropriate.The absence of a gold standard for measuring standing balance has contributed to the proliferation of outcome measures. These recommendations represent an important first step towards greater standardization in the assessment and measurement of this critical skill and will inform clinical research and practice internationally

Automated versus manual post-processing of perfusion-CT data in patients with acute cerebral ischemia: influence on interobserver variability

The purpose of this study is to compare the variability of PCT results obtained by automatic selection of the arterial input function (AIF), venous output function (VOF) and symmetry axis versus manual selection. Imaging data from 30 PCT studies obtained as part of standard clinical stroke care at our institution in patients with suspected acute hemispheric ischemic stroke were retrospectively reviewed. Two observers performed the post-processing of 30 CTP datasets. Each observer processed the data twice, the first time employing manual selection of AIF, VOF and symmetry axis, and a second time using automated selection of these same parameters, with the user being allowed to adjust them whenever deemed appropriate. The volumes of infarct core and of total perfusion defect were recorded. The cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT) and blood-brain barrier permeability (BBBP) values in standardized regions of interest were recorded. Interobserver variability was quantified using the Bland and Altman's approach. Automated post-processing yielded lower coefficients of variation for the volume of the infarct core and the volume of the total perfusion defect (15.7% and 5.8%, respectively) compared to manual post-processing (31.0% and 12.2%, respectively). Automated post-processing yielded lower coefficients of variation for PCT values (11.3% for CBV, 9.7% for CBF, and 9.5% for MTT) compared to manual post-processing (23.7% for CBV, 32.8% for CBF, and 16.7% for MTT). Automated post-processing of PCT data improves interobserver agreement in measurements of CBV, CBF and MTT, as well as volume of infarct core and penumbra

Cross-Linking Amine-Rich Compounds into High Performing Selective CO2 Absorbents

Amine-based absorbents play a central role in CO2 sequestration and utilization. Amines react selectively with CO2, but a drawback is the unproductive weight of solvent or support in the absorbent. Efforts have focused on metal organic frameworks (MOFs) reaching extremely high CO2 capacity, but limited selectivity to N2 and CH4, and decreased uptake at higher temperatures. A desirable system would have selectivity (cf. amine) and high capacity (cf. MOF), but also increased adsorption at higher temperatures. Here, we demonstrate a proof-of-concept where polyethyleneimine (PEI) is converted to a high capacity and highly selective CO2 absorbent using buckminsterfullerene (C60) as a cross-linker. PEI-C60 (CO2 absorption of 0.14 g/g at 0.1 bar/90°C) is compared to one of the best MOFs, Mg-MOF-74 (0.06 g/g at 0.1 bar/90°C), and does not absorb any measurable amount of CH4 at 50 bar. Thus, PEI-C60 can perform better than MOFs in the sweetening of natural gas

Regulation of N-WASP and the Arp2/3 Complex by Abp1 Controls Neuronal Morphology

Polymerization and organization of actin filaments into complex superstructures is indispensable for structure and function of neuronal networks. We here report that knock down of the F-actin-binding protein Abp1, which is important for endocytosis and synaptic organization, results in changes in axon development virtually identical to Arp2/3 complex inhibition, i.e., a selective increase of axon length. Our in vitro and in vivo experiments demonstrate that Abp1 interacts directly with N-WASP, an activator of the Arp2/3 complex, and releases the autoinhibition of N-WASP in cooperation with Cdc42 and thereby promotes N-WASP-triggered Arp2/3 complex-mediated actin polymerization. In line with our mechanistical studies and the colocalization of Abp1, N-WASP and Arp2/3 at sites of actin polymerization in neurons, we reveal an essential role of Abp1 and its cooperativity with Cdc42 in N-WASP-induced rearrangements of the neuronal cytoskeleton. We furthermore show that introduction of N-WASP mutants lacking the ability to bind Abp1 or Cdc42, Arp2/3 complex inhibition, Abp1 knock down, N-WASP knock down and Arp3 knock down, all cause identical neuromorphological phenotypes. Our data thus strongly suggest that these proteins and their complex formation are important for cytoskeletal processes underlying neuronal network formation

The heteronomy of choice architecture

Choice architecture is heralded as a policy approach that does not coercively reduce freedom of choice. Still we might worry that this approach fails to respect individual choice because it subversively manipulates individuals, thus contravening their personal autonomy. In this article I address two arguments to this effect. First, I deny that choice architecture is necessarily heteronomous. I explain the reasons we have for avoiding heteronomous policy-making and offer a set of four conditions for non-heteronomy. I then provide examples of nudges that meet these conditions. I argue that these policies are capable of respecting and promoting personal autonomy, and show this claim to be true across contrasting conceptions of autonomy. Second, I deny that choice architecture is disrespectful because it is epistemically paternalistic. This critique appears to loom large even against non-heteronomous nudges. However, I argue that while some of these policies may exhibit epistemically paternalistic tendencies, these tendencies do not necessarily undermine personal autonomy. Thus, if we are to find such policies objectionable, we cannot do so on the grounds of respect for autonomy

Curriculum in early childhood education: critical questions about content, coherence, and control

A continuing struggle over curriculum in early childhood education is evident in contemporary research and debate at national and international levels. This reflects the dominant influence of developmental psychology in international discourses, and in policy frameworks that determine approaches to curriculum, pedagogy, and assessment. Focusing on early childhood education, we argue that this struggle generates critical questions about three significant themes within curriculum theory: content, coherence, and control. We outline two positions from which these themes can be understood: Developmental and Educational Psychology and contemporary policy frameworks. We argue that within and between these positions, curriculum content, coherence, and control are viewed in different and sometimes oppositional ways. Following this analysis, we propose that a focus on ‘working theories’ as a third position offers possibilities for addressing some of these continuing struggles, by exploring different implications for how content, coherence, and control might be understood. We conclude that asking critical questions of curriculum in early childhood education is a necessary endeavour to develop alternative theoretical frameworks for understanding the ways in which curriculum can be considered alongside pedagogy, assessment, play, and learning