Symmetry Breaking and Emergence of Directional Flows in Minimal Actomyosin Cortices

Cortical actomyosin flows, among other mechanisms, scale up spontaneous symmetry breaking and thus play pivotal roles in cell differentiation, division, and motility. According to many model systems, myosin motor-induced local contractions of initially isotropic actomyosin cortices are nucleation points for generating cortical flows. However, the positive feedback mechanisms by which spontaneous contractions can be amplified towards large-scale directed flows remain mostly speculative. To investigate such a process on spherical surfaces, we reconstituted and confined initially isotropic minimal actomyosin cortices to the interfaces of emulsion droplets. The presence of ATP leads to myosin-induced local contractions that self-organize and amplify into directed large-scale actomyosin flows. By combining our experiments with theory, we found that the feedback mechanism leading to a coordinated directional motion of actomyosin clusters can be described as asymmetric cluster vibrations, caused by intrinsic non-isotropic ATP consumption with spatial confinement. We identified fingerprints of vibrational states as the basis of directed motions by tracking individual actomyosin clusters. These vibrations may represent a generic key driver of directed actomyosin flows under spatial confinement in vitro and in living systems.(This article belongs to the Special Issue Symmetry Breaking in Cells and Tissues

Groovy and gnarly : surface wrinkles as a multifunctional motif for terrestrial and marine environments

From large ventral pleats of humpback whales to nanoscale ridges on flower petals, wrinkled structures are omnipresent, multifunctional, and found at hugely diverse scales. Depending on the particulars of the biological system—its environment, morphology, and mechanical properties—wrinkles may control adhesion, friction, wetting, or drag; promote interfacial exchange; act as flow channels; or contribute to stretching, mechanical integrity, or structural color. Undulations on natural surfaces primarily arise from stress-induced instabilities of surface layers (e.g., buckling) during growth or aging. Variation in the material properties of surface layers and in the magnitude and orientation of intrinsic stresses during growth lead to a variety of wrinkling morphologies and patterns which, in turn, reflect the wide range of biophysical challenges wrinkled surfaces can solve. Therefore, investigating how surface wrinkles vary and are implemented across biological systems is key to understanding their structure-function relationships. In this work, we synthesize the literature in a metadata analysis of surface wrinkling in various terrestrial and marine organisms to review important morphological parameters and classify functional aspects of surface wrinkles in relation to the size and ecology of organisms. Building on our previous and current experimental studies, we explore case studies on nano/micro-scale wrinkles in biofilms, plant surfaces, and basking shark filter structures to compare developmental and structure-vs-function aspects of wrinkles with vastly different size scales and environmental demands. In doing this and by contrasting wrinkle development in soft and hard biological systems, we provide a template of structure-function relationships of biological surface wrinkles and an outlook for functionalized wrinkled biomimetic surfaces

Probing inner and outer disk misalignments in transition disks: constraints from VLTI/GRAVITY and ALMA observations

Stars and planetary system

Probing inner and outer disk misalignments in transition disks

This is the final version. Available from EDP Sciences via the DOI in this record. All codes used for the data analysis, as well as example data files, are available at https://github.com/18alex96/disk_misalignmentsContext. Transition disks are protoplanetary disks with dust-depleted cavities, possibly indicating substantial clearing of their dust content by a massive companion. For several known transition disks, dark regions interpreted as shadows have been observed in scattered light imaging and are hypothesized to originate from misalignments between distinct regions of the disk. Aims. We aim to investigate the presence of misalignments in transition disks. We study the inner disk (10 au). Methods. We fit simple parametric models to the visibilities and closure phases of the GRAVITY data to derive the inclination and position angle of the inner disks. The outer disk geometries were derived from Keplerian fits to the ALMA velocity maps and compared to the inner disk constraints. We also predicted the locations of expected shadows for significantly misaligned systems. Results. Our analysis reveals six disks to exhibit significant misalignments between their inner and outer disk structures. The predicted shadow positions agree well with the scattered light images of HD 100453 and HD 142527, and we find supporting evidence for a shadow in the south of the disk around CQ Tau. In the other three targets for which we infer significantly misaligned disks, V1247 Ori, V1366 Ori, and RY Lup, we do not see any evident sign of shadows in the scattered light images. The scattered light shadows observed in DoAr 44, HD 135344 B, and HD 139614 are consistent with our observations, yet the underlying morphology is likely too complex to be described properly by our models and the accuracy achieved by our observations. Conclusions. The combination of near infrared and submillimeter interferometric observations allows us to assess the geometries of the innermost disk regions and those of the outer disk. Whereas we can derive precise constraints on the potential shadow positions for well-resolved inner disks around Herbig Ae/Be stars, the large statistical uncertainties for the marginally resolved inner disks around the T Tauri stars of our sample make it difficult to extract conclusive constraints for the presence of shadows in these systems.European Research CouncilEuropean Research CouncilEuropean Research CouncilEuropean Research CouncilEuropean Research CouncilDeutsche Forschungsgemeinschaft (DFG, German Research Foundation)Science Foundation Irelan

Different Outcomes Require Different Explanations

In general, we agree with almost everything mentioned in the commentary by Cross and Campbell (2017). We feel, however, that their line of argumentation is largely based on a misunderstanding that we will try to clarify in this reply

Intra-versus intersex aggression: testing theories of sex differences using aggression networks

Two theories offer competing explanations of sex differences in aggressive behavior: sexual-selection theory and social-role theory. While each theory has specific strengths and limitations depending on the victim's sex, research hardly differentiates between intrasex and intersex aggression. In the present study, 11,307 students (mean age = 14.96 years; 50% girls, 50% boys) from 597 school classes provided social-network data (aggression and friendship networks) as well as physical (body mass index) and psychosocial (gender and masculinity norms) information. Aggression networks were used to disentangle intra- and intersex aggression, whereas their class-aggregated sex differences were analyzed using contextual predictors derived from sexual-selection and social-role theories. As expected, results revealed that sexual-selection theory predicted male-biased sex differences in intrasex aggression, whereas social-role theory predicted male-biased sex differences in intersex aggression. Findings suggest the value of explaining sex differences separately for intra- and intersex aggression with a dual-theory framework covering both evolutionary and normative components

Positive and negative asymmetry of intergroup contact: A dynamic approach 2016-2019

In the course of this project, we have conducted several studies that allowed us to collect a variety of unique data, which we describe in further detail below. (1) A diary study with the aim to obtain data about the frequency, intensity and location of positive and negative contact experiences and to, furthermore, investigate the effects of personality variables (e.g., RWA and SDO), perceived norms and contextual predictors on these daily positive and negative contact experiences. The 13-day diary study was conducted by an external survey company (Ipsos MORI). Respondents were N = 780 majority (White British) and N = 605 minority (British Asians) respondents, purposely sampled from ethnically mixed neighbourhoods (Lower Super Output Areas, LSOA). The core of this diary study was a daily report of the frequency of overall, positive, and negative intergroup contact, with open answers to provide information about qualitative aspects of the most memorable positive and negative contact experience for each day. As planned, we also run a pre-test and a post-test survey. Regarding the latter, we asked half of the sample 2 weeks and half of the sample 6 weeks after the diary study to recall positive and negative contact experiences. (2) The two-wave longitudinal survey is, to our knowledge, the first longitudinal dataset including positive and negative contact experiences as well as the theoretically most important moderators and mediators in this respect. The main focus of this study was to test the longitudinal effects of and interactions between positive and negative intergroup contact. The survey was conducted in line with the proposed planning by an external survey company (Ipsos MORI), which used a face-to-face random location quota approach. Respondents were sampled from diverse areas with a mix of White British and Asian British (of Indian, Pakistani and Bangladeshi heritage) residents as well as low, medium, and high levels of deprivation. In line with our estimated number of participants, White British (n = 1520) and Asian British participants (n = 1474) from 290 neighborhoods were recruited and longitudinally followed. (3) The main aim of the school social network study was to obtain social network measures of contact between adolescents in schools, and to examine the co-development of adolescents’ social networks and outgroup attitudes over time. We have collected five waves of data over the academic year 2017-2018 in year 2 (Wave 1: 10/2017, Wave 2: 11/2017, Wave 3: 02/2018, Wave 4: 03/2018, & Wave 5: 05/2018). Respondents were N = 1328 students (aged 11-14) nested in six year-group networks in two schools in North West England. As this study focused on relations between White British and Asian British individuals, the final analytic sample included N = 1170 students (n = 341 White British & n = 829 Asian British). Students completed identical surveys at each of the five waves, which contained four social network measures (friendship, bullying, positive contact, & negative contact), and a range of self-reported measures (e.g., outgroup attitudes). Although positive intergroup contact has been shown to reduce prejudice, negative contact has the potential to worsen intergroup relations. The efficacy of intergroup contact hence has policy implications for wider debates about diversity, multiculturalism, and social conflict; but doubt has recently been cast on its potential in applied settings because whilst contact can be positive (e.g., having outgroup friends) it can also be negative (e.g., being bullied by an ethnic outgroup member). Moreover, diverse settings (e.g., schools, neighbourhoods) could potentially have unintended consequences of actually increasing prejudice because they may expose people to greater frequency of both positive and negative contact (which may undermine positive effects of contact). Yet little is known about the combined effects of positive and negative contact, and the consequences for increasingly diverse nations and communities. Using a variety of different methodological approaches, and testing participants in UK, GER and NL (where in each case majority group members interact with a different set of minority groups) we test the claim that negative contact exerts stronger effects on various outcomes than positive contact. In a series of studies involving both ethnic majority and minority participants, and using different methodological paradigms (diary, experimental, longitudinal survey, and social network studies), we seek to test three hypotheses that emerge from a critical reading of the relevant literature: buffering (i.e., positive contact weakens any negative effect of negative contact), augmentation (i.e., negative contact augments the impact of positive contact, because it contrasts the positive with the negative contact), and poisoning (i.e., negative contact reduces the impact of positive contact) effects. Finally, we use the cumulative knowledge of the project to test and seek to improve a large-scale social intervention, which is premised on promoting positive contact, but that has ignored any possible role for negative contact. This research further examines how and when positive and negative contact have their joint effects. They may have their impact, for example, via category salience (when contact is negative, categories are more salient). And the effect of positive vs negative contact on category salience may be qualified by various 'psychological' and 'social' factors. Among key psychological moderators, we will explore the order in which positive and negative contact are experienced (are outcomes worse when initial contact is negative?), and the intensity and consistency of the (positive or negative; are outcomes worst when one instance of negative contact follows another?). Among more 'social' factors, we will explore the impact of social norms.</p

Ostracism in childhood and adolescence: Emotional, cognitive, and behavioral effects of social exclusion

Drawing on theories of development, motivation, and personality, we examined children’s and adolescents’ emotional and cognitive perception of and explained their behavioral reactions to ostracism, in two experimental studies. In study one, 93 fourth and eighth graders (49 girls) were either socially included or excluded within a virtual ball-tossing game (cyberball). Results demonstrated that ostracism causes negative emotions and a selective memory for social events, similarly for children and adolescents, which verifies the usefulness of cyberball beyond self-reports. In study two, 97 fourth to ninth graders (43 girls) behaviorally reacted to the previously induced ostracism episode within a modified paradigm (cyberball-R). Multinomial logistic regression demonstrated that psychosocial differences between participants displaying prosocial, avoidant, and antisocial reactions followed the expected pattern, which provides initial evidence concerning moderators that prevent children and adolescents from receiving further aggression

Beyond the dyadic perspective: 10 Reasons for using social network analysis in intergroup contact research

This article presents 10 reasons why social network analysis, a novel but still surprisingly underused approach in social psychology, can advance the analysis of intergroup contact. Although intergroup contact has been shown to improve intergroup relations, conventional methods leave some questions unanswered regarding the underlying social mechanisms that facilitate social cohesion between different groups in increasingly diverse societies. We will therefore explain the largely unknown conceptual and methodological advantages of social network analysis for studying intergroup contact in naturally existing groups, which are likely to help contact researchers to gain a better understanding of intergroup relations and guide attempts to overcome segregation, prejudice, discrimination, and intergroup conflict