A hexamer origin of the echinoderms' five rays

Of the major deuterostome groups, the echinoderms with their multiple forms and complex development are arguably the most mysterious. Although larval echinoderms are bilaterally symmetric, the adult body seems to abandon the larval body plan and to develop independently a new structure with different symmetries. The prevalent pentamer structure, the asymmetry of Loven's rule and the variable location of the periproct and madrepore present enormous difficulties in homologizing structures across the major clades, despite the excellent fossil record. This irregularity in body forms seems to place echinoderms outside the other deuterostomes. Here I propose that the predominant five-ray structure is derived from a hexamer structure that is grounded directly in the structure of the bilaterally symmetric larva. This hypothesis implies that the adult echinoderm body can be derived directly from the larval bilateral symmetry and thus firmly ranks even the adult echinoderms among the bilaterians. In order to test the hypothesis rigorously, a model is developed in which one ray is missing between rays IV-V (Loven's schema) or rays C-D (Carpenter's schema). The model is used to make predictions, which are tested and verified for the process of metamorphosis and for the morphology of recent and fossil forms. The theory provides fundamental insight into the M-plane and the Ubisch', Loven's and Carpenter's planes and generalizes them for all echinoderms. The theory also makes robust predictions about the evolution of the pentamer structure and its developmental basis. *** including corrections (see footnotes) ***Comment: 10 pages, 6 figure

Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw.

The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition

The Neural Crest Migrating into the Twenty-First Century

From the initial discovery of the neural crest over 150 years ago to the seminal studies of Le Douarin and colleagues in the latter part of the twentieth century, understanding of the neural crest has moved from the descriptive to the experimental. Now, in the twenty-first century, neural crest research has migrated into the genomic age. Here, we reflect upon the major advances in neural crest biology and the open questions that will continue to make research on this incredible vertebrate cell type an important subject in developmental biology for the century to come

Digital Disconnection in Swedish News Media. A critical discourse analysis.

The use of new information- and communication technologies, and social media platforms in particular, has rapidly increased from 2010-2012, when social media ‘boomed’ in Sweden. Thereafter, these platforms have become integrated in all aspects of everyday life – in the social as well as the functional, e.g. communicating with friends or performing tasks at work. Yet, some people choose not to participate in the online community, for various reasons (political standpoints, life-style choices, et cetera). These are, in this thesis, referred to as ‘digital disconnecters’. Previous research on digital disconnection has mostly dealt with motivations to disconnect, or the consequences of disconnecting (e.g. health implications or social implications), but it is a rather small field as of today, and not much research has dealt with the discourse surrounding disconnection, in contrary to ‘constant connection’. The purpose of this thesis is to examine media representations of digital disconnection, as portrayed in Swedish legacy news media (Dagens Nyheter, Svenska Dagbladet, Aftonbladet and Expressen), and furthermore to describe how digital disconnection is ‘talked and written about’ in Sweden during 2010-2012, when social media boomed, and 2018-2020, when social media platforms – and Facebook in particular – have received a fair amount of criticism from experts and Silicon Valley ‘insiders’. The theories used to explain the results are ‘media representations’, ‘media discourse’ and ‘political consumerism’, and a critical discourse analysis has been undertaken to examine and describe the phenomenon. The study moreover showed that digital disconnection is mostly represented as healthy and authentic, while constant connection is represented as harmful (to relationships and one’s mental health) and addictive. Those who disconnect are framed as ‘enlightened’ and firm in their values, e.g. by boycotting Facebook for political reasons. However, no clear difference could be seen between the two time periods (2010-2012 and 2018-2020)