Effects of exotic grasses on soil seed banks in southeastern Arizona grasslands

Species richness in Madrean mixed-grass prairies dominated by native or exotic species in southeastern Arizona was characterized at the community and point scales using ten 1-m 2 quadrats nested within each of eight 1000-m 2 plots. In the 1000-m 2 plots average richness was significantly higher in oak savanna (OS, 121.0 species) than in exotic grassland on mesa tops (EMT, 52.0 species), whereas native grassland on mesa slopes (NMS, 92.5 species) and native grassland on mesa tops (NMT, 77.0 species) did not differ significantly in richness from OS or EMT. When richness was partitioned by life form, EMT was notably poorer than other community types in species of perennial grasses, perennial herbs, and summer annuals. In the 1-m 2 quadrats, OS (21.2 species), NMS (20.9 species), and NMT (20.7 species) were significantly richer than EMT (5.9 species). Cover in 1-m 2 plots was significantly higher in EMT than in NMT, NMS, or OS. Species richness at the point scale showed a unimodal relation to canopy cover, with cover accounting for 30% of the variation in number of species in 1-m2 quadrats. Competitive exclusion and allelopathy have perhaps limited species richness at the point scale in exotic grassland. There was no evidence of a species-pool effect between point and community scales, but such an effect between community and landscape scales was supported. Madrean mixed-grass prairies are landscapes with high species richness in comparison to other grassland types in North America, providing a large pool of potential colonizing species at the community scale. Beta-diversity (between communities) within the landscape of the Appleton-Whittell Research Ranch was consequently high despite a relative lack of habitat diversity.     

A Limit to Our Thinking and Some Unanticipated Moral Consequences: A Science of Conceptual Systems Perspective with Some Potential Solutions

One paradox of modern society is the widespread use of highly complex mechanisms of economic and social self-regulation which produce a large number of unintended and often undesirable side-effects. Human conceptual systems (theories, policies, and mental models which support our thinking) are good enough to keep the self-regulatory mechanisms in operation; yet they are not good enough to prevent and control the undesirable contingencies. Systems thinking, and complexity science are growing in their usefulness for understanding our social systems as well as our conceptual systems. The present paper examines and explains this paradox by combining the ideas from the burgeoning science of conceptual systems and Niklas Luhmann’s social systems theory. Drawing on Luhmann’s argument that social systems build up their internal complexity by disregarding the complexity of the environment, we propose to differentiate between those conceptual systems that reflect the intra-systemic complexity of simpler systems and those that reflect the intra-systemic complexity of sub-systems in combination with systems of systems to include the environmental complexity. Thus it comes about that the former conceptual systems, exemplified by physics, are much more effective and successful than the latter ones, often corresponding to social sciences. The chasm between the qualities of these systems can be overcome by using the tools of Integrative Propositional Analysis.     

Comparison of desert valvata snail growth at three densities of the invasive New Zealand mudsnail

Invasive species are of concern to natural resource managers and conservation biologists. The New Zealand mudsnail ( Potamopyrgus antipodarum ) has invaded many freshwaters of the western United States with unknown consequences on the native benthic invertebrate fauna. We conducted a laboratory investigation to determine if mudsnails affected the growth of the desert valvata snail ( Valvata utahensis ), a species native to the Snake River in southern Idaho. Results indicated that increasing densities of mudsnails limited the growth rate and absolute growth of the desert valvata. We suggest that absolute growth is a better metric than growth rate for comparing snail species and assessing interactions between them.     

Nectin family of cell-adhesion molecules: structural and molecular aspects of function and specificity

Cell–cell adhesive processes are central to the physiology of multicellular organisms. A number of cell surface molecules contribute to cell–cell adhesion, and the dysfunction of adhesive processes underlies numerous developmental defects and inherited diseases. The nectins, a family of four immunoglobulin superfamily members (nectin-1 to -4), interact through their extracellular domains to support cell–cell adhesion. While both homophilic and heterophilic interactions among the nectins are implicated in cell–cell adhesion, cell-based and biochemical studies suggest heterophilic interactions are stronger than homophilic interactions and control a range of physiological processes. In addition to interactions within the nectin family, heterophilic associations with nectin-like molecules, immune receptors, and viral glycoproteins support a wide range of biological functions, including immune modulation, cancer progression, host-pathogen interactions and immune evasion. We review current structural and molecular knowledge of nectin recognition processes, with a focus on the biochemical and biophysical determinants of affinity and selectivity that drive distinct nectin associations. These proteins and interactions are discussed as potential targets for immunotherapy.     

Half-metallic graphene nanoribbons

Electrical current can be completely spin polarized in a class of materials known as half-metals, as a result of the coexistence of metallic nature for electrons with one spin orientation and insulating nature for electrons with the other. Such asymmetric electronic states for the different spins have been predicted for some ferromagnetic metals--for example, the Heusler compounds--and were first observed in a manganese perovskite. In view of the potential for use of this property in realizing spin-based electronics, substantial efforts have been made to search for half-metallic materials. However, organic materials have hardly been investigated in this context even though carbon-based nanostructures hold significant promise for future electronic devices. Here we predict half-metallicity in nanometre-scale graphene ribbons by using first-principles calculations. We show that this phenomenon is realizable if in-plane homogeneous electric fields are applied across the zigzag-shaped edges of the graphene nanoribbons, and that their magnetic properties can be controlled by the external electric fields. The results are not only of scientific interest in the interplay between electric fields and electronic spin degree of freedom in solids but may also open a new path to explore spintronics at the nanometre scale, based on graphene.     

Subgroup-specific structural variation across 1,000 medulloblastoma genomes

Medulloblastoma, the most common malignant paediatric brain tumour, is currently treated with nonspecific cytotoxic therapies including surgery, whole-brain radiation, and aggressive chemotherapy. As medulloblastoma exhibits marked intertumoural heterogeneity, with at least four distinct molecular variants, previous attempts to identify targets for therapy have been underpowered because of small samples sizes. Here we report somatic copy number aberrations (SCNAs) in 1,087 unique medulloblastomas. SCNAs are common in medulloblastoma, and are predominantly subgroup-enriched. The most common region of focal copy number gain is a tandem duplication of SNCAIP, a gene associated with Parkinson's disease, which is exquisitely restricted to Group 4α. Recurrent translocations of PVT1, including PVT1-MYC and PVT1-NDRG1, that arise through chromothripsis are restricted to Group 3. Numerous targetable SCNAs, including recurrent events targeting TGF-β signalling in Group 3, and NF-κB signalling in Group 4, suggest future avenues for rational, targeted therapy.