Looking and homing: how displaced ants decide where to go

We caught solitary foragers of the Australian Jack Jumper ant, Myrmecia croslandi, and released them in three compass directions at distances of 10 and 15 m from the nest at locations they have never been before. We recorded the head orientation and the movements of ants within a radius of 20 cm from the release point and, in some cases, tracked their subsequent paths with a differential GPS. We find that upon surfacing from their transport vials onto a release platform, most ants move into the home direction after looking around briefly. The ants use a systematic scanning procedure, consisting of saccadic head and body rotations that sweep gaze across the scene with an average angular velocity of 90° s⁻¹ and intermittent changes in turning direction. By mapping the ants’ gaze directions onto the local panorama, we find that neither the ants’ gaze nor their decisions to change turning direction are clearly associated with salient or significant features in the scene. Instead, the ants look most frequently in the home direction and start walking fast when doing so. Displaced ants can thus identify home direction with little translation, but exclusively through rotational scanning. We discuss the navigational information content of the ants’ habitat and how the insects’ behaviour informs us about how they may acquire and retrieve that information.     

Race statistics: how to get from where we are to where we should be: a rejoinder

America's race statistics are inadequate to the policy challenges of the twenty-first century, especially for social justice and immigrant incorporation policy. But inertial forces – technical and political – complicate change. Overcome technical barriers by taking advantage of an experiment fielded in 2010. To miss that opportunity would be a huge failure. Political barriers are more difficult. Start with what is familiar – more emphasis on national origin – and add flexibility and granularity, both are politically desirable. Introduce change without disrupting the existing policy practices. Phase in improvements gradually, taking advantage of generational turnover. One generation changes the statistical basis for policy. The next generation, which has grown up with the new statistics, implements the policy changes. An example of how this works is found in the multiple-race option introduced in the 2000 census but probably not put to policy use until after the 2030 census.     

Craniofacial growth in a whole rat head transplant: how does a non-functional head grow?

To evaluate factors intrinsic to the regulation of craniofacial bone growth, we have developed a new experimental model in which the whole head of an infant rat is transplanted to the body of an isohistogenic rat by means of microvascular anastomosis. In our model, the transplanted head has neither scars nor any moving soft tissue that could modify growth around facial bones. Using this model, we evaluated the growth pattern of the craniofacial complex by means of serial roentgenographic cephalometrics. Ten transplantations were performed using 10-day-old rats as donors and 8-week-old rats as recipients. Cephalograms were taken from the lateral direction at 10, 20, 30, and 40 days after transplantation. Several reference points were selected to analyze the growth pattern. In the present study, we conclude that the size and form of the bony complex are mainly determined genetically. There is craniofacial skeletal growth in the absence of muscle function and brain growth. Further, both the nasal cartilage and the sutures appear to be autonomous growth centers having intrinsic growth potential. Genetic or epigenetic information plays an important role at the skeletal level, but it also affects the muscles through the medium of the muscular tonus responsible for posture and other related phenomena.     

Ras redux: rethinking how and where Ras acts

Ras proteins couple surface receptor stimulation to an ever-expanding array of effector pathways. The integrated activities of these signaling pathways result in a range of biological responses depending on cellular context and conditions. Decoding the various inputs that underlie Ras-induced proliferation and transformation, in particular, holds the promise of more effective cancer therapies. Recent findings have provided new and unexpected insights into the predominant pathways Ras employs to transform human cells and the subcellular platforms from which it can act.     

Trees are rarely most abundant where they grow best

Aims A common assumption in ecology is that where a species is found to be most abundant must correspond to the environmental context in which the species performs the best (i.e. optimal niche space). This assumption is central to common conservation and management tools such as habitat suitability assessment and species distribution modeling. I test this hypothesis.Methods I use the US Forest Inventory Assessment data for the abundance of trees across eastern North America. I use the FORAST tree-ring dataset for ontogenetic growth rate (tree-ring increment), a measure of niche performance and correlated with intrinsic rate of increase, r .Important findings I find that across 15 species, there are significantly more negative correlations than expected by chance. This negative correlation between abundance and performance across space contradicts common assumptions but is consistent with an inclusive niche structuring of the community.     

Salmonella intracellular proliferation: where, when and how?

Salmonella species proliferate within membrane-bound vacuoles of eukaryotic cells. Recent work has shown that macrophages are the main cell type supporting bacterial growth in vivo. In contrast, tissue culture models have traditionally described epithelial cells as the most permissive cells for bacterial growth. Unfortunately, no mechanism used by Salmonella to initiate growth within a vacuole has been characterised. Recently, it has been shown that Salmonella is capable of attenuating intracellular proliferation. This finding suggests that both the host and the pathogen contribute to a fine adjustment of the intracellular growth rate.     

Membrane lipids: where they are and how they behave

Throughout the biological world, a 30 A hydrophobic film typically delimits the environments that serve as the margin between life and death for individual cells. Biochemical and biophysical findings have provided a detailed model of the composition and structure of membranes, which includes levels of dynamic organization both across the lipid bilayer (lipid asymmetry) and in the lateral dimension (lipid domains) of membranes. How do cells apply anabolic and catabolic enzymes, translocases and transporters, plus the intrinsic physical phase behaviour of lipids and their interactions with membrane proteins, to create the unique compositions and multiple functionalities of their individual membranes?     

Polar auxin transport: controlling where and how much.

Auxin is transported through plant tissues, moving from cell to cell in a unique polar manner. Polar auxin transport controls important growth and developmental processes in higher plants. Recent studies have identified several proteins that mediate polar auxin transport and have shown that some of these proteins are asymmetrically localized, paving the way for studies of the mechanisms that regulate auxin transport. New data indicate that reversible protein phosphorylation can control the amount of auxin transport, whereas protein secretion through Golgi-derived vesicles and interactions with the actin cytoskeleton might regulate the localization of auxin efflux complexes.     

Starch biosynthesis: experiments on how starch granules grow in vivo

Four varieties of starch granules from potato, wheat, maize, and rice were fractionated into homogeneous 10-μm-sized ranges. The size with the largest amount of granules was reacted with ADP-[¹⁴C]Glc, washed, and peeled into 7−9 layers, using a controlled peeling process, involving 90:10 volume proportions of Me₂SO-H₂O at 10 °C. All of the starches showed biosynthesis of starch throughout the granules. Starch synthase activities were determined for each of the layers. Three of the starches had a relatively large amount of synthase activity in the second layer, with only a small amount in the first layer. Potato starch had the largest amount of activity in the first layer. Starch synthase activity was found to alternate between higher and lower activities throughout all of the varieties of granules, showing that the synthesis was not uniform and also was not exclusively occurring at the surface of the starch granules, which had previously been hypothesized. From these results and our previous studies on the mechanism of starch chain elongation by the addition of d-glucose to the reducing end of a growing chain that is covalently attached to the active site of starch synthase, a hypothesis is proposed for how starch granules grow in vivo.     

Oscillatory signaling processes: the how, the why and the where

Oscillatory processes in biological signal transduction have come under progressively increasing scrutiny in terms of their functional significance and mechanisms of emergence and regulation. Since oscillatory processes can be a by-product of rapid adaptation and can also easily emerge if the feedback underlying adaptive processes is inadvertently artificially enhanced, one needs to exercise caution in both claiming the existence of in vivo oscillations and seeking to assign to them a specific functional significance. Nevertheless, oscillations can be a powerful means of encoding and transferring information both in time and in space, thus possessing important potential advantages for evolutionary selection and stabilization. Thus periodicity in the cell responses to diverse persistent external stimuli might become a more recognized and even expected feature of signaling processes.     

Pseudouridine in RNA: what, where, how, and why

Pseudouridine (5-ribosyluracil) is a ubiquitous yet enigmatic constituent of structural RNAs (transfer, ribosomal, small nuclear, and small nucleolar). Although pseudouridine (psi) was the first modified nucleoside to be discovered in RNA, and is the most abundant, its biosynthesis and biological roles have remained poorly understood since its identification as a "fifth nucleoside" in RNA. Recently, a combination of biochemical, biophysical, and genetic approaches has helped to illuminate the structural consequences of psi in polyribonucleotides, the biochemical mechanism of U-->psi isomerization in RNA, and the role of modification enzymes (psi synthases) and box H/ACA snoRNAs, a class of eukaryotic small nucleolar RNAs, in the site-specific biosynthesis of psi. Through its unique ability to coordinate a structural water molecule via its free N1-H, psi exerts a subtle but significant "rigidifying" influence on the nearby sugar-phosphate backbone and also enhances base stacking. These effects may underlie the biological role of most (but perhaps not all) of the psi residues in RNA. Certain genetic mutants lacking specific psi residues in tRNA or rRNA exhibit difficulties in translation, display slow growth rates, and fail to compete effectively with wild-type strains in mixed culture. In particular, normal growth is severely compromised in an Escherichia coli mutant deficient in a pseudouridine synthase responsible for the formation of three closely spaced psi residues in the mRNA decoding region of the 23S rRNA. Such studies demonstrate that pseudouridylation of RNA confers an important selective advantage in a natural biological context.     

Axonal growth: where neurotrophins meet Wnts

Axonal guidance is influenced by many cues, including polypeptide trophic factors, cytokines, diffusible attractants and repellents and changes in calcium. How these signals are conveyed and integrated is not well defined. Recent data suggest that molecules of the canonical Wnt signaling pathway may have direct actions on axonal growth through neurotrophin signaling. This surprising mechanism is supported by local inactivation of glycogen synthase kinase 3beta (GSK-3beta) by nerve growth factor through the integrin-linked kinase. Inhibition of GSK-3beta provides a positive regulatory signal for the cytoskeleton re-arrangement involved in axon extension. Moreover, microtubule stabilization is stimulated by adenomatous polyposis coli protein, a downstream target of GSK3, in response to neurotrophins. Therefore, components of the Wnt signaling pathway are downstream of trophic factors, providing new insights into cytoskeletal regulatory events during axonal growth.     

The conservation of non-marine molluscs in South America: where we are and how to move forward

Biodiversity and Conservation - South America is a high biodiversity continent with five out of 13 countries considered megadiverse. Many major groups within this fauna exhibit high diversity,...     

Visual attention: the where,what, how and why of saliency

Attention influences the processing of visual information even in the earliest areas of primate visual cortex. There is converging evidence that the interaction of bottom-up sensory information and top-down attentional influences creates an integrated saliency map, that is, a topographic representation of relative stimulus strength and behavioral relevance across visual space. This map appears to be distributed across areas of the visual cortex, and is closely linked to the oculomotor system that controls eye movements and orients the gaze to locations in the visual scene characterized by a high salience.