Voronoi Tessellation Captures Very Early Clustering of Single Primary Cells as Induced by Interactions in Nascent Biofilms

Biofilms dominate microbial life in numerous aquatic ecosystems, and in engineered and medical systems, as well. The formation of biofilms is initiated by single primary cells colonizing surfaces from the bulk liquid. The next steps from primary cells towards the first cell clusters as the initial step of biofilm formation remain relatively poorly studied. Clonal growth and random migration of primary cells are traditionally considered as the dominant processes leading to organized microcolonies in laboratory grown monocultures. Using Voronoi tessellation, we show that the spatial distribution of primary cells colonizing initially sterile surfaces from natural streamwater community deviates from uniform randomness already during the very early colonisation. The deviation from uniform randomness increased with colonisation — despite the absence of cell reproduction — and was even more pronounced when the flow of water above biofilms was multidirectional and shear stress elevated. We propose a simple mechanistic model that captures interactions, such as cell-to-cell signalling or chemical surface conditioning, to simulate the observed distribution patterns. Model predictions match empirical observations reasonably well, highlighting the role of biotic interactions even already during very early biofilm formation despite few and distant cells. The transition from single primary cells to clustering accelerated by biotic interactions rather than by reproduction may be particularly advantageous in harsh environments — the rule rather than the exception outside the laboratory

Therapeutic hypothermia translates from ancient history in to practice

Acute postasphyxial encephalopathy around the time of birth remains a major cause of death and disability. The possibility that hypothermia may be able to prevent or lessen asphyxial brain injury is a “dream revisited”. In this review, a historical perspective is provided from the first reported use of therapeutic hypothermia for brain injuries in antiquity, to the present day. The first uncontrolled trials of cooling for resuscitation were reported more than 50 y ago. The seminal insight that led to the modern revival of studies of neuroprotection was that after profound asphyxia, many brain cells show initial recovery from the insult during a short “latent” phase, typically lasting ~6 h, only to die hours to days later during a “secondary” deterioration phase characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Studies designed around this conceptual framework showed that mild hypothermia initiated as early as possible before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, is associated with potent, long-lasting neuroprotection. There is now compelling evidence from randomized controlled trials that mild induced hypothermia significantly improves intact survival and neurodevelopmental outcomes to midchildhood

Introgression and rapid species turnover in sympatric damselflies

<p>Abstract</p> <p>Background</p> <p>Studying contemporary hybridization increases our understanding of introgression, adaptation and, ultimately, speciation. The sister species <it>Ischnura elegans </it>and <it>I. graellsii </it>(Odonata: Coenagrionidae) are ecologically, morphologically and genetically similar and hybridize. Recently, <it>I. elegans </it>has colonized northern Spain, creating a broad sympatric region with <it>I. graellsii</it>. Here, we review the distribution of both species in Iberia and evaluate the degree of introgression of <it>I. graellsii </it>into <it>I. elegans </it>using six microsatellite markers (442 individuals from 26 populations) and five mitochondrial genes in sympatric and allopatric localities. Furthermore, we quantify the effect of hybridization on the frequencies of the genetically controlled colour polymorphism in females of both species.</p> <p>Results</p> <p>In a principal component analysis of the microsatellite data, the first two principal components summarised almost half (41%) of the total genetic variation. The first axis revealed a clear separation of <it>I. graellsii </it>and <it>I</it>. <it>elegans </it>populations, while the second axis separated <it>I. elegans </it>populations. Admixture analyses showed extensive hybridization and introgression in <it>I. elegans </it>populations, consistent with <it>I. elegans </it>backcrosses and occasional F₁-hybrids, suggesting hybridization is on-going. More specifically, approximately 58% of the 166 Spanish <it>I. elegans </it>individuals were assigned to the <it>I. elegans </it>backcross category, whereas not a single of those individuals was assigned to the backcross with <it>I. graellsii</it>. The mitochondrial genes held little genetic variation, and the most common haplotype was shared by the two species.</p> <p>Conclusions</p> <p>The results suggest rapid species turnover in sympatric regions in favour of <it>I. elegans</it>, corroborating previous findings that <it>I. graellsii </it>suffers a mating disadvantage in sympatry with <it>I. elegans</it>. Examination of morph frequency dynamics indicates that hybridization is likely to have important implications for the maintenance of multiple female morphs, in particular during the initial period of hybridization.</p

Anthropogenically-mediated density dependence in a declining farmland bird

Land management intrinsically influences the distribution of animals and can consequently alter the potential for density-dependent processes to act within populations. For declining species, high densities of breeding territories are typically considered to represent productive populations. However, as density-dependent effects of food limitation or predator pressure may occur (especially when species are dependent upon separate nesting and foraging habitats), high territory density may limit per-capita productivity. Here, we use a declining but widespread European farmland bird, the yellowhammer Emberiza citrinella L., as a model system to test whether higher territory densities result in lower fledging success, parental provisioning rates or nestling growth rates compared to lower densities. Organic landscapes held higher territory densities, but nests on organic farms fledged fewer nestlings, translating to a 5 times higher rate of population shrinkage on organic farms compared to conventional. In addition, when parental provisioning behaviour was not restricted by predation risk (i.e. at times of low corvid activity), nestling provisioning rates were higher at lower territory densities, resulting in a much greater increase in nestling mass in low density areas, suggesting that food limitation occurred at high densities. These findings in turn suggest an ecological trap, whereby preferred nesting habitat does not provide sufficient food for rearing nestlings at high population density, creating a population sink. Habitat management for farmland birds should focus not simply on creating a high nesting density, but also on ensuring heterogeneous habitats to provide food resources in close proximity to nesting birds, even if this occurs through potentially restricting overall nest density but increasing population-level breeding success

Decline of Birds in a Human Modified Coastal Dune Forest Landscape in South Africa

Previous studies demonstrate that old-growth forest remnants and vegetation regenerating after anthropogenic disturbance provide habitat for birds in a human modified coastal dune forest landscape in northern KwaZulu-Natal, South Africa. However, occurrence does not ensure persistence. Based on a 13-year monitoring database we calculated population trends for 37 bird species and general trends in overall bird density in different vegetation types. We evaluated species' characteristics as covariates of population trend and assessed changes in rainfall and proportional area and survey coverage per vegetation type. 76% of species assessed have declined, 57% significantly so at an average rate of 13.9% per year. Overall, bird density has fallen at 12.2% per year across old-growth forest and woody regenerating vegetation types. Changes in proportional area and coverage per vegetation type may partly explain trends for a few species but are unlikely to account for most. Below average rainfall may have contributed to bird declines. However, other possibilities warrant further investigation. Species with larger range extents tended to decline more sharply than did others, and these species may be responding to environmental changes on a broader geographical scale. Our results cast doubt on the future persistence of birds in this human modified landscape. More research is needed to elucidate the mechanisms driving population decline in the study area and to investigate whether the declines identified here are more widespread across the region and perhaps the continent

Decisions that hasten death: double effect and the experiences of physicians in Australia

BACKGROUND: In Australian end-of-life care, practicing euthanasia or physician-assisted suicide is illegal. Despite this, death hastening practices are common across medical settings. Practices can be clandestine or overt but in many instances physicians are forced to seek protection behind ambiguous medico-legal imperatives such as the Principle of Double Effect. Moreover, the way they conceptualise and experience such practices is inconsistent. To complement the available statistical data, the purpose of this study was to understand the reasoning behind how and why physicians in Australia will hasten death. METHOD: A qualitative investigation was focused on palliative and critical/acute settings. A thematic analysis was conducted on semi-structured in-depth interviews with 13 specialist physicians. Attention was given to eliciting meanings and experiences in Australian end-of-life care. RESULTS: Highlighting the importance of a multidimensional approach, physicians negotiated multiple influences when death was regarded as hastened. The way they understood and experienced end-of-life care practices were affected by politico-religious and cultural influences, medico-legal imperatives, and personal values and beliefs. Interpersonal and intrapsychic aspects further emphasised the emotional and psychological investment physicians have with patients and others. In most cases death occurred as a result of treating suffering, and sometimes to fulfil the wishes of patients and others who requested death. Experience was especially subject to the efficacy with which physicians negotiated complex but context-specific situations, and was reflective of how they considered a good death. Although many were compelled to draw on the Principle of Double Effect, every physician reported its inadequacy as a medico-legal guideline. CONCLUSIONS: The Principle of Double Effect, as a simplistic and generalised guideline, was identified as a convenient mechanism to protect physicians who inadvertently or intentionally hastened death. But its narrow focus on the physician’s intent illuminated how easily it may be manipulated, thus impairing transparency and a physician’s capacity for honesty. It is suggested the concept of “force majeure” be examined for its applicability in Australian medical end-of-life law where, consistent with a multidimensional and complex world, a physician’s motivations can also be understood in terms of the emotional and psychological pressures they face in situations that hasten death

More than 75 percent decline over 27 years in total flying insect biomass in protected areas

Global declines in insects have sparked wide interest among scientists, politicians, and the general public. Loss of insect diversity and abundance is expected to provoke cascading effects on food webs and to jeopardize ecosystem services. Our understanding of the extent and underlying causes of this decline is based on the abundance of single species or taxonomic groups only, rather than changes in insect biomass which is more relevant for ecological functioning. Here, we used a standardized protocol to measure total insect biomass using Malaise traps, deployed over 27 years in 63 nature protection areas in Germany (96 unique location-year combinations) to infer on the status and trend of local entomofauna. Our analysis estimates a seasonal decline of 76%, and mid-summer decline of 82% in flying insect biomass over the 27 years of study. We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline. This yet unrecognized loss of insect biomass must be taken into account in evaluating declines in abundance of species depending on insects as a food source, and ecosystem functioning in the European landscape

Habitat-Specific Population Growth of a Farmland Bird

BACKGROUND: To assess population persistence of species living in heterogeneous landscapes, the effects of habitat on reproduction and survival have to be investigated. METHODOLOGY/PRINCIPAL FINDINGS: We used a matrix population model to estimate habitat-specific population growth rates for a population of northern wheatears Oenanthe oenanthe breeding in farmland consisting of a mosaic of distinct habitat (land use) types. Based on extensive long-term data on reproduction and survival, habitats characterised by tall field layers (spring- and autumn-sown crop fields, ungrazed grasslands) displayed negative stochastic population growth rates (log lambda(s): -0.332, -0.429, -0.168, respectively), that were markedly lower than growth rates of habitats characterised by permanently short field layers (pastures grazed by cattle or horses, and farmyards, log lambda(s): -0.056, +0.081, -0.059). Although habitats differed with respect to reproductive performance, differences in habitat-specific population growth were largely due to differences in adult and first-year survival rates, as shown by a life table response experiment (LTRE). CONCLUSIONS/SIGNIFICANCE: Our results show that estimation of survival rates is important for realistic assessments of habitat quality. Results also indicate that grazed grasslands and farmyards may act as source habitats, whereas crop fields and ungrazed grasslands with tall field layers may act as sink habitats. We suggest that the strong decline of northern wheatears in Swedish farmland may be linked to the corresponding observed loss of high quality breeding habitat, i.e. grazed semi-natural grasslands