1,499 research outputs found
Host coenzyme Q redox state is an early biomarker of thermal stress in the coral Acropora millepora
© 2015 Lutz et al.This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Bleaching episodes caused by increasing seawater temperatures may induce mass coral mortality and are regarded as one of the biggest threats to coral reef ecosystems worldwide. The current consensus is that this phenomenon results from enhanced production of harmful reactive oxygen species (ROS) that disrupt the symbiosis between corals and their endosymbiotic dinoflagellates, Symbiodinium. Here, the responses of two important antioxidant defence components, the host coenzyme Q (CoQ) and symbiont plastoquinone (PQ) pools, are investigated for the first time in colonies of the scleractinian coral, Acropora millepora, during experimentally-induced bleaching under ecologically relevant conditions. Liquid chromatography-mass spectrometry (LC-MS) was used to quantify the states of these two pools, together with physiological parameters assessing the general state of the symbiosis (including photosystem II photochemical efficiency, chlorophyll concentration and Symbiodinium cell densities). The results show that the responses of the two antioxidant systems occur on different timescales: (i) the redox state of the Symbiodinium PQ pool remained stable until twelve days into the experiment, after which there was an abrupt oxidative shift; (ii) by contrast, an oxidative shift of approximately 10% had occurred in the host CoQ pool after 6 days of thermal stress, prior to significant changes in any other physiological parameter measured. Host CoQ pool oxidation is thus an early biomarker of thermal stress in corals, and this antioxidant pool is likely to play a key role in quenching thermally-induced ROS in the coral-algal symbiosis. This study adds to a growing body of work that indicates host cellular responses may precede the bleaching process and symbiont dysfunction
Berry phase and persistent current in disordered mesoscopic rings
A novel quantum interference effect in disordered quasi-one-dimensional rings
in the inhomogeneous magnetic field is reported. We calculate the canonical
disorder averaged persistent current using the diagrammatic perturbation
theory. It is shown that within the adiabatic regime the average current
oscillates as a function of the geometric flux which is related to the Berry
phase and the period becomes half the value of the case of a single
one-dimensional ring. We also discuss the magnetic dephasing effect on the
averaged current.Comment: 6 pages, RevTeX, 2 figures. To appear in Phys. Rev. B Rapid
Communications Vol.60 No.12 (1999
Orbital Magnetism in the Ballistic Regime: Geometrical Effects
We present a general semiclassical theory of the orbital magnetic response of
noninteracting electrons confined in two-dimensional potentials. We calculate
the magnetic susceptibility of singly-connected and the persistent currents of
multiply-connected geometries. We concentrate on the geometric effects by
studying confinement by perfect (disorder free) potentials stressing the
importance of the underlying classical dynamics. We demonstrate that in a
constrained geometry the standard Landau diamagnetic response is always
present, but is dominated by finite-size corrections of a quasi-random sign
which may be orders of magnitude larger. These corrections are very sensitive
to the nature of the classical dynamics. Systems which are integrable at zero
magnetic field exhibit larger magnetic response than those which are chaotic.
This difference arises from the large oscillations of the density of states in
integrable systems due to the existence of families of periodic orbits. The
connection between quantum and classical behavior naturally arises from the use
of semiclassical expansions. This key tool becomes particularly simple and
insightful at finite temperature, where only short classical trajectories need
to be kept in the expansion. In addition to the general theory for integrable
systems, we analyze in detail a few typical examples of experimental relevance:
circles, rings and square billiards. In the latter, extensive numerical
calculations are used as a check for the success of the semiclassical analysis.
We study the weak-field regime where classical trajectories remain essentially
unaffected, the intermediate field regime where we identify new oscillations
characteristic for ballistic mesoscopic structures, and the high-field regime
where the typical de Haas-van Alphen oscillations exhibit finite-size
corrections. We address the comparison with experimental data obtained in
high-mobility semiconductor microstructures discussing the differences between
individual and ensemble measurements, and the applicability of the present
model.Comment: 88 pages, 15 Postscript figures, 3 further figures upon request, to
appear in Physics Reports 199
Some Rare Indo-Pacific Coral Species Are Probable Hybrids
Background: coral reefs worldwide face a variety of threats and many coral species are increasingly endangered. It is often assumed that rare coral species face higher risks of extinction because they have very small effective population sizes, a predicted consequence of which is decreased genetic diversity and adaptive potential.\ud
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Methodology/Principal Findings: here we show that some Indo-Pacific members of the coral genus Acropora have very small global population sizes and are likely to be unidirectional hybrids. Whether this reflects hybrid origins or secondary hybridization following speciation is unclear.\ud
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Conclusions/Significance: the interspecific gene flow demonstrated here implies increased genetic diversity and adaptive potential in these coral species. Rare Acropora species may therefore be less vulnerable to extinction than has often been assumed because of their propensity for hybridization and introgression, which may increase their adaptive potential
Observations of simultaneous sperm release and larval planulation suggest reproductive assurance in the coral Pocillopora acuta
Despite being an extensively studied group of corals, the reproductive biology of the scleractinian genus Pocillopora remains a mystery. Pocillopora acuta has been proposed to exhibit a mixed reproductive mode, sexually producing gametes (sperm and eggs) and asexually brooding larvae simultaneously within a single colony. Here, we report observations of night-time spawning of sperm during the peak monthly larval release period. We offer a new hypothesis for the regulation of sexual and asexual reproduction in the species and posit that sexual reproduction may occur more often than previously suggested. However, the success of internal oocyte fertilization and subsequent zygote development is dependent on sperm making contact with a fertile colony. We hypothesize that asexual development of larvae occurs when sperm is absent, but more extensive genetic, genomic, and histological data are required to determine the pathway by which unfertilized oocytes may develop. We also propose that this mixed mode of reproduction is an adaptation to mating failure, common in sessile marine invertebrates. The reproductive assurance enjoyed by the species may therefore be the key to its ecological and evolutionary persistence
Genetic markers for antioxidant capacity in a reef-building coral
© 2016 The Authors. The current lack of understanding of the genetic basis underlying environmental stress tolerance in reef-building corals impairs the development of new management approaches to confronting the global demise of coral reefs. On the Great Barrier Reef (GBR), an approximately 51% decline in coral cover occurred over the period 1985-2012. We conducted a gene-by-environment association analysis across 12 latitude on the GBR, as well as both in situ and laboratory genotype-by-phenotype association analyses. These analyses allowed us to identify alleles at two genetic loci that account for differences in environmental stress tolerance and antioxidant capacity in the common coral Acropora millepora. The effect size for antioxidant capacity was considerable and biologically relevant (32.5 and 14.6% for the two loci). Antioxidant capacity is a critical component of stress tolerance because a multitude of environmental stressors cause increased cellular levels of reactive oxygen species. Our findings provide the first step toward the development of novel coral reef management approaches, such as spatial mapping of stress tolerance for use in marine protected area design, identification of stress-tolerant colonies for assisted migration, and marker-assisted selective breeding to create more tolerant genotypes for restoration of denuded reefs
Does the Clinical Frailty Scale at Triage Predict Outcomes From Emergency Care for Older People?
Study objective:
We determine whether the Clinical Frailty Scale applied at emergency department (ED) triage is associated with important service- and patient-related outcomes.
Methods:
We undertook a single-center, retrospective cohort study examining hospital-related outcomes and their associations with frailty scores assessed at ED triage. Participants were aged 65 years or older, registered on their first ED presentation during the study period at a single, centralized ED in the United Kingdom. Baseline data included age, sex, Clinical Frailty Scale score, National Early Warning Score–2 and the Charlson Comorbidity Index score; outcomes included length of stay, readmissions (any future admissions), and mortality (inhospital or out of hospital) up to 2 years after ED presentation. Survival analysis methods (standard and competing risks) were applied to assess associations between ED triage frailty scores and outcomes. Unadjusted incidence curves and adjusted hazard ratios are presented.
Results:
A total of 52,562 individuals representing 138,328 ED attendances were included; participants’ mean age was 78.0 years, and 55% were women. Initial admission rates generally increased with frailty. Mean length of stay after 30- or 180-day follow-up was relatively low; all Clinical Frailty Scale categories included patients who experienced zero days’ length of stay (ie, ambulatory care) and patients with relatively high numbers of inhospital days. Overall, 46% of study participants were readmitted by the 2-year follow-up. Readmissions increased with Clinical Frailty Scale score up until a score of 6 and then attenuated. Mortality rates increased with increasing frailty; the adjusted hazard ratio was 3.6 for Clinical Frailty Scale score 7 to 8 compared with score 1 to 3.
Conclusion:
Frailty assessed at ED triage (with the Clinical Frailty Scale) is associated with adverse outcomes in older people. Its use in ED triage might aid immediate clinical decisionmaking and service configuration
Coulomb-assisted braiding of Majorana fermions in a Josephson junction array
We show how to exchange (braid) Majorana fermions in a network of
superconducting nanowires by control over Coulomb interactions rather than
tunneling. Even though Majorana fermions are charge-neutral quasiparticles
(equal to their own antiparticle), they have an effective long-range
interaction through the even-odd electron number dependence of the
superconducting ground state. The flux through a split Josephson junction
controls this interaction via the ratio of Josephson and charging energies,
with exponential sensitivity. By switching the interaction on and off in
neighboring segments of a Josephson junction array, the non-Abelian braiding
statistics can be realized without the need to control tunnel couplings by gate
electrodes. This is a solution to the problem how to operate on topological
qubits when gate voltages are screened by the superconductor
Temporal variation in the microbiome of Acropora coral species does not reflect seasonality
The coral microbiome is known to fluctuate in response to environmental variation and has been suggested to vary seasonally. However, most studies to date, particularly studies on bacterial communities, have examined temporal variation over a time frame of less than 1 year, which is insufficient to establish if microbiome variations are indeed seasonal in nature. The present study focused on expanding our understanding of long-term variability in microbial community composition using two common coral species, Acropora hyacinthus, and Acropora spathulata, at two mid-shelf reefs on the Great Barrier Reef. By sampling over a 2-year time period, this study aimed to determine whether temporal variations reflect seasonal cycles. Community composition of both bacteria and Symbiodiniaceae was characterized through 16S rRNA gene and ITS2 rDNA metabarcoding. We observed significant variations in community composition of both bacteria and Symbiodiniaceae among time points for A. hyacinthus and A. spathulata. However, there was no evidence to suggest that temporal variations were cyclical in nature and represented seasonal variation. Clear evidence for differences in the microbial communities found between reefs suggests that reef location and coral species play a larger role than season in driving microbial community composition in corals. In order to identify the basis of temporal patterns in coral microbial community composition, future studies should employ longer time series of sampling at sufficient temporal resolution to identify the environmental correlates of microbiome variation
Climate change and the Great Barrier Reef: a vulnerability assessment
Reef-building corals (Order Scleractinia Class Anthozoa) form extensive skeletons of calcium
carbonate (limestone), depositing enough material over time to form vast reef structures that may be
easily seen from space. The majority of reef-building corals are hard (stony) scleractinian corals. Many
octocorals (especially soft corals in the family Alcyoniidae and the blue coral Heliopora) and some
hydrozoan corals (such as Millepora) also contribute to reef-building. Corals form the framework of
reef structures, while other organisms such as calcareous algae (especially red coralline algae) play a
key role in cementing and consolidating the reef framework. This chapter focuses on the vulnerability
of reef-building corals to climate change. The implications of climate change for macroalgae are
covered in chapter 7 and a broader treatment of reef processes is provided in chapter 17.This is Chapter 10 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13
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