Ocean acidification does not impact shell growth or repair of the Antarctic brachiopod Liothyrella uva (Broderip, 1833)

Marine calcifiers are amongst the most vulnerable organisms to ocean acidification due to reduction in the availability of carbonate ions for skeletal/shell deposition. However, there are limited long-term studies on the possible impacts of increased pCO2 on these taxa. A 7 month CO2 perturbation experiment was performed on one of the most calcium carbonate dependent species, the Antarctic brachiopod Liothyrella uva, which inhabits the Southern Ocean where carbonate ion saturation levels are amongst the lowest on Earth. The effects of the predicted environmental conditions in 2050 and 2100 on the growth rate and ability to repair shell in L.uva were tested with four treatments; a low temperature control (0°C, pH7.98), a pH control (2°C, pH8.05), mid-century scenario (2°C, pH7.75) and end-century scenario (2°C, pH7.54). Environmental change impacts on shell repair are rarely studied, but here repair was not affected by either acidified conditions or temperature. Growth rate was also not impacted by low pH. Elevated temperature did, however, increase growth rates. The ability of L.uva to continue, and even increase shell production in warmer and acidified seawater suggests that this species can acclimate to these combined stressors and generate suitable conditions for shell growth at the site of calcification.Emma Cross is supported by the NERC PhD Studentship (NE/T/A/2011).This is the accepted manuscript. The final version is available at http://www.sciencedirect.com/science/article/pii/S0022098114002743

Instability of a four-dimensional de Sitter black hole with a conformally coupled scalar field

We study the stability of new neutral and electrically charged four-dimensional black hole solutions of Einstein's equations with a positive cosmological constant and conformally coupled scalar field. The neutral black holes are always unstable. The charged black holes are also shown analytically to be unstable for the vast majority of the parameter space of solutions, and we argue using numerical techniques that the configurations corresponding to the remainder of the parameter space are also unstable.Comment: revtex4, 8 pages, 4 figures, minor changes, accepted for publication in Phys. Rev.

A 120-year record of resilience to environmental change in brachiopods

The inability of organisms to cope in changing environments poses a major threat to their survival. Rising carbon dioxide concentrations, recently exceeding 400 μatm, are rapidly warming and acidifying our oceans. Current understanding of organism responses to this environmental phenomenon is based mainly on relatively short‐ to medium‐term laboratory and field experiments, which cannot evaluate the potential for long‐term acclimation and adaptation, the processes identified as most important to confer resistance. Here, we present data from a novel approach that assesses responses over a centennial timescale showing remarkable resilience to change in a species predicted to be vulnerable. Utilising museum collections allows the assessment of how organisms have coped with past environmental change. It also provides a historical reference for future climate change responses. We evaluated a unique specimen collection of a single species of brachiopod (Calloria inconspicua) collected every decade from 1900 to 2014 from one sampling site. The majority of brachiopod shell characteristics remained unchanged over the past century. One response, however, appears to reinforce their shell by constructing narrower punctae (shell perforations) and laying down more shell. This study indicates one of the most calcium‐carbonate‐dependent species globally to be highly resilient to environmental change over the last 120 years and provides a new insight for how similar species might react and possibly adapt to future change

Outer organic layer and internal repair mechanism protects pteropod Limacina helicina from ocean acidification

Scarred shells of polar pteropod Limacina helicina collected from the Greenland Sea in June 2012 reveal a history of damage, most likely failed predation, in earlier life stages. Evidence of shell fracture and subsequent re-growth is commonly observed in specimens recovered from the sub-Arctic and further afield. However, at one site within sea–ice on the Greenland shelf, shells that had been subject to mechanical damage were also found to exhibit considerable dissolution. It was evident that shell dissolution was localised to areas where the organic, periostracal sheet that covers the outer shell had been damaged at some earlier stage during the animal’s life. Where the periostracum remained intact, the shell appeared pristine with no sign of dissolution. Specimens which appeared to be pristine following collection were incubated for four days. Scarring of shells that received periostracal damage during collection only became evident in specimens that were incubated in waters undersaturated with respect to aragonite, ΩAr≤1. While the waters from which the damaged specimens were collected at the Greenland Sea sea–ice margin were not ΩAr≤1, the water column did exhibit the lowest ΩAr values observed in the Greenland and Barents Seas, and was likely to have approached ΩAr≤1 during the winter months. We demonstrate that L. helicina shells are only susceptible to dissolution where both the periostracum has been breached and the aragonite beneath the breach is exposed to waters of ΩAr≤1. Exposure of multiple layers of aragonite in areas of deep dissolution indicate that, as with many molluscs, L. helicina is able to patch up dissolution damage to the shell by secreting additional aragonite internally and maintain their shell. We conclude that, unless breached, the periostracum provides an effective shield for pteropod shells against dissolution in waters ΩAr≤1, and when dissolution does occur the animal has an effective means of self-repair. We suggest that future studies of pteropod shell condition are undertaken on specimens from which the periostracum has not been removed in preparation

Blue mussel shell shape plasticity and natural environments: a quantitative approach

Shape variability represents an important direct response of organisms to selective environments. Here, we use a combination of geometric morphometrics and generalised additive mixed models (GAMMs) to identify spatial patterns of natural shell shape variation in the North Atlantic and Arctic blue mussels, Mytilus edulis and M. trossulus, with environmental gradients of temperature, salinity and food availability across 3980 km of coastlines. New statistical methods and multiple study systems at various geographical scales allowed the uncoupling of the developmental and genetic contributions to shell shape and made it possible to identify general relationships between blue mussel shape variation and environment that are independent of age and species influences. We find salinity had the strongest effect on the latitudinal patterns of Mytilus shape, producing shells that were more elongated, narrower and with more parallel dorsoventral margins at lower salinities. Temperature and food supply, however, were the main drivers of mussel shape heterogeneity. Our findings revealed similar shell shape responses in Mytilus to less favourable environmental conditions across the different geographical scales analysed. Our results show how shell shape plasticity represents a powerful indicator to understand the alterations of blue mussel communities in rapidly changing environments

The evolution of the cemented habit in the bivalved molluscs

The ability to cement to a hard substratum has evolved repeatedly in the bivalved molluscs. Twenty clades of cementing bivalves have been identified from a broad range of bivalve taxa. Such polyphyletic acquisition of the habit raises a number of questions concerning the preadaptations which allow bivalves to cement and the selection pressures which favour this mode of attachment. Detailed examination of cementation in members of the Ostreidae reveals that a calcareous extra-periostracal cement is responsible for attachment. Spherulitic growth of cement, whose composition is identical to that of the shell layers, results in structures reminiscent of diagenetic cements. These observations suggest that extrapallial fluid leaks' through a permeable periostracum; resulting in precipitation of calcium carbonate between the periostracum and the substratum. Similar observations are made for most other living shell cementing bivalves, implying a convergence of mechanism. The only exception are the chamids which appear to utilise a weaker organic bond. Less than 10% of fossil Chamacea are preserved attached to their substrata, suggesting that this weaker mode of attachment has been employed in this superfamily throughout its evolutionary history. Having established a common mechanism by which most bivalves cement it is possible to suggest the possible preadaptations. Principal requirements are the possession of a thin and 'leaky' periostracum, a highly extensible mantle edge and a suitable life orientation. Indeed, most cementing bivalves have evolved from pleurothetic byssate stock. The Pectinidae, in which the cemented habit has evolved at least four times, are shown to possess these key preadaptations. Mytiloids have never cemented despite having members which have dwelt on hard substrates since the Ordovician. Examination of modem Mytilacea suggests that the group lacks all the fundamental preadaptations for cementation. There is little evidence to support the traditional view that cementation is an adaptation to life in a high energy environment. The independent appearance of many of the cementing clades during the early Mesozoic coincides with the increased predation pressure which has been documented for that time. A causal link is implied by experimental work: predators display a significant preference for more easily manipulated byssate prey

Pteropods counter mechanical damage and dissolution through extensive shell repair

The dissolution of the delicate shells of sea butterflies, or pteropods, has epitomised discussions regarding ecosystem vulnerability to ocean acidification over the last decade. However, a recent demonstration that the organic coating of the shell, the periostracum, is effective in inhibiting dissolution suggests that pteropod shells may not be as susceptible to ocean acidification as previously thought. Here we use micro-CT technology to show how, despite losing the entire thickness of the original shell in localised areas, specimens of polar species Limacina helicina maintain shell integrity by thickening the inner shell wall. One specimen collected within Fram Strait with a history of mechanical and dissolution damage generated four times the thickness of the original shell in repair material. The ability of pteropods to repair and maintain their shells, despite progressive loss, demonstrates a further resilience of these organisms to ocean acidification but at a likely metabolic cost

Semi-direct allorecognition

Adaptive CD8 T-cell immunity is the principal arm of the cellular alloimmune response, but its development requires help. This can be provided by CD4 T cells that recognize alloantigen "indirectly," as self-restricted allopeptide, but this process remains unexplained, because the target epitopes for CD4 and CD8 T-cell recognition are "unlinked" on different cells (recipient and donor antigen presenting cells (APCs), respectively). Here, we test the hypothesis that the presentation of intact and processed MHC class I alloantigen by recipient dendritic cells (DCs) (the "semidirect" pathway) allows linked help to be delivered by indirect-pathway CD4 T cells for generating destructive cytotoxic CD8 T-cell alloresponses. We show that CD8 T-cell-mediated rejection of murine heart allografts that lack hematopoietic APCs requires host secondary lymphoid tissue (SLT). SLT is necessary because within it, recipient dendritic cells can acquire MHC from graft parenchymal cells and simultaneously present it as intact protein to alloreactive CD8 T cells and as processed peptide alloantigen for recognition by indirect-pathway CD4 T cells. This enables delivery of essential help for generating cytotoxic CD8 T-cell responses that cause rapid allograft rejection. In demonstrating the functional relevance of the semidirect pathway to transplant rejection, our findings provide a solution to a long-standing conundrum as to why SLT is required for CD8 T-cell allorecognition of graft parenchymal cells and suggest a mechanism by which indirect-pathway CD4 T cells provide help for generating effector cytotoxic CD8 T-cell alloresponses at late time points after transplantation.This work was supported by a British Heart Foundation project grant, the National Institute of Health Research Cambridge Biomedical Research Centre and the National Institute of Health Research Blood and Transplant Research Unit. SH was supported by an Academy of Medical Sciences / Wellcome Trust starter grant and the European Society for Organ Transplantation Junior Basic Science Research Grant. JA and IH were supported by Wellcome Trust Clinical Research Training Fellowships and Raymond and Beverly Sackler Scholarships.This is the author accepted manuscript. The final version is available from PNAS via http://dx.doi.org/10.1073/pnas.151353311

Adult acclimation to combined temperature and pH stressors significantly enhances reproductive outcomes compared to short-term exposures

1.This study examined the effects of long-term culture under altered conditions on the Antarctic sea urchin, Sterechinus neumayeri. 2.Sterechinus neumayeri was cultured under the combined environmental stressors of lowered pH (−0·3 and −0·5 pH units) and increased temperature (+2 °C) for 2 years. This time-scale covered two full reproductive cycles in this species and analyses included studies on both adult metabolism and larval development. 3.Adults took at least 6–8 months to acclimate to the altered conditions, but beyond this, there was no detectable effect of temperature or pH. 4.Animals were spawned after 6 and 17 months exposure to altered conditions, with markedly different outcomes. At 6 months, the percentage hatching and larval survival rates were greatest in the animals kept at 0 °C under current pH conditions, whilst those under lowered pH and +2 °C performed significantly less well. After 17 months, performance was not significantly different across treatments, including controls. However, under the altered conditions urchins produced larger eggs compared with control animals. 5.These data show that under long-term culture adult S. neumayeri appear to acclimate their metabolic and reproductive physiology to the combined stressors of altered pH and increased temperature, with relatively little measureable effect. They also emphasize the importance of long-term studies in evaluating effects of altered pH, particularly in slow developing marine species with long gonad maturation times, as the effects of altered conditions cannot be accurately evaluated unless gonads have fully matured under the new conditions

Experimental actinomycosis: The pathogenic action of Actinomycetes in mice

Hitherto, laboratory investigations into the disease actinomycosis have been almost wholly restricted to cultural and serological studies of the causal organism, Actinomyces israelii. The reason for this limitation is lack of a method of inducing a satisfactory infection in laboratory animals. 2 The literature on actinomycosis contains many references to unsuccessful attempts to infect laboratory animals. There are also accounts of methods of infection which succeeded only irregularly or depended upon methods which introduced such a degree of artificiality that the resulting infections were of little value for any comparative purposes - for example, the testing of therapeutic substances that might be used. for the treatment of actinomycosis in man or domestic animals. A critical review of the relevant literature is presented. By inoculating mice with cultures of A. israelii grown in thioglycollate broth I found that lesions developed in the inoculated animals with sufficient regularity to suggest the usefulness of further investigation of the disease so produced in mice. Success in establishing a useful experimental infection in mice probably depended on three influences; (1) the use of fluid matures grown for a relatively short period (4 - 5 days), which gave high yields of infective material; (2) the U80 of "rough" strains of A. israelii; and (3) awareness that non-fatal lesions developed in the inoculated animals. 4. A comparative study of the lesions so produced in mice and of those found in natural infections of the human, subject showed moray striking points of similarity between the two. 5. Histological studies of organs of infected mice revealed the presence of abscesses in liver and spleen but not in other organs. The abscesses showed branching filaments of Actinomyces arranged in a radial disposition, giving a picture closely akin to that of the "sulphur granule" typical of the lesions found in natural infection of man, In the mouse, clubs at the edge of the lesion wore net observed; co that the picture approximated more closely to that found In man than to that observed in bovines. By killing animals at different times after inoculation I found that the abscesses underwent spontaneous regression from about 6 weeks after inoculation. 6. In fluid culture A. israelii may grow either in the rough form with long branching, a characteristic deposit, and clear supernatant or in the smooth form with diphtheroid morphology and even turbidity throughout the medium. The lesions in mice already described were produced by inoculation of the rough form. When inoculated, into mice, smooth cultures gave rise to macroscopic lesions which superficially appeared to be similar to those produced by the organism in the rough filamentous form, bat a clear difference in the tissue reaction was shown by histological examination. With smooth cultures nothing like a sulphur granule was seen, the diphtheroids did not give rise to branching filaments in the animal and large lipophagic macrophages were not seen. 7. Among the mice which recovered from the initial actinomycotic infection but died at 6 months after inoculation, some showed, tubular nephritis, which is a type of lesion not previously described in mice. Other survivors of the initial infection died at about 12 - 18 months after inoculation; these did not show the presence of tubular nephritis, Attempts were made on a limited, scale to produce tubular nephritis in mice by endotoxins of A. lsraelii, The results, though inconclusive, were suggestive they are given and discussed in the thesis, Experiments were also carried out to compare the action of two other members of the order Actinogyeetales with that of israelii upon insolation into mice, Nocardia asteroides aerobic acid-fast branching and relatively uncommon pathogen of man and animals produced a fatal infection in the mouse, Abscesses formed in liver, spleen and kidney. Contrary to what was found with A. israelii the kidney became a focal point of the experimental infection which was invariably fatal within two months. The type of lesion and tissue reactions were entirely different from those produced by A. israelii. Actinomyces graminins, the aerobic saprophyte aerobic saprophyte commonly found in grasses, had no effect upon mice, whether the inoculum employed was in the sporing or non-sporing phase. 9. The experimental infections thus produced with A. israelii in mice are reproducible if the necessary care is taken to observe the details of method emphasised in this thesis as important. The findings assist in establishing the status of the organism as an undoubted pathogen but of low virulence. The experimental infection has obvious uses in assessing the value of chemotherapy and for studying the pathology of the disease. In this connection the renal lesions would appear to merit particular attention