Estimating potential for adaption of corals to climate warming

University of Technology, Sydney. Faculty of Science.Open AccessClimate models predict rapidly warming oceans throughout the 21st century along with increased mortalities in reef-building coral-algal symbioses. Yet the ability of corals to adapt genetically in an evolutionary sense to a warmer climate is unknown. The adaptive potential of corals can be approximated by the extent to which variation in thermal tolerance is caused by genetic factors (i.e. by the broad-sense heritability, H²). This thesis investigated H² in a total of eleven thermal tolerance traits from two populations of the reef-building coral species Acropora millepora in the central Great Barrier Reef, Australia. The first population that was investigated associates with thermo-tolerant algal symbionts of the genus Symbiodinium (clade D), and came from Magnetic Island (MI), while the second population from Orpheus Island (OI) associates with the intermediately tolerant Symbiodinium type C2. Traits investigated were characteristic of the coral host, the algal symbiont, and the holobiont (whole symbiosis). The present thesis revealed extensive genetic variation in algal symbiont traits, which, together with short generation times, allows for rapid symbiont adaptation to climate warming. A significant adaptive potential was also found for coral colony growth rates, defined here as a holobiont trait. This is in stark contrast to the coral host, which did not display heritability for the majority of the traits investigated for either population. The coral host with its long generation time has therefore only a low potential to adapt to rapidly warming oceans. Five of the six thermal tolerance traits yielded significant heritabilities in each of the two symbiont types. In clade D symbionts from MI, the adaptive potential was given for the maximum quantum yield of photosystem II, Fv/Fm, one of the most commonly studied stress parameters in coral biology which indicates the overall health condition of photosystems. The one trait that did not yield a significant heritability in D symbionts was non-photochemical quenching (ФNPQ) of excess excitation energy. The trait ФNPQ can be considered as a switch for xanthophyll cycling, a mechanism that protects photosystems through conversion of the pigment diadinoxanthin (DD) into diatoxanthin (DT). However, D symbionts diverted 50 % of the incoming light energy for the initiation of the xanthophyll cycle (i.e. via ФNPQ), and the xanthophyll cycle mechanism itself showed significant heritability in either symbiont type. Both symbiont types also displayed significant heritability for another measure of photoprotection, the ability to regulate the pool size of photoprotective xanthophyll pigments (XP) relative to total light-harvesting pigments (LH). Although Fv/Fm did not yield a significant heritability in C2 symbionts from OI, both symbiont types again showed heritability for the effective quantum yield of photosystem II (ФPSII), and for unregulated energy dissipation (ФNO). For traits reflecting the function of the coral host, messenger RNA (mRNA) expression levels of four fundamental genes involved in the oxidative stress response were investigated. These genes code for cellular defences which regulate cellular iron homeostasis (i.e. Ferritin), repair denatured proteins (i.e. the heat shock protein Hsp70), detoxify harmful oxygen radicals (i.e. the mitochondrial enzyme manganese superoxide dismutase MnSOD), and might be involved in the dysfunction of coral cell-adhesion proteins during bleaching via a remodelling of surface receptors in the extra-cellular matrix (i.e. a zinc- metalloprotease, Zn²⁺-met). Each coral host population, however, showed heritability for expression of just one of those four genes (i.e. MnSOD in the MI population, and Zn²⁺-met in the OI population), therefore displaying only a limited capacity for evolution of thermal tolerance. Holobiont growth showed a significant heritability in both coral-algal populations, thus providing the basis for evolutionary adaptation. In the long term, however, this trait might be impaired by ocean acidification, which has a negative impact on coral calcification and, therefore, on holobiont growth rates. In summary, algal symbionts have short generation times and considerable genetic variation in functional traits, thus allowing for rapid adaptation to higher temperatures. However, adaptive response estimates based on low heritabilities in coral host traits along with the coral’s mainly sexual reproduction and long generation time raise concerns about the timely adaptation of the holobiont in the face of rapid climate warming

Measurement of calcium isotopes (δ44Ca) using a multicollector TIMS technique

We propose a new“multicollector technique” for the thermal ionization mass spectrometer (TIMS) measurement of calcium (Ca) isotope ratios improving average internal statistical uncertainty of the 44Ca/40Ca measurements by a factor of 2–4 and average sample throughput relative to the commonly used “peak jumping method” by a factor of 3. Isobaric interferences with potassium (40K+) and titanium (48Ti+) or positively charged molecules like 24Mg19F+, 25Mg19F+, 24Mg16O+ and 27Al16O+ can either be corrected or are negligible. Similar, peak shape defects introduced by the large dispersion of the whole Ca isotope mass range from 40–48 atomic mass units (amu) do not influence Ca-isotope ratios. We use a 43Ca/48Ca double spike with an iterative double spike correction algorithm for precise isotope measurement

Molecular basis of glutamate toxicity in retinal ganglion cells

Loss of retinal ganglion cells (RGCs) is a hallmark of many ophthalmic diseases including glaucoma, retinal ischemia due to central artery occlusion, anterior ischemic optic neuropathy and may be significant in optic neuritis, optic nerve trauma, and AIDS. Recent research indicates that neurotoxicity is caused by excessive stimulation of receptors for excitatory amino acids (EAAs). In particular, the amino acid glutamate has been shown to act as a neurotoxin which exerts its toxic effect on RGCs predominantly through the N-methyl-d-aspartate (NMDA) subtype of glutamate receptor. NMDA-receptor-mediated toxicity in RGCs is dependent on the influx of extracellular Ca2+. The increase in [Ca2+]i acts as a second messenger that sets in motion the cascade leading to eventual cell death. Glutamate stimulates its own release in a positive feedback loop by its interaction with the non-NMDA receptor subtypes. Ca2+-induced Ca2+ release and further influx of Ca2+ through voltage-gated Ca2+ channels after glutamate-induced depolarization contribute to glutamate toxicity. In vitro and in vivo studies suggest that the use of selective NMDA receptor antagonists or Ca2+ channel blockers should be useful in preventing or at least abating neuronal loss in the retina. Of particular importance for future clinical use of NMDA receptor antagonists in the treatment of acute vascular insults is the finding that some drugs can prevent glutamate-induced neurotoxicity, even when administered a few hours after the onset of retinal ischemia

Principal infinity-bundles - General theory

The theory of principal bundles makes sense in any infinity-topos, such as that of topological, of smooth, or of otherwise geometric infinity-groupoids/infinity-stacks, and more generally in slices of these. It provides a natural geometric model for structured higher nonabelian cohomology and controls general fiber bundles in terms of associated bundles. For suitable choices of structure infinity-group G these G-principal infinity-bundles reproduce the theories of ordinary principal bundles, of bundle gerbes/principal 2-bundles and of bundle 2-gerbes and generalize these to their further higher and equivariant analogs. The induced associated infinity-bundles subsume the notions of gerbes and higher gerbes in the literature. We discuss here this general theory of principal infinity-bundles, intimately related to the axioms of Giraud, Toen-Vezzosi, Rezk and Lurie that characterize infinity-toposes. We show a natural equivalence between principal infinity-bundles and intrinsic nonabelian cocycles, implying the classification of principal infinity-bundles by nonabelian sheaf hyper-cohomology. We observe that the theory of geometric fiber infinity-bundles associated to principal infinity-bundles subsumes a theory of infinity-gerbes and of twisted infinity-bundles, with twists deriving from local coefficient infinity-bundles, which we define, relate to extensions of principal infinity-bundles and show to be classified by a corresponding notion of twisted cohomology, identified with the cohomology of a corresponding slice infinity-topos. In a companion article [NSSb] we discuss explicit presentations of this theory in categories of simplicial (pre)sheaves by hyper-Cech cohomology and by simplicial weakly-principal bundles; and in [NSSc] we discuss various examples and applications of the theory.Comment: 46 pages, published versio

Symmetry conserving non-perturbative s-wave renormalization of the pion in hot and baryon dense medium

A non-perturbative s-wave renormalization of the pion in a hot and baryon rich medium is presented. This approach proceeds via a mapping of the canonical pion into the axial Noether's charge. The mapping was made dynamical in the Hartree-Fock-Bogoliubov random phase approximation (HFB-RPA). It is shown that this approach, while order mixing, is still symmetry conserving both in the baryon free and baryon rich sectors, at zero as well as finite temperature. The systematic character of this approach is emphasized and it is particularly argued that it may constitute an interesting alternative for the non-perturbative assessment of the nuclear matter saturation properties.Comment: Latex, 22 pages, 3 figure

Three-dimensional normal human neural progenitor tissue-like assemblies: A model of persistent Varicella-Zoster virus infection

Varicella-zoster virus (VZV) is a neurotropic human alphaherpesvirus that causes varicella upon primary infection, establishes latency in multiple ganglionic neurons, and can reactivate to cause zoster. Live attenuated VZV vaccines are available; however, they can also establish latent infections and reactivate. Studies of VZV latency have been limited to the analyses of human ganglia removed at autopsy, as the virus is strictly a human pathogen. Recently, terminally differentiated human neurons have received much attention as a means to study the interaction between VZV and human neurons; however, the short life-span of these cells in culture has limited their application. Herein, we describe the construction of a model of normal human neural progenitor cells (NHNP) in tissue-like assemblies (TLAs), which can be successfully maintained for at least 180 days in three-dimensional (3D) culture, and exhibit an expression profile similar to that of human trigeminal ganglia. Infection of NHNP TLAs with cell-free VZV resulted in a persistent infection that was maintained for three months, during which the virus genome remained stable. Immediate-early, early and late VZV genes were transcribed, and low-levels of infectious VZV were recurrently detected in the culture supernatant. Our data suggest that NHNP TLAs are an effective system to investigate long-term interactions of VZV with complex assemblies of human neuronal cells