1,098 research outputs found
Environmental proxies of antigen exposure explain variation in immune investment better than indices of pace of life.
Investment in immune defences is predicted to covary with a variety of ecologically and evolutionarily relevant axes, with pace of life and environmental antigen exposure being two examples. These axes may themselves covary directly or inversely, and such relationships can lead to conflicting predictions regarding immune investment. If pace of life shapes immune investment then, following life history theory, slow-living, arid zone and tropical species should invest more in immunity than fast-living temperate species. Alternatively, if antigen exposure drives immune investment, then species in antigen-rich tropical and temperate environments are predicted to exhibit higher immune indices than species from antigen-poor arid locations. To test these contrasting predictions we investigated how variation in pace of life and antigen exposure influence immune investment in related lark species (Alaudidae) with differing life histories and predicted risks of exposure to environmental microbes and parasites. We used clutch size and total number of eggs laid per year as indicators of pace of life, and aridity, and the climatic variables that influence aridity, as correlates of antigen abundance. We quantified immune investment by measuring four indices of innate immunity. Pace of life explained little of the variation in immune investment, and only one immune measure correlated significantly with pace of life, but not in the predicted direction. Conversely, aridity, our proxy for environmental antigen exposure, was predictive of immune investment, and larks in more mesic environments had higher immune indices than those living in arid, low-risk locations. Our study suggests that abiotic environmental variables with strong ties to environmental antigen exposure can be important correlates of immunological variation.Financial support came from the Schure-Beijerinck-Poppings Fonds (to NPCH and AH), BirdLife Netherlands (to BIT), NSF grant IBN 0212587 (to JBW), and VENI and VIDI grants from the Netherlands Organisation for Scientific Research (to KDM and BIT).This is the accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007%2Fs00442-014-3136-y
Maximal supergravity in D=10: forms, Borcherds algebras and superspace cohomology
We give a very simple derivation of the forms of supergravity from
supersymmetry and SL(2,\bbR) (for IIB). Using superspace cohomology we show
that, if the Bianchi identities for the physical fields are satisfied, the
(consistent) Bianchi identities for all of the higher-rank forms must be
identically satisfied, and that there are no possible gauge-trivial Bianchi
identities () except for exact eleven-forms. We also show that the
degrees of the forms can be extended beyond the spacetime limit, and that the
representations they fall into agree with those predicted from Borcherds
algebras. In IIA there are even-rank RR forms, including a non-zero
twelve-form, while in IIB there are non-trivial Bianchi identities for
thirteen-forms even though these forms are identically zero in supergravity. It
is speculated that these higher-rank forms could be non-zero when higher-order
string corrections are included.Comment: 15 pages. Published version. Some clarification of the tex
Are antimicrobial defences in bird eggs related to climatic conditions associated with risk of trans-shell microbial infection?
INTRODUCTION: All bird eggs are exposed to microbes in the environment, which if transmitted to the developing embryo, could cause hatching failure. However, the risk of trans-shell infection varies with environmental conditions and is higher for eggs laid in wetter environments. This might relate to generally higher microbial abundances and diversity in more humid environments, including on the surface of eggshells, as well as the need for moisture to facilitate microbial penetration of the eggshell. To protect against microbial infection, the albumen of avian eggs contains antimicrobial proteins, including lysozyme and ovotransferrin. We tested whether lysozyme and ovotransferrin activities varied in eggs of larks (Alaudidae) living along an arid-mesic gradient of environmental aridity, which we used as a proxy for risk of trans-shell infection. RESULTS: Contrary to expectations, lysozyme activity was highest in eggs from hotter, more arid locations, where we predicted the risk of trans-shell infection would be lower. Ovotransferrin concentrations did not vary with climatic factors. Temperature was a much better predictor of antimicrobial protein activity than precipitation, a result inconsistent with studies stressing the importance of moisture for trans-shell infection. CONCLUSIONS: Our study raises interesting questions about the links between temperature and lysozyme activity in eggs, but we find no support for the hypothesis that antimicrobial protein deposition is higher in eggs laid in wetter environments
The "Solar Model Problem" Solved by the Abundance of Neon in Stars of the Local Cosmos
The interior structure of the Sun can be studied with great accuracy using
observations of its oscillations, similar to seismology of the Earth. Precise
agreement between helioseismological measurements and predictions of
theoretical solar models has been a triumph of modern astrophysics (Bahcall et
al. 2005). However, a recent downward revision by 25-35% of the solar
abundances of light elements such as C, N, O and Ne (Asplund et al. 2004) has
broken this accordance: models adopting the new abundances incorrectly predict
the depth of the convection zone, the depth profiles of sound speed and
density, and the helium abundance (Basu Antia 2004, Bahcall et al. 2005). The
discrepancies are far beyond the uncertainties in either the data or the model
predictions (Bahcall et al. 2005b). Here we report on neon abundances relative
to oxygen measured in a sample of nearby solar-like stars from their X-ray
spectra. They are all very similar and substantially larger than the recently
revised solar value. The neon abundance in the Sun is quite poorly determined.
If the Ne/O abundance in these stars is adopted for the Sun the models are
brought back into agreement with helioseismology measurements (Antia Basu 2005,
Bahcall et al. 2005c).Comment: 13 pages, 3 Figure
Tensor hierarchies, Borcherds algebras and E11
Gauge deformations of maximal supergravity in D=11-n dimensions generically
give rise to a tensor hierarchy of p-form fields that transform in specific
representations of the global symmetry group E(n). We derive the formulas
defining the hierarchy from a Borcherds superalgebra corresponding to E(n).
This explains why the E(n) representations in the tensor hierarchies also
appear in the level decomposition of the Borcherds superalgebra. We show that
the indefinite Kac-Moody algebra E(11) can be used equivalently to determine
these representations, up to p=D, and for arbitrarily large p if E(11) is
replaced by E(r) with sufficiently large rank r.Comment: 22 pages. v2: Published version (except for a few minor typos
detected after the proofreading, which are now corrected
Note on New KLT relations
In this short note, we present two results about KLT relations discussed in
recent several papers. Our first result is the re-derivation of Mason-Skinner
MHV amplitude by applying the S_{n-3} permutation symmetric KLT relations
directly to MHV amplitude. Our second result is the equivalence proof of the
newly discovered S_{n-2} permutation symmetric KLT relations and the well-known
S_{n-3} permutation symmetric KLT relations. Although both formulas have been
shown to be correct by BCFW recursion relations, our result is the first direct
check using the regularized definition of the new formula.Comment: 15 Pages; v2: minor correction
Three-Fold Diffraction Symmetry in Epitaxial Graphene and the SiC Substrate
The crystallographic symmetries and spatial distribution of stacking domains
in graphene films on SiC have been studied by low energy electron diffraction
(LEED) and dark field imaging in a low energy electron microscope (LEEM). We
find that the graphene diffraction spots from 2 and 3 atomic layers of graphene
have 3-fold symmetry consistent with AB (Bernal) stacking of the layers. On the
contrary, graphene diffraction spots from the buffer layer and monolayer
graphene have apparent 6-fold symmetry, although the 3-fold nature of the
satellite spots indicates a more complex periodicity in the graphene sheets.Comment: An addendum has been added for the arXiv version only, including one
figure with five panels. Published paper can be found at
http://link.aps.org/doi/10.1103/PhysRevB.80.24140
Comammox Nitrospira Clade B is the most abundant complete ammonia oxidizer in a dairy pasture soil and inhibited by dicyandiamide and high ammonium concentrations
The recent discovery of comammox Nitrospira, a complete ammonia oxidizer, capable of completing the nitrification on their own has presented tremendous challenges to our understanding of the nitrification process. There are two divergent clades of comammox Nitrospira, Clade A and B. However, their population abundance, community structure and role in ammonia and nitrite oxidation are poorly understood. We conducted a 94-day microcosm study using a grazed dairy pasture soil amended with urea fertilizers, synthetic cow urine, and the nitrification inhibitor, dicyandiamide (DCD), to investigate the growth and community structure of comammox Nitrospira spp. We discovered that comammox Nitrospira Clade B was two orders of magnitude more abundant than Clade A in this fertile dairy pasture soil and the most abundant subcluster was a distinctive phylogenetic uncultured subcluster Clade B2. We found that comammox Nitrospira Clade B might not play a major role in nitrite oxidation compared to the role of canonical Nitrospira nitrite-oxidizers, however, comammox Nitrospira Clade B is active in nitrification and the growth of comammox Nitrospira Clade B was inhibited by a high ammonium concentration (700 kg synthetic urine-N ha¯¹) and the nitrification inhibitor DCD. We concluded that comammox Nitrospira Clade B: (1) was the most abundant comammox in the dairy pasture soil; (2) had a low tolerance to ammonium and can be inhibited by DCD; and (3) was not the dominant nitrite-oxidizer in the soil. This is the first study discovering a new subcluster of comammox Nitrospira Clade B2 from an agricultural soil
Spacelike Singularities and Hidden Symmetries of Gravity
We review the intimate connection between (super-)gravity close to a
spacelike singularity (the "BKL-limit") and the theory of Lorentzian Kac-Moody
algebras. We show that in this limit the gravitational theory can be
reformulated in terms of billiard motion in a region of hyperbolic space,
revealing that the dynamics is completely determined by a (possibly infinite)
sequence of reflections, which are elements of a Lorentzian Coxeter group. Such
Coxeter groups are the Weyl groups of infinite-dimensional Kac-Moody algebras,
suggesting that these algebras yield symmetries of gravitational theories. Our
presentation is aimed to be a self-contained and comprehensive treatment of the
subject, with all the relevant mathematical background material introduced and
explained in detail. We also review attempts at making the infinite-dimensional
symmetries manifest, through the construction of a geodesic sigma model based
on a Lorentzian Kac-Moody algebra. An explicit example is provided for the case
of the hyperbolic algebra E10, which is conjectured to be an underlying
symmetry of M-theory. Illustrations of this conjecture are also discussed in
the context of cosmological solutions to eleven-dimensional supergravity.Comment: 228 pages. Typos corrected. References added. Subject index added.
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