2,037 research outputs found
Seawater acidification more than warming presents a challenge for two Antarctic macroalgal-associated amphipods
Elevated atmospheric pCO2 concentrations are triggering seawater pH reductions and seawater temperature increases along the western Antarctic Peninsula (WAP). These factors in combination have the potential to influence organisms in an antagonistic, additive, or synergistic manner. The amphipods Gondogeneia antarctica and Paradexamine fissicauda represent prominent members of macroalgal-associated mesograzer assemblages of the WAP. Our primary objective was to investigate amphipod behavioral and physiological responses to reduced seawater pH and elevated temperature to evaluate potential cascading ecological impacts. For 90 d, amphipods were exposed to combinations of seawater conditions based on present ambient (pH 8.0, 1.5°C) and predicted end-of-century conditions (pH 7.6, 3.5°C). We recorded survival, molt frequency, and macroalgal consumption rates as well as change in wet mass and proximate body composition (protein and lipid). Survival for both species declined significantly at reduced pH and co-varied with molt frequency. Consumption rates in G. antarctica were significantly higher at reduced pH and there was an additive pH-temperature effect on consumption rates in P. fissicauda. Body mass was reduced for G. antarctica at elevated temperature, but there was no significant effect of pH or temperature on body mass in P. fissicauda. Exposure to the pH or temperature levels tested did not induce significant changes in whole body biochemical composition of G. antarctica, but exposure to elevated temperature resulted in a significant increase in whole body protein content of P. fissicauda. Our study indicates that while elevated temperature causes sub-lethal impacts on both species of amphipods, reduced pH causes significant mortality
Palatability and chemical defenses of sponges from the western Antarctic Peninsula
The present study surveyed the palatability of all sponge species that could be collected in sufficient quantities in a shallow-water area along the western Antarctic Peninsula. Of 27 species assayed, 78% had outermost tissues that were significantly unpalatable to the sympatric, omnivorous sea star Odontaster validus. Of those species with unpalatable outer tissues, 62% had inner tissues that were also unpalatable to the sea stars. Sea stars have often been considered as the primary predators of sponges in other regions of Antarctica, and their extra-oral mode of feeding threatens only the outermost sponge tissues. The observation that many of the sponges allocate defenses to inner tissues suggests the possibility that biting predators such as mesograzers, which could access inner sponge layers, may also be important in communities along the Antarctic Peninsula. In feeding bioassays with extracts from 12 of the unpalatable species in artificial foods, either lipophilic or hydrophilic extracts were deterrent in each species. These data indicate an overall level of chemical defenses in these Antarctic sponges that is comparable to, and slightly greater than, that found in a previous survey of tropical species
Algicidal activity and potential antifouling defenses in macroalgae from the western Antarctic Peninsula including probable synergistic effects of multiple compounds
Juvenile morphology of the large Antarctic canopy-forming brown alga, Desmarestia menziesii J. Agardh
Open Access via Springer Compact Agreement. We are grateful to the UK Natural Environment Research Council for funding to FCK (grants NE/D521522/1 and NE/J023094/1), in particular through the Collaborative Antarctic Science Scheme (Grant CASS-134, 2017) to FCK and LSP. Funding for cruise-based observations in 2019 was from US National Science Foundation award OPP-1744550 to CDA. We thank Kate Stanton, Teresa Murphy and Ben Robinson (British Antarctic Survey) for support with diving operations around Rothera in JanuaryâFebruary 2018, and also Richard L. Moe (UC Berkeley) for locating specimens corresponding to the morphology described here in the UC collection. Special thanks are due to Charlie Bibby (Financial Times) for taking professional photographs of the unknown Desmarestia sp. in the aquarium of the Bonner Lab at Rothera (Fig. 2a). We would also like to thank Richard L. Moe (UC Berkeley) and Christian Wiencke (AWI Bremerhaven) for their very helpful reviews of this paper. Also, the MASTS pooling initiative (Marine Alliance for Science and Technology for Scotland, funded by the Scottish Funding Council and contributing institutions; grant reference HR09011) is gratefully acknowledged for supporting FCK. This research contributes to the SCAR Ant-ERA research programme.Peer reviewedPublisher PD
The Time is Right for an Antarctic Biorepository Network
Antarctica is a central driver of the Earthâs climate and health. The Southern Ocean surrounding Antarctica serves as a major sink for anthropogenic CO2 and heat (1), and the loss of Antarctic ice sheets contributes significantly to sea level rise and will continue to do so as the loss of ice sheets accelerates, with sufficient water stores to raise sea levels by 58 m (2). Antarctica\u27s marine environment is home to a number of iconic species, and the terrestrial realm harbors a remarkable oasis for life, much of which has yet to be discovered (3). Distinctive oceanographic features of the Southern Oceanâincluding the Antarctic Circumpolar Current, the Antarctic Polar Front, and exceptional depths surrounding the continentâcoupled with chronically cold temperatures have fostered the evolution of a vast number of uniquely coldadapted species, many of which are found nowhere else on the Earth (4). The Antarctic marine biota, for example, displays the highest level of species endemism on the Earth (5). However, warming, ocean acidification, pollution, and commercial exploitation threaten the integrity of Antarctic ecosystems (6). Understanding changes in the biota and its capacities for adaptation is imperative for establishing effective policies for mitigating the impacts of climate change and sustaining the Antarctic ecosystems that are vital to global health
Nearest-Neighbour Interaction from an Abelian Symmetry and Deviations from Hermiticity
We show that Nearest-Neighbour Interaction (NNI) textures for the quark mass
matrices can be obtained through the introduction of an Abelian flavour
symmetry. The minimal realisation requires a Z_4 symmetry in the context of a
two Higgs doublet model. It is further shown that the NNI textures can be in
agreement with all present experimental data on quark masses and mixings,
provided one allows for deviations of Hermiticity in the quark mass matrices at
the 20% level.Comment: 11 pages, 1 figure; references and minor corrections adde
The Benefits of B ---> K* l+ l- Decays at Low Recoil
Using the heavy quark effective theory framework put forward by Grinstein and
Pirjol we work out predictions for B -> K* l+ l-, l = (e, mu), decays for a
softly recoiling K*, i.e., for large dilepton masses sqrt{q^2} of the order of
the b-quark mass m_b. We work to lowest order in Lambda/Q, where Q = (m_b,
sqrt{q^2}) and include the next-to-leading order corrections from the charm
quark mass m_c and the strong coupling at O(m_c^2/Q^2, alpha_s). The leading
Lambda/m_b corrections are parametrically suppressed. The improved Isgur-Wise
form factor relations correlate the B -> K* l+ l- transversity amplitudes,
which simplifies the description of the various decay observables and provides
opportunities for the extraction of the electroweak short distance couplings.
We propose new angular observables which have very small hadronic
uncertainties. We exploit existing data on B -> K* l+ l- distributions and show
that the low recoil region provides powerful additional information to the
large recoil one. We find disjoint best-fit solutions, which include the
Standard Model, but also beyond-the-Standard Model ones. This ambiguity can be
accessed with future precision measurements.Comment: 31 pages, 8 figures; Instability near minimal recoil from numerics
removed, Fig. 1 replaced and minor shifts in short distance uncertainties in
SM predictions; typos corrected and references added; main results and
conclusions unchange
Radiative and Semileptonic B Decays Involving Higher K-Resonances in the Final States
We study the radiative and semileptonic B decays involving a spin-
resonant with parity for and for
in the final state. Using the large energy effective theory (LEET)
techniques, we formulate transition form factors in the large
recoil region in terms of two independent LEET functions
and , the values of
which at zero momentum transfer are estimated in the BSW model. According to
the QCD counting rules, exhibit a dipole
dependence in . We predict the decay rates for ,
and . The
branching fractions for these decays with higher -resonances in the final
state are suppressed due to the smaller phase spaces and the smaller values of
. Furthermore, if the spin of
becomes larger, the branching fractions will be further suppressed due to the
smaller Clebsch-Gordan coefficients defined by the polarization tensors of the
. We also calculate the forward backward asymmetry of the decay, for which the zero is highly insensitive to the
-resonances in the LEET parametrization.Comment: 27 pages, 4 figures, 7 tables;contents and figures corrected, title
and references revise
Theoretical and Phenomenological Constraints on Form Factors for Radiative and Semi-Leptonic B-Meson Decays
We study transition form factors for radiative and rare semi-leptonic B-meson
decays into light pseudoscalar or vector mesons, combining theoretical
constraints and phenomenological information from Lattice QCD, light-cone sum
rules, and dispersive bounds. We pay particular attention to form factor
parameterisations which are based on the so-called series expansion, and study
the related systematic uncertainties on a quantitative level. In this context,
we also provide the NLO corrections to the correlation function between two
flavour-changing tensor currents, which enters the unitarity constraints for
the coefficients in the series expansion.Comment: 52 pages; v2: normalization error in (29ff.) corrected, conclusion
about relevance of unitarity bounds modified; form factor fits unaffected;
references added; v3: discussion on truncation of series expansion added,
matches version to be published in JHEP; v4: corrected typos in Tables 5 and
Charmless Decays Based on the six-quark Effective Hamiltonian with Strong Phase Effects II
We provide a systematic study of charmless decays (
and denote pseudoscalar and vector mesons, respectively) based on an
approximate six-quark operator effective Hamiltonian from QCD. The calculation
of the relevant hard-scattering kernels is carried out, the resulting
transition form factors are consistent with the results of QCD sum rule
calculations. By taking into account important classes of power corrections
involving "chirally-enhanced" terms and the vertex corrections as well as weak
annihilation contributions with non-trivial strong phase, we present
predictions for the branching ratios and CP asymmetries of decays into
PP, PV and VV final states, and also for the corresponding polarization
observables in VV final states. It is found that the weak annihilation
contributions with non-trivial strong phase have remarkable effects on the
observables in the color-suppressed and penguin-dominated decay modes. In
addition, we discuss the SU(3) flavor symmetry and show that the symmetry
relations are generally respected
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