Cumulative stress restricts niche filling potential of habitat-forming kelps in a future climate

1. Climate change is driving range contractions and local population extinctions across the globe. When this affects ecosystem engineers the vacant niches left behind are likely to alter the wider ecosystem unless a similar species can fulfil them. 2. Here, we explore the stress physiology of two coexisting kelps undergoing opposing range shifts in the Northeast Atlantic and discuss what differences in stress physiology may mean for future niche filling. 3. We used chlorophyll florescence (Fv/Fm) and differentiation of the heat shock response (HSR) to determine the capacity of the expanding kelp, Laminaria ochroleuca, to move into the higher shore position of the retreating kelp, Laminaria digitata. We applied both single and consecutive exposures to immersed and emersed high and low temperature treatments, replicating low tide exposures experienced in summer and winter. 4. No interspecific differences in HSR were observed which was surprising given the species? different biogeographic distributions. However, chlorophyll florescence revealed clear differences between species with L. ochroleuca better equipped to tolerate high immersed temperatures but showed little capacity to tolerate frosts or high emersion temperatures. 5. Many patterns observed were only apparent after consecutive exposures. Such cumulative effects have largely been overlooked in tolerance experiments on intertidal organisms despite being more representative of the stress experienced in natural habitats. We therefore suggest future experiments incorporate consecutive stress into their design. 6. Climate change is predicted to result in fewer ground frosts and increased summer temperatures. Therefore, L. ochroleuca may be released from its summer cold limit in winter but still be prevented from moving up the shore due to desiccation in the summer. Laminaria ochroleuca will, however, likely be able to move into tidal pools. Therefore, only partial niche filling by L. ochroleuca will be possible in this system as climate change advancespublishersversionPeer reviewe

Developmental competence of bovine oocytes: effects of follicle size and the phase of follicular wave on in vitro embryo production.

Abstract Developmental competence of bovine oocytes collected from follicles of different size categories (in either the growth or the dominant phase of the first follicular wave) was studied, with the aim of improving in vitro embryo production. Estrus and ovulation of 39 cyclic Holstein dairy cows were synchronized by two prostaglandin F 2a treatments at 11-day intervals and one hCG treatment on the day of onset of estrus (Day 0). Cows with follicles in either the growth (Day 3, n ¼ 25) or the dominant phase (Day 7, n ¼ 14) were slaughtered, and follicles >5 mm were counted. Three oocyte populations were recovered separately from large (11-15 mm), medium (6-10 mm) and small (2-5 mm) follicles in both follicular phases. All collected cumulus-oocyte complexes (COC), except for markedly atretic oocytes without cumulus cells, were used in experiments. Oocytes were matured, fertilized and cultured by standard methods. There were no significant differences between the growth and the dominant phases for mean numbers of large follicles, useable oocytes and embryos per donor. Generally, those numbers were low, but the development rates of oocytes into blastocysts were high, particularly in the growth phase (60.0%). Mean (AES.E.M.) numbers of medium follicles, oocytes and embryos per donor were higher in the growth as compared with the dominant phase; in the useable oocytes and embryos, this difference was significant (9:6 AE 1:4 and 3:5 AE 0:6 versus 3:9 AE 0:6 and 1:1 AE 0:3; P < 0:01). The development rates of oocytes into blastocysts, however, did not differ significantly between the growth and the dominant phases (36.7% versus 27.8%). Mean numbers of useable oocytes and embryos per donor recovered from small follicles in both follicular wave phases were similar. The development rate of oocytes into blastocysts was generally low, but higher (P < 0:01) in the growth than in the dominant phase (24.5% versus 11.7%). Comparison between the two phases showed that mean number of all counted follicles and all useable oocytes collected per donor were similar, but the mean number of embryos per donor and the development rate of oocytes into blastocysts were higher in the growth phase than in the dominant phase (8:0 AE 1:2 versus 3:8 AE 2:4; P ¼ 0:012 and 30.3% versus 14.9%; P < 0:01). The interaction between follicle size and the phase of follicular wave affected the efficiency of embryo production. The yield of embryos was primarily influenced by the number of oocytes collected from medium follicles and the developmental competence of oocytes from small follicles. The growth phase was more effective for oocyte collection; the number of oocytes from medium follicles and the developmental competence of oocytes from small follicles decreased in the dominant phase.

Electronic Structure of Dangling Bonds in Amorphous Silicon Studied via a Density-Matrix Functional Method

A structural model of hydrogenated amorphous silicon containing an isolated dangling bond is used to investigate the effects of electron interactions on the electronic level splittings, localization of charge and spin, and fluctuations in charge and spin. These properties are calculated with a recently developed density-matrix correlation-energy functional applied to a generalized Anderson Hamiltonian, consisting of tight-binding one-electron terms parametrizing hydrogenated amorphous silicon plus a local interaction term. The energy level splittings approach an asymptotic value for large values of the electron-interaction parameter U, and for physically relevant values of U are in the range 0.3-0.5 eV. The electron spin is highly localized on the central orbital of the dangling bond while the charge is spread over a larger region surrounding the dangling bond site. These results are consistent with known experimental data and previous density-functional calculations. The spin fluctuations are quite different from those obtained with unrestricted Hartree-Fock theory.Comment: 6 pages, 6 figures, 1 tabl

Ab initio molecular dynamics using density based energy functionals: application to ground state geometries of some small clusters

The ground state geometries of some small clusters have been obtained via ab initio molecular dynamical simulations by employing density based energy functionals. The approximate kinetic energy functionals that have been employed are the standard Thomas-Fermi $(T_{TF})$ along with the Weizsacker correction $T_W$ and a combination $F(N_e)T_{TF} + T_W$. It is shown that the functional involving $F(N_e)$ gives superior charge densities and bondlengths over the standard functional. Apart from dimers and trimers of Na, Mg, Al, Li, Si, equilibrium geometries for $Li_nAl, n=1,8$ and $Al_{13}$ clusters have also been reported. For all the clusters investigated, the method yields the ground state geometries with the correct symmetries with bondlengths within 5\% when compared with the corresponding results obtained via full orbital based Kohn-Sham method. The method is fast and a promising one to study the ground state geometries of large clusters.Comment: 15 pages, 3 PS figure

Density-functional-based predictions of Raman and IR spectra for small Si clusters

We have used a density-functional-based approach to study the response of silicon clusters to applied electric fields. For the dynamical response, we have calculated the Raman activities and infrared (IR) intensities for all of the vibrational modes of several clusters (SiN with N=3-8, 10, 13, 20, and 21) using the local density approximation (LDA). For the smaller clusters (N=3-8) our results are in good agreement with previous quantum-chemical calculations and experimental measurements, establishing that LDA-based IR and Raman data can be used in conjunction with measured spectra to determine the structure of clusters observed in experiment. To illustrate the potential of the method for larger clusters, we present calculated IR and Raman data for two low-energy isomers of Si10 and for the lowest-energy structure of Si13 found to date. For the static response, we compare our calculated polarizabilities for N=10, 13, 20, and 21 to recent experimental measurements. The calculated results are in rough agreement with experiment, but show less variation with cluster size than the measurements. Taken together, our results show that LDA calculations can offer a powerful means for establishing the structures of experimentally fabricated clusters and nanoscale systems

Thyroid Hormone Promotes Remodeling of Coronary Resistance Vessels

Low thyroid hormone (TH) function has been linked to impaired coronary blood flow, reduced density of small arterioles, and heart failure. Nonetheless, little is known about the mechanisms by which THs regulate coronary microvascular remodeling. The current study examined the initial cellular events associated with coronary remodeling induced by triiodothyronine (T3) in hypothyroid rats. Rats with established hypothyroidism, eight weeks after surgical thyroidectomy (TX), were treated with T3 for 36 or 72 hours. The early effects of T3 treatment on coronary microvasculature were examined morphometrically. Gene expression changes in the heart were assessed by quantitative PCR Array. Hypothyroidism resulted in arteriolar atrophy in the left ventricle. T3 treatment rapidly induced small arteriolar muscularization and, within 72 hours, restored arteriolar density to control levels. Total length of the capillary network was not affected by TX or T3 treatment. T3 treatment resulted in the coordinate regulation of Angiopoietin 1 and 2 expression. The response of Angiopoietins was consistent with vessel enlargement. In addition to the well known effects of THs on vasoreactivity, these results suggest that THs may affect function of small resistance arteries by phenotypic remodeling of vascular smooth muscle cells (VSMC)

The CALBC Silver Standard Corpus for Biomedical Named Entities - A Study in Harmonizing the Contributions from Four Independent Named Entity Taggers

The production of gold standard corpora is time-consuming and costly. We propose an alternative: the 'silver standard corpus' (SSC), a corpus that has been generated by the harmonisation of the annotations that have been delivered from a selection of annotation systems. The systems have to share the type system for the annotations and the harmonisation solution has use a suitable similarity measure for the pair-wise comparison of the annotations. The annotation systems have been evaluated against the harmonised set (630.324 sentences, 15, 956, 841 tokens). We can demonstrate that the annotation of proteins and genes shows higher diversity across all used annotation solutions leading to a lower agreement against the harmonised set in comparison to the annotations of diseases and species. An analysis of the most frequent annotations from all systems shows that a high agreement amongst systems leads to the selection of terms that are suitable to be kept in the harmonised set. This is the first large-scale approach to generate an annotated corpus from automated annotation systems. Further research is required to understand, how the annotations from different systems have to be combined to produce the best annotation result for a harmonised corpus

Surface reconstruction induced geometries of Si clusters

We discuss a generalization of the surface reconstruction arguments for the structure of intermediate size Si clusters, which leads to model geometries for the sizes 33, 39 (two isomers), 45 (two isomers), 49 (two isomers), 57 and 61 (two isomers). The common feature in all these models is a structure that closely resembles the most stable reconstruction of Si surfaces, surrounding a core of bulk-like tetrahedrally bonded atoms. We investigate the energetics and the electronic structure of these models through first-principles density functional theory calculations. These models may be useful in understanding experimental results on the reactivity of Si clusters and their shape as inferred from mobility measurements.Comment: 9 figures (available from the author upon request) Submitted to Phys. Rev.