Plant speciation in the Namib Desert : potential origin of a widespread derivative species from a narrow endemic

This research was funded in part by the award of a Natural Environment Research Council (NERC) CASE research studentship to J.J.M.Background:  Parapatric (or ‘budding’) speciation is increasingly recognised as an important phenomenon in plant evolution but its role in extreme (e.g. desert) environments is poorly documented.  Aims:  To test this speciation model in a hypothesised sister pair, the Southwest – North African disjunct Senecio flavus and its putative progenitor, the Namibian Desert endemic S. englerianus.  Methods:  Phylogenetic inferences were combined with niche divergence tests, morphometrics, and experimental-genetic approaches. We also evaluated the potential role of an African Dry Corridor (ADC) in promoting the hypothesised northward expansion of S. flavus (from Namibia), using palaeodistribution models.  Results:  Belonging to an isolated (potential ‘relict’) clade, the two morphologically distinct species showed pronounced niche divergence in Namibia and signs of digenic-epistatic hybrid incompatibility (based on F2 pollen fertility). The presence of ‘connate-fluked’ pappus hairs in S. flavus, likely increasing dispersal ability, is controlled by a single gene locus.  Conclusions:  Our results provide evidence for a possible (and rare) example of ‘budding’ speciation in which a wider-ranged derivative (S. flavus) originated at the periphery of a smaller-ranged progenitor (S. englerianus) in the Namib Desert region. The Southwest – North African disjunction of S. flavus could have been established by dispersal across intermediate ADC areas during periods of (Late) Pleistocene aridification.Publisher PDFPeer reviewe

Generarized Cubic Model for BaTiO3_3-like Ferroelectric Substance

We propose an order-disorder type microscopic model for BaTiO$_3$-like Ferroelectric Substance. Our model has three phase transitions and four phases. The symmetry and directions of the polarizations of the ordered phases agree with the experimental results of BaTiO$_3$. The intermediate phases in our model are known as an incompletely ordered phase, which appears in a generalized clock model.Comment: 6 pages, 4figure

Hybridisation and detection of a hybrid zone between mesic and desert ragworts (Senecio) across an aridity gradient in the eastern Mediterranean

Background: Hybrid zones provide excellent opportunities for studying plant adaptation and speciation. Aims: We tested whether two herbaceous species of Senecio, S. vernalis and S. glaucus, hybridise in the eastern Mediterranean region and form a hybrid zone across an aridity gradient in the Jordan Rift Valley. Methods: Allozyme variation surveyed across both species was analysed by the programme STRUCTURE to assign individuals to genetic groups and determine levels of admixture. Populations in the Jordan Rift Valley were subsequently subjected to a cline analysis. Results: STRUCTURE showed that interspecific hybrids were produced at low frequency along the Israeli coastal plain where S. glaucus is represented by ssp. glaucus. In contrast, hybrids were more commonly produced in central populations of the Jordan Rift Valley. Here, the two species form a hybrid zone with S. vernalis occurring in mesic sites to the north and S. glaucus (ssp. coronopifolius) in arid sites to the south. Cline analysis showed that the hybrid zone is centred towards the northern end of the Dead Sea, but the analysis failed to distinguish how it is maintained. Conclusions: Future detailed genetic and ecological analysis of the Senecio hybrid zone should improve our understanding of plant adaptation and speciation across aridity gradients

The Energetics of Li Off-Centering in K1−x_{1-x}Lix_xTaO3_3; First Principles Calculations

K$_{1-x}$Li$_{x}$TaO$_3$ (KLT) solid solutions exhibit a variety of interesting physical phenomena related to large displacements of Li-ions from ideal perovskite A-site positions. First-principles calculations for KLT supercells were used to investigate these phenomena. Lattice dynamics calculations for KLT exhibit a Li off-centering instability. The energetics of Li-displacements for isolated Li-ions and for Li-Li pairs up to 4th neighbors were calculated. Interactions between nearest neighbor Li-ions, in a Li-Li pair, strongly favor ferroelectric alignment along the pair axis. Such Li-Li pairs can be considered "seeds" for polar nanoclusters in KLT. Electrostriction, local oxygen relaxation, coupling to the KT soft-mode, and interactions with neighboring Li-ions all enhance the polarization from Li off-centering. Calculated hopping barriers for isolated Li-ions and for nearest neighbor Li-Li pairs are in good agreement with Arrhenius fits to experimental dielectric data.Comment: 14 pages including 10 figures. To Physical Review B. Replaced after corrections due to referees' remark

A novel theranostic gold nanorods- and adriamycin-loaded micelle for EpCA M targeting, laser ablation, and photoacoustic imaging of cancer stem cells in hepatocellular carcinoma

Introduction and purpose: Cancer stem cells (CSCs) present a higher capacity to evade being killed by cancer agents and developing chemoresistance, thus leading to failure of conventional anticancer therapeutics. Nanomaterials specifically designed for targeting and treating not only tumor cells, but also CSCs, may encompass therapeutic and diagnostic tools, thus successfully eradicating the tumor. Materials and methods: Polymeric micelles simultaneously loaded with gold nanorods (GNRs) and Adriamycin were prepared and used as a novel therapeutic and diagnostic weapon. Epithelial cell adhesion molecule (EpCAM) is an important CSC surface marker and has been exploited in this work as an active targeting agent. Photoacoustic imaging was applied for GNR individuation and tissue recognition. Results: The nanosystem was demonstrated to be able to elicit effective targeting of cancer cells and cause their killing, in particular under laser ablation. Moreover, ex vivo photoacoustic imaging is able to clearly identify tumor regions thanks to GNR\u2019s contrast. Conclusion: The nanosystem can be considered a powerful and promising theranostic weapon for hepatocellular carcinoma treatment

Testing the daytime oxidizing capacity of the troposphere: 1994 OH field campaign at the Izaña Observatory, Tenerife

A field campaign was carried out during May 1994 at the Izaña station, Tenerife. This campaign was part of the program Environment and Climate sponsored by the European Commission to study the influence of European emissions on the oxidizing capacity of a clean tropospheric environment. Daytime and also nighttime measurements were made, covering the OH as well as the NO3 chemistry. This paper presents the OH measurements taken with a multipass optical absorption spectrometer (MOAS) and discusses the daytime chemistry in a statistical and therefore more preliminary way. All relevant parameters influencing the OH concentration were monitored. From the data the two main contributions to the OH production can clearly be discerned and are given by the primary production following the ozone photolysis and the O(1D)-H2O reaction and by the catalytic reactions of NOx in the recycling process. The latter processes prove to contribute a dominant part to the OH concentration. The measurements of the nonmethane hydrocarbons (NMHC) especially of the biogenics, indicate a considerable influence of the NMHC on the absolute values of the OH concentration at Tenerife.This work has been financially supported by the European Commission (grant EV5V-CT93-0321), by the DFG, and by the Fonds der Chemischen Industrie, which is gratefully acknowledged

Dynamics of cubic-tetragonal phase transition in KNbO3_3 perovskite

The low-energy part of the vibration spectrum in KNbO$_3$ was studied by cold neutron inelastic scattering in the cubic phase. In addition to acoustic phonons, we observe strong diffuse scattering, which consists of two components. The first one is quasi-static and has a temperature-independent intensity. The second component appears as quasi-elastic scattering in the neutron spectrum indicating a dynamic origin. From analysis of the inelastic data we conclude that the quasi-elastic component and the acoustic phonon are mutually coupled. The susceptibility associated with the quasi-elastic component grows as the temperature approaches T$_C$

Polarization Dependence of Born Effective Charge and Dielectric Constant in KNbO3_3

The Born effective charge Z^{*} and dielectric tensor \epsilon_{\infty} of KNbO_3 are found to be very sensitive to the atomic geometry, changing by as much as 27% between the paraelectric cubic and ferroelectric tetragonal and rhombohedral phases. Subtracting the bare ionic contribution reveals changes of the dynamic component of Z^{*} as large as 50%, for atomic displacements that are typically only a few percent of the lattice constant. Z^{*}, \epsilon_{\infty} and all phonon frequencies at the Brillouin zone center were calculated using the {\it ab initio} linearized augmented plane-wave linear response method with respect to the reference cubic, experimental tetragonal, and theoretically determined rhombohedral ground state structures. The ground state rhombohedral structure of KNbO_3 was determined by minimizing the forces on the relaxed atoms. By contrast with the cubic structure, all zone center phonon modes of the rhombohedral structure are stable and their frequencies are in good agreement with experiment. In the tetragonal phase, one of the soft zone center modes in the cubic phase is stablized. In view of the small atomic displacements involved in the ferroelectric transitions, it is evident that not only the soft mode frequencies but also the Born effective charge and dielectric constants are very sensitive to the atomic geometry.Comment: 26 pages, revtex, no figures; to appear in Phys. Rev. B15 (Oct.), 199