Fate of Quasiparticles at High Temperature in the Correlated Metal Sr_{2}RuO_{4}

We study the temperature evolution of quasiparticles in the correlated metal Sr_{2}RuO_{4}. Our angle resolved photoemission data show that quasiparticles persist up to temperatures above 200 K, far beyond the Fermi liquid regime. Extracting the quasiparticle self-energy, we demonstrate that the quasiparticle residue Z increases with increasing temperature. Quasiparticles eventually disappear on approaching the bad metal state of Sr_{2}RuO_{4} not by losing weight but via excessive broadening from super-Planckian scattering. We further show that the Fermi surface of Sr_{2}RuO_{4}-defined as the loci where the spectral function peaks-deflates with increasing temperature. These findings are in semiquantitative agreement with dynamical mean field theory calculations.

Mott insulators with boundary zeros

The topological classification of electronic band structures is based on symmetry properties of Bloch eigenstates of single-particle Hamiltonians. In parallel, topological field theory has opened the doors to the formulation and characterization of non-trivial phases of matter driven by strong electron-electron interaction. Even though important examples of topological Mott insulators have been constructed, the relevance of the underlying non-interacting band topology to the physics of the Mott phase has remained unexplored. Here, we show that the momentum structure of the Green's function zeros defining the "Luttinger surface" provides a topological characterization of the Mott phase related, in the simplest description, to the one of the single-particle electronic dispersion. Considerations on the zeros lead to the prediction of new phenomena: a topological Mott insulator with an inverted gap for the bulk zeros must possess gapless zeros at the boundary, which behave as a form of "topological antimatter" annihilating conventional edge states. Placing band and Mott topological insulators in contact produces distinctive observable signatures at the interface, revealing the otherwise spectroscopically elusive Green's function zeros.

Distinct spin and orbital dynamics in Sr2RuO4

The unconventional superconductor Sr2RuO4 has long served as a benchmark for theories of correlated-electron materials. The determination of the superconducting pairing mechanism requires detailed experimental information on collective bosonic excitations as potential mediators of Cooper pairing. We have used Ru L3-edge resonant inelastic x-ray scattering to obtain comprehensive maps of the electronic excitations of Sr2RuO4 over the entire Brillouin zone. We observe multiple branches of dispersive spin and orbital excitations associated with distinctly different energy scales. The spin and orbital dynamical response functions calculated within the dynamical mean-field theory are in excellent agreement with the experimental data. Our results highlight the Hund metal nature of Sr2RuO4 and provide key information for the understanding of its unconventional superconductivity.

Epigenetic and phenotypic characterization of iPSCs-derived smooth muscle cells: towards a cellular model for complex arterial diseases

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): European Research Council

Introduction

Smooth muscle cells (SMCs) capacity to switch between proliferative (synthetic) and quiescent (contractile) phenotypes is a widely studied mechanism in cardiovascular disease. Primary SMCs tend to lose many physiological features in culture, which makes the study of their contractile function challenging. Recently, an optimized protocol of induced pluripotent stem cells (iPSCs) differentiation into contractile SMCs was described.

Purpose

We aimed at obtaining a deep characterization of cellular phenotypes during the differentiation into synthetic or contractile SMCs, and evaluate these cellular models in the context of complex cardiovascular diseases.

Methods

We differentiated 4 human iPSC lines (2 males, 2 females) towards either contractile (Repsox induced) or synthetic (PDGF-BB/TGF-β induced) SMC phenotypes using a 24-days protocol (Figure). We performed RNA-Seq and assay for transposase accessible chromatin (ATAC)-Seq at 6 time points of differentiation. We compared gene expression and open chromatin profiles between them and to existing datasets of primary human SMCs and artery tissues. We characterized the extracellular matrix (matrisome) generated by SMCs using mass spectrometry.

Results

iPSCs derived SMCs showed expected morphology and positive expression of SMC markers. Synthetic SMCs exhibited greater capacity of proliferation, migration, lower contractility and calcium release capacity, compared to contractile SMCs. RNA-Seq results showed that multiple disease-associated genes involved in the contractile function of arteries, including smooth-muscle myosin heavy chain (MYH11), myosin light chain kinase (MYLK) and angiotensin type 1 receptor (AGTR1) genes, were highly expressed in contractile compared to synthetic SMCs. Interestingly, multiple genes coding for extracellular matrix components were also enriched in contractile SMCs. Matrisome characterization confirmed that contractile SMCs generated a rich extracellular matrix, compared to synthetic cells.  Analysis of transcriptomic and open chromatin profiles suggests contractile SMCs retained a higher level of activity for transcription factors involved in vascular smooth muscle development. Synthetic SMCs however presented open chromatin profiles similar to cultured primary SMCs. Open chromatin regions of contractile SMCs were highly enriched for variants associated with vascular diseases such as hypertension and intracranial aneurysm, whereas synthetic SMCs were more enriched for variants associated to peripheral artery disease and aortic aneurysm.

Conclusions

Differentiation of SMCs from iPSCs using two complementary protocols provides valid cellular models suitable for the study of a variety of vascular diseases. Utilization of these cells in combination with genome-editing tools is a promising approach to the study of complex regulatory mechanisms at genetic risk loci while considering phenotypic variability of arterial cellular components.

Epigenetic regulation at LRP1 risk locus for cardiovascular diseases and assessment of cellular function in hiPSC derived smooth muscle cells

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Research Council (ERC)

Background/Introduction

Spontaneous coronary artery dissection (SCAD) is an increasingly recognized cause of myocardial infarction in young and middle-aged women. A common genetic variant, rs11172113, located in LRP1 (low density lipoprotein receptor-related protein 1) first intron, was associated with several vascular diseases, including SCAD, coronary artery disease and migraine. However, the biological mechanisms through which rs11172113 influence LRP1 function in the context of non-atherosclerotic arterial lesions is not fully understood.

Purpose

We aim at defining the specific mechanisms of rs11172113 genotype affecting LRP1 expression in contractile smooth muscle cells (SMCs), leading to alterations of their physiological function.

Methods

We applied in silico functional annotation to select variants and measured their enhancer activity using luciferase reporter assay in rat primary SMCs (A7r5). We performed siRNA knockdown of LRP1 and 4 transcription factors (TFs) predicted to interact with rs11172113 in human induced pluripotent stem cells (iPSCs) derived SMCs, harboring either synthetic or contractile phenotype. We edited iPSCs prior to differentiation using CRISPR-Cas9 to generate 100 bp deletion of the enhancer region containing rs11172113. We also created frame-shift indels in exons 2 or 5 of LRP1 in iPSCs to create SMCs knockouts and differentiated into SMCs. We then performed a proteomic and transcriptomic characterization of LRP1 knockout effect in these iPSC derived SMCs. We used a computational method of cell tracking and relative cell surface area change to characterize the contractility of LRP1 knockout effect in these iPSC derived SMCs. We performed the assessment of fluo-4 labeled Ca2+ mobilization to characterize the ability of calcium release in iPSC derived SMCs after LPR1 knockout.

Results

Seven variants in LRP1 locus co-located with enhancer (histone marks) and open chromatin regions (ATAC-Seq peaks) in SMCs and arterial tissues. Reporter assay in rat SMCs confirmed that rs11172113 belongs to a genomic region showing enhancer activity in vitro. iPSCs with homozygous deletion of rs11172113 enhancer region presented the same pluripotency compared with wild type, and iPSC derived SMCs showed positive expression of specific markers for each phenotype (ACTA2, TAGLN for both, MYH11 for contractile SMCs and CALM2 for synthetic SMCs). We found that the deletion of rs11172113 enhancer region decreased the expression of LRP1 while LRP1 knockdown increased cell migration capacity in SMCs. Preliminary results in LRP1-knockout iPSC-derived SMCs suggest LRP1 to enhance the expression of cell contraction markers and decrease capacity of cell proliferation.

Conclusions We confirmed rs11172113 to regulate LRP1 expression in iPSCs derived synthetic and contractile SMCs. Our results support LRP1 effect on SMCs cellular function alteration as a potential mechanism in genetic susceptibility for vascular disease.

Health promotion in Swiss municipalities: towards proportionate universalism

Background

Health promotion goes beyond the health sector. Municipalities, the local public authorities in Switzerland, have a crucial role to promote population health in all their decisions.

Initially developed by Promotion Santé Valais, the label “Healthy municipality” exists in the canton of Vaud since 2015. The label takes stock of existing measures in health promotion and prevention in all sectors and incentivise new interventions. The labelling process respects different criteria and is validated by an external committee. It is voluntarist, free of charge for the municipality but requires time and intersectoral communication. This abstract explores equity in the uptake of the label.

Results

In Vaud, 17 municipalities have been labelled “healthy”. Two external evaluations by Swiss universities highlighted that small villages are less involved in the label than urban areas. To achieve health equity, we need to identify and approach municipalities with limited human and financial resources, that might be less active in health promotion and/or whose population is socioeconomically disadvantaged. Preliminary results indicate that municipalities below 1000 inhabitants, in rural areas, should be targeted first. We are currently investigating the barriers and facilitators for them to enrol in the label.

Lessons

As labels rewarding healthy cities are expanding worldwide, it is important to document and reflect on who benefits from them, and who does not. Our practice is now focusing more on villages in rural areas, with less resources than urban settings. We investigate their needs regarding the type of support that we, public health professionals, can provide. Proportionate universalism principles should also apply to advocacy for health promotion, at the municipality level.

Key messages

To achieve health in all policies, the role of municipalities is essential. More efforts in health promotion should target specifically small and rural municipalities, with limited resources.

Probing spin correlations using angle-resolved photoemission in a coupled metallic/Mott insulator system

A nearly free electron metal and a Mott insulating state can be thought of as opposite ends of the spectrum of possibilities for the motion of electrons in a solid. Understanding their interaction lies at the heart of the correlated electron problem. In the magnetic oxide metal PdCrO₂, nearly free and Mott-localized electrons exist in alternating layers, forming natural heterostructures. Using angle-resolved photoemission spectroscopy, quantitatively supported by a strong coupling analysis, we show that the coupling between these layers leads to an "intertwined" excitation that is a convolution of the charge spectrum of the metallic layer and the spin susceptibility of the Mott layer. Our findings establish PdCrO₂ as a model system in which to probe Kondo lattice physics and also open new routes to use the a priori nonmagnetic probe of photoemission to gain insights into the spin susceptibility of correlated electron materials.

[Unilateral pigmentary retinopathy : about 2 cases]

We present the case of two patients in whom unilateral retinal involvement with pigmentary lesions on the fundus examination was observed. Apart from the unilateral nature of the lesions, a diagnosis of retinitis pigmentosa could have been made in view of the morphological and functional aspects of the retina. However, in these two clinical cases, an association between retinal lesions and Bartonella in one case, and pre-existing multiple sclerosis in the other case, has been proposed with a final diagnosis of unilateral pigmentary retinopathy. Nevertheless, a sufficiently long period of patient follow-up is necessary to rule out delayed onset in the unaffected eye, suggesting an asymmetrical bilateral retinitis pigmentosa.

Perspectives on the clonal persistence of presumed 'ghost' genomes in unisexual or allopolyploid taxa arising via hybridization

Although hybridization between non-sibling species rarely results in viable or fertile offspring, it occasionally produces self-perpetuating or sexually-parasitic lineages in which ancestral genomes are inherited clonally and thus may persist as ‘ghost species’ after ancestor extinction. Ghost species have been detected in animals and plants, for polyploid and diploid organisms, and across clonal, semi-clonal, and even sexual reproductive modes. Here we use a detailed investigation of the evolutionary and taxonomic status of a newly-discovered, putative ghost lineage (HX) in the fish genus Hypseleotris to provide perspectives on several important issues not previously explored by other studies on ghost species, but relevant to ongoing discussions about their detection, conservation, and artificial re-creation. Our comprehensive genetic (allozymes, mtDNA) and genomic (SNPs) datasets successfully identified a threatened sexual population of HX in one tiny portion of the extensive distribution displayed by two hemi-clonal HX-containing lineages. We also discuss what confidence should be placed on any assertion that an ancestral species is actually extinct, and how to assess whether any putative sexual ancestor represents a pure remnant, as shown here, or a naturally-occurring resurrection via the crossing of compatible clones or hemi-clones.

Conservation implications of turtle declines in Australia's Murray River system

Conservation requires rapid action to be effective, which is often difficult because of funding limitations, political constraints, and limited data. Turtles are among the world’s most endangered vertebrate taxa, with almost half of 356 species threatened with extinction. In Australia’s Murray River, nest predation by invasive foxes (Vulpes vulpes) was predicted to drive turtle declines in the 1980s. We assessed populations of the broad-shelled turtle (Chelodina expansa), eastern long-necked turtle (C. longicollis), and Murray River turtle (Emydura macquarii) in the Murray River and some of its associated waterways. Our results suggest that the predicted decline is occurring. All three species are rare in the lower Murray River region, and were undetected in many locations in South Australia. Moreover, E. macquarii had considerable population aging almost everywhere, possibly due to comprehensive nest destruction by foxes. Chelodina longicollis also had population aging at some sites. Sustained low recruitment has potential to lead to collapses as turtles age, which is particularly worrying because it was predicted over 30 years ago and may have already occurred in South Australia. Our results show that turtle declines were not mitigated since that prediction. If the crash continues, a vertebrate guild responsible for considerable nutrient cycling in the aquatic ecosystem will disappear. Our results highlight a worst-case outcome when species declines are predicted, but insufficiently mitigated.

Hallmarks of Hunds coupling in the Mott insulator Ca2RuO4

A paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling is realized in Ca₂RuO₄. Progress in understanding the nature of this Mott insulating phase has been impeded by the lack of knowledge about the low-energy electronic structure. Here we provide—using angle-resolved photoemission electron spectroscopy—the band structure of the paramagnetic insulating phase of Ca₂RuO₄ and show how it features several distinct energy scales. Comparison to a simple analysis of atomic multiplets provides a quantitative estimate of the Hund's coupling J=0.4 eV. Furthermore, the experimental spectra are in good agreement with electronic structure calculations performed with Dynamical Mean-Field Theory. The crystal field stabilization of the d_xy orbital due to c-axis contraction is shown to be essential to explain the insulating phase. These results underscore the importance of multi-band physics, Coulomb interaction and Hund's coupling that together generate the Mott insulating state of Ca₂RuO₄.

Detailed knowledge of the low-energy electronic structure is required to understand the Mott insulating phase of Ca₂RuO₄. Here, Sutter et al. provide directly the experimental band structure of the paramagnetic insulating phase of Ca₂RuO₄ and unveil the electronic origin of its Mott phase.

Theory of Laser-Controlled Competing Superconducting and Charge Orders

We investigate the nonequilibrium dynamics of competing coexisting superconducting (SC) and charge-density wave (CDW) orders in an attractive Hubbard model. A time-periodic laser field A[over →](t) lifts the SC-CDW degeneracy, since the CDW couples linearly to the field (A[over →]), whereas SC couples in second order (A[over →]^{2}) due to gauge invariance. This leads to a striking resonance: When the photon energy is red detuned compared to the equilibrium single-particle energy gap, CDW is enhanced and SC is suppressed, while this behavior is reversed for blue detuning. Both orders oscillate with an emergent slow frequency, which is controlled by the small amplitude of a third induced order, namely η pairing, given by the commutator of the two primary orders. The induced η pairing is shown to control the enhancement and suppression of the dominant orders. Finally, we demonstrate that light-induced superconductivity is possible starting from a predominantly CDW initial state.

[PERIOPERATIVE VISUAL LOSS AFTER SPINE SURGERY: A CASE REPORT]

Perioperative visual loss is a rare but devastating complication that may follow spine surgery in the prone position. So far, the incidence, mechanisms and risk factors have not been clearly established. Most commonly, the visual loss results from an ischemic optic neuropathy. We describe the case of a 68 year-old woman who underwent a lumbar laminectomy in the prone position. Upon recovery from anesthesia, the patient complained of total left blindness. This visual loss was, slowly and only partially, recovered after 72 hours. We discuss the most common causes of postoperative visual loss, the risk factors and preventive strategy.

Digestion of cooked meat proteins is slightly affected by age as assessed using the dynamic gastrointestinal TIM model and mass spectrometry

The main goal of the present study was to compare the degradation of meat proteins in adult and elderly digestive conditions.

Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5

Terahertz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structures. In complex oxides, this method has been used to melt electronic order, drive insulator-to-metal transitions and induce superconductivity. Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature (300 kelvin) in YBa2Cu3O6+x (refs 9, 10). Here we report the crystal structure of this exotic non-equilibrium state, determined by femtosecond X-ray diffraction and ab initio density functional theory calculations. We find that nonlinear lattice excitation in normal-state YBa2Cu3O6+x at above the transition temperature of 52 kelvin causes a simultaneous increase and decrease in the Cu-O2 intra-bilayer and, respectively, inter-bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause drastic changes in the electronic structure. Among these, the enhancement in the character of the in-plane electronic structure is likely to favour superconductivity.

Coherent quasiparticles with a small fermi surface in lightly doped Sr(3)Ir(2)O(7)

We characterize the electron doping evolution of (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3x/2, where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z≈0.5 in lightly doped Sr_{3}Ir_{2}O_{7}.

Peltier cooling of fermionic quantum gases

We propose a cooling scheme for fermionic quantum gases, based on the principles of the Peltier thermoelectric effect and energy filtering. The system to be cooled is connected to another harmonically trapped gas acting as a reservoir. The cooling is achieved by two simultaneous processes: (i) the system is evaporatively cooled, and (ii) cold fermions from deep below the Fermi surface of the reservoir are injected below the Fermi level of the system, in order to fill the "holes" in the energy distribution. This is achieved by a suitable energy dependence of the transmission coefficient connecting the system to the reservoir. The two processes can be viewed as simultaneous evaporative cooling of particles and holes. We show that both a significantly lower entropy per particle and faster cooling rate can be achieved in this way than by using only evaporative cooling.

Optical response of Sr2RuO4 reveals universal fermi-liquid scaling and quasiparticles beyond Landau theory

We report optical measurements demonstrating that the low-energy relaxation rate (1/τ) of the conduction electrons in Sr(2)RuO(4) obeys scaling relations for its frequency (ω) and temperature (T) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, 1/τ ∝ (ħω)(2)+(pπk(B)T)(2) with p = 2, and ω/T scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing "resilient" quasiparticle excitations above the Fermi energy.

Investigating underage youth access to alcohol in Switzerland: inventory of modes of access and association with youth characteristics

AIMS

While laws restrict alcohol access to youth under the age of 16/18 (fermented/distilled beverages) in Switzerland, direct underage accessibility is high. Focusing on underage youth, our study presents an inventory of primary and alternative modes of access to alcohol and investigates associations with youth characteristics.

METHODS

Data were collected using semi-structured interviews and self-report questionnaires. In total, 223 underage youth aged 15-17 years were interviewed.

RESULTS

Overall, about half of the participants reported illegal commercial purchase, either direct or by underage peer, in on- (49.3%) and/or off-premise (48.0%) contexts. Off-premise purchase by proxy of legal age (30.5%; excluding shoulder-tapping), social supply off-premise (i.e. receiving/exchanging alcohol; 26.5%) and direct purchases in on- (13.9%) and off-premise (11.2%) contexts were the most recurrent primary modes of access. Significant associations of direct purchases with frequency of consumption and perceived alcohol availability were recorded. Associations between primary and alternative ways to access alcohol, in particular, between on-premise modes, were also evidenced.

CONCLUSION

Providing an overview of the context of underage alcohol access in Switzerland and an indirect view of youth perceptions of limitations of existing structural measures has identified particularly the need for enforcement of existing legislation.

Theoretical prediction and spectroscopic fingerprints of an orbital transition in CeCu2Si2

We show that the heavy-fermion compound CeCu2Si2 undergoes a transition between two regimes dominated by different crystal-field states. At low pressure P and low temperature T the Ce 4f electron resides in the atomic crystal-field ground state, while at high P or T, the electron occupancy and spectral weight is transferred to an excited crystal-field level that hybridizes more strongly with itinerant states. These findings result from first-principles dynamical-mean-field-theory calculations. We predict experimental signatures of this orbital transition in x-ray spectroscopy. The corresponding fluctuations may be responsible for the second high-pressure superconducting dome observed in this and similar materials.

Raman-scattering measurements and theory of the energy-momentum spectrum for underdoped Bi2Sr2CaCuO(8+δ) superconductors: evidence of an s-wave structure for the pseudogap

We reveal the full energy-momentum structure of the pseudogap of underdoped high-Tc cuprate superconductors. Our combined theoretical and experimental analysis explains the spectral-weight suppression observed in the B2g Raman response at finite energies in terms of a pseudogap appearing in the single-electron excitation spectra above the Fermi level in the nodal direction of momentum space. This result suggests an s-wave pseudogap (which never closes in the energy-momentum space), distinct from the d-wave superconducting gap. Recent tunneling and photoemission experiments on underdoped cuprates also find a natural explanation within the s-wave pseudogap scenario.

Comparing and combining distance-based and character-based approaches for barcoding turtles

Molecular barcoding can serve as a powerful tool in wildlife forensics and may prove to be a vital aid in conserving organisms that are threatened by illegal wildlife trade, such as turtles (Order Testudines). We produced cytochrome oxidase subunit one (COI) sequences (650 bp) for 174 turtle species and combined these with publicly available sequences for 50 species to produce a data set representative of the breadth of the order. Variability within the barcode region was assessed, and the utility of both distance-based and character-based methods for species identification was evaluated. For species in which genetic material from more than one individual was available (n = 69), intraspecific divergences were 1.3% on average, although divergences greater than the customary 2% barcode threshold occurred within 15 species. High intraspecific divergences could indicate species with a high degree of internal genetic structure or possibly even cryptic species, although introgression is also probable in some of these taxa. Divergences between species of the same genus were 6.4% on average; however, 49 species were <2% divergent from congeners. Low levels of interspecific divergence could be caused by recent evolutionary radiations coupled with the low rates of mtDNA evolution previously observed in turtles. Complementing distance-based barcoding with character-based methods for identifying diagnostic sets of nucleotides provided better resolution in several cases where distance-based methods failed to distinguish species. An online identification engine was created to provide character-based identifications. This study constitutes the first comprehensive barcoding effort for this seriously threatened order.

Fermi-liquid behavior of the normal phase of a strongly interacting gas of cold atoms

We measure the magnetic susceptibility of a Fermi gas with tunable interactions in the low-temperature limit and compare it to quantum Monte Carlo calculations. Experiment and theory are in excellent agreement and fully compatible with the Landau theory of Fermi liquids. We show that these measurements shed new light on the nature of the excitations of the normal phase of a strongly interacting Fermi gas.

Quantitative determination of temperature in the approach to magnetic order of ultracold fermions in an optical lattice

We perform a quantitative simulation of the repulsive Fermi-Hubbard model using an ultracold gas trapped in an optical lattice. The entropy of the system is determined by comparing accurate measurements of the equilibrium double occupancy with theoretical calculations over a wide range of parameters. We demonstrate the applicability of both high-temperature series and dynamical mean-field theory to obtain quantitative agreement with the experimental data. The reliability of the entropy determination is confirmed by a comprehensive analysis of all systematic errors. In the center of the Mott insulating cloud we obtain an entropy per atom as low as 0.77k(B) which is about twice as large as the entropy at the Néel transition. The corresponding temperature depends on the atom number and for small fillings reaches values on the order of the tunneling energy.

Sex chromosome evolution in lizards: independent origins and rapid transitions

Reptiles epitomize the variability of reproductive and sex determining modes and mechanisms among amniotes. These modes include gonochorism (separate sexes) and parthenogenesis, oviparity, viviparity, and ovoviviparity, genotypic sex determination (GSD) with male (XX/XY) and female (ZZ/ZW) heterogamety and temperature-dependent sex determination (TSD). Lizards (order Squamata, suborder Sauria) are particularly fascinating because the distribution of sex-determining mechanisms shows no clear phylogenetic segregation. This implies that there have been multiple transitions between TSD and GSD, and between XY and ZW sex chromosome systems. Approximately 1,000 species of lizards have been karyotyped and among those, fewer than 200 species have sex chromosomes, yet they display remarkable diversity in morphology and degree of degeneration. The high diversity of sex chromosomes as well as the presence of species with TSD, imply multiple and independent origins of sex chromosomes, and suggest that the mechanisms of sex determination are extremely labile in lizards. In this paper, we review the current state of knowledge of sex chromosomes in lizards and the distribution of sex determining mechanisms and sex chromosome forms within and among families. We establish for the first time an association between the occurrence of female heterogamety and TSD within lizard families, and propose mechanisms by which female heterogamety and TSD may have co-evolved. We suggest that lizard sex determination may be much more the result of an interplay between sex chromosomes and temperature than previously thought, such that the sex determination mode is influenced by the nature of heterogamety as well as temperature sensitivity and the stage of sex chromosome degeneration.

DNA detective: a review of molecular approaches to wildlife forensics

Illegal trade of wildlife is growing internationally and is worth more than USD$20 billion per year. DNA technologies are well suited to detect and provide evidence for cases of illicit wildlife trade yet many of the methods have not been verified for forensic applications and the diverse range of methods employed can be confusing for forensic practitioners. In this review, we describe the various genetic techniques used to provide evidence for wildlife cases and thereby exhibit the diversity of forensic questions that can be addressed using currently available genetic technologies. We emphasise that the genetic technologies to provide evidence for wildlife cases are already available, but that the research underpinning their use in forensics is lacking. Finally we advocate and encourage greater collaboration of forensic scientists with conservation geneticists to develop research programs for phylogenetic, phylogeography and population genetics studies to jointly benefit conservation and management of traded species and to provide a scientific basis for the development of forensic methods for the regulation and policing of wildlife trade.

Nodal-antinodal dichotomy and the two gaps of a superconducting doped Mott insulator

We study the superconducting state of the hole-doped two-dimensional Hubbard model using cellular dynamical mean-field theory, with the Lanczos method as impurity solver. In the underdoped regime, we find a natural decomposition of the one-particle (photoemission) energy gap into two components. The gap in the nodal regions, stemming from the anomalous self-energy, decreases with decreasing doping. The antinodal gap has an additional contribution from the normal component of the self-energy, inherited from the normal-state pseudogap, and it increases as the Mott insulating phase is approached.

Impact of cutting and sheep grazing on ground-active spiders and carabids in intertidal salt marshes (Western France)

The aims of this study were to characterize spider (Araneae) and ground beetle (Coleoptera Carabidae) communities in managed (cutting and sheep grazing) and non-managed salt marshes and to assess the efficiency of management regimes in these particular ecosystems. The two groups were studied during 2002 in salt marshes of the Mont Saint-Michel Bay (NW France) using pitfall traps. By opening soil and vegetation structures cutting and grazing enhanced the abundances of some halophilic species of spiders and ground beetles. Nevertheless, grazing appeared to be too intensive as spider species richness decreased. We discuss the implications of management practices in terms of nature conservation and their application in the particular area of intertidal salt marshes.

[About a case of congenital hypothyroidism]

A boy presented at birth dyspnea, jaundice, meteorism and hypospadias; biochemical testing revealed hyponatremia. He benefited on day 4 of neonatal screening for hypothyroidism and congenital adrenal hyperplasia (CAH) and assays showed high concentrations of 17-OHP and TSH. Because of clinical features and hyponatremia, the diagnosis of CAH was plausible. A serum control (17-OHP and TSH) carried out on day 8 showed a normal concentration of 17-OHP and a persistently elevated concentration of TSH confirmed by a second assay a few days later. A 131I scan of neck revealed an ectopic lingual thyroid. The considerable progression of false positive screening tests for CAH is mainly due to the increasing number of premature babies. We show by a retrospective analysis (7 yrs), that children with hypothyroidism also present frequently higher concentrations of 17-OHP than normal children. However, whatever the aetiology (apart from CAH), the concentrations of 17-OHP rapidly normalise.