Sub-Terahertz Monochromatic Transduction with Semiconductor Acoustic Nanodevices

We demonstrate semiconductor superlattices or nanocavities as narrow band acoustic transducers in the sub-terahertz range. Using picosecond ultrasonics experiments in the transmission geometry with pump and probe incident on opposite sides of the thick substrate, phonon generation and detection processes are fully decoupled. Generating with the semiconductor device and probing on the metal, we show that both superlattices and nanocavities generate spectrally narrow wavepackets of coherent phonons with frequencies in the vicinity of the zone center and time durations in the nanosecond range, qualitatively different from picosecond broadband pulses usually involved in picosecond acoustics with metal generators. Generating in the metal and probing on the nanoacoustic device, we furthermore evidence that both nanostructured semiconductor devices may be used as very sensitive and spectrally selective detectors

First-generation linkage map for the European tree frog (Hyla arborea) with utility in congeneric species.

BACKGROUND: Western Palearctic tree frogs (Hyla arborea group) represent a strong potential for evolutionary and conservation genetic research, so far underexploited due to limited molecular resources. New microsatellite markers have recently been developed for Hyla arborea, with high cross-species utility across the entire circum-Mediterranean radiation. Here we conduct sibship analyses to map available markers for use in future population genetic applications. FINDINGS: We characterized eight linkage groups, including one sex-linked, all showing drastically reduced recombination in males compared to females, as previously documented in this species. Mapping of the new 15 markers to the ~200 My diverged Xenopus tropicalis genome suggests a generally conserved synteny with only one confirmed major chromosome rearrangement. CONCLUSIONS: The new microsatellites are representative of several chromosomes of H. arborea that are likely to be conserved across closely-related species. Our linkage map provides an important resource for genetic research in European Hylids, notably for studies of speciation, genome evolution and conservation

The molecular and dusty composition of Betelgeuse's inner circumstellar environment

The study of the atmosphere of red supergiant stars in general and of Betelgeuse (alpha Orionis) in particular is of prime importance to understand dust formation and how mass is lost to the interstellar medium in evolved massive stars. A molecular shell, the MOLsphere (Tsuji, 2000a), in the atmosphere of Betelgeuse has been proposed to account for the near- and mid-infrared spectroscopic observations of Betelgeuse. The goal is to further test this hypothesis and to identify some of the molecules in this MOLsphere. We report on measurements taken with the mid-infrared two-telescope beam combiner of the VLTI, MIDI, operated between 7.5 and 13.5 $\mu$m. The data are compared to a simple geometric model of a photosphere surrounded by a warm absorbing and emitting shell. Physical characteristics of the shell are derived: size, temperature and optical depth. The chemical constituents are determined with an analysis consistent with available infrared spectra and interferometric data. We are able to account for the measured optical depth of the shell in the N band, the ISO-SWS spectrum and K and L band interferometric data with a shell whose inner and outer radii are given by the above range and with the following species: H2O, SiO and Al2O3. These results confirm the MOLsphere model. We bring evidence for more constituents and for the presence of species participating in the formation of dust grains in the atmosphere of the star, i.e. well below the distance at which the dust shell is detected. We believe these results bring key elements to the understanding of mass loss in Betelgeuse and red supergiants in general and bring support to the dust-driven scenario.Comment: 11 pages, 10 figures, accepted for publication in A&

Dirac neutrino mass from the beta decay end-point modified by the dynamics of a Lorentz-violating equation of motion

Using a generalized procedure for obtaining the equation of motion of a propagating fermionic particle, we examine previous claims for a lightlike preferred axis embedded in the framework of Lorentz-invariance violation with preserved algebra. In a high energy scale, the corresponding equation of motion is reduced to a conserving lepton number chiral (VSR) equation, and in a low energy scale, the Dirac equation for a free is recovered. The new dynamics introduces some novel ingredients (modified cross section) to the phenomenology of the tritium beta decay end-point.Comment: 11 pages, 4 figure

Range-Wide Sex-Chromosome Sequence Similarity Supports Occasional XY Recombination in European Tree Frogs (Hyla arborea).

In contrast with mammals and birds, most poikilothermic vertebrates feature structurally undifferentiated sex chromosomes, which may result either from frequent turnovers, or from occasional events of XY recombination. The latter mechanism was recently suggested to be responsible for sex-chromosome homomorphy in European tree frogs (Hyla arborea). However, no single case of male recombination has been identified in large-scale laboratory crosses, and populations from NW Europe consistently display sex-specific allelic frequencies with male-diagnostic alleles, suggesting the absence of recombination in their recent history. To address this apparent paradox, we extended the phylogeographic scope of investigations, by analyzing the sequences of three sex-linked markers throughout the whole species distribution. Refugial populations (southern Balkans and Adriatic coast) show a mix of X and Y alleles in haplotypic networks, and no more within-individual pairwise nucleotide differences in males than in females, testifying to recurrent XY recombination. In contrast, populations of NW Europe, which originated from a recent postglacial expansion, show a clear pattern of XY differentiation; the X and Y gametologs of the sex-linked gene Med15 present different alleles, likely fixed by drift on the front wave of expansions, and kept differentiated since. Our results support the view that sex-chromosome homomorphy in H. arborea is maintained by occasional or historical events of recombination; whether the frequency of these events indeed differs between populations remains to be clarified

Are invasive marsh frogs (Pelophylax ridibundus) replacing the native P. lessonae /P. esculentus hybridogenetic complex in Western Europe? Genetic evidence from a field study.

The water-frog L-E system, widespread in Western Europe, comprises the pool frog Pelophylax lessonae and the hybridogenetic edible frog P. esculentus, which originated from hybridization between pool frogs and marsh frogs (P. ridibundus). In P. esculentus, the lessonae (L) genome is eliminated during meiosis and has to be gained anew each generation from a P. lessonae partner, while the ridibundus (R') genome is transmitted clonally. It therefore accumulates deleterious mutations, so that R'R' offspring from P. esculentus x P. esculentus crosses are normally unviable. This system is now threatened by invasive P. ridibundus (RR) imported from Eastern Europe and the Balkans. We investigated the genetic interactions between invasive marsh frogs and native water frogs in a Swiss wetland area, and used genetic data collected in the field to validate several components of a recently postulated mechanism of species replacement. We identified neo-ridibundus individuals derived from crosses between invasive ridibundus and native esculentus, as well as newly arisen hybridogenetic esculentus lineages stemming from crosses between invasive ridibundus (RR) and native lessonae (LL). As their ridibundus genomes are likely to carry less deleterious mutations, such lineages are expected to produce viable ridibundus offspring, contributing to species replacement. However, such crosses with invasive ridibundus only occurred at a limited scale; moreover, RR x LL crosses did not induce any introgression from the ridibundus to the lessonae genome. We did not find any ridibundus stemming from crosses between ancient esculentus lineages. Despite several decades of presence on the site, introduced ridibundus individuals only represent 15% of sampled frogs, and their spatial distribution seems shaped by specific ecological requirements rather than history of colonization. We therefore expect the three taxa to coexist stably in this area

Timeframe of speciation inferred from secondary contact zones in the European tree frog radiation (Hyla arborea group).

BACKGROUND: Hybridization between incipient species is expected to become progressively limited as their genetic divergence increases and reproductive isolation proceeds. Amphibian radiations and their secondary contact zones are useful models to infer the timeframes of speciation, but empirical data from natural systems remains extremely scarce. Here we follow this approach in the European radiation of tree frogs (Hyla arborea group). We investigated a natural hybrid zone between two lineages (Hyla arborea and Hyla orientalis) of Mio-Pliocene divergence (~5 My) for comparison with other hybrid systems from this group. RESULTS: We found concordant geographic distributions of nuclear and mitochondrial gene pools, and replicated narrow transitions (~30 km) across two independent transects, indicating an advanced state of reproductive isolation and potential local barriers to dispersal. This result parallels the situation between H. arborea and H. intermedia, which share the same amount of divergence with H. orientalis. In contrast, younger lineages show much stronger admixture at secondary contacts. CONCLUSIONS: Our findings corroborate the negative relationship between hybridizability and divergence time in European tree frogs, where 5 My are necessary to achieve almost complete reproductive isolation. Speciation seems to progress homogeneously in this radiation, and might thus be driven by gradual genome-wide changes rather than single speciation genes. However, the timescale differs greatly from that of other well-studied amphibians. General assumptions on the time necessary for speciation based on evidence from unrelated taxa may thus be unreliable. In contrast, comparative hybrid zone analyses within single radiations such as our case study are useful to appreciate the advance of speciation in space and time

Joint evolution of multiple social traits: a kin selection analysis

General models of the evolution of cooperation, altruism and other social behaviours have focused almost entirely on single traits, whereas it is clear that social traits commonly interact. We develop a general kin-selection framework for the evolution of social behaviours in multiple dimensions. We show that whenever there are interactions among social traits new behaviours can emerge that are not predicted by one-dimensional analyses. For example, a prohibitively costly cooperative trait can ultimately be favoured owing to initial evolution in other (cheaper) social traits that in turn change the cost-benefit ratio of the original trait. To understand these behaviours, we use a two-dimensional stability criterion that can be viewed as an extension of Hamilton's rule. Our principal example is the social dilemma posed by, first, the construction and, second, the exploitation of a shared public good. We find that, contrary to the separate one-dimensional analyses, evolutionary feedback between the two traits can cause an increase in the equilibrium level of selfish exploitation with increasing relatedness, while both social (production plus exploitation) and asocial (neither) strategies can be locally stable. Our results demonstrate the importance of emergent stability properties of multidimensional social dilemmas, as one-dimensional stability in all component dimensions can conceal multidimensional instability