Simultaneous TE Analysis of 19 Heliconiine Butterflies Yields Novel Insights into Rapid TE-Based Genome Diversification and Multiple SINE Births and Deaths

Transposable elements (TEs) play major roles in the evolution of genome structure and function. However, because of their repetitive nature, they are difficult to annotate and discovering the specific roles they may play in a lineage can be a daunting task. Heliconiine butterflies are models for the study of multiple evolutionary processes including phenotype evolution and hybridization. We attempted to determine how TEs may play a role in the diversification of genomes within this clade by performing a detailed examination of TE content and accumulation in 19 species whose genomes were recently sequenced. We found that TE content has diverged substantially and rapidly in the time since several subclades shared a common ancestor with each lineage harboring a unique TE repertoire. Several novel SINE lineages have been established that are restricted to a subset of species. Furthermore, the previously described SINE, Metulj, appears to have gone extinct in two subclades while expanding to significant numbers in others. This diversity in TE content and activity has the potential to impact how heliconiine butterflies continue to evolve and diverge

The Radial Dependence of Proton-scale Magnetic Spectral Break in Slow Solar Wind during PSP Encounter 2

International audienceMagnetic field fluctuations in the solar wind are commonly observed to follow a power-law spectrum. Near proton-kinetic scales, a spectral break occurs that is commonly interpreted as a transition to kinetic turbulence. However, this transition is not yet entirely understood. By studying the scaling of the break with various plasma properties, it may be possible to constrain the processes leading to the onset of kinetic turbulence. Using data from the Parker Solar Probe, we measure the proton-scale break over a range of heliocentric distances, enabling a measurement of the transition from inertial to kinetic-scale turbulence under various plasma conditions. We find that the break frequency f(b) increases as the heliocentric distance r decreases in the slow solar wind following a power law of f(b) similar to r(-1.11). We also compare this to the characteristic plasma ion scales to relate the break to the possible physical mechanisms occurring at this scale. The ratio f(b)/f(c) (f(c) for Doppler-shifted ion cyclotron resonance scale) is close to unity and almost independent of plasma beta(p). While f(b)/f(p) (f(p) for Doppler-shifted proton thermal gyroradius) increases with beta(p) approaching to unity at larger beta(p), f(b)/f(d) (f(d) for Doppler-shifted proton inertial length) decreases with beta(p) from unity at small beta(p). Due to the large comparable Alfven and solar wind speeds, we analyze these results using both the standard and modified Taylor hypotheses, demonstrating the robust statistical results

Cross Helicity Reversals in Magnetic Switchbacks

International audienceWe consider 2D joint distributions of normalized residual energy, sigma(r)(s, t), and cross helicity, sigma(c)(s, t), during one day of Parker Solar Probe's (PSP's) first encounter as a function of wavelet scale s. The broad features of the distributions are similar to previous observations made by Helios in slow solar wind, namely well-correlated and fairly Alfvenic wind, except for a population with negative cross helicity that is seen at shorter wavelet scales. We show that this population is due to the presence of magnetic switchbacks, or brief periods where the magnetic field polarity reverses. Such switchbacks have been observed before, both in Helios data and in Ulysses data in the polar solar wind. Their abundance and short timescales as seen by PSP in its first encounter is a new observation, and their precise origin is still unknown. By analyzing these MHD invariants as a function of the wavelet scale, we show that magnetohydrodynamic (MHD) waves do indeed follow the local mean magnetic field through switchbacks, with a net Elsasser flux propagating inward during the field reversal and that they, therefore, must be local kinks in the magnetic field and not due to small regions of opposite polarity on the surface of the Sun. Such observations are important to keep in mind as computing cross helicity without taking into account the effect of switchbacks may result in spurious underestimation of sigma(c) as PSP gets closer to the Sun in later orbits

Strong selection on male plumage in a hybrid zone between a hybrid bird species and one of its parents

Homoploid hybrid speciation (HHS) requires reproductive barriers between hybrid and parent species, despite incomplete reproductive isolation (RI) between the parents. Novel secondary sexual trait values in hybrids may cause prezygotic isolation from both parents, whereas signals inherited by the hybrid from one parent species may cause prezygotic isolation with the other. Here we investigate whether differences in male plumage function as a premating barrier between the hybrid Italian sparrow and one of its parent species, the house sparrow, in a narrow Alpine hybrid zone. Italian sparrow male plumage is a composite mosaic of the parental traits, with its head plumage most similar to its other parent, the Spanish sparrow. We use geographical cline analysis to examine selection on three plumage traits, 75 nuclear single nucleotide polymorphisms (SNPs) and hybrid indices based on these SNPs. Several SNPs showed evidence of restricted introgression in the Alps, supporting earlier findings. Crown colour exhibited the narrowest plumage cline, representing a 37% (range 4–65%) drop in fitness. The cline was too narrow to be due to neutral introgression. Only crown colour was significantly bimodal in the hybrid zone. Bimodality may be due to RI or a major QTL, although fitness estimates suggest that selection contributes to the pattern. We discuss the implications with respect to HHS and the species status of the Italian sparrow

Constraining Ion-Scale Heating and Spectral Energy Transfer in Observations of Plasma Turbulence

International audienceWe perform a statistical study of the turbulent power spectrum at inertial and kinetic scales observed during the first perihelion encounter of the Parker Solar Probe. We find that often there is an extremely steep scaling range of the power spectrum just above the ion-kinetic scales, similar to prior observations at 1 A.U., with a power-law index of around −4. Based on our measurements, we demonstrate that either a significant (>50%) fraction of the total turbulent energy flux is dissipated in this range of scales, or the characteristic nonlinear interaction time of the turbulence decreases dramatically from the expectation based solely on the dispersive nature of nonlinearly interacting kinetic Alfvén waves

Ion-scale Electromagnetic Waves in the Inner Heliosphere

International audienceUnderstanding the physical processes in the solar wind and corona that actively contribute to heating, acceleration, and dissipation is a primary objective of NASA's Parker Solar Probe (PSP) mission. Observations of circularly polarized electromagnetic waves at ion scales suggest that cyclotron resonance and wave-particle interactions are dynamically relevant in the inner heliosphere. A wavelet-based statistical study of circularly polarized events in the first perihelion encounter of PSP demonstrates that transverse electromagnetic waves at ion resonant scales are observed in 30-50% of radial field intervals. Average wave amplitudes of approximately 4 nT are measured, while the mean duration of wave events is on the order of 20 s; however, long-duration wave events can exist without interruption on hour-long timescales. Determination of wave vectors suggests propagation parallel/antiparallel to the mean magnetic field. Though ion-scale waves are preferentially observed during intervals with a radial mean magnetic field, we show that measurement constraints, associated with single spacecraft sampling of quasi-parallel waves superposed with anisotropic turbulence, render the measured coherent ion-wave spectrum unobservable when the mean magnetic field is oblique to the solar wind flow; these results imply that the occurrence of coherent ion-scale waves is not limited to a radial field configuration. The lack of radial scaling of characteristic wave amplitudes and duration suggests that the waves are generated in situ through plasma instabilities. Additionally, observations of proton distribution functions indicate that temperature anisotropy may drive the observed ion-scale

Kinetic‐Scale Turbulence in the Venusian Magnetosheath

While not specifically designed as a planetary mission, NASA's Parker Solar Probe (PSP) mission uses a series of Venus gravity assists (VGAs) in order to reduce its perihelion distance. These orbital maneuvers provide the opportunity for direct measurements of the Venus plasma environment at high cadence. We present first observations of kinetic scale turbulence in the Venus magnetosheath from the first two VGAs. In VGA1, PSP observed a quasi‐parallel shock, β ∼ 1 magnetosheath plasma, and a kinetic range scaling of k−2.9. VGA2 was characterized by a quasi‐perpendicular shock with β ∼ 10, and a steep k−3.4 spectral scaling. Temperature anisotropy measurements from VGA2 suggest an active mirror mode instability. Significant coherent waves are present in both encounters at sub‐ion and electron scales. Using conditioning techniques to exclude these electromagnetic wave events suggests the presence of developed sub‐ion kinetic turbulence in both magnetosheath encounters

Properties of Graphene: A Theoretical Perspective

In this review, we provide an in-depth description of the physics of monolayer and bilayer graphene from a theorist's perspective. We discuss the physical properties of graphene in an external magnetic field, reflecting the chiral nature of the quasiparticles near the Dirac point with a Landau level at zero energy. We address the unique integer quantum Hall effects, the role of electron correlations, and the recent observation of the fractional quantum Hall effect in the monolayer graphene. The quantum Hall effect in bilayer graphene is fundamentally different from that of a monolayer, reflecting the unique band structure of this system. The theory of transport in the absence of an external magnetic field is discussed in detail, along with the role of disorder studied in various theoretical models. We highlight the differences and similarities between monolayer and bilayer graphene, and focus on thermodynamic properties such as the compressibility, the plasmon spectra, the weak localization correction, quantum Hall effect, and optical properties. Confinement of electrons in graphene is nontrivial due to Klein tunneling. We review various theoretical and experimental studies of quantum confined structures made from graphene. The band structure of graphene nanoribbons and the role of the sublattice symmetry, edge geometry and the size of the nanoribbon on the electronic and magnetic properties are very active areas of research, and a detailed review of these topics is presented. Also, the effects of substrate interactions, adsorbed atoms, lattice defects and doping on the band structure of finite-sized graphene systems are discussed. We also include a brief description of graphane -- gapped material obtained from graphene by attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic

HelioSwarm: A Multipoint, Multiscale Mission to Characterize Turbulence

HelioSwarm (HS) is a NASA Medium-Class Explorer mission of the Heliophysics Division designed to explore the dynamic three-dimensional mechanisms controlling the physics of plasma turbulence, a ubiquitous process occurring in the heliosphere and in plasmas throughout the universe. This will be accomplished by making simultaneous measurements at nine spacecraft with separations spanning magnetohydrodynamic and sub-ion spatial scales in a variety of near-Earth plasmas. In this paper, we describe the scientific background for the HS investigation, the mission goals and objectives, the observatory reference trajectory and instrumentation implementation before the start of Phase B. Through multipoint, multiscale measurements, HS promises to reveal how energy is transferred across scales and boundaries in plasmas throughout the universe

Diversity in warning coloration: selective paradox or the norm?

Aposematic theory has historically predicted that predators should select for warning signals to converge on a single form, as a result of frequency-dependent learning. However, widespread variation in warning signals is observed across closely related species, populations and, most problematically for evolutionary biologists, among individuals in the same population. Recent research has yielded an increased awareness of this diversity, challenging the paradigm of signal monomorphy in aposematic animals. Here we provide a comprehensive synthesis of these disparate lines of investigation, identifying within them three broad classes of explanation for variation in aposematic warning signals: genetic mechanisms, differences among predators and predator behaviour, and alternative selection pressures upon the signal. The mechanisms producing warning coloration are also important. Detailed studies of the genetic basis of warning signals in some species, most notably Heliconius butterflies, are beginning to shed light on the genetic architecture facilitating or limiting key processes such as the evolution and maintenance of polymorphisms, hybridisation, and speciation. Work on predator behaviour is changing our perception of the predator community as a single homogenous selective agent, emphasising the dynamic nature of predator-prey interactions. Predator variability in a range of factors (e.g. perceptual abilities, tolerance to chemical defences, and individual motivation), suggests that the role of predators is more complicated than previously appreciated. With complex selection regimes at work, polytypisms and polymorphisms may even occur in Mullerian mimicry systems. Meanwhile, phenotypes are often multifunctional, and thus subject to additional biotic and abiotic selection pressures. Some of these selective pressures, primarily sexual selection and thermoregulation, have received considerable attention, while others, such as disease risk and parental effects, offer promising avenues to explore. As well as reviewing the existing evidence from both empirical studies and theoretical modelling, we highlight hypotheses that could benefit from further investigation in aposematic species. Finally by collating known instances of variation in warning signals, we provide a valuable resource for understanding the taxonomic spread of diversity in aposematic signalling and with which to direct future research. A greater appreciation of the extent of variation in aposematic species, and of the selective pressures and constraints which contribute to this once-paradoxical phenomenon, yields a new perspective for the field of aposematic signalling.Peer reviewe