Uncovering trophic interactions in arthropod predators through DNA shotgun-sequencing of gut contents

Characterizing trophic networks is fundamental to many questions in ecology, but this typically requires painstaking efforts, especially to identify the diet of small generalist predators. Several attempts have been devoted to develop suitable molecular tools to determine predatory trophic interactions through gut content analysis, and the challenge has been to achieve simultaneously high taxonomic breadth and resolution. General and practical methods are still needed, preferably independent of PCR amplification of barcodes, to recover a broader range of interactions. Here we applied shotgun-sequencing of the DNA from arthropod predator gut contents, extracted from four common coccinellid and dermapteran predators co-occurring in an agroecosystem in Brazil. By matching unassembled reads against six DNA reference databases obtained from public databases and newly assembled mitogenomes, and filtering for high overlap length and identity, we identified prey and other foreign DNA in the predator guts. Good taxonomic breadth and resolution was achieved (93% of prey identified to species or genus), but with low recovery of matching reads. Two to nine trophic interactions were found for these predators, some of which were only inferred by the presence of parasitoids and components of the microbiome known to be associated with aphid prey. Intraguild predation was also found, including among closely related ladybird species. Uncertainty arises from the lack of comprehensive reference databases and reliance on low numbers of matching reads accentuating the risk of false positives. We discuss caveats and some future prospects that could improve the use of direct DNA shotgun-sequencing to characterize arthropod trophic networks

Physics of GaAs/AlAs Superlattices

We describe the main problems encountered in MBE growth of GaAs/AlAs superlattices and heterostructures. Then, basic features for the understanding of their electronic properties are given, in the envelope-function formalism, and some related optical experiments are reviewed

Optical Bistability Due to Photo-Induced Charge Transfer in a Type-II GaAs/AlAs Quantum Well

We present a bistability of low temperature photoluminescence in a n-i-n type-II GaAs/AlAs quantum heterostructure. Spectral analysis and electrical measurements indicate that the two states correspond to hole accumulation in different layers. The transition occurs with the alignment of electronic Γ and X states due to optical pumping, and no external voltage bias is needed

Optical non-linearities due to charge transfer in type II heterostructures

We present experimental studies of photocreated carrier population in type II heterostructures. The main effects are related to charge separation and band filling : Blue shift and broadening of the luminescence line, transition from indirect recombination to pseudo-direct, and then to direct-type I recombination. They may lead to more complex non-linear effects such as bistability. These effects can be accounted for by theory in the framework of the Envelope-Function Approximation, by self consistent treatment of the Poisson and Schroedinger equations

Growth of strained Ga_1-xIn_xP layers on GaP (001) by gas source molecular beam epitaxy: similarities and differences with the growth of strained arsenides

International audienceUsing reflection high energy electron diffraction and atomic force microscopy, the growth of Ga1−xInxP alloys on GaP (0 0 1) with x varying from 0.2 to 1 (InP) is investigated and compared to that of arsenides on GaAs (0 0 1) or InP (0 0 1). At 520°C, the evolution of the critical thickness for 3D growth versus In content is rather similar to that observed in the GaInAs/GaAs system. For x⩽0.5, 3D growth leads to the development of wire-like structures along the [1 1 0] direction which can be related to recent results on the phosphide surface reconstructions. Finally, for the growth of InP on GaP at 520°C, the critical thickness is 2.1 MLs and we observe a small density of very large islands, in contrast to the InAs/GaAs case. At 400°C, the critical thickness decreases (1.7 MLs) as well as the island mean size whereas the density increases. We discuss this behavior in terms of surface energy

Hemt structures and technology on GAAS and inp for power amplification in millimetre wave range

The paper introduces a simple and efficient approach for the modelling of low-frequency dispersive phenomena in FETs. It is based on the definition of a virtual, non-dispersive associated device controlled by equivalent port voltages and it is suitable for modelling based on standard nonlinear dynamic approaches, such as lumped-element equivalent circuits. The proposed approach is justified on the basis of a physically-consistent, charge-controlled description of the device, but the results are general and provide a valuable tool for taking into account dispersive effects in FETs by means of an intuitive circuit solution, in the framework of any existing nonlinear dynamic model of the associated non-dispersive device. The new equivalent-voltage description, identified on the basis of conventional measurements carried out under static and small-signal dynamic operating conditions, allows for the accurate prediction of dispersive effects above the frequency cut-off, but the formulation is still compatible, without for al modification, for the modelling of the device behaviour under signal excitations having spectral components in the dispersive low-frequency range. Preliminary results are presented which conferm the validity of the proposed approach

Experimental study of hot electron inelastic scattering rate in p-type InGaAs

International audienceThe inelastic scattering rates of electrically injected minority hot electrons measured using a continuous-wave spatially resolved electroluminescence spectroscopy are reported. To our knowledge, this constitutes direct experimental determination of this parameter related to the individual inelastic interactions. The evolution of the electron relaxation rate with increasing majority hole density is explored. Remarkably, an attenuation of the scattering rate is measured for p-doping levels higher than 2×1019 cm-3. Additionally, the measured hot-electron energy distributions further indicate that the relaxation mechanisms are dominated by LO phonon-plasmons coupled modes in the range 1018 to 1019 cm-3 hole density. Finally, the temperature dependence of inelastic scattering rate is also measured to learn on the potential implication of ballistic transport in RT operating hot-electron devices

ELECTRIC FIELD ENHANCEMENT OF OPTICAL ABSORPTION IN GaAs-AlAs TYPE-II SUPERLATTICES

Nous observons l'augmentation de la probabilité de transition optique sous champ électrique longitudinal, dans des super-réseaux GaAs/AlAs de type "indirect". Cela prouve la séparation spatiale des électrons et des trous dans ces structures.The spatial separation of electrons and holes in GaAs/AlAs "indirect" type superlattices is evidenced by the enhancement of optical transition probability under a longitudinal electric field