HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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Vertical and temporal niche partitioning in Amazonian butterflies: implications for the evolution of thermal tolerance
No full textInternational audienceClosely related species living in sympatry are often partitioned into divergent ecological niches. Such specialization can be enabled by the evolution of divergent traits enhancing adaptation to different niches. In this study, we investigate the partitioning of closely related butterfly species into different forest strata and daily activity time and test the effects of such spatio‐temporal niches on the evolution of thermal traits. First, using experiments in the field in Amazonia, we precisely characterized the daily activity patterns of nine species of Morpho butterflies, therefore documenting extensive temporal segregation among species and observing significant variations in temperature between their respective niches. Using controlled experiments in the lab, we then tested the thermal tolerance of wild individuals to both hot and cold conditions. The vertical distribution of species (understory versus canopy micro‐habitats) had a significant effect on several thermal traits, even when controlling for the phylogenetic distances between species, suggesting that forest stratification may have shaped thermal adaptation in these tropical butterflies. However, butterfly activity time did not correlate with any thermal traits measured. The extensive temporal segregation observed between these sympatric species might thus stem from ecological interactions observed between species rather than thermal factors
Evolution of opsin genes in closely-related species of butterflies specialized in different microhabitats
No full textInternational audienceMultiple selective pressures can shape the evolution of color vision in animals, by acting on the co- evolution of the opsin genes. How do adaptive processes shape the duplications of opsins, the evolution of their amino acids and the modification of their patterns of expression? At large phylogenetic scales, natural selection due to the contrasted light environments has been found to have a profound impact on the evolution of the opsin gene family. However, in closely-related species, species interactions due to sexual selection or competition may also influence opsin evolution. Here, we investigate the diversification of opsin sequences and their expression in closely-related blue Morpho butterfly species, living in different microhabitats, to shed light on the effect of biotic and abiotic selective pressures shaping the evolution of their opsin gene family. First, we combined genomics, transcriptomics and immunochemistry to precisely characterize the expression and the spatial distribution of the opsin proteins found in the eyes of Morpho helenor . We found unique ommatidial types compared to other butterfly species. We then investigated the evolution of opsin genes among 18 Morpho species, found signature of positive selection on two opsin genes, and identified key co-evolving amino-acids shaping the diversification of the Morpho visual system. We showed that such opsin evolution was correlated to both light environment and wing coloration, highlighting the joint effect of several selective pressures in the evolution of those proteins. Overall, our study underlines the peculiar evolution of visual systems in closely-related species specialized in divergent microhabitats
Phonon thermal Hall as a lattice Aharonov-Bohm effect
No full textInternational audienceIn a growing list of insulators, experiments find that magnetic field induces a misalignment between the heat flux and the thermal gradient vectors. This phenomenon, known as the phonon thermal Hall effect, implies energy flow without entropy production along the orientation perpendicular to the temperature gradient. The experimentally-measured thermal Hall angle in various insulators does not exceed a bound and becomes maximal at the temperature of peak longitudinal thermal conductivity. The present paper aims to propose a scenario providing and explanation for these two experimental facts. It begins by noticing that at this temperature, T max , Normal phonon-phonon collisions become most frequent in comparison with Umklapp and boundary scattering events. Furthermore, the Born-Oppenheimer approximated molecular wave functions are known to acquire a phase in the presence of a magnetic field. In an anharmonic crystal, in which tensile and compressive strain do not cancel out, this field-induced atomic phase gives rise to a phonon Berry phase and generates phonon-phonon interference. The rough amplitude of the thermal Hall angle expected in this picture is set by the phonon wavelength, λ p h , and the crest atomic displacement, δu m at T max . The derived expression is surprisingly close to what has been experimentally found in black phosphorus, germanium and silicon.</div
Characterizing semiflexible network structure of wormlike micelles by dynamic techniques
No full textInternational audienceUnderstanding the structure-property relationships of semiflexible polymer networks is essential for their rational design and application across diverse fields. While classical static structural characterizations have been widely used, dynamic investigations also provide a powerful approach to analyzing these networks across multiple hierarchical levels in both time and length scales. This study presents a comprehensive methodology to dynamically determine key structural parameters in semiflexible polymer networks, characterizing time, length, volume, and molecular weight of unit segments at their respective hierarchical levels, such as Kuhn monomers, correlation blobs, and network strands. A wormlike micellar solution of sodium dodecyl sulfate and aluminum nitrate was used as a model system representing semiflexible polymers with a large Kuhn length. By combining dynamic experimental techniques, including dynamic light scattering, macrorheology, and microrheology, crucial structural information was obtained. Integrating information derived from the characteristic parameters successfully revealed the hierarchical network structure of the wormlike micelles, with results validated against static light scattering measurements. Notably, this study effectively utilizes the complex viscoelastic modulus obtained through microrheology, which has received limited attention in the literature. This approach holds potential applicability to a wide range of semiflexible polymer networks
Why cutting is easier than tearing elastomers
No full textInternational audienceTearing tough soft solids such as rubbers, leather or meat is much harder than cutting them with a sharp blade. To understand why, we use samples labeled with mechanically sensitive fluorophores to investigate cutting and fracture behavior in PDMS elastomers and quantify the extent of bond scission resulting from cutting pre-stretched samples. Our findings reveal that stretch-induced cracks produce significant deformation, bond scission and blunting near the crack tip, requiring more energy to propagate. In contrast, using blades reduces the amount of stretching and blunting required for crack propagation, resulting in a lower fracture energy. The measured linear correlation between fracture energy and the areal density of broken chains clarifies the relationship between pre-stretching, blunting, and molecular damage. These multi-scale insights demonstrate the key differences between fracture and cutting mechanics of soft materials, allowing to optimize engineering applications, such as rubber and food processing, energy-efficient recycling, biomedical and surgical devices, protective equipment and sports gear
Topological defect engineering enables size and shape control in self-assembly
No full textThe self-assembly of complex structures from engineered subunits is a major goal of nanotechnology, but controlling their size becomes increasingly difficult in larger assemblies. Existing strategies present significant challenges, among which the use of multiple subunit types or the precise control of their shape and mechanics. Here we introduce an alternative approach based on identical subunits whose interactions promote crystals, but also favor crystalline defects. We theoretically show that topological restrictions on the scope of these defects in large assemblies imply that the assembly size is controlled by the magnitude of the defect-inducing interaction. Using DNA origami, we experimentally demonstrate both size and shape control in two-dimensional disk- and fiber-like assemblies. Our basic concept of defect engineering could be generalized well beyond these simple examples, and thus provide a broadly applicable scheme to control self-assembly
Visible-Light-Mediated Radical Truce–Smiles Rearrangement via Arylazo Sulfones
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Approche matricielle de la microscopie optique en régime de diffusion multiple
No full textThis work focuses on a matrix-based approach to microscopy, which relies experimentally on measuring the reflection matrix of the inspected medium. Post-processing operations are then applied to this matrix in order to compensate for aberrations and to image the medium in depth. To study this approach and understand its limitations, a numerical simulation tool was developed to simulate light propagation in biological tissues. This allowed us to identify various phenomena occurring in the multiple scattering regime (such as coherent backscattering and anisoplanatism) that hinder matrix-based imaging in such conditions. To overcome these issues, we developed a multi-conjugate approach that enables control over multiple forward scattering paths, thereby extending the penetration depth of label-free optical microscopy techniques. Moreover, this approach paves the way for more quantitative imaging, as it allows mapping of the medium's refractive index in reflection.Le travail est porté sur une approche matricielle de de la microscopie quirepose expérimentalement sur la mesure de la matrice de réflexion dumilieu inspecté et qui consiste ensuite à lui appliquer un ensembled'opérations en post-traitement afin de compenser les phénomènesd'aberrations et d'imager le milieu en profondeur . Pour étudiercette approche et comprendre ses limites, a été développé un outilde simulation numérique permettant de simuler la propagation de lalumière dans les tissus biologiques. Ont ainsi pu être identifiésdifférents phénomènes en régime de diffusion multiple(rétrodiffusion cohérente, anisoplanétisme) qui faisaient échouerl'imagerie matricielle dans ce régime. Pour s'affranchir de cesproblèmes, nous avons développé une approche multi-conjuguée permettantde maîtriser les chemins de diffusion multiple vers l'avant et ainsirepousser la profondeur de pénétration des techniques de microscopieoptique sans marquage. En outre, cette approche ouvre une nouvellevoie vers une imagerie plus quantitative puisqu'elle permet decartographier l'indice de réfraction du milieu en réflexion
