Similarities in butterfly emergence dates among populations suggest local adaptation to climate

Phenology shifts are the most widely cited examples of the biological impact of climate change, yet there are few assessments of potential effects on the fitness of individual organisms or the persistence of populations. Despite extensive evidence of climate-driven advances in phenological events over recent decades, comparable patterns across species' geographic ranges have seldom been described. Even fewer studies have quantified concurrent spatial gradients and temporal trends between phenology and climate. Here we analyse a large data set (~129 000 phenology measures) over 37 years across the UK to provide the first phylogenetic comparative analysis of the relative roles of plasticity and local adaptation in generating spatial and temporal patterns in butterfly mean flight dates. Although populations of all species exhibit a plastic response to temperature, with adult emergence dates earlier in warmer years by an average of 6.4 days per °C, among-population differences are significantly lower on average, at 4.3 days per °C. Emergence dates of most species are more synchronised over their geographic range than is predicted by their relationship between mean flight date and temperature over time, suggesting local adaptation. Biological traits of species only weakly explained the variation in differences between space-temperature and time-temperature phenological responses, suggesting that multiple mechanisms may operate to maintain local adaptation. As niche models assume constant relationships between occurrence and environmental conditions across a species' entire range, an important implication of the temperature-mediated local adaptation detected here is that populations of insects are much more sensitive to future climate changes than current projections suggest

Interacting Effects of Phenotypic Plasticity and Evolution on Population Persistence in a Changing Climate

Climate change affects individual organisms by altering development, physiology, behavior, and fitness, and populations by altering genetic and phenotypic composition, vital rates, and dynamics. We sought to clarify how selection, phenotypic plasticity, and demography are linked in the context of climate change. On the basis of theory and results of recent empirical studies of plants and animals, we believe the ecological and evolutionary issues relevant to population persistence as climate changes are the rate, type, magnitude, and spatial pattern of climate-induced abiotic and biotic change; generation time and life history of the organism; extent and type of phenotypic plasticity; amount and distribution of adaptive genetic variation across space and time; dispersal potential; and size and connectivity of subpopulations. An understanding of limits to plasticity and evolutionary potential across traits, populations, and species and feedbacks between adaptive and demographic responses is lacking. Integrated knowledge of coupled ecological and evolutionary mechanisms will increase understanding of the resilience and probabilities of persistence of populations and species

Propriétés optiques de défauts ponctuels dans le nitrure de bore hexagonal

The purpose of this thesis was to explore and caracterize optically the point defects in hexagonal boron nitride. The study of defects in this semiconductor is of fundamental importance firstly for the material science in which it plays a key role thanks to its lamellar structure (2D material) and its high thermal and chemical stability, and secondly for the quantum nanotechnology domain where its large bandgap (~ 6 eV) allows for exploiting deep levels point imperfections as «artificial atom» in the crystal lattice. During this thesis, defects in two spectral ranges have been studied: a first family emitting in the visible wavelengths, and a second one emitting in the ultraviolet range.Firstly, we made use of a scanning confocal microscope working in ambient conditions and at visible wavelengths. The recording of photoluminescence spatial maps permited to show the existence of localised hot spot of light, under the diffraction limit of the miscroscope, and emitting around 600 nm (2 eV). Time photon-correlation measurements revealed on one hand that we were dealing with single quantum emitters, and on the other hand allowed for probing the photodynamics of those systems, in particular at very long time-scale. Various photostability regimes are observed and discussed. Last but not least, power resolved study was also performed and demonstrated that a number of the emitters (~ 5%) are photo-stable at high excitation power and saturate at few millions counts per second: those point defects are one of the brightest single-photon source at room temperature in solid-state systems.Secondly, we explored the defects in the ultraviolet spectral range. A prerequisite to the engineering of defects in semiconductors for technological applications is the knowledge of their chemical origin. With this in mind, we studied shallow and deep levels in carbon-doped hBN samples by combining macro-photoluminescence and reflectance measurements. We showed the existence of new optically-active transitions (around 300 nm) and discussed the implication of carbon in these levels. The in-depth study of these levels have required the development of a new scanning micro-photoluminescence confocal microscope operating at 266 nm under cryogenic environment. The design and performances of the optical system are described, and the experimental challenges explained in details. Using this new setup, we went further into the examination of the deep levels. In particular, a study was carried out regarding the spatial correlation between these new spectral lines and the well-known point defect at 4.1 eV. Then, we used new crystals with isotopically-purified carbon doping as a strategy to investigate the long-standing question concerning the chemical origin of the 4.1 eV defect. Through this attempt, we brought to light the spatial dependence of the optical features for this specific emitter. Last but not least, we present our work dedicated to isolate the emission of a single 4.1 eV defect. We studied the photoluminescence of thin undoped flakes, pre-characterized with an electron microscope, that contain a low density of emitters, and inspected in particular their photostability in these thin crystals.L’objectif de cette thèse était d’explorer et de caractériser optiquement les défauts ponctuels dans le nitrure de bore hexagonal. L’étude des défauts dans ce semiconducteur revêt un intérêt fondamental à la fois pour la science des matériaux dans laquelle il joue un rôle clé de part sa nature lamellaire (matériau 2D) et sa stabilité thermique et chimique très élevées, et également dans le domaine des technologies quantiques où son grand gap (~ 6 eV) permet d’exploiter les défauts ponctuels profonds comme «atome artificiel» dans la matrice cristalline. Au cours de cette thèse, des défauts appartenant à deux gammes spectrales ont été étudiés: une première classe émettant dans le visible, et une seconde émettant dans la gamme ultraviolette.Ainsi, dans un premier temps, nous avons exploité un microscope confocal à balayage fonctionnant à l’ambiante et dans les longueurs d’onde visibles. La réalisation de cartes spatiales de photoluminescence a permis de mettre en évidence l’existence de points chauds de photoluminescence localisés, sous la limite de diffraction du microscope, et émettant autour de 600 nm (2 eV). Des mesures de corrélations temporelles de photons montre d’une part qu’il s’agit d’émetteurs quantiques uniques, et permet d’autre part de sonder la photo-dynamique de ces systèmes, en particulier aux très longues échelles de temps. Différents régimes de photo-stabilité sont observés et discutés. Enfin, l’étude en puissance a aussi été effectuée et montre qu’une part des émetteurs (~ 5%) sont photo-stables à haute puissance d’excitation optique et saturent à un taux d’émission de plusieurs millions de coups par seconde: ces défauts ponctuels constituent une source de photons uniques parmi les plus brillantes à température ambiante dans un système à l’état solide.Dans un second temps, nous avons exploré les défauts émettant dans la gamme ultraviolette. Un préalable à la maitrise et l’utilisation des défauts dans les semiconducteurs à des fins technologiques est la connaissance de leur origine chimique. Dans cette optique nous avons tout d’abord étudié les niveaux énergétiques superficiels et profonds d’échantillons de nitrure de bore hexagonal enrichis en carbone en combinant des mesures de macro-photoluminescence et de réflectivité. L’existence de nouvelles transitions optiquement actives est révélée (autour de 300 nm), et l’implication du carbone comme origine de ces transitions est discutée. L’étude approfondie de ces nouvelles émissions a requiert la réalisation d’un microscope confocal à balayage fonctionnant dans l’ultraviolet à 266 nm et à température cryogénique. Le design du microscope est détaillé, les difficultés de sa mise en oeuvre expliquées, et ses performances démontrées. Ce nouvel outil expérimental nous permet d’examiner avec précision les défauts profonds. En particulier, une étude est faite sur la corrélation spatiale de ces nouvelles raies avec celle du défaut ponctuel bien connu à 4.1 eV. Ensuite, nous avons utilisé des nouveaux échantillons dopés en carbone isotopiquement purifié comme stratégie pour déterminer la nature chimique du défaut à 4.1 eV. À travers cette tentative, nous avons mis en lumière l’inhomogénéité spatiale des caractéristiques optiques de cet émetteur. Enfin, dans la dernière partie, on tente d’isoler l’émission provenant d’un défaut unique à 4.1 eV. Pour cela, on utilise des flocons fins pré-caractérisés en microscopie électronique et contenant une faible densité d’émetteurs. Leur photostabilité est étudiée

Raman scattering signatures of strong spin-phonon coupling in the bulk magnetic van der Waals material CrSBr

International audienceMagnetic excitations in layered magnetic materials that can be thinned down to the twodimensional (2D) monolayer limit are of high interest from a fundamental point of view and for applications perspectives. Raman scattering has played a crucial role in exploring the properties of magnetic layered materials and, even-though it is essentially a probe of lattice vibrations, it can reflect magnetic ordering in solids through the spin-phonon interaction or through the observation of magnon excitations. In bulk CrSBr, a layered A type antiferromagnet (AF), we show that the magnetic ordering can be directly observed in the temperature dependence of the Raman scattering response i) through the variations of the scattered intensities, ii) through the activation of new phonon lines reflecting the change of symmetry with the appearance of the additional magnetic periodicity, and iii) through the observation, below the Néel temperature (TN) of second order Raman scattering processes. We additionally show that the three different magnetic phases encountered in CrSBr, including the recently identified low temperature phase, have a particular Raman scattering signature. This work demonstrates that magnetic ordering can be observed directly in the Raman scattering response of bulk CrSBr with in-plane magnetization, and that it can provide a unique insight into the magnetic phases encountered in magnetic layered materials

Deep ultraviolet hyperspectral cryomicroscopy in boron nitride: Photoluminescence in crystals with an ultra-low defect density

we report the development of a scanning confocal microscope dedicated to photoluminescence in the 200 nm-wavelength range for samples at cryogenic temperatures (5-300K). We demonstrate the performances of our deep ultraviolet cryomicroscope in high- quality hexagonal boron nitride (hBN) crystals, although it can be utilized for biological studies in its range of operating wavelengths. From the mapping of the photoluminescence, we bring evidence for the suppression of extrinsic recombination channels in regions free from defects. The observation of emission spectra dominated by intrinsic recombination processes was never reported before in hBN, by means of photoluminescence spectroscopy. We show that photoluminescence tomography now competes with cathodoluminescence, and that deep ultraviolet cryomicroscopy by photoluminescence is a novel powerful tool in materials science applications, with the great advantage of an efficient non-invasive photo- excitation of carriers

Loss of adaptive variation during evolutionary responses to climate change

The changes in species' geographical distribution demanded by climate change are often critically limited by the availability of key interacting species. In such cases, species' persistence will depend on the rapid evolution of biotic interactions. Understanding evolutionary limits to such adaptation is therefore crucial for predicting biological responses to environmental change. The recent poleward range expansion of the UK brown argus butterfly has been associated with a shift in female preference from its main host plant, rockrose (Cistaceae), onto Geraniaceae host plants throughout its new distribution. Using reciprocal transplants onto natural host plants across the UK range, we demonstrate reduced fitness of females from recently colonised Geraniaceae-dominated habitat when moved to ancestral rockrose habitats. By contrast, individuals from ancestral rockrose habitats show no reduction in fitness on Geraniaceae. Climate-driven range expansion in this species is therefore associated with the rapid evolution of biotic interactions and a significant loss of adaptive variation

Average field mesocosm R_H (μmol CO₂ m-2 s-1 ± SE), through time, for biota treatments, averaged across warming treatments.

<p>Average field mesocosm R_H (μmol CO₂ m-2 s-1 ± SE), through time, for biota treatments, averaged across warming treatments.</p

Proportion invertebrate mortality, in biota treatments with macroinvertebrates, across warming treatments.

<p>Proportion invertebrate mortality, in biota treatments with macroinvertebrates, across warming treatments.</p