Perception catégorielle et prise de décision chez les crocodiliens

Selon la théorie de l'information, la communication acoustique nécessite des variations acoustiques. Plus l'entropie est grande, plus le signal acoustique peut contenir de l'information. Cependant, les caractéristiques acoustiques utilisées par les animaux pour la communication acoustique sont assez variées selon les espèces. Des études précédentes ont montré que les crocodiles utilisent principalement la hauteur (F0) et la modulation de fréquence de la hauteur (FM) pendant la communication entre femelles et jeunes. Nous pouvons donc nous attendre à ce que ces deux caractéristiques soient particulièrement bien codées dans le cerveau des crocodiles. Cette étude vise à mieux comprendre la précision de ce codage de l’information au sein de vocalisations de jeunes crocodiles. Nous créons des signaux chimériques dans un espace acoustique tridimensionnel afin de déterminer les indices qui sont utilisés par les crocodiles pour reconnaître et catégoriser des cris de contact. Menées tant en laboratoire avec un paradigme de go/no-go, qu’en milieu naturel, au travers d’expériences de playback, ces études permettent de mieux comprendre comment ces animaux perçoivent leur environnement acoustique et comment ils intègrent l’information afin de prendre des décisions

Sound categorization by crocodilians

International audienceRapidly sorting the information contained in a stream of stimuli is a major challenge for animals. One cognitive mechanism for achieving this goal is categorization, where the receiving individual considers a continuous variation of a stimulus as belonging to discrete categories. Using playback experiments in a naturalistic setup, here we show that crocodiles confronted with an acoustic continuum ranging from a frog call to a crocodile call classify each acoustic variant into one of these two categories, establishing a meaningful boundary where no acoustic boundary exists. With GO/NOGO experiments, we then observe that this boundary is defined along the continuum following learning. We further demonstrate that crocodilians rely on the spectral envelope of sounds to categorize stimuli. This study suggests that sound categorization in crocodilians is a pre-wired faculty allowing rapid decision making, and highlights the learning-dependent plasticity involved in defining the boundary between sound categories

Anthropogenic noise does not strengthen multiple‐predator effects in a freshwater invasive fish

International audienceAnthropogenic noise has the potential to alter community dynamics by modifying the strength of nested ecological interactions such as predation. Direct effects of noise on per capita predation rates have received much attention but the context in which predation occurs is often oversimplified. For instance, many animals interact with conspecifics while foraging and these nontrophic interactions can positively or negatively influence per capita predation rates. These effects are often referred to as multiple‐predator effects (MPEs). The extent to which noise can modulate MPEs and thereby indirectly alter per capita predation remains unknown. To address this question, we derived the relationship between per capita predation rate and prey density, namely the functional response (FR), of single and pairs of the invasive topmouth gudgeon Pseudorasbora parva when feeding on water fleas under two noise conditions: control ambient noise estimated at 95 dB re 1 μPa and ambient noise supplemented with motorboat sounds whose relative importance over ambient noise ranged from 4.81 to 27 dB. In addition, we used video recordings to track fish movements. To detect MPEs, we compared the observed group‐level FRs to predicted group‐level FRs inferred from the individual FRs and based on additive effects only. Regardless of the number of fish and the noise condition, the FR was always of type II, showing predation rate in a decelerating rise to an upper asymptote. Compared to the noiseless condition, the predation rate of single fish exposed to noise did not differ at high prey densities but was significantly lower at low prey densities, resulting in an FR with the same asymptote but a less steep initial slope. Noise also reduced fish mobility, which might explain the decrease in predation rate at low prey densities. Conspecific presence suppressed the individual response to noise, the FRs of two fish (observed group‐level FRs) being perfectly similar between the two noise conditions. Although observed and predicted group‐level FRs did not differ significantly, observed group‐level FRs tended to fall in the low range of predicted group‐level FRs, suggesting antagonism and a negative effect of nontrophic interactions on individual foraging performance. Interestingly, the difference between predicted and observed group‐level FRs was not greater with noise, which means that noise did not strengthen MPEs. Our results show that when considering the social context of foraging, here through the presence of a conspecific, anthropogenic noise does not compromise foraging in the invasive P. parva

Production of unstable proteins through the formation of stable core complexes

International audiencePurification of proteins that participate in large transient complexes is impeded by low amounts, heterogeneity, instability and poor solubility. To circumvent these difficulties we set up a methodology that enables the production of stable complexes for structural and functional studies. This procedure is benchmarked and applied to two challenging protein families: the human steroid nuclear receptors (SNR) and the HIV-1 pre-integration complex. In the context of transcriptional regulation studies, we produce and characterize the ligand-binding domains of the glucocorticoid nuclear receptor and the oestrogen receptor beta in complex with a TIF2 (transcriptional intermediary factor 2) domain containing the three SNR-binding motifs. In the context of retroviral integration, we demonstrate the stabilization of the HIV-1 integrase by formation of complexes with partner proteins and DNA. This procedure provides a powerful research tool for structural and functional studies of proteins participating in non-covalent macromolecular complexes

Buckling and collapse during drying of a single aqueous dispersion of casein micelle droplet

The drying process for dairy products is based on rapid removal of water, quickly concentrating milk components to finally form dry particles. The change in concentration may have a considerable effect on the product structure and influence the final characteristics of the dry material. The aim of this study was to investigate the drying behaviour of a major milk protein, i.e. caseins. The droplet – particle conversion was investigated through a single droplet system and by combining complementary methods. Our results showed that the drying process for caseins comprised three stages involving different evaporation rates and droplet dynamics. A thin layer was formed in the early stage of drying that underwent surface instabilities such as buckling and invagination of the droplet. The drying of caseins led to the formation of a deflated and wrinkled particle shape. These results suggest particular mechanical properties of the casein shell leading to a predictable and a characteristic particle shape

The HIV-1 Pre-Integration Complexes: Structures, Functions and Dynamics

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Mechanical properties of milk protein skins layers after drying: understanding the mechanisms of particle formation from whey protein isolate and native phosphocaseinate

The spray drying of milk proteins usually leads to dry particles of which the final shape can influencesphysical and functional properties of powders. The aim of this study was to understand the mechanismsof particle formation by considering the mechanical properties of materials making up the two mainclasses of milk proteins: whey proteins and casein micelles. The progressive solidification of the interfaceof the droplet during drying time was studied by high speed camera and fluorescence microscopy, indifferent experimental conditions. The mechanical properties of the final protein materials were thencharacterized by micro indentation testing. The drying dynamics of whey protein and casein micelledroplets showed different timescales and mechanical lengths, whatever the drying conditions and thedroplet configurations, leading to typical mechanical instability at the surface i.e. buckling and fracture.The interface of casein micelles reached solegel transition earlier estimated at around 156 g.L 1following by elastic and plastic regimes in which the shell distorted and buckled to form a final wrinkledparticle. In contrast, the interface of whey proteins became elastic at only half the drying time estimatedat around 414 g.L 1, retaining a spherical shape, which finally fractured at the end of drying. The mechanicaldifference between the two plastic shells might be explained by the behaviour of proteins injamming conditions. Analogous behaviour could be discussed between the casein micelles and soft anddeformable colloids on the one hand, and between whey proteins and hard spheres on the other

Shape, shell, and vacuole formation during the drying of a single concentrated whey protein droplet

International audienceThe drying of milk concentrate droplets usually leads to specific particle morphology influencing their properties and their functionality. Understanding how the final shape of the particle is formed therefore represents a key issue for industrial applications. In this study, a new approach to the investigation of droplet−particle conversion is proposed. A single droplet of concentrated globular proteins extracted from milk was deposited onto a hydrophobic substrate and placed in a dry environment. Complementary methods (high-speed camera, confocal microscopy, and microbalance) were used to record the drying behavior of the concentrated protein droplets. Our results showed that whatever the initial concentration, particle formation included three dynamic stages clearly defined by the loss of mass and the evolution of the internal and external shapes of the droplet. A new and reproducible particle shape was related in this study. It was observed after drying a smooth, hemispherical cap-shaped particle, including a uniform protein shell and the nucleation of an internal vacuole. The particle morphology was strongly influenced by the drying environment, the contact angle, and the initial protein concentration, all of which governed the duration of the droplet shrinkage, the degree of buckling, and the shell thickness. These results are discussed in terms of specific protein behaviors in forming a predictable and a characteristic particle shape. The way the shell is formed may be the starting point in shaping particle distortion and thus represents a potential means of tuning the particle morphology.Anglai