Ref HAL: hal-05391292_v1
DOI: 10.1101/2025.03.21.644586
Exporter : BibTex | endNote
Résumé:

While island biogeography focuses on species richness equilibrium driven by immigration and extinction, and metapopulation theory examines single-species dynamics across fragmented habitats, their interplay remains poorly understood. In particular, the species-area relationship remains a subject of ongoing debate, yet there are limited theoretical foundations to explain it. To address this, we developed a multiscale stochastic metapopulation model to investigate diversity patterns on islands, bridging the gap between island biogeography and metapopulation theory. Our model integrates regional colonization from a mainland with local colonization-extinction processes within islands at the single-species level, then extends this to multiple, independent species. By analyzing the stationary properties of this model, we generate novel predictions of Species Area Relationship (SAR) based on local extinction rates, within-island colonization rates, and mainland immigration rates. We demonstrate how the interplay of these parameters influences the relationship, predicting patterns that can resemble either the power-law of Arrhenius or the semi-logarithmic relationship of Gleason, depending on the relative importance of mainland immigration versus within-island dynamics, and on the nature of the species abundance distribution in the mainland. This unified framework offers new insights into the mechanisms driving species richness and distribution across spatial scales, providing a more holistic understanding of biodiversity patterns in fragmented landscapes.

Ref HAL: hal-05386141_v1
Exporter : BibTex | endNote

Ref HAL: hal-05347389_v1
Exporter : BibTex | endNote
Résumé:

Gravity affects the flow and the behavior at rest of complex fluids and flows by inducing sedimentation, drainage, and interfacial deformation, which can mask more fundamental physical processes. On Earth, standard countermeasures against gravity come with limitations in terms of possible formulations or the quality and homogeneity of the applied strain. Alternatively, one can run these experiments in free-fall or in orbit where the effects of gravity are canceled i.e., under microgravity conditions. In this short review, we present several European Space Agency-led projects of interest to rheologists that leverage microgravity environments: FAST/FASTER , which studies interfacial rheology using Capillary Pressure Tensiometers; SMD-FOAM, fundamental experiments on foam coarsening ; SMD-PASTA and SEEDS, aimed at understanding the dynamics of emulsion droplets, its evolution and microrheology using Diffusing Wave Spectroscopy; results associated with studies on granular materials in microgravity, including AstEx and CompGran; COLIS, which examines the thermally driven perturbation of soft colloidal glasses monitored by Dynamic Light Scattering; BIOMICS/KRABS, investigating the aggregation and migration of soft particles and red blood cells under flow. Microgravity experiments allowed for high-precision measurements of interfacial viscoelasticity, detailed studies of emulsion aging and drop coalescence, observed plastic rearrangements in colloidal glasses, characterized the dynamics under flow of red blood cell analogues, and rationalized the impact of gravity on convection and fluidization in agitated granular matter. Collectively, these experiments demonstrate the complementarity and the relevance of ESA's microgravity platforms in expanding the frontiers of soft matter rheology.

Commentaires: Accepted for publication in Journal of Rheology

Ref HAL: hal-05335459_v1
DOI: 10.1038/s41467-025-64557-x
Exporter : BibTex | endNote
Résumé:

Bacteria’s ability to withstand mechanical challenges is enhanced in their biofilm lifestyle, where they are encased in a viscoelastic polymer matrix. Under fluid flow, biofilms can form as streamers – slender filaments tethered to solid surfaces and suspended in the flowing fluid. Streamers thrive in environments subjected to intense hydrodynamic stresses, such as medical devices and water filters, often resulting in catastrophic clogging. Their colonisation success may depend on a highly adaptable mechanical response to varying stress conditions, though the evidence and underlying mechanisms of this adaptation remain elusive. Here, we demonstrate that biofilm streamers exhibit a stress-hardening behaviour, with both differential elastic modulus and effective viscosity increasing linearly with external stress. This stress-hardening is consistent across biofilms with different matrix compositions, formed by various bacterial species, and under diverse growth conditions. We further demonstrate that this mechanical response originates from the properties of extracellular DNA (eDNA) molecules, which constitute the structural backbone of the streamers. In addition, our results identify extracellular RNA (eRNA) as a modulator of the matrix network, contributing to both the structure and rheological properties of the eDNA backbone. Our findings reveal an instantaneous, purely physical mechanism enabling streamers to adapt to hydrodynamic stresses. Given the ubiquity of extracellular nucleic acids (eNA) in biofilms, this discovery prompts a re-evaluation of their functional role in biofilm mechanics, with potential implications for biofilm structural integrity, ecological resilience, and colonisation dynamics.

Ref HAL: hal-05268810_v1
Exporter : BibTex | endNote

Ref HAL: hal-05268733_v1
Exporter : BibTex | endNote

Ref HAL: hal-05268687_v1
Exporter : BibTex | endNote