Biology subjects

Saade, C.

Publications and source records attributed to Saade, C..

6 recordsLinked to original sources

bioRxiv2026

Nutrient heterogeneity emerges from dynamical abiotic-biotic feedback in a spatially explicit plant-herbivore occupancy model

Spatial heterogeneity of abiotic resources is essential for species coexistence. Ecological theory often assumes predefined heterogeneity of resources that constrains community dynamics, but the recent developments of meta-ecosystem ecology and zoogeochemistry highlight nutrient patterns could result from the interactions between the activities and movements of organisms and their abiotic environment. Here we investigate the mechanisms by which biotic-abiotic feedbacks could generate nutrient spatial heterogeneity in a simple plant-herbivore occupancy model where populations forage, recycle, and disperse in a homogenous landscape. By systematically varying organisms ranges of foraging and dispersal, and recycling levels, we found that limited dispersal of plants plays a key role on the emergence of nutrient patchiness by favoring small clusters of vegetation that shape their environment through consumption and recycling. However, herbivores could also create nutrient spatial heterogeneity when large foraging and dispersal ranges, and high recycling, allow them to efficiently track plant hot spots and to increase population persistence. Unexpectedly, strong aggregation of herbivore populations did not necessarily result in nutrient clustering. Rather than via recycling, herbivores mainly affected nutrient distribution indirectly, through their top-down impact on plant distribution. When evenly spread in the landscape, herbivore populations with large foraging ranges created areas of strong herbivory pressure unfavorable to plant colonization where nutrient can accumulate. These results can help understand the dynamical feedback between biota and abiotic resources. In a context where human activities alter both nutrient distribution and species abundances, a better understanding of this biotic-abiotic feedback will be key to anticipate the response of ecosystems to current perturbations.

ecology↗

bioRxiv2025

The S. aureus serine protease-like protein B (SplB) is a potent allergen causing eosinophilic airway inflammation in mice

Background: Asthma is associated with Staphylococcus aureus colonization. Two hypotheses were proposed to explain this phenomenon: (1) the allergic environment in asthma favors S. aureus colonization and (2) S. aureus colonization creates a pro-allergic environment. Since several S. aureus virulence factors, such as the serine protease-like protein (Spl) B, elicit a type 2 biased immune response, we asked whether the pathogen itself can cause asthma. Objective: Test the ability of recombinant SplB of S. aureus to sensitize mice and induce allergic airway inflammation (AAI). Methods: Mice were treated with repeated intratracheal inoculations of either catalytically active SplB or an inactive mutant. AAI was assessed by evaluating airway hypersensitivity, immune cell infiltration, cytokines, mucus production, fibrosis, and specific serum IgE. We compared the outcome between wild-type and gene-deficient C57BL/6J mice, including recombination-activating gene knockout mice (Rag2-/-), interleukin-33 knockout mice (Il33 -/-), and protease-activated receptor 2 knockout mice (F2rl1-/-). Results: Intratracheal exposure to SplB sensitized the mice and caused eosinophilic airway inflammation and hyperresponsiveness. The development of asthma required both the proteolytic activity of SplB and a functional adaptive immune system. The soluble protease sensor IL-33 was necessary for eosinophil tissue invasion, whereas the membrane-bound protease sensor PAR2 was not. Conclusion: The serine protease SplB of S. aureus is a potent allergen. Based on this finding we propose a third mechanism to explain the relationship between S. aureus colonization and asthma: S. aureus can release allergens, such as SplB, that sensitize individuals and lead to the development of asthma.

immunology↗

bioRxiv2025

Identification of novel human cellular substrates of Staphylococcus aureus serine protease SplB

Staphylococcus aureus colonizes up to one third of the human population yet retains the capacity to cause invasive, life-threatening infections. The growing prevalence of antimicrobial resistance further complicates treatment. A major contributor to the versatility of S. aureus is its broad repertoire of virulence factors, among which secreted proteases facilitate dissemination from colonization sites into deeper tissues. Twelve extracellular proteases are secreted, with the serine protease-like protein (Spl) family (SplA-SplF), encoded within a single operon, accounting for half of them. Despite this prominence, the pathophysiological roles and substrate specificities of the Spl proteases remain poorly understood. Here, we employed a direct protein-protein interaction approach to identify novel SplB substrates in human serum. We demonstrate that SplB cleaves three intermediate filament proteins, namely desmin, vimentin, and nestin, as well as heat shock protein {beta}1 and -enolase, which have not previously been recognized as targets of S. aureus proteases. Moreover, SplB was found to cleave native IgG, a feature otherwise described only for the glutamyl endopeptidase V8. These findings expand the host protein repertoire targeted by SplB and suggest broader roles for Spl proteases in immune evasion and tissue invasion.

immunology↗

bioRxiv2021

Landscape structure and dispersal rate drive large scale catastrophic shifts in spatially explicit metapopulations

Even when environments deteriorate gradually, ecosystems may shift abruptly from one state to another. Such catastrophic shifts are difficult to predict and reverse (hysteresis). While well studied in simplified contexts, we lack a general understanding of how catastrophic shifts spread in realistic spatial contexts. For different types of landscape structure, including typical terrestrial modular and riverine dendritic networks, we here investigate landscape-scale stability in metapopulations made of bistable patches. We find that such metapopulations usually exhibit large scale catastrophic shifts and hysteresis, and that the properties of these shifts depend strongly on metapopulation spatial structure and dispersal rate: intermediate dispersal rates and a riverine spatial structure can largely reduce hysteresis size. Interestingly, our study suggests that large-scale restoration is easier with spatially clustered restoration efforts and in populations characterized by an intermediate dispersal rate.

ecology↗

bioRxiv2020

Spatial distribution of local patch extinctions drives recovery dynamics in metacommunities

Human activities lead more and more to the disturbance of plant and animal communities with local extinctions as a consequence. While these negative effects are clearly visible at a local scale, it is less clear how such local patch extinctions affect regional processes, such as metacommunity dynamics and the distribution of diversity in space. Since local extinctions may not be isolated events in space but rather cluster together, it is crucial to investigate their effects in a spatially explicit framework. Here, we use experimental microcosms and numerical simulations to understand the relationship between local patch extinctions and metacommunity dynamics. More specifically, we investigate the effects of the amount and spatial autocorrelation of extinctions in a full factorial design. Experimentally, we found that local patch extinctions increased inter-patch ({beta}-) diversity by creating differences between perturbed and unperturbed patches and at the same time increased local (-) diversity by delaying the competitive exclusion of inferior competitors. Most importantly, recolonization dynamics depended more strongly on the spatial distribution of patch extinctions than on the amount of extinctions per se. Clustered local patch extinctions reduced mixing between perturbed and unperturbed patches which led to slower recovery, lower -diversity in unperturbed patches and higher {beta}-diversity. Results from a metacommunity model matched the experimental observations qualitatively when the model included ranked competitive interactions, giving a hint at the underlying mechanisms. Our results highlight that local patch extinctions can increase the diversity within and between communities, that the strength of these effects depends on the spatial distribution of extinctions and that the effects of local patch extinctions can spread regionally, throughout a landscape. These findings are highly relevant for conservation and management of spatially structured communities under global change.

ecology↗

bioRxiv2020

Trade-off between virulence and dispersal drives parasite evolution at experimental invasion front

Eco-evolutionary processes may play an important role in the spatial spread of infectious disease. Current theory predicts more exploitative parasites to evolve in highly connected populations or at the front of spreading epidemics. However, many parasites rely on host dispersal to reach new populations. This may lead to conflict between local transmission and global spread, possibly counteracting selection for higher virulence. Here, we used the freshwater host Paramecium caudatum and its bacterial parasite Holospora undulata to investigate parasite evolution under an experimental range expansion scenario with natural host dispersal. We find that parasites evolving at experimental range fronts favoured higher dispersal rates of infected hosts than did parasites evolving in core populations. Front parasites further showed lower levels of virulence (host division and survival) and delayed development of infection, consistent with parameter estimates from an epidemiological model that we fitted on experimental time-series data. This combined evidence suggests an evolutionary trade-off between virulence and host-mediated dispersal, with a concomitant reduction in the investment into horizontal transmission. Our experiment illustrates how parasite evolution can be shaped by divergent selection encountered in different segments of an epidemic wave. Such an interplay between demography and spatial selection has important implications for the understanding and management of emerging diseases, and, more generally, for biological invasions and other non-equilibrium scenarios of spreading populations. SIGNIFICANCE STATEMENTWhat drives parasite evolution in spatially expanding epidemics? Many parasites require dispersal of infected hosts to reach new patches, and this may produce specific adaptations enhancing spatial spread. We performed experimental range expansions in an aquatic model system, with natural dispersal of infected hosts. Parasites from experimental range fronts were less virulent and interfered less with host dispersal, but also invested less in horizontal transmission than parasites from the range core. Thus, dispersal adaptation at the front may come at a cost of reduced horizontal transmission, a trade-off rarely considered in theoretical models on parasite virulence evolution. These results have important implications in the context of emerging diseases, and for parasite evolution during biological invasions or other spatial non-equilibrium scenarios.

evolutionary biology↗