Biology subjects

Lamy, D.

Publications and source records attributed to Lamy, D..

5 recordsLinked to original sources

bioRxiv2025

Higher trophic status leads to more diverse and divergent microeukaryote communities over time in urban lakes from the Greater Paris (France)

Effects of trophic status on lake microeukaryote community dynamics remain underexplored. Spanning oligotrophic to hypereutrophic conditions, peri-urban lakes located in the Greater Paris region (France) offer unique opportunities to compare these dynamics along a eutrophication gradient. Here, community composition was characterized using 18S rRNA gene metabarcoding, and analyzed in the context of environmental parameters and chlorophyll a-derived trophic status throughout an 18-month sampling period. Microeukaryote assemblages were dominated by Cryptophyceae, Spirotrichea, Chrysophyceae, and Chlorophyceae, with mixotrophic and heterotrophic taxa dominating across all lakes. Taxa richness peaked at intermediate trophic levels, consistent with the intermediate disturbance hypothesis. Beta-diversity and network analyses revealed increasing community modularity, reduced connectivity, and enhanced temporal variability with higher trophic status. In lakes reaching the hypereutrophic status, communities diverged progressively over time, suggesting the onset of regime shifts. Conversely, oligo-to mesotrophic lakes maintained more connected and stable assemblages. These findings demonstrate that eutrophication fosters more diverse and increasingly divergent microeukaryote communities, underscoring its role as a central driver of microbial community restructuring in urban freshwater systems.

microbiology↗

bioRxiv2024

A summer in the Greater Paris: trophic status of peri-urban lakes shapes prokaryotic community structure and functional potential

With more than 12 million inhabitants, the Greater Paris offers a "natural laboratory" to explore the effects of eutrophication on freshwater lakes within a relatively restricted area. Here, a four-month time-series was carried out during summertime to monitor planktonic microbial communities of nine lakes located within a [~]70 km radius around Paris (Ile-de-France, France) of comparable morphologies, yet distinct trophic statuses (mesotrophic to hypereutrophic). The contribution of the trophic status and intra-summer variations were investigated on prokaryotic community structures (16S rRNA gene sequencing) and functions (shotgun metagenomics). Sampled lakes harbored highly distinct and diverse prokaryotic communities. Although their gene pool was quite stable and shared among lakes, taxonomical and functional changes were correlated. The trophic status appears as the main driver of both community structure and functional potential. When focusing on function involved in biogeochemical cycles, responses to phosphorus limitation (mostly polyphosphate-related processes) were highlighted between trophic statuses. Hypereutrophic lakes communities displayed the highest contrast and heterogeneity over time, suggesting a regime shift compared to lakes of lower trophic status. This study explores the influence of eutrophication on lakes microbiome ecology, by comparing for the first time the planktonic microbial communities and their functional potential of lakes of distinct trophic status in close vicinity over a summer season.

microbiology↗

bioRxiv2022

Identification of microbial exopolymer producers in sandy and muddy intertidal sediments by compound-specific isotope analysis

Extracellular polymeric substances (EPS) refer to a wide variety of high molecular weight molecules secreted outside the cell membrane by biofilm microorganisms. In the present study, EPS from marine microphytobenthic biofilms were extracted and their isotope ratios were analysed. A comparison of these ratios with the carbon isotope ratios of fatty acid biomarkers allowed the identification of the main EPS producers of two contrasting types of intertidal marine sediments. Our study reveals that EPS sources are more diverse in sandy sediments than in muddy sediments. We also found distinct patterns in the production and breakdown of EPS in sandy and muddy environments. The main difference observed was in how epipelic and epipsammic diatoms affected the chemistry of EPS, which had significant implications for the growth of bacteria specialized in utilizing EPS. These differences were likely linked to variations in the functioning of epipelic and epipsammic communities, specifically in how EPS was used either for motility or for cell attachment.

ecology↗

bioRxiv2020

Spatial cueing effects do not always index attentional capture: Evidence for a Priority Accumulation Framework

In visual search, improved performance when a target appears at a recently cued location is taken as strong evidence that attention was shifted to this cue. Here, we provide evidence challenging the canonical interpretation of spatial-cueing (or cue-validity) effects and supporting the Priority Accumulation Framework (PAF). According to PAF, attentional priority accumulates over time at each location until the search context triggers selection of the highest-priority location. Spatial-cueing effects reflect how long it takes to resolve the competition and can thus be observed even when attention was never shifted to the cue. Here, we used a spatial-cueing paradigm with abruptly onset cues and search displays varying in target-distractor similarity. We show search performance on valid-cue trials deteriorated the more difficult the search, a finding that is incompatible with the standard interpretation of spatial-cueing effects. By using brief displays (Experiment 1) and by examining the effect of search difficulty on the fastest trials (Experiment 2), we invalidate alternative accounts invoking post-perceptual verification processes (Experiment 1) or occasional failures of the onset cue to capture attention (Experiment 2). In Experiment 3, we used a combination of the spatial-cueing and dot-probe paradigms. We show that the events that occurred in both the cue and search displays affected attentional distribution, and that the relative attentional priority weight that accumulated at the target location determined how easily the competition was resolved. These findings fully support PAFs predictions. Public significance statementMany studies aim at establishing whether certain objects mandatorily capture our attention. Here, we show that there is no "yes-or-no" answer to this question because the context in which an object appears determines whether this object captures attention. We show that our attention is not shifted to the highest-priority object at any given time: instead, information about priority is collected across time until some signal indicates that the appropriate moment for deploying our attention has arrived. Striking failures to notice conspicuous events routinely illustrate how limited our attentional system is: we can attend to very few objects at any given time, and probably to just one. In natural conditions, when we move the focus of our attention from one object to another, we also shift our gaze towards the attended location: this allows us to place the object of most interest in the center of our fovea, which maximizes the quality of its perceptual processing. Tracking the locus of such overt attention is easily achieved by using eye-tracking devices. However, in order to isolate the benefits of attention from the benefits of visual acuity, one must study covert attention - that is, attentional shifts in the absence of eye movements. These shifts are not directly observable and must therefore be inferred using indirect measures of processing.

neuroscience↗

bioRxiv2020

Spatial cueing effects are not what we thought: on the timing of attentional deployment

Extensive research has shown that objects that are salient or match our task goals are most likely to capture attention. But are we at the mercy of the constant changes occurring in our environment, and automatically move our attention to the ever-changing location with the highest priority? Or do we wait for clues that the appropriate moment has arrived to deploy our attention? We addressed this hitherto neglected issue in three experiments. Using a spatial-cueing paradigm, we examined whether attention is deployed as soon as a salient change occurs (the cue), or only when the context signaling that attention should be deployed appears (the search display). The cue matched the target color and was therefore expected to enjoy high attentional priority. We used two separate response compatibility manipulations, one pertaining to the cue, in the cueing display, and the other to the cued distractor, in the search display. Neutral conditions allowed us to disentangle the respective effects of these manipulations. Our results support the hypothesis that attention does not occur until the search-relevant context appears. These findings challenge the traditional interpretation of spatial-cueing effects. They are discussed within the Priority Accumulation Framework (PAF) that we confront to other attention models.

neuroscience↗