Vixseboxse, P. | bioRxiv Science

bioRxiv2026

Experimental evidence for a microbial origin of reduction spots in red beds

Perseverance rover recently discovered sedimentary rocks reddened by ferric oxides and peppered with bleached spots lacking these oxides. Some of these spots are associated with phosphate, iron sulfide minerals, and organic matter, and are regarded as "potential biosignatures", suggestive of microbial iron-and sulfate-reduction and organic matter oxidation. Similar mm-cm-scale "reduction spots" occur in many ancient "red beds" on Earth. Although terrestrial reduction spots are widely considered biogenic, the available evidence is not decisive, and the proposed microbial mechanism of spot formation has not been tested experimentally. Here, we report a successful laboratory demonstration of bleached spot-formation in ferruginous sediment. Mm-cm-scale rounded bleached spots appeared within weeks on the underside of anaerobic sand-ferrihydrite slurries inoculated with mixed microbial communities obtained from the reducing zones of Winogradsky columns. The spatial and temporal distribution of observed bleaching events, which did not occur in sterile controls, are best explained by a microbially induced process, and DNA sequencing confirms that bacteria of iron-reducing genera are abundant in the bleached areas. These results strongly support the longstanding hypothesis that microbial colonies can indeed generate visibly bleached reduction spots in ferruginous sediments and rocks. Further experiments are needed to establish whether and how non-biological processes can mimic these features, and to search for features that disambiguate biogenic and abiogenic reduction spots.

paleontology↗

bioRxiv2018

The relative influence of niche versus neutral processes on Ediacaran communities

A fundamental question in community ecology is the relative influence of niche versus neutral processes in determining ecosystem dynamics. The extent to which these processes structured early animal communities is yet to be explored. Here we use spatial point process analyses (SPPA) to determine the influence of niche versus neutral processes on early total-group metazoan paleocommunities from the Ediacaran Period [~]565 million years in age. Preservation of these sessile organisms in large in-situ populations on exposed bedding planes enables inference of the most likely underlying processes governing their spatial distributions by SPPA. We conducted comprehensive spatial mapping of six of the largest Ediacaran paleocommunities in Newfoundland, Canada and Charnwood Forest, UK using LiDAR, photogrammetry and a laser-line probe. For each paleocommunity we determined the best-fit spatial model for each univariate and bivariate species distribution, comparing four sets of spatial models (complete spatial randomness, dispersal, habitat, and combined dispersal with habitat) using goodness-of-fit tests. Random and dispersal models are considered neutral processes while habitat and combined models are considered niche processes. We find the dynamics of these paleocommunities to be dominated by neutral processes, with limited influence from niche processes. Our findings are consistent with community model predictions of when neutral dynamics dominate, but are in stark contrast to the niche-dominated communities of the modern marine realm. Thus, while the underlying processes determining metazoan community assembly appear to have been in place since the appearance of the first macroscopic, complex animals, the dynamics of these early metazoan communities were fundamentally different to those of extant communities.\n\nSignificance statementThe extent to which habitat and dispersal processes structure the earliest animal communities found during the Ediacaran Period [~]565 million years ago, is unknown. In this study we analyse six of the largest and most diverse fossil assemblages from Newfoundland, Canada and Charnwood Forest, UK, using spatial point processes analyses to determine the relative influence of habitat processes (niche) and dispersal processes (neutral) on the spatial distribution of taxa. The vast majority of Ediacaran taxon distributions were controlled by neutral processes, in striking contrast to niche-dominated modern marine ecosystems, but consistent with model predictions of when neutral dynamics dominate communities. Thus the underlying processes determining metazoan community assembly have been in place since the appearance of the first macroscopic, complex animals.

ecology↗