Biogeomorphological eco-evolutionary feedback between life and geomorphology: a theoretical framework using fossorial mammals.

Engineer organisms not only adapt to pre-existing environmental conditions but also co-construct their physical environment. By doing so, they can subsequently change selection pressures for themselves and other species, as well as change community and ecosystem structures and functions. Focusing on one representative example, i.e., fossorial mammals, we show that geomorphological Earth system components are crucial for understanding and quantifying links between evolutionary and ecosystem dynamics and that feedbacks between geomorphology and engineer organisms constitute a major driver of geomorphological organization on the Earth's surface. We propose a biogeomorphological eco-evolutionary feedback synthesis from the gene to the landscape where eco-evolutionary feedbacks are mediated by the geomorphological dimensions of a niche that are affected by engineer organisms, such as fossorial mammals. Our concept encompasses (i) the initial responses of fossorial mammals to environmental constraints that enhance the evolution of their morphological and biomechanical traits for digging in the soil; (ii) specific adaptations of engineer fossorial mammals (morphological, biomechanical, physiological and behavioural feedback traits for living in burrows) to their constructed geomorphological environment; and (iii) ecological and evolutionary feedbacks diffusing at the community and ecological levels. Such a new perspective in geomorphology may lead to a better conceptualization and analysis of Earth surface processes and landforms as parts of complex adaptive systems in which Darwinian selection processes at lower landscape levels lead to self-organization of higher-level landforms and landscapes.

Trophic Conditions Influence Widespread Distribution of Aster-Like Nanoparticles Within Aquatic Environments.

Aster-like nanoparticles (ALNs) are newly described femto-entities. Their ecology (e.g., geographic distribution, spatial dynamic, preferences, forcing factors) is still unknown. Here, we report that these entities, which have largely been ignored until now, can develop or maintain themselves in most aquatic environments in the Loire River catchment, France. We observed a significant influence of the trophic state on ALN ecological distributions. A positive relationship between prokaryotic abundance and ALN (r2 = 0.72, p < 0.01) has been identified, but its exact nature remains to be clarified. Combined with their ubiquitous distribution and high abundances (up to 7.9 × 106 ALNs mL-1) recorded in our samples, this probably makes ALNs an overlooked functional component in aquatic ecosystems.

A multi-scale approach of fluvial biogeomorphic dynamics using photogrammetry.

Over the last twenty years, significant technical advances turned photogrammetry into a relevant tool for the integrated analysis of biogeomorphic cross-scale interactions within vegetated fluvial corridors, which will largely contribute to the development and improvement of self-sustainable river restoration efforts. Here, we propose a cost-effective, easily reproducible approach based on stereophotogrammetry and Structure from Motion (SfM) technique to study feedbacks between fluvial geomorphology and riparian vegetation at different nested spatiotemporal scales. We combined different photogrammetric methods and thus were able to investigate biogeomorphic feedbacks at all three spatial scales (i.e., corridor, alluvial bar and micro-site) and at three different temporal scales, i.e., present, recent past and long term evolution on a diversified riparian landscape mosaic. We evaluate the performance and the limits of photogrammetric methods by targeting a set of fundamental parameters necessary to study biogeomorphic feedbacks at each of the three nested spatial scales and, when possible, propose appropriate solutions. The RMSE varies between 0.01 and 2 m depending on spatial scale and photogrammetric methods. Despite some remaining difficulties to properly apply them with current technologies under all circumstances in fluvial biogeomorphic studies, e.g. the detection of vegetation density or landform topography under a dense vegetation canopy, we suggest that photogrammetry is a promising instrument for the quantification of biogeomorphic feedbacks at nested spatial scales within river systems and for developing appropriate river management tools and strategies.

Signatures of Life Detected in Images of Rocks Using Neural Network Analysis Demonstrate New Potential for Searching for Biosignatures on the Surface of Mars.

Microorganisms play a role in the construction or modulation of various types of landforms. They are especially notable for forming microbially induced sedimentary structures (MISS). Such microbial structures have been considered to be among the most likely biosignatures that might be encountered on the martian surface. Twenty-nine algorithms have been tested with images taken during a laboratory experiment for testing their performance in discriminating mat cracks (MISS) from abiotic mud cracks. Among the algorithms, neural network types produced excellent predictions with similar precision of 0.99. Following that step, a convolutional neural network (CNN) approach has been tested to see whether it can conclusively detect MISS in images of rocks and sediment surfaces taken at different natural sites where present and ancient (fossil) microbial mat cracks and abiotic desiccation cracks were observed. The CNN approach showed excellent prediction of biotic and abiotic structures from the images (global precision, sensitivity, and specificity, respectively, 0.99, 0.99, and 0.97). The key areas of interest of the machine matched well with human expertise for distinguishing biotic and abiotic forms (in their geomorphological meaning). The images indicated clear differences between the abiotic and biotic situations expressed at three embedded scales: texture (size, shape, and arrangement of the grains constituting the surface of one form), form (outer shape of one form), and pattern of form arrangement (arrangement of the forms over a few square meters). The most discriminative components for biogenicity were the border of the mat cracks with their tortuous enlarged and blistered morphology more or less curved upward, sometimes with thin laminations. To apply this innovative biogeomorphological approach to the images obtained by rovers on Mars, the main physical and biological sources of variation in abiotic and biotic outcomes must now be further considered.

The Search for a Signature of Life on Mars: A Biogeomorphological Approach.

Geological evidence shows that life on Earth evolved in line with major concomitant changes in Earth surface processes and landforms. Biogeomorphological characteristics, especially those involving microorganisms, are potentially important facets of biosignatures on Mars and are generating increasing interest in astrobiology. Using Earth as an analog provides reasons to suspect that past or present life on Mars could have resulted in recognizable biogenic landforms. Here, we discuss the potential for, and limitations of, a biogeomorphological approach to identifying the subsets of landforms that are modulated or created through biological processes and thus present signatures of life on Mars. Subsets especially involving microorganisms that are potentially important facets of biosignatures on Mars are proposed: (i) weathering features, biocrusts, patinas, and varnishes; (ii) microbialites and microbially induced sedimentary structures (MISS); (iii) bioaccumulations of skeletal remains; (iv) degassing landforms; (v) cryoconites; (vi) self-organized patterns; (vii) unclassified non-analog landforms. We propose a biogeomorphological frequency histogram approach to identify anomalies/modulations in landform properties. Such detection of anomalies/modulations will help track a biotic origin and lead to the development of an integrative multiproxy and multiscale approach combining morphological, structural, textural, and geochemical expertise. This perspective can help guide the choice of investigation sites for future missions and the types and scales of observations to be made by orbiters and rovers.