Résumé
A trophic radiation in the South-American annual killifish genus Austrolebias has led to the evolution of large specialized piscivores from small generalized carnivores. It has been proposed that this occurred in a single series of vicariant speciation events. An alternative hypothesis is denoted giant-dwarf speciation: piscivores would have evolved in sympatry by character displacement and cannibalism. We test the plausibility of both scenarios using size measures combined with distributional data and new phylogenetic trees based on mitochondrial and nuclear molecular markers. Our analysis uses historical biogeography models and Ornstein-Uehlenbeck processes describing trait evolution across the posterior distributions of phylogenetic trees. Large species most likely evolved three times from small ones. For the clade containing A. elongatus, we argue that vicariance was not involved in the origin of these large and specialized piscivores. They experience stabilizing selection with an optimum shifted towards larger bodies and longer jaws. The branch leading to this clade has the fastest evolving jaw lengths across the phylogeny, in agreement with expectations for giant-dwarf speciation. For A. wolterstorffi, the support for giant-dwarf speciation is weaker. When the species is placed at the root of Austrolebias, ancestral reconstructions are unreliable and vicariance cannot be ruled out. For the remaining large species, we can reject vicariance and giant dwarf speciation. Our results give rise to two new additional scenarios for the evolution of specialized piscivores. In the first, two successive speciation events in sympatry or parapatry produced large and piscivorous species. In the second, the immigration of a different annual killifish genus (Cynopoecilus) in the Patos area of endemism has contributed to in-situ diversification of Austrolebias species.
Auteurs, date et publication :
Auteurs Tom Van Dooren , Henri A. Thomassen , Femmie Smit , Andrew J. Helmstetter , Vincent Savolainen
Publication : bioRxiv
Date : 2018
Pages : 121806
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Continental atmospheric relative humidity (RH) is a key climate-parameter. Combined with atmospheric temperature, it allows us to estimate the concentration of atmospheric water vapor which is one of the main components of the global water cycle and the most important gas contributing to the natural greenhouse effect. However, there is a lack of proxies suitable for reconstructing, in a quantitative way, past changes of continental atmospheric humidity. This reduces the possibility to make model-data comparisons necessary for the implementation of climate models. Over the past 10 years, analytical developments have enabled a few laboratories to reach sufficient precision for measuring the triple oxygen isotopes, expressed by the 17O-excess (17O-excess = ln (δ17O + 1) − 0.528 × ln (δ18O + 1)), in water, water vapor and minerals. The 17O-excess represents an alternative to deuterium-excess for investigating relative humidity conditions that prevail during water evaporation. Phytoliths are micrometric amorphous silica particles that form continuously in living plants. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators. In the present study, we examine whether changes in atmospheric RH imprint the 17O-excess of phytoliths in a measurable way and whether this imprint offers a potential for reconstructing past RH. For that purpose, we first monitored the 17O-excess evolution of soil water, grass leaf water and grass phytoliths in response to changes in RH (from 40 to 100 %) in a growth chamber experiment where transpiration reached a steady state. Decreasing RH decreases the 17O-excess of phytoliths by 4.1 per meg / % as a result of kinetic fractionation of the leaf water subject to evaporation. In order to model with accuracy the triple oxygen isotope fractionation in play in plant water and in phytoliths we recommend direct and continuous measurements of the triple isotope composition of water vapor. Then, we measured the 17O-excess of 57 phytolith assemblages collected from top soils along a RH and vegetation transect in inter-tropical West and Central Africa. Although scattered, the 17O-excess of phytoliths decreases with RH by 3.4 per meg / %. The similarity of the trends observed in the growth chamber and nature supports that RH is an important control of 17O-excess of phytoliths in the natural environment. However, other parameters such as changes in the triple isotope composition of the soil water or phytolith origin in the leaf tissue may come into play. Assessment of these parameters through additional growth chambers experiments and field campaigns will bring us closer to an accurate proxy of changes in relative humidity.
Auteurs, date et publication :
Auteurs Anne Alexandre , Amarelle Landais , Christine Vallet-Coulomb , Clément Piel , Sébastien Devidal , Sandrine Pauchet , Corinne Sonzogni , Martine Couapel , Marine Pasturel , Pauline Cornuault , Jingming Xin , Jean-Charles Mazur , Frédéric Prié , Ilhem Bentaleb , Elizabeth Webb , Françoise Chalié , Jacques Roy
Publication : Biogeosciences Discussions
Date : 2025
Volume : 15
Pages : 3223–3241
Catégorie(s)
#CNRS #Ecotron de MontpellierRésumé
In the context of increasing population and decreasing acreages, the reduction in crop yields induced by tropospheric ozone should be better evaluated. Therefore, ozone-resistant and ˗sensitive tobacco (cv. Bel-B and Bel-W3), barley and rapeseed plants were submitted to ozone-enriched air, during pre-flowering period. Six ozone concentrations (ranging from 30 to 130 ppb for six hours during the photoperiod) and two treatment durations (1 or 2 weeks) were applied. These treatments correspond to low, moderate and high exposure levels that occurs in France. Several leaf parameters were measured: necrosis development, chlorophyll content, chlorophyll fluorescence (Fv/Fm, ΦPSII), gas exchange (carbon assimilation and leaf conductance), seed yield, and fatty acid composition in cell membranes. The fatty acid composition was used to calculate the "Omega-3 index", a biomarker based on stress-induced changes in leaf 18:3 content, developed to assess soil quality. To estimate the oxidative load in leaf tissues, quantification of targets of oxidative stress (such as intracellular proteins carbonylation) was rather used instead poorly reproductible ROS quantification. Results show that ozone treatments decrease chlorophyll content and omega-3 index. The extent of the declines and the threshold levels of ozone exposure triggering the declines observed in the different plant species studied will be discussed. Direct continuation of this study, will involve a water stress applied to the plants subsequent to the ozone treatments. The same physiological approach will then be used to characterize the plant responses to the combined stress treatments, to assess their resilience to drought after an ozone pollution episode.
Auteurs, date et publication :
Auteurs Ruben Puga-Freitas , Matthieu Bagard , Luis Leitao , Elodie Merlier , Christophe Espinasse , Anne Repellin , Jean-Jacques Bessoule , Marina Le Guédard , Amandine Hansart , Simon Chollet , Juliette Leymarie
Date : 2018
Catégorie(s)
#CNRS #Ecotron IleDeFrance #ENSRésumé
Nitrogen is an essential nutrient for life on Earth, but in excess, it can lead to environmental issues (e.g., N saturation, loss of biodiversity, acidification of lakes, etc.). Understanding the nitrogen budget (i.e., inputs and outputs) is essential to evaluate the prospective decay of the ecosystem services (e.g., freshwater quality, erosion control, loss of high patrimonial-value plant species, etc.) that subalpine headwater catchments provide, especially as these ecosystems experience high atmospheric nitrogen deposition. Here, we use a multi-isotopic tracer (Δ17O, δ15N and δ18O) of nitrate in aerosols, snow, and streams to assess the fate of atmospherically deposited nitrate in the subalpine watershed of the Lautaret Pass (French Alps). We show that atmospheric N deposition contributes significantly to stream nitrate pool year-round, either by direct inputs (up to 35%) or by in situ nitrification of atmospheric ammonium (up to 35%). Snowmelt in particular leads to high exports of atmospheric nitrate, most likely fast enough to impede assimilation by surrounding ecosystems. Yet, in a context of climate change, with shorter snow seasons, and increasing nitrogen emissions, our results hint at possibly stronger ecological consequences of nitrogen atmospheric deposition in the close future.
Auteurs, date et publication :
Auteurs Ilann Bourgeois , Joël Savarino , Nicolas Caillon , Hélène Angot , Albane Barbero , Franck Delbart , Didier Voisin , Jean-Christophe Clément
Publication : Environmental Science & Technology
Date : 2018
Volume : 52
Issue : 10
Pages : 5561-5570
Catégorie(s)
#CNRS #Lautaret #UGARésumé
Abstract. At a local level, biogenic isoprene emissions can greatly affect the air quality of urban areas surrounded by large vegetation sources, such as in the Mediterranean region. The impacts of future warmer and drier conditions on isoprene emissions from Mediterranean emitters are still under debate. Seasonal variations of Quercus pubescens gas exchange and isoprene emission rates (ER) were studied from June 2012 to June 2013 at the O3HP site (French Mediterranean) under natural (ND) and amplified (AD, 32%) drought. While AD significantly reduced stomatal conductance to water vapour throughout the research period excluding August, it did not significantly preclude CO2 net assimilation, which was lowest in summer (≈-1µmolCO2m−2s−1). ER followed a significant seasonal pattern regardless of drought intensity, with mean ER maxima of 78.5 and 104.8µgCgDM-1h−1 in July (ND) and August (AD) respectively and minima of 6 and <2µgCgDM-1h−1 in October and April respectively. The isoprene emission factor increased significantly by a factor of 2 in August and September under AD (137.8 and 74.3µgCgDM-1h−1) compared with ND (75.3 and 40.21µgCgDM-1h−1), but no significant changes occurred on ER. Aside from the June 2012 and 2013 measurements, the MEGAN2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) model was able to assess the observed ER variability only when its soil moisture activity factor γSM was not operating and regardless of the drought intensity; in this case more than 80% and 50% of ER seasonal variability was assessed in the ND and AD respectively. We suggest that a specific formulation of γSM be developed for the drought-adapted isoprene emitter, according to that obtained for Q. pubescens in this study (γSM=0.192e51.93 SW with SW the soil water content). An isoprene algorithm (G14) was developed using an optimised artificial neural network (ANN) trained on our experimental dataset (ER+O3HP climatic and edaphic parameters cumulated over 0 to 21 days prior to the measurements). G14 assessed more than 80% of the observed ER seasonal variations, regardless of the drought intensity. ERG14 was more sensitive to higher (0 to −7 days) frequency environmental changes under AD in comparison to ND. Using IPCC RCP2.6 and RCP8.5 climate scenarios, and SW and temperature as calculated by the ORCHIDEE land surface model, ERG14 was found to be mostly sensitive to future temperature and nearly insensitive to precipitation decrease (an annual increase of up to 240% and at the most 10% respectively in the most severe scenario). The main impact of future drier conditions in the Mediterranean was found to be an enhancement (+40%) of isoprene emissions sensitivity to thermal stress.
Auteurs, date et publication :
Auteurs Anne-Cyrielle Genard-Zielinski , Christophe Boissard , Elena Ormeño , Juliette Lathière , Ilja M. Reiter , Henri Wortham , Jean-Philippe Orts , Brice Temime-Roussel , Bertrand Guenet , Svenja Bartsch , Thierry Gauquelin , Catherine Fernandez
Publication : Biogeosciences
Date : 2018
Volume : 15
Issue : 15
Pages : 4711-4730
Catégorie(s)
#CNRS #FORET O3HPRésumé
Genome duplication is essential for cell proliferation, and the mechanisms regulating its execution are highly conserved. These processes give rise to a spatiotemporal organization of replication initiation across the genome, referred to as the replication program. Despite the identification of such programs in diverse eukaryotic organisms, their biological importance for cellular physiology remains largely unexplored. We address this fundamental question in the context of genome maintenance, taking advantage of the inappropriate origin firing that occurs when fission yeast cells lacking the Rad3/ATR checkpoint kinase are subjected to replication stress. Using this model, we demonstrate that the replication program quantitatively dictates the extent of origin de-regulation and the clustered localization of these events. Furthermore, our results uncover an accumulation of abnormal levels of single-stranded DNA (ssDNA) and the Rad52 repair protein at de-regulated origins. We show that these loci constitute a defining source of the overall ssDNA and Rad52 hotspots in the genome, generating a signature pattern of instability along the chromosomes. We then induce a genome-wide reprogramming of origin usage and evaluate its consequences in our experimental system. This leads to a complete redistribution of the sites of both inappropriate initiation and associated Rad52 recruitment. We therefore conclude that the organization of genome duplication governs the checkpoint control of origin-associated hotspots of instability and plays an integral role in shaping the landscape of genome maintenance.
Auteurs, date et publication :
Auteurs Blanca Gómez-Escoda , Pei-Yun Jenny Wu
Publication : Genome Research
Date : 2018
Volume : 28
Issue : 8
Pages : 1179-1192
Catégorie(s)
#CNRS #EcoGenO #Université de RennesRésumé
Reconstructions of evolutionary and historical biogeographic processes can improve our understanding of how species assemblages developed and permit inference of ecological drivers affecting coexistence. We explore this approach in Austrolebias, a genus of annual fishes possessing a wide range of body sizes. Regional assemblages composed of different species with similar size distributions are found in four areas of eastern South America. Using phylogenetic trees, species distribution models and size data we show how trait evolution and historical biogeography have affected the composition of species assemblages. We extend age-range correlations to improve estimates of local historical biogeography. We find that size variation principally arose in a single area and infer that ecological interactions drove size divergence. This large-size lineage spread to two other areas. One of these assemblages was likely shaped by adaptation to a new environment, but this was not associated with additional size divergence. We found only weak evidence that environmental filtering has been important in the construction of the remaining assemblage with the smallest range of sizes. The repeated assemblage structures were the result of different evolutionary and historical processes. Our approach sheds light on how species assemblages were built when typical clustering approaches may fall short.
Auteurs, date et publication :
Auteurs Andrew J. Helmstetter , Tom J. M. Van Dooren , Alexander S. T. Papadopulos , Javier Igea , Armand M. Leroi , Vincent Savolainen
Publication : bioRxiv
Date : 2018
Pages : 436808
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Glioblastoma (GB) is a highly invasive primary brain tumor that nearly always systematically recurs at the site of resection despite aggressive radio-chemotherapy. Previously, we reported a gene expression signature related to tumor infiltration. Within this signature, the EMX2 gene encodes a homeodomain transcription factor that we found was down regulated in glioblastoma. As EMX2 is reported to play a role in carcinogenesis, we investigated the impact of EMX2 overexpression in glioma-related cell lines.
Auteurs, date et publication :
Auteurs Annabelle Monnier , Rachel Boniface , Régis Bouvet , Amandine Etcheverry , Marc Aubry , Tony Avril , Véronique Quillien , Eric Chevet , Jean Mosser
Publication : BMC Cancer
Date : 2018
Volume : 18
Issue : 1
Pages : 1213
Catégorie(s)
#CNRS #EcoGenO #Université de RennesAuteurs, date et publication :
Auteurs Roland Lupoli
Publication : Zoosystema
Date : 2025
Volume : 40
Issue : sp1
Pages : 21-29
Catégorie(s)
#CNRS #FORET NouraguesAuteurs, date et publication :
Auteurs Emily R Naylor , Timothy E Higham
Publication : Integrative and comparative biology
Date : 2025
Volume : 59
Issue : 1
Pages : 168-181