Biology subjects

Lecuyer, C.

Publications and source records attributed to Lecuyer, C..

4 recordsLinked to original sources

bioRxiv2025

Establishment, maintenance and consequences of inter-individual transcriptional variability for a gene involved in nitrate nutrition in plants

Differences in phenotypes and gene expression are observed between genetically identical plants grown in the same environment. While we now have a good knowledge of the source and consequences of transcriptional differences observed between cells, in particular in unicellular organisms, it is still very scarce when it comes to variability between multicellular organisms. Using NRT2.1, a high affinity nitrate transporter gene, as a model for high inter-individual transcriptional variability, we showed that differences in expression between plants for that gene are established in young seedlings, maintained over time but not transmitted to the next generation. Our results also indicate that these differences in expression could have phenotypic consequences. Indeed, they can explain phenotypic variability for the root growth as well as the amount of nitrate imported by the NRT2.1 protein in the plant. Finally, we found an enrichment for genes involved in photosynthesis among the ones with an expression correlated with NRT2.1 in single seedlings. All in all, our study suggests that a global coordination of the genes involved in the carbon/nitrate balance in plants is established in young seedlings, with differences in this state between plants, and then maintained over time.

plant biology↗

bioRxiv2025

Towards a tracking of bird migratory behaviour through geological time: an isotopic and histological approach

O_LIBird seasonal migration is a remarkable biogeographic phenomenon, yet its deep-time origin(s) and evolutionary history remain poorly understood, with the bird fossil record largely overlooked. This study explores the predictability of bird migratory behaviour from the oxygen isotope composition of their bone apatite phosphate ({delta}18Op), a promising approach in this regard because: (i) sedentary and migratory birds tend to occupy distinct climatic niches year-round; (ii) their {delta}18Op values primarily reflect the climate-driven isotopic composition of their drinking water; and (iii) this isotopic signature can persist through fossilisation. C_LIO_LIBone tissues were categorised based on their potential to yield spatio-temporally distinct climatic records: Early Bone Tissues (EBT), deposited before somatic maturity, and Late Bone Tissues (LBT), formed through bone remodelling over the lifespan. The predictability of migratory behaviour was theoretically assessed by modelling tissue-specific {delta}18Op values for thousands of birds across 77 migratory and sedentary species, using tracking and observational data along with a revised phosphate-water fractionation equation. These theoretical results were confronted with data from 11 extant bird species, obtained using a new experimental framework combining histological and isotopic analyses. C_LIO_LIA significantly positive correlation between {delta}18Op and the proportion of LBT in bone samples was observed both theoretically and experimentally in migratory birds - particularly in long-distance migrants - and is predicted to be virtually absent in sedentary species at temperate latitudes. Migratory birds that died outside their natal sites can also be identified when their {delta}18Op,EBT values fall outside the range observed in local juvenile and sedentary birds. C_LIO_LIWe conclude that bird migratory behaviour can be inferred from the {delta}18Op values of their skeletal remains, provided the individuals migrated across sufficiently contrasting climatic zones. While this approach cannot detect all migratory behaviours - such as short-distance or longitudinal movements - it is unlikely to misclassify sedentary birds as migratory at temperate latitudes. We therefore argue that this approach can be extended to well-preserved fossil bones to infer past bird migratory behaviours, as long as the palaeoclimatic context is carefully considered. More broadly, this study establishes a framework for inferring migratory behaviour in any vertebrate from non-fully remodelled biomineralised remains. C_LI

evolutionary biology↗

bioRxiv2024

High δ15N values in Predynastic Egyptian archeological remains: A potential indicator for localised soil fertilisation practices in extreme conditions

Predynastic Egypt arose around 5700 BC when nomadic people settled in the Nile Valley. Without voluntary practice related to anthropic mummification, as will be seen with the Egyptian Dynastic empires, human remains from this period were naturally mummified because of the natural environmental conditions, possibly enveloped in plant mats and animal skins. This study focuses on four mummies from the Natural History Museum of Musee des Confluences in Lyon (France). The geographic origin of the mummies and climatic conditions at that time were deduced from o18O measurements on teeth and bones. These measurements confirm that the primary source of drinking water was the Nile, and that one mummy of unknown origin also originated from Upper Egypt like the other three. The diet and life habits of these individuals were inferred from carbon (o13C), nitrogen (o15N) and sulfur (o34S) isotope compositions of their skins and bone collagens. Our study is of particular interest as we were able to analyse the animal skins and plant material enveloping the mummies using the same isotopic systems. The mean o15N values obtained in human skins (17.9{+/-}2.4{per thousand}, AIR) were found to be high, and consistent with the values measured in animal skins (16.0{+/-}2.9{per thousand}, AIR). The analysed plants have even higher values, with an average of 22.1{+/-}2.2{per thousand}, AIR. The most probable explanation for the markedly elevated {delta}15N values observed in all the materials investigated is localised soil amendment practices. This is corroborated by the consistent nitrogen isotopic signatures across all the examined tissues, with a notable prevalence in plant tissues.

ecology↗

bioRxiv2024

Reassessment of body temperature and thermoregulation strategies in Mesozoic marine reptiles

Ichthyosauria, Plesiosauria and Metriorhynchidae were apex predators in Mesozoic oceanic trophic networks. Previous stable oxygen isotope studies suggested that several taxa belonging to these groups were endothermic and for some of them homeothermic organisms. However, these conclusions remain contentious owing to the associated uncertainties regarding the {delta}18O value and oxygen isotope fractionation relative to environmental sea water. Here, we present new hydroxylapatite phosphate {delta}18O values ({delta}18Op) of Ichthyosauria, Plesiosauria and Metriorhynchidae (Middle Jurassic to Early Cretaceous) recovered from mid- to high-paleolatitudes to better constrain their thermophysiology and investigate the presence of regional heterothermies. The intra-skeletal {delta}18Op variability failed to reveal distinct heterothermic patterns within any of the specimens, indicating either intra-body temperature homogeneity or an overriding diagenetic overprint of the original biological {delta}18Op bone record. Body temperature estimates have then been reassessed from new and published {delta}18Op values of well-preserved isolated teeth, recently revised Mesozoic latitudinal {delta}18O oceanic gradient and 18O-enrichment factor of fully aquatic air-breathing vertebrates. Our results confirm that Ichthyosauria were homeothermic endotherms (31{degrees}C to 41{degrees}C), while Plesiosauria were likely poikilothermic endotherms (27{degrees}C to 34{degrees}C). The new body temperature estimates of the Metriorhynchidae (25{degrees}C to 32{degrees}C) closely follow ambient temperatures and point to poikilothermic strategy with no or little endothermic abilities. These results improve our understanding of Mesozoic marine reptile thermoregulation and indicate that due to their limited body temperature variations, the {delta}18Op values from Ichthyosauria fossil remains could be used as valuable archives of Mesozoic oceans {delta}18Osw values that may help improve palaeoenvironmental and palaeoclimatic reconstructions. Non-technical abstractSome marine reptiles from the Mesozoic such as ichthyosaurs, plesiosaurs and metriorhynchids, were capable of reaching elevated body temperatures and for some of them to maintain it few degrees above that of their marine environment, a characteristic similar to that observed in modern cetaceans. Nevertheless, the estimation of their body temperature from the chemical oxygen signature of their fossil remains (bones and teeth) is accompanied by uncertainties associated with the chemical oxygen signature of the surrounding water and the mineralisation processes of the bones and teeth. In this study, new data were collected from four ichthyosaurs, three plesiosaurs and one metriorhynchid in order to gain a deeper understanding of the mechanisms by which these marine reptiles were able to maintain a body temperature higher than that of their environment. The chemical signatures of oxygen in the bones and teeth of the specimens did not exhibit any discernible patterns indicative of specific zones of heat production or loss, as observed in modern marine vertebrates. Concurrently, we reassessed the estimated body temperature of these marine reptiles, thereby corroborating the hypothesis that ichthyosaurs were homeothermic endotherms. Conversely, our novel estimates suggest that plesiosaurs were likely poikilothermic endotherms, whereas metriorhynchids were probably also poikilothermic endotherms but with a limited capacity for heat production. Finally, the narrow range of body temperatures maintained by ichthyosaurs indicates that the oxygen chemical signature of fossilised remains could serve as a valuable marker for reconstructing variations in the oxygen isotope composition of the Mesozoic oceans, paving the way to enhance our understanding of the environment and climate of this period in Earths history.

paleontology↗