ERC Advanced Grants 2025: Three scientists affiliated with Université Paris-Saclay receive grants

Tatiana Giraud, an agronomist and CNRS research director at the Ecology, Society and Evolution Laboratory (ESE - Université Paris-Saclay/CNRS/AgroParisTech), has received an ERC Advanced Grant for her project DEGENSEX, “Sex chromosome degeneration and its effects on fitness”.

In many living organisms, certain regions of sex chromosomes no longer exchange genetic material, as is the case with the X and Y chromosomes in humans. Such exchanges normally play an important role in “cleaning up” the genome by removing harmful mutations. When this exchange stops, genes located in these regions can gradually deteriorate: some disappear, while others function less effectively or are expressed at lower levels. This process, known as genomic degeneration, may contribute to differences in disease susceptibility or lifespan observed between the sexes in many species. Despite its importance, we still have a limited understanding of how this degeneration evolves and what its actual consequences are, particularly during the early stages of the process.

To address these questions, the DEGENSEX project will study groups of fungi whose reproductive chromosomes display a wide range of configurations, with numerous independent evolutionary transitions towards suppressed recombination and ages that vary considerably but are generally relatively recent. This diversity provides a natural laboratory for tracing the early stages of genomic degeneration, including gene loss, disrupted gene expression and chromosomal rearrangements.

The project will also seek to determine whether certain mechanisms can limit this degeneration. For example, organisms may sometimes compensate for the loss of gene activity by increasing the expression of their remaining gene copies or by acquiring new genes. The extent to which these mechanisms actually contribute to limiting degeneration remains a matter of debate among evolutionary biologists.

Studying fungi offers two key advantages: it will help determine whether phenomena observed in animals and plants are universal, while also making it possible to directly test in the laboratory the effects of genomic degeneration on organismal fitness and survival. By reconstructing the history of chromosome degeneration and the mechanisms that compensate for it, DEGENSEX will shed new light on a fundamental question in biology: how do genomes evolve when they cease to recombine, and what consequences does this have for organisms’ ability to survive?

Mathieu Daëron, a CNRS researcher at the Laboratory of Climate and Environmental Sciences (LSCE – Université Paris-Saclay/UVSQ/CEA/CNRS), has received an ERC Advanced Grant for his project TONIC, “Triple Oxygen Fingerprinting of Ice Sheets”.

Glaciations have profoundly shaped the climate and natural systems throughout Earth’s geological history. However, our understanding of how ice sheets respond to orbital forcing, greenhouse gases and plate tectonics remains limited by the lack of robust and widely applicable methods for tracing the presence of ice depleted in oxygen-18 over geological timescales (>100 ka). Reconstructing the oxygen-18 content of ice sheets, a key factor influenced by hydrology, climate and ice-sheet geometry (extent, continentality and altitude), would provide valuable insights into Earth’s history.

The TONIC project aims to fill this gap by establishing the combination of isotope clumping² and triple oxygen isotopes in marine carbonates as tracers of the oxygen-18 content of meltwater and, consequently, of ice-sheet dynamics. To this end, the project will establish a one-of-a-kind analytical laboratory equipped with state-of-the-art spectroscopic techniques, before calibrating this new tracer using modern carbonates and waters. It will then be applied to exceptionally well-preserved micro- and macrofossils to detect and characterise ice sheets from the Pleistocene to the Late Palaeozoic.

This work will provide key insights into (a) oxygen-18 ratios in now-vanished Pleistocene ice sheets; (b) Pleistocene megafloods linked to European glacial dynamics; (c) the formation, dynamics and composition of Antarctic ice during the Cenozoic, with major implications for interpreting oxygen-18 records in benthic carbonates; (d) the highly debated glaciations of the Mesozoic Era; and (e) the palaeolatitudinal isotopic gradient of Late Palaeozoic ice sheets.

The results will enable a critical reassessment of the canonical assumptions that seawater oxygen-18 content remained constant during supposedly ice-free periods, shed light on ice-sheet dynamics over both short and long timescales, and open up broad new avenues of research in the geosciences. The spectroscopic tools developed as part of the project will represent a major technical breakthrough in the isotopic analysis of CO₂ and other gases, with numerous multidisciplinary applications.

Vincent Pilloni, a CNRS research director at the Orsay Mathematics Laboratory (LMO - Université Paris-Saclay/CNRS), a specialist in arithmetic algebraic geometry and the Langlands programme, has received an ERC Advanced Grant for his project MOMO, “p-adic modular forms and modularity”.

The Langlands programme predicts a correspondence between algebraic varieties defined over number fields and certain automorphic forms. This correspondence remains largely conjectural, given the very different nature of the objects involved, which are algebraic and analytical respectively. Surprisingly, the most natural algebraic varieties, such as abelian varieties and Artin motives, appear to be related to highly mysterious automorphic forms. These forms can sometimes be found in the p-adic cohomology of Shimura varieties, particularly in completed cohomology and in higher Hida and Coleman theories, which are non-classical cohomology theories.

The aim of this project is to develop new techniques combining p-adic geometry, D-modules and p-adic Hodge theory to analyse these non-classical cohomology theories and identify the automorphic forms they contain. One of the project's objectives is to prove the modularity of abelian surfaces over the field of rational numbers. The modularity of elliptic curves has been known for almost thirty years.