DS10 - Défi des autres savoirs

Genomics of clonality: A novel approach using sex in asexuals – GENASEX

Submission summary

The observation that most eukaryotic species are sexual and that asexual species are rare and recent remains one of the greatest puzzles of contemporary evolutionary biology. This puzzle is a theoretical one because sex involves very strong costs relative to asexual reproduction (e.g., the famous twofold cost of males). Yet, it is also an empirical challenge as performing experiments aimed at understanding the maintenance of sex have proven extremely difficult, despite very intensive effort over several decades. Recently, population genomics approaches have increasingly been used to study asexuality. They have started to provide answers on a number of questions, such as the ages of clones and differentiation from related sexual species. While these studies have improved of our understanding of asexuality, they were nonetheless unable to overcome two major empirical limitations: First, asexuals sampled in nature represent a highly selected subset of the most successful lineages, which strongly complicates the interpretation of any results obtained on them. Second, the inability to perform crosses and to study segregating variation in asexuals by their very definition (they reproduce without crossing) largely makes classical genetics unavailable for asexuals. This is problematic because, even after the advent of genomics, classical genetics remains an extremely powerful tool for understanding the inheritance of characters, notably because crosses allow manipulating genotypes rather than performing correlations on existing variation. To overcome both limitations, we propose three innovative empirical breakthroughs: (1) Clone engineering is a method to generate new clones in the laboratory (already designed and tested by us and others on two model organisms, Daphnia and Artemia). (2) Asexual mapping is a new technique to study the linkage map of asexuals. This technique takes advantage of so-called “rare males” in asexual lineages, making it possible to study asexuals with classical and modern genetic/genomic tools that rely on crosses. We already obtained pilot results with this method, and this project will use it at a full scale. (3) An estimation of genetic load in asexuals using inbreeding depression in asexuals, assessed via back-crosses. The experimental studies will be complemented by a population genomic and theoretical approach. These key innovations and their combination will allow us to address three outstanding questions, each corresponding to one of the three objectives of the project: What is the genetic basis of asexuality (objective 1)? What are the genomic consequences of asexuality and the genome structure of asexuals (objective 2)? What are the fitness consequences of asexuality (objective 3)? Together, this project offers a highly original, powerful, and novel (because hitherto largely unexplored) approach to the study of asexuality, and answering these questions will represent a very large step forward in our understanding of the maintenance of sex, in particular by determining how much of the “cost of males” can be paid by the accumulation of deleterious mutations in asexuals.

Project coordination

Christoph HAAG (Centre d'Ecologie Fonctionnelle et Evolutive)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

ISEM CNRS UMR 5554 Institut des Sciences de l'Evolution de Montpellier
BEEA CNRS UMI 3614 Biologie Evolutive et Ecologie des Algues
Indiana Univ USA Department of Biology
ECOBIO Institut des Sciences de l'Evolution de Montpellier
CEFE CNRS UMR 5175 Centre d'Ecologie Fonctionnelle et Evolutive

Help of the ANR 543,391 euros
Beginning and duration of the scientific project: June 2018 - 48 Months

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