MINIGAN

The concept of genetic conflict is one of the most important legacies of twentieth century evolutionary biology, and has now become, in the era of massive sequencing, a major foundation of our understanding of genome evolution. Genetic conflicts occur within organisms between different genes that maximize their transmission in different ways. A spectacular example is cytoplasmic male sterility (CMS), whereby maternally transmitted mitochondrial genes suppress the male function in hermaphrodites, to the detriment of nuclear genes. The result is a sexual polymorphism called gynodioecy, whereby hermaphrodites coexist with females in populations. CMS and gynodioecy have been well studied theoretically, and empirically in plants. They have become one of the textbook examples of genetic conflicts. However CMS has surprisingly never been described in animals. In addition, tests of the evolutionary theory of gynodioecy remained indirect, as the long generation time of most gynodioecious plants made it complicated to observe evolutionary dynamics over generations, in real time. We recently discovered the first animal example of CMS in a hermaphroditic freshwater snail Physa acuta (Pa) and propose to use this species as a new model to study genetic conflicts. Capitilizing on the short generation time of this snail - easy to breed in the lab-, and on the preliminary data accumulated in the past two years, we propose a project that will not only open this field of evolutionary genetics to a new clade (animals), but also follow hitherto unexplored, exciting research avenues, such as experimental evolution. MINIGAN is organized along four axes / questions. (i) What is the geographical distribution of CMS and does it occur in specific environmental conditions? (ii) Is male sterility compensated by a female advantage, how and when is this advantage expressed ? (iii) Can we directly observe the co-evolutionary cycles of mitochondrial and nuclear genomes predicted by models, as a consequence of mtDNA suppressing male function while some nuclear genes restore it ? (iv) What is the genomic signature of gynodioecy ? How does CMS affect mitochondrial and nuclear genomes and transcriptomes? We will rely on a variety of approaches already used in plant models including field sampling, PCR, intensive lab experiments, together with more innovative methods such as experimental evolution, genome scans, and transcriptomics. This project is ambitious, requiring long-term (2yr) experimental evolution and a de-novo assembly of the snail genome, and a large re-sequencing effort. This combination of various techniques results in a balanced mix of relatively low-risk and high-risk, high-gain approaches. The diversity of methods also echoes the complementarity of competences present in the three different partners of the consortium and their respective scientific leaders. The project is coordinated by P. David in CEFE (Montpellier), broad-spectrum evolutionary biologist, quantitative and population geneticist, and specialist of animal mating systems with long experience with working with snails as model systems. A whole team, including a specialist of gynodioecy in plants, will assist him in the CEFE. Both E. Luquet and J. Romiguier (respectively leaders of the LEHNA partner in Lyon and ISEM partner in Montpellier) are talented young researchers who, together with their associated teams, will bring their knowledge in life-history evolution, transcriptomics and genomics. Collaboration will be facilitated by geographical proximity, and the succesful past collaborations between the partners on the snail model, already materialized by common publications and by the obtention of the preliminary results forming the basis of this project. Gathering a well-integrated consortium of high-profile research teams with complementary skills, MINIGAN has the potential to shed a new light on the dynamics of CMS, and more generally on genetic conflicts.