Guillemet M. auteur aut IRD Chabas H. auteur aut IRD Nicot A. auteur aut IRD Gatchich F. auteur aut IRD Ortega Abboud Enrique auteur aut IRD Buus C. auteur aut IRD Hindhede L. auteur aut IRD Rousseau G.M. auteur aut IRD Bataillon T. auteur aut IRD Moineau S. auteur aut IRD Gandon S. auteur aut IRD text journalArticle eng text/pdf born digital access The diversity of resistance challenges the ability of pathogens to spread and to exploit host populations. Yet, how this host diversity evolves over time remains unclear because it depends on the interplay between intraspecific competition among host genotypes and coevolution with pathogens. Here we study experimentally the effect of coevolving phage populations on the diversification of bacterial CRISPR immunity across space and time. We demonstrate that the negative-frequency-dependent selection generated by coevolution is a powerful force that maintains host resistance diversity and selects for new resistance mutations in the host. We also find that host evolution is driven by asymmetries in competitive abilities among different host genotypes. Even if the fittest host genotypes are targeted preferentially by the evolving phages, they often escape extinctions through the acquisition of new CRISPR immunity. Together, these fluctuating selective pressures maintain diversity, but not by preserving the pre-existing host composition. Instead, we repeatedly observe the introduction of new resistance genotypes stemming from the fittest hosts in each population. These results highlight the importance of competition on the transient dynamics of host-pathogen coevolution. specialized 074MICFLO01 020BIOL 6 10 1480-1488 2022 2397-334X https://www.documentation.ird.fr/hor/fdi:010095219 10.1038/s41559-022-01841-9 2397-334X [F B010095219] https://www.documentation.ird.fr/hor/fdi:010095219 https://www.documentation.ird.fr/intranet/publi/2025-11/010095219.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2025-11-03 2025-11-12 fdi:010095219 fre