Horizon 1 1 17 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES Molecular Ecology 1016-1029 coevolution endosymbiont replacement maternally inherited bacteria microbial community symbiosis ticks 2020 fdi:010077931 ENG Molecular Ecology 0962-1083 ISI:000515069900001 5 10.1111/mec.15373 https://www.documentation.ird.fr/hor/fdi:010077931 https://www.documentation.ird.fr/intranet/publi/depot/2020-11-19/010077931.pdf 29 Horizon (IRD) Mutualistic interactions with microbes have facilitated the adaptation of major eukaryotic lineages to restricted diet niches. Hence, ticks with their strictly blood-feeding lifestyle are associated with intracellular bacterial symbionts through an essential B vitamin supplementation. In this study, examination of bacterial diversity in 25 tick species of the genus Amblyomma showed that three intracellular bacteria, Coxiella-like endosymbionts (LE), Francisella-LE and Rickettsia, are remarkably common. No other bacterium is as uniformly present in Amblyomma ticks. Almost all Amblyomma species were found to harbour a nutritive obligate symbiont, Coxiella-LE or Francisella-LE, that is able to synthesize B vitamins. However, despite the co-evolved and obligate nature of these mutualistic interactions, the structure of microbiomes does not mirror the Amblyomma phylogeny, with a clear exclusion pattern between Coxiella-LE and Francisella-LE across tick species. Coxiella-LE, but not Francisella-LE, form evolutionarily stable associations with ticks, commonly leading to co-cladogenesis. We further found evidence for symbiont replacements during the radiation of Amblyomma, with recent, and probably ongoing, invasions by Francisella-LE and subsequent replacements of ancestral Coxiella-LE through transient co-infections. Nutritional symbiosis in Amblyomma ticks is thus not a stable evolutionary state, but instead arises from conflicting origins between unrelated but competing symbionts with similar metabolic capabilities. 052 ; 020 UR224 Gabon