Ecological contacts and host specificity promote replacement of nutritional endosymbionts in ticks

Abstract Symbiosis with vitamin-provisioning microbes is essential for the nutrition of animals with specialized feeding habits. While coevolution stabilizes the interactions between symbiotic partners, their associations are not necessarily permanent: Recently acquired symbionts can replace ancestral symbionts. In this study, we demonstrate successful replacement dynamics of Francisella-Like Endosymbionts (-LE), a group of invasive B-vitamin-provisioning endosymbionts, across tick communities driven by a complex web of horizontal transfers. Using a broad collection of Francisella-LE-infected tick species, we determined the diversity of Francisella-LE haplotypes through a multi-locus strain typing approach, and further characterized their phylogenetic relationships and their association with biological traits of their tick hosts. The patterns observed showed that Francisella-LE commonly transfer through similar ecological networks and geographic distributions shared among different tick species, and, in certain cases, through preferential shuffling across congeneric tick species. Altogether, these findings reveal the importance of both routes in shaping the invasive pattern in which new nutritional symbioses are initiated.