Are ecological communities the seat of endosymbiont horizontal transfer and diversification? A case study with soil arthropod community.

Maternally inherited endosymbionts of arthropods are one of the most abundant and diverse group of bacteria. These bacterial endosymbionts also show extensive horizontal transfer to taxonomically unrelated hosts and widespread recombination in their genomes. Such horizontal transfers can be enhanced when different arthropod hosts come in contact like in an ecological community. Higher rates of horizontal transfer can also increase the probability of recombination between endosymbionts, as they now share the same host cytoplasm. However, reports of community-wide endosymbiont data are rare as most studies choose few host taxa and specific ecological interactions among the hosts. To better understand endosymbiont spread within host populations, we investigated the incidence, diversity, extent of horizontal transfer, and recombination of three endosymbionts (, and ) in a specific soil arthropod community. strains were characterized with MLST genes whereas 16 gene was used for and . Among 3,509 individual host arthropods, belonging to 390 morphospecies, 12.05% were infected with , 2.82% with and 2.05% with . Phylogenetic incongruence between host and endosymbiont indicated extensive horizontal transfer of endosymbionts within this community. Three cases of recombination between supergroups and eight incidences of within-supergroup recombination were also found. Statistical tests of similarity indicated supergroup A and show a pattern consistent with extensive horizontal transfer within the community but not for supergroup B and . We highlight the importance of extensive community-wide studies for a better understanding of the spread of endosymbionts across global arthropod communities.