Supergroup F Wolbachia in terrestrial isopods: Horizontal transmission from termites?

Abstract

Horizontal transmission between distantly related species has been used to explain how Wolbachia infect multiple species at astonishing rates despite the selection for resistance. Recently, a terrestrial isopod species was found to be infected by an unusual strain of supergroup F Wolbachia. However, only Wolbachia of supergroup B is typically found in isopods. One possibility is that these isopods acquired the infection because of their recurrent contact with termites-a group with strong evidence of infection by supergroup F Wolbachia. Thus, our goals were: (1) check if the infection was an isolated case in isopods, or if it revealed a broader pattern; (2) search for Wolbachia infection in the termites within Brazil; and (3) look for evidence consistent with horizontal transmission between isopods and termites. We collected Neotroponiscus terrestrial isopods and termites along the Brazilian coastal Atlantic forest. We sequenced and identified the Wolbachia strains found in these groups using coxA, dnaA, and fpbA genes. We constructed phylogenies for both bacteria and host taxa and tested for coevolution. We found the supergroup F Wolbachia in other species and populations of Neotroponiscus, and also in Nasutitermes and Procornitermes termites. The phylogenies showed that, despite the phylogenetic distance between isopods and termites, the Wolbachia strains clustered together. Furthermore, cophylogenetic analyses showed significant jumps of Wolbachia between terrestrial isopods and termites. Thus, our study suggests that the horizontal transmission of supergroup F Wolbachia between termites and terrestrial isopods is likely. Our study also helps understanding the success and worldwide distribution of this symbiont.

Multiple long-range host shifts of major Wolbachia supergroups infecting arthropods

“…Although Wolbachia HS is a well-documented phenomenon 6 , 7 , 18 , 31 – 34 , a large amount of the literature depicts it as a rare event 19 , 20 . Our comparative genomic analyses of several Wolbachia strains and their hosts reinforce the occurrence of HS in these bacteria, showing many cases in which different host species share Wolbachia more similar than would be expected by long-term coevolution of vertically transmitted endosymbionts with their hosts.…”

“…HS depends on specific environmental conditions to happen, alongside the ability of a Wolbachia strain to infect a new host and maintain the infection 7 . It has been hypothesised that the closer the phylogenetic relationship of the hosts, the more likely HS is to occur 34 , which may induce novel phenotypes in the new host 18 . The underlying mechanisms of HS are not yet fully understood, leading it to be overlooked on many occasions.…”

Extremely reduced supergroup F Wolbachia: transition to obligate insect symbionts

“…For example, the two strains from philopterid lice, wAlce and wPaur, do not cluster as sister taxa in any of the analyses. While the tree resolution is rather poor and does not provide clear evidence, horizontal transfers within the F supergroup have been deduced previously, e.g., between isopods and termites (13). This apparent lack of a coevolutionary signal is also concurrent with the absence of Wolbachia in all other screened SRA data for chewing lice (discussed below), and with the presence of a phylogenetically distant gammaproteobacterial symbiont in Columbicola columbae (27,62,63).…”

“…Occasional screenings suggest that the supergroups underrepresented by genomic data may encompass a high diversity of Wolbachia strains. As an example, supergroup F, currently represented by four genomes and genome drafts from two nematodes and two arthropods (1,(8)(9)(10), seems to contain a wide variety of Wolbachia from different hosts when screened for specific Wolbachia genes (2,(11)(12)(13).…”

Narrow Genetic Diversity of Wolbachia Symbionts in Acrididae Grasshopper Hosts (Insecta, Orthoptera)

“…There are ~20 lineages of Wolbachia called supergroups, and these are designated alphabetically with some omissions [ 4 , 5 , 6 ]. Strains belonging to supergroups A and B are predominant in arthropods, especially in insects, and the F supergroup seems to take third place and is partitularly detectable in Nematoda [ 7 ], Coleoptera [ 8 , 9 , 10 ], Diptera [ 11 ], Hemiptera [ 12 ], Hymenoptera [ 1 , 13 , 14 ], Isopoda [ 15 ], Odonata [ 16 ], Scorpiones [ 17 ], Strepsiptera [ 18 ], and Termites [ 1 , 19 , 20 , 21 ]. Strains of other Wolbachia lineages are found much less frequently and are often associated with a specific host taxon.…”