ADAPTIVE SUCCESS OF WOLBACHIA IN ARTHROPODS – ADaWOL

The endosymbiotic '-proteobacteria of the genus Wolbachia inflict an impressive arsenal of reproductive alterations to increase their frequency in their host's offspring. Wolbachia can also express direct virulence, especially upon transfection, reducing the life span of their host. 'Wolbachia based control strategies' propose to trick Wolbachia into fighting their hosts, using these effects to restrict populations of arthropod pest and disease vector. Such strategies would spare the environment from pesticides. But this means successfully releasing Wolbachia strains in new environments, by injecting them in hosts or by invading hosts populations with natural Wolbachia carriers. Such a procedure cannot be considered safe if we do not control Wolbachia spread. That, actually, is a major issue, because Wolbachia do not transmit only maternally but also frequently capture new hosts, as demonstrates the poor congruence between Wolbachia and hosts phylogenies. Wolbachia dispersal through horizontal transmission is now a well accepted concept, but the mechanisms involved remain unknown. Insect models, producing a high number of generations in a short time, are appreciated to study the long-term consequences of host-switching. But insect life span is so short that host-switching experiments abruptly result in a colonized host, locking up in a black box all the fine steps of the colonization process, possible host riposte and retaliation. Terrestrial isopods, in constrast, have a three-year life span and a much longer development, and allow monitoring these processes in slow motion, i.e. opening this black box. The LEES group works on Wolbachia-Isopod symbioses since 1970, with perspectives ranging from symbiont genomics to using isopods as bioindicators. The first transfection experiments were published as soon as 1974: Indeed, it is easy to inject Wolbachia to these large animals and the puncture heals very well, whereas insects require tiresome microinjection techniques, often applicable to embryos only. Our rearings now count 35 species of isopods (~250,000 individuals) including 18 Wolbachia infected species serving as 'live containers' to grow the Wolbachia strains. We possess both feminizing and cytoplasmic incompatibility (CI) inducing strains, the latter being the type mostly found in insects. ADaWOL ("Add a Wolbachia") will investigate Wolbachia adaptative skills toward new hosts by switching feminizers and CI-inducers across naïve or already infected isopod species. We will monitor Wolbachia virulence on host survival and development, we will track colonization dynamics through qPCR and Fluorescence in situ Hybridization, and we will watch for consequences on host-immunocompetence. To link proximal and distal consequences of host-switching, we will survey host fitness, Wolbachia transmission rate and reproductive alteration through at least three generations. Additionally, the collected data will be implemented to the software Sexdet to simulate the evolution of Wolbachia invasion and effect in populations through n generations.