D3361: Do symbiont communities that manipulate spider reproduction and phenotype respond to selection?

Maternally-inherited symbionts are pervasive across arthropods, yet are often only studied as singular infections. These bacteria, estimated to infect approximately half of terrestrial arthropod species, primarily persist in populations through vertical transmission from mother to offspring. To facilitate the spread of infected lineages in the populations, these symbionts often manipulate the reproduction of their host. The Linyphiid spider, Mermessus fradeorum, is naturally co-infected with up to five strains of endosymbiotic bacteria (Rickettsiella, Tisiphia, and 3 strains of Wolbachia) and provides a novel opportunity to further our understanding of symbiont communities and their response to selective pressures. Spiders co-infected with all five symbionts have entirely female, feminized offspring. However, while the removal of a single Wolbachia symbiont strain degrades feminization, the strain cannot produce feminization on its own. Another symbiont, Rickettsiella, can induce and rescue a different reproductive manipulation, cytoplasmic incompatibility (CI). The expression of this phenotype is dependent on the endosymbiont community context. Therefore, the symbionts in this spider induce two contrasting reproductive manipulations in the same host individuals and hosts exhibit different reproductive phenotypes within a population. In this multigenerational experiment, we investigate the interactions of a community of coexisting endosymbionts within a shared host influence the phenotype and population dynamics and how, in return, host population dynamics shape the symbiont community.