Spiders are host to a plethora of heritable endosymbiotic bacteria. Broad-taxa screening studies indicate that endosymbionts are particularly common among spiders, however, little is known about how these bacteria affect their spider hosts. In insects these bacteria ensure vertical transmission by either conveying a benefit to the host or manipulating host reproduction to eliminate males that serve as evolutionary dead-ends for maternally-inherited bacteria. Common modes of reproductive manipulation include parthenogenesis, male killing, feminization, and cytoplasmic incompatibility. Screening an assemblage of Mermessus genus spiders, I detected a high frequency and diversity of endosymbiont infection. Within a single species, M. fradeorum, I detected three endosymbionts in multiple combinations. Rearing two natural infection types of M. fradeorum demonstrated two distinct endosymbiotic reproductive manipulations. Mothers infected with Rickettsia and Wolbachia produced extremely female-biased offspring, and antibiotic elimination of the symbionts successfully restored the sex ratio to the expected 1:1 in subsequent generations. A two-way factorial mating assay detected strong cytoplasmic incompatibility induced by a different strain of Wolbachia: cured females mated with infected males produced 70% fewer offspring than all other pairings. These results show that M. fradeorum is subject to multiple layers of reproductive manipulation that likely drive host evolution and ecology.

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