Data from: Wolbachia feminises a spider host with assistance from co-infecting symbionts

Arthropods commonly harbor maternally-transmitted bacterial symbionts that
manipulate host biology. Multiple heritable symbionts can co-infect the
same individual, allowing these host-restricted bacteria to engage in
cooperation or conflict, which can ultimately affect host phenotype. The
spider Mermessus fradeorum is variably infected with up to five heritable
symbionts: Rickettsiella (R), Tisiphia (T), and three strains of Wolbachia
(W1-3). Quintuply infected spiders are feminized, causing genetic males to
develop as phenotypic females and produce almost exclusively female
offspring. We compared feminization rates (proportion of female offspring
out of total) across nine infection combinations. We also compared
feminization rates across a subset of three infection types (Uninfected,
RTW1, and RTW123) in a second iteration of the experiment to validate
coinfection effects on feminization strength observed in the first
iteration of the feminization experiment. In both experiments we found
that the Wolbachia strain W1 was required for feminization and this
phenotype was strongest in quintuply infected spiders, implying a
synergistic effect of coinfection on W1 feminization. Using digital PCR
(dPCR), we estimated the amount of symbionts in different infection
combinations to determine if a) symbiont titer changes across
coinfections, and b) if W1 titer correlates with feminization strength. We
extraction the DNA of adult females from the first feminization experiment
and use species specific dPCR primers to analyze titer. We found limited
changes in symbiont titer in different symbiont co-infections, suggestive
of subtle effects of co-infection on the composition of the symbiont
community. The synergistic effect of co-infection on Wolbachia
feminization may help promote the spread of all five symbionts in spider
populations. These results confirm the first instance of Wolbachia-induced
feminization in spiders and demonstrate that co-infecting symbionts can
improve the efficacy of symbiont-induced feminization.