A new strain of Wolbachia in the harlequin beetle riding pseudoscorpion: Male killing, reproductive compensation and horizontal transfer.

摘要

The cellular endosymbiont, Wolbachia, kills or feminizes males or causes cytoplasmic incompatibility in a wide array of arthropod hosts. Here, we describe a new female-biasing Wolbachia strain (NFB) from the harlequin beetle-riding pseudoscorpion, Cordylochernes scorpioides . Pseudoscorpions are viviparous, with embryos developing in a translucent brood sac. This "external womb" facilitates visual assessment of embryonic development and the consequences of endosymbiont infection for host fitness. In an investigation that combined inheritance studies, antibiotic treatment and molecular assays, sex-ratio distortion was found to be maternally inherited and associated with lower female reproductive success. Antibiotic treatment cured females of the Wolbachia infection, restored offspring sex ratio to 1:1 and significantly improved reproductive success. Photomicroscopy documented that, although infected C. scorpioides females produced similar numbers of early-stage embryos as tetracycline-cured females, they gave birth to significantly fewer offspring, indicating that female bias results from the killing of male embryos. However, infected females gave birth to significantly more female offspring than the tetracycline-cured females. Furthermore, these female offspring were larger than those of the treated group, and female size is known to be positively correlated with protonymphs production. The increased number and size of female offspring born to infected females appears to result from reproductive compensation in which maternal resources are reallocated from dead male embryos to female siblings. Phylogenetic analysis, using Multilocus Sequence Typing (MLST), indicates that the NFB Wolbachia strain is closely related to a strain previously described from C. scorpioides, but the two differ extensively in their Wolbachia surface protein gene sequences, because of possible recombination with a nematode-infecting Wolbachia strain. Even one of the highly conserved MLST genes, coxA revealed incongruencies that can be explained with horizontal gene transfer (HGT). These apparent HGT events are associated with increased potential for the spread of the NFB Wolbachia strain within C. scorpioides populations.