Shape change in viable eggs of the collembolan Folsomia candida provides insight into the role of Wolbachia endosymbionts

The endosymbiotic bacteria of the genus Wolbachia that infect the collembolan species Folsomia candida are responsible for facilitating parthenogenetic reproduction in their hosts. This study made empirical observations of the development of eggs of F. candida which contained normal populations of Wolbachia and of eggs which were cured of Wolbachia by treatment with the antibiotic rifampicin. A marked increase in egg size accompanied by a significant change in shape from spherical to discoid occurred in viable eggs three to four days after laying. These changes did not occur in the universally inviable eggs which came from the antibiotic treatment or in the 7% of untreated eggs which were naturally inviable. We infer that Wolbachia plays a critical role in zygotic or embryonic development during or before the first three days after laying and we draw on existing knowledge in speculating on the developmental mechanisms that Wolbachia may influence.