Masculinization of female isopods (Crustacea) correlated with non-Mendelian inheritance of cytoplasmic viruses.

When in genetic females external male characters differentiate, the phenomenon is called "male pseudohermaphroditism." This male differentiation occurs in terrestrial isopods (Crustacea, suborder Oniscoidea) and sometimes involves only some epithelial areas (gynandromorphous mosaics). It is not induced by male hormones or by abnormal ovary function. This intersexuality is transmitted maternally (by the intersex females) or paternally (by the brothers of intersex females) to between 30% and 60% of their offspring. Although it occurs at 20 degrees C, the male differentiation disappears when breeding takes place at 27 degrees C. Male characters differentiate in normal females--even in other Oniscoidea species (Porcellio dilatatus, Porcellio laevis, Armadillidium vulgare)--after injection of a 0.22-micron filtered tissue extract. Since an inhibitor of bacterial protein synthesis (gentamycin) does not inhibit this masculinizing effect, we infer that neither organelles nor bacteria are involved. Intersexuality is always correlated with the presence of cytoplasmic viral particles in both intersex-female and transmitter-male tissues. Striking similarities to the Drosophila S virus are noted. A reovirus-like Oniscoidea masculinizing virus, which probably acts only on the epithelial areas sensitive to the male hormones, is most likely the causative agent of this intersexuality. Here we report the conversion of secondary sexual characters putatively caused by a virus.