STERILE INTERSEXUALITY IN AN ISOPOD INDUCED BY THE INTERACTION BETWEEN A BACTERIUM (WOLBACHIA) AND THE ENVIRONMENT

An endocellular bacterium of the genus Wolbachia changes chromosomic ( ZZ) males into functional females in a number of populations of the wo odlouse Armadillidium vulgare. The interaction between the feminizing effect of Wolbachia and the lethal effect of high temperature on these bacteria is shown to be responsible for the appearance of high propor tions of sterile intersexes (Si). Wolbachia-infected females produced an average of 15% Si when reared for 200 days under a daily thermoperi odic regime that included 4 h at 30 degrees C. A temperature of 30 deg rees C is known to destroy Wolbachia. The Si phenotype may therefore b e due to the partial destruction (or inhibition) of the feminizing bac teria by high temperature during development. This induction of a prop ortion of Si differs in two ways from the intersexuality induced by th e conflict between the feminizing agent and a host autosomal gene. Fir st, the genomic conflict does not lead to the production of numerous S i, and second, the temperature-dependent production of Si is a sporadi c event induced by the environment, rather than being a heritable trai t. The overproduction of sterile offspring at high temperatures can re sult in Wolbachia-infected females of A. vulgare suffering a loss of f itness.