| Abstract: | The woodlouse Armadillidium vulgare is characterized by female heterogamety (ZW) and male homogamety (ZZ). However, in several populations, sex determination is influenced by cytoplasmic sex factors (endosymbiotic bacteria = F). At 20 °C these maternally transmitted bacteria reverse genetic males into functional neo-females (ZZ + F) producing highly female broods. When these neo-females were reared at 30° C, the sex ratio of their broods became male-biased. The major process involved in this heat-induced sex ratio inversion was the disappearance of bacteria in embryos in the course of their development, which allowed the young to express a phenotype that conforms with their genotype (i.e. male ZZ). No heat-sensitive stage of development was observed, but at least 35 days at 30° C seem to be necessary to induce F-degradation. The presence of F at 30° C (before its degradation) also induced mortality during vitellogenesis. Daily thermoperiods including a thermophase at 30° C had effects on F similar to that of a constant temperature of 30° C. A. vulgare can live in climates having such thermoperiods (at least during one period of the year), temperature appears to be capable of limiting the presence of F-bacteria in natural populations, and then modifying the evolution of sex-determining mechanisms in such populations. |
