Heterogeneous distribution of sex ratio distorters in natural populations of the isopod Armadillidium vulgare .

In the isopod , many females produce progenies with female-biased sex ratios, owing to two feminizing sex ratio distorters (SRD): endosymbionts and the element. We investigated the distribution and population dynamics of these SRD and mitochondrial DNA variation in 16 populations from Europe and Japan. Confirming and extending results from the 1990s, we found that the SRD are present at variable frequencies in populations and that the element is overall more frequent than . The two SRD never co-occur at high frequency in any population, suggesting an apparent mutual exclusion. We also detected or the element in some males, which probably reflects insufficient titer to induce feminization or presence of masculinizing alleles. Our results are consistent with a single integration event of a genome in the genome at the origin of the element, which contradicts an earlier hypothesis of frequent losses and gains. We identified strong linkage between strains and mitochondrial haplotypes, but no association between the element and mitochondrial background. Our results open new perspectives on SRD evolutionary dynamics in , the evolution of genetic conflicts and their impact on the variability of sex determination systems.