Heterogeneous distribution of sex ratio distorters in natural populations of the isopodArmadillidium vulgare

Abstract

AbstractIn the isopodArmadillidium vulgare, many females produce progenies with female-biased sex ratios, due to two feminizing sex ratio distorters (SRD):Wolbachiaendosymbionts and thefelement. 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 1990’s, we found that the SRD are present at variable frequencies in populations, and that thefelement is overall more frequent thanWolbachia. The two SRD never co-occur at high frequency in any population, suggesting an apparent mutual exclusion. We also detectedWolbachiaor thefelement in some males, which likely reflects insufficient titer to induce feminization or presence of masculinizing alleles. Our results are consistent with a single integration event of aWolbachiagenome in theA. vulgaregenome at the origin of thefelement, which contradicts an earlier hypothesis of frequent losses and gains. We identified strong linkage betweenWolbachiastrains and mitochondrial haplotypes, but no association between thefelement and mitochondrial background. Our results open new perspectives on SRD evolutionary dynamics inA. vulgare, the evolution of genetic conflicts and their impact on the variability of sex determination systems.