In the terrestrial isopod Armadillidium vulgare, many females produce progenies with female-biased sex ratios due to two feminizing sex ratio distorters (SRD): Wolbachia endosymbionts and a nuclear non-mendelian locus called the f element. To investigate the potential impact of these SRD on the evolution of sex determination, we analyzed their temporal distribution in 6 A. vulgare populations sampled up to 6 times over 12 years, for a total of 29 time points. SRD distribution was heterogeneous among populations despite their close geographic locations, so that when one SRD was frequent in a population, the other SRD was rare. In contrast with spatial heterogeneity, our results overall did not reveal substantial temporal variability in SRD prevalence within populations, suggesting equilibria in SRD evolutionary dynamics may have been reached or nearly so. SRD temporal stability was also reflected in mitochondrial and nuclear variation, with two exceptions. One population was affected by anthropogenic alteration at the sampling spot between the earliest and second time points, likely explaining a rapid shift in genetic composition. However, subsequent global stability suggested that population dynamics equilibrium may be reached in a few generations. In another population, a Wolbachia strain replacement coincided with changes in mitochondrial composition but no change in nuclear composition, thus constituting a typical example of mitochondrial sweep caused by endosymbiont rise in frequency. Rare incongruence between Wolbachia strains and mitochondrial haplotypes further highlighted the occurrence of intraspecific horizontal transmission, making it a biologically relevant parameter for Wolbachia evolutionary dynamics in A. vulgare.

Temporal stability of sex ratio distorter prevalence in natural populations of the isopod Armadillidium vulgare