Mitochondrial DNA polymorphism, sex ratio distorters and population genetics in the isopod Armadillidium vulgare

Two maternally inherited sex ratio distorters (SRD) impose female-biased se x ratios on the wood louse Armadillidium vulgare by feminizing putative mal es. These SRD are (i) an intracytoplasmic bacterium of the genus Wolbachia, and (ii) another non-Mendelian element of unknown nature: the f element. M itochondrial DNA variation was investigated in A. vulgare field populations to trace the evolution of host-SRD relationships and to investigate the ef fect of SRD on host cytoplasmic polymorphism. The Wolbachia endosymbionts s howed no polymorphism in their ITS2 sequence and were associated with two c losely related mitochondrial types. This situation probably reflects a sing le infection event followed by a slight differentiation of mitochondria. Th ere was no association between the f element and a given mitochondrial type , which may confirm the fact that this element can be partially paternally transmitted. The spreading of a maternally inherited SRD in a population sh ould reduce the mitochondrial diversity by a hitchhiking process. In A. vul gare, however, a within-population mtDNA polymorphism was often found, beca use of the deficient spread of Wolbachia and the partial paternal inheritan ce of the f element. The analysis of molecular variance indicated that A. v ulgare populations are genetically structured, but without isolation by dis tance.