Evolutionary consequences of Wolbachiaisopod interactions Diverse sexratio distorters in Armadillidium vulgare

In A. vulgare, chromosomal sex determination follows a female heterogamety (i.e ., ZW females and ZZ males; Juchault and Legrand, 1972). Two parasitic feminizing factors are known in this species . The first one is the Wolbachia endosymbiont, which is located in all tissues of females and especially concentrated in oocytes (Martin et al ., 1973; Rigaud et al , 1991) Whatever their sexual genotype, all zygotes inheriting Wolbachia will develop a female phenotype In this respect, ZZ males are changed into functional females which, in turn, produce female-biased broods . It has been shown that, in natural populations, all Wolbachia-infected females actually are ZZ individuals sexually reversed by the symbionts (Juchault et al ., 1993) .

By contrast, many female-biased lineages of A. vulgare lack Wolbachia. Many of the traits exhibited by these lineages are similar to those recorded in Wolbachia-infected lineages: females are genotypic males (i e , ZZ) reversed by a feminizing factor termed f element (Legrand and Juchault, 1984) . If inheritance of the feminizing effect is mainly maternal in these host lineages, sex-ratios of the progenies are very unstable, varying from all male to all female broods . Conversely, Wolbachia-infected host lineages produce stable female-biased broods over generations But the main difference from lineages harboring Wolbachia is that the f element is occasionally transmitted by males with a non-Mendelian pattern Finally, females of these lineages can be experimentally reversed into males by the implantation of an androgenic gland: resulting neo-males are able to transmit the feminizing phenotype to their offspring (Legrand and Juchault, 1984) Although the nature of the f element is unknown, it has been suggested that its transmission and expression are analogous to those of transposable elements or viruses Therefore, the f element might be a nuclear mobile element carrying feminization capability Following progenies of a ZW female inoculated with Wolbachia during five generations, Legrand and Juchault (1984) observed the spontaneous appearance of f occurring after Wolbachia had failed to be transmitted Because lines were maintained in inbreeding, the f factor could not be imported through paternal inheritance Based on the direct link between the prior infection by Wol-bachia and the appearance of f, Legrand and Juchault (1984) proposed a bacterial origin for the f element This hypothesis is strengthened by recent reports suggesting widespread and recurrent lateral gene transfers in Wolbachia-host interactions (Hotopp et al ., 2007) .

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