Abstracts (first author)
Evolutionary innovations in sex determination mechanisms driven by Wolbachia bacterial endosymbionts in the isopod Armadillidium vulgare
In the isopod Armadillidium vulgare, genetic sex determination follows female heterogamety (ZZ males and ZW females). However, many A. vulgare populations harbor maternally-inherited Wolbachia bacterial endosymbionts which can convert genetic males into phenotypic females, leading to populations with female-biased sex ratios (1). The W sex chromosome has been lost in lines infected by Wolbachia and all individuals are ZZ genetic males. The female sex is determined by the inheritance of Wolbachia by the A. vulgare individual, thereby leading to a shift from genetic to cytoplasmic sex determination. We are using comparative genomics and expression profiles to identify Wolbachia gene(s) responsible for feminization of A. vulgare males. Surprisingly, some A. vulgare lines exhibit female-biased sex ratios despite the lack of Wolbachia. In these lines, female individuals are ZZ genetic males carrying an unknown feminizing factor. To elucidate the genetic basis of female sex determination in these lines, we sequenced the genome of a female by illumina. We identified a large piece of the Wolbachia genome transferred to the A. vulgare nuclear genome. The transferred genomic fragment shows non-Mendelian inheritance and co-segregates perfectly with the female sex in pedigrees, in agreement with observed biased sex ratios. These results suggest that sex determination in these A. vulgare lines is under the control of nuclear gene(s) of bacterial origin. Overall, our results indicate that Wolbachia bacteria can drive shifts in sex determination mechanisms in A. vulgare. More generally, they emphasize that bacterial endosymbionts can be powerful sources of evolutionary novelty for fundamental biological processes in eukaryotes, such as sex determination. This research is funded by an ERC Starting Grant (EndoSexDet) to RC.
(1) Cordaux et al. (2011) The impact of endosymbionts on the evolution of host sex-determination mechanisms. Trends in Genetics. 27, 332-341.