Abstracts (first author)

Talk 

Evolutionary innovations in sex determination mechanisms driven by Wolbachia bacterial endosymbionts in the isopod Armadillidium vulgare

Author(s): Cordaux R, Badawi M, Grève P, Giraud I, Ernenwein L, Leclercq S

Summary:

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.



Abstracts (coauthor)

Summary:

Recent studies in paleovirology have uncovered myriads of viral genome fragments integrated in the genome of their eukaryotic hosts. These fragments result from endogenization, i.e., integration (often accidental) of the viral genome into the host germline genome followed by vertical inheritance. So far, most studies have used a virus-centered approach, whereby endogenous copies of a particular group of viruses were searched in all available sequenced genomes. Here we follow a host-centered approach whereby the genome of a given species (the crustacean isopod Armadillidium vulgare) is screened for the presence of endogenous viruses using all viral genomes sequenced to date (n = 2048) as queries. This search and downstream evolutionary analyses revealed that 50 viral genome fragments belonging to 10 viral families became endogenized in A. vulgare. We show that viral endogenization occurred recurrently during the evolution of isopods and that some endogenous virus loci are polymorphic in A. vulgare, suggesting they result from recent endogenization of viruses likely to be currently infecting isopod populations. Overall, our work shows that isopods have been and are still infected by a large variety of DNA and RNA viruses. It also extends the host range of several families of viruses and brings new insights into their evolution. More generally, our results underline the power of paleovirology in characterizing the viral diversity currently infecting eukaryotic taxa.

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Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

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