Bacterial endosymbionts and the evolution of host sex determination mechanisms

Richard Cordaux
UMR 7267, CNRS, Poitiers - richard.cordaux@univ-poitiers.fr

(Seminar in English)

In animals, sex differences between males and females are generally determined by genetic factors carried by sex chromosomes. Sex chromosomes are remarkably variable in origin and they can differ even between closely related species, indicating that transitions occur frequently and independently in different groups of organisms. However, the evolutionary causes underlying sex chromosome turnovers are poorly known. I will present results supporting that genetic elements distorting host sex ratio can be powerful agents of transitions between sex determination mechanisms.

In the common pillbug Armadillidium vulgare, chromosomal 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. Wolbachia can drive shifts in sex determination mechanisms in A. vulgare in several ways, such as direct incorporation of its genome in the pillbug nuclear genome. Our analyses indicate that the pillbug chromosome carrying a Wolbachia insert termed "f element" evolved as a new W sex chromosome. Overall, our results emphasize that bacterial endosymbionts can be powerful sources of evolutionary novelty for fundamental biological processes in animals, such as sex determination.

Recent publications:

Leclercq S. et al. (2016) Birth of a W sex chromosome by horizontal transfer of Wolbachia bacterial symbiont genome. PNAS. 113: 15036–15041.

Cordaux R. et al. (2011) The impact of endosymbionts on the evolution of host sex-determination mechanisms. Trends Genet. 27: 332-341.