Genetic bases and evolutionary consequences of symbiont-driven sex determination

Informations

Funding country

France

Acronym

CytoSexDet

URL

-

Start date

1/1/2015

End date

-

Budget

501,000 EUR

Fundings

Abstract

Multicellular organisms have been continuously involved in complex interactions with microorganisms during their evolution, the most intimate of which is endosymbiosis, a type of symbiosis in which a microbial partner lives within its host cells. Endosymbiosis has played a key role in the emergence of major life forms on Earth and in the generation of biological diversity. However, appreciation of endosymbiosis as an important source of evolutionary novelty has developed relatively recently. The evolutionary significance of endosymbiosis is perhaps best exemplified by the evolution of mitochondria and chloroplasts, both of which result from endosymbiotic events. Over the past years, evidence has been accumulating that endosymbionts further affect animal biology in many ways, such as host nutrition and development, defense against natural enemies and immunity. In this proposal, we investigate another critical evolutionary process influenced by microbial endosymbionts: the mechanisms of sex determination of their eukaryotic hosts. Sex determination is one of the most fascinating developmental pathways in metazoans. It governs sexual differentiation and it is both evolutionarily ancient and ubiquitous. In animals, sexual differences between males and females are usually determined by chromosomal sex factors, commonly carried by sex chromosomes. Sex determination can also be affected by inherited microbial endosymbionts, a phenomenon known as cytoplasmic sex determination (CSD). Disrupting the mode of sex determination of their hosts in favor of females may be advantageous for endosymbionts because these intracellular microorganisms are predominantly transmitted vertically through female egg cytoplasm, not male sperm. However, very few systems have been analyzed in detail and there is no extensive empirical evidence of how nucleo-cytoplasmic conflicts can shape sex-determining systems. In this proposal, we aim at filling this gap in our knowledge, by investigating CSD genetic bases and evolutionary impact in two distinct host-endosymbiont systems: (i) terrestrial isopods and their prokaryote endosymbionts Wolbachia, and (ii) freshwater amphipods and their eukaryotic endosymbionts microsporidia. This collaborative research project brings together the two French labs working on CSD in animals: UMR 7267 "Ecologie et Biologie des Interactions", CNRS/Université de Poitiers (expert on the Wolbachia/isopod model), and UMR 6282 "Biogéosciences", CNRS/Université de Bourgogne (expert on the microsporidia/amphipod model). The project is divided into three work packages (WP) aimed at elucidating the genetic bases and evolutionary consequences of CSD at two levels: (i) micro-evolutionary patterns within focal species in the Wolbachia/isopod (WP1) and microsporidia/amphipod (WP2) systems, and (ii) macro-evolutionary patterns at broader taxonomic scales in both isopods and amphipods (WP3). The joint study of the Wolbachia/isopod and microsporidia/amphipod models provides a unique opportunity for directly investigating the impact of endosymbionts on the evolution of host sex determination mechanisms at the molecular genetic level. The latest developments of molecular biology technologies such as next-generation DNA sequencing, in a multidisciplinary framework combining comparative genomics, evolutionary ecology and population biology, now make it possible to tackle these exciting questions. It will allow us for the first time to draw broad conclusions on CSD evolution and impact on animal evolution.