Species tree, frequent HGT and gene conversions in Bdelloid Rotifers

The vast majority of animals reproduce sexually, i.e. with recombination of genetic material between generations. This genetic mixing is thought to favor the persistence of sexual lineages despite a theoretical advantage of asexuals regarding colonization capacity and population growth. In this context Bdelloid Rotifers, a highly diversified group of animals evolving asexually for millions of years, appears as a puzzle but also as an outstanding model to better understand long-term evolution in the absence of sexual reproduction.
The sequencing of the first Bdelloid Rotifer genome (Flot et al. 2013) revealed a peculiar organization, characterized by a degenerate tetraploidy, numerous rearrangements and the absence of homologous chromosomes. This structure, incompatible with meiosis, likely testifies the long asexual evolution of this genome. Besides, population genetic studies suggest that Bdelloids might exchange DNA within and between species, which likely plays a major role in their evolutionary history (Debortoli et al. 2016).
To better understand the dynamics of gene conversion and horizontal genetic transfers on these asexually evolving genomes and their importance in the success of Bdelloids, we are generating genomic data (RAD sequencing) from a large number of species distributed across the four existing families. We will show how methods involving the reconciliation of gene and species trees can help resolving species phylogeny of Bdelloids despite asexuality, polyploidy, gene conversions, transfers and losses. The resolution of the species tree is indeed a requirement for further study of the dynamics of horizontal transfers, which might play a key role in their evolution.