Transposable elements (TEs) are selfish genomic parasites whose ability to spread autonomously is facilitated by sexual reproduction in their hosts. If hosts become obligately asexual, TE frequencies and dynamics are predicted to change dramatically, but the long-term outcome is unclear. Here, we test current theory using whole-genome sequence data from eight species of bdelloid rotifers, a class of invertebrates in which males are thus far unknown. Contrary to expectations, we find a variety of active TEs in bdelloid genomes, at an overall frequency within the range seen in sexual species. We find no evidence that TEs are spread by cryptic recombination or restrained by unusual DNA repair mechanisms. Instead, we find that that TE content evolves relatively slowly in bdelloids and that gene families involved in RNAi-mediated TE suppression have undergone significant expansion, which might mitigate the deleterious effects of active TEs and compensate for the consequences of long-term asexuality.
All raw sequencing data have been deposited in the relevant International Nucleotide Sequence Database Collaboration (INSDC) databases under the Study ID PRJEB39843. Genome assemblies and gene predictions have been deposited at DDBJ/ENA/GenBank with the same Study ID. Figure 2--source data 2 has been uploaded to Dryad Digital Repository (doi:10.5061/dryad.fbg79cnsr).
Evolutionary dynamics of transposable elements in bdelloid rotifersEuropean Nucleotide Archive (ENA), PRJEB39843.
Figure 2--source data 2. Reference and maxhap assembly RepeatMasker output filesDryad Digital Repository, doi:10.5061/dryad.fbg79cnsr.
Comparative genomics of bdelloid rotifers: evaluating the effects of asexuality and desiccation tolerance on genome evolutionEuropean Nucleotide Archive (ENA), PRJEB23547.
Genome sequencing of Adineta vagaEuropean Nucleotide Archive (ENA), PRJEB1171.
Brachionus plicatilis species complex Genome sequencing and assemblyEuropean Nucleotide Archive (ENA), PRJNA541909.
- Timothy G Barraclough
- Christopher G Wilson
- Timothy G Barraclough
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Antonis Rokas, Vanderbilt University, United States
© 2021, Nowell et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.