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Transposable elements in sexual and ancient asexual taxa
1Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA.
Summary
Asexual reproduction in bdelloid rotifers may prevent the spread of harmful transposable elements. This study found these elements absent in bdelloids, supporting their ancient asexual evolution and unique genetic makeup.
Area of Science:
- Evolutionary Biology
- Genetics
- Molecular Biology
Background:
- Sexual reproduction facilitates the proliferation of deleterious transposable elements.
- Asexual reproduction has been predicted to lead to populations free of such elements.
- Transposable elements, including LINE-like and gypsy-like retrotransposons, are mobile genetic sequences.
Purpose of the Study:
- To test the hypothesis that the loss of sex prevents the spread of transposable elements.
- To screen various animal phyla for the presence of specific transposable elements.
- To investigate the genetic characteristics of bdelloid rotifers in relation to asexual reproduction.
Main Methods:
- Screening of animal phyla representatives for LINE-like and gypsy-like reverse transcriptases.
- Screening for mariner/Tc1-like transposases.
- Molecular genetic analysis to support evidence of ancient asexuality in bdelloid rotifers.
Main Results:
- All tested species, except bdelloid rotifers, were positive for reverse transcriptases.
- Bdelloid rotifers, a taxon lacking males, hermaphrodites, and meiosis, showed a lack of LINE-like and gypsy-like retrotransposons.
- Mariner-like transposases were found sporadically and were present in bdelloid rotifers.
Conclusions:
- The absence of LINE-like and gypsy-like retrotransposons in bdelloid rotifers supports their ancient asexual evolution.
- Eukaryotic retrotransposons are likely sexually transmitted nuclear parasites.
- Bdelloid rotifers provide a unique case study for understanding the long-term consequences of asexual reproduction on genome integrity.