Your News Feature 'Sex-starved and still surviving' (Nature 452, 678–680; 2008) about bdelloid rotifers sheds some much-needed light on this understudied group of organisms. But for those of us working with unicellular eukaryotes — protozoa and the like — this lack of sexual habit is not so scandalous. After all, the idea that sex is widespread among eukaryotes is based on relatively large organisms.
Still, a proper understanding of eukaryotic ecology and evolution must start with unicellular eukaryotes. These drive major ecological processes and form the principal part of the eukaryotic phylogenetic tree, whereas multicellular eukaryotes are mainly figureheads. Any textbook on evolution authored by a protozoon would give large multicellular organisms and their sexual problems little more attention than a footnote.
Being eukaryotes ourselves, it is interesting for us to know why some of our relatives are sexual beings and others are not. The sexual preferences of our cousins the rotifers are probably more akin to those of protozoa than to our own. Bdelloid rotifers share many features with protozoa apart from their lack of sex life, including small body size and very large populations. The adaptational reasons for the absence of sex are not fully understood. Part of the explanation may be that the microniches these small organisms inhabit have remained unchanged for millions of years — so mechanisms for substantial genetic change are not needed.
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Ekelund, F., Rønn, R. If you don't need change, maybe you don't need sex. Nature 453, 587 (2008). https://doi.org/10.1038/453587a
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