Bdelloid rotifers : progress in understanding the success of an evolutionary scandal

Despite considerable attention, what drives asexual populations to extinction and allows the maintenance of sexual reproduction remains a mystery. Bdelloid rotifers appear to be an exception to the general rule that multicellular eukaryotes that abandon sex are doomed to early extinction, and an understanding of their biology may reveal how they have avoided the fate of other asexual lineages. Here, we discuss aspects of the ecology, physiology, and genome evolution of bdelloid rotifers that may contribute to their evolutionary success. We propose that many of the unusual characteristics of bdelloids derive from their adaptation to desiccation-prone habitats but may also contribute to their long-term success in the absence of sexual reproduction. However, many unanswered questions about these characteristics and the basic biology of bdelloids remain. Population genetics and molecular ecology are promising approaches for the next generation of studies using this model system to provide answers to the questions of how and why sex is the dominant form of reproduction in plants and animals.