Bdelloid rotifers are one of only three types of invertebrate metozoan known to undergo anhydrobiosis at all life stages, the others being tardigrades and (some) nematodes. The cysts of Artemia sp. (brine shrimp) are also well-recognised for their anhydrobiotic capability (reviewed in Crowe et al., 1992; Clegg, 2001). Van Leeuwenhoek's first description of anhydrobiosis in a letter to Hendrik van Bleyswijk in 1702 probably described a bdelloid rotifer now classified as Philodina roseola (see figure).
Bdelloid rotifers (“leech-like wheel bearers") are swimming or creeping unsegmented metazoans, ranging in size from 100 to 2000 µm, with almost 400 taxonomic species comprising a class within phylum Rotifera. They inhabit freshwater ponds, lakes, temporary pools, brackish waters, sewage and the interstices of soil, mosses and lichens. Some of these habitats dry out frequently, and the ability of most bdelloid species to withstand desiccation must represent a selective advantage.
A second remarkable characteristic of bdelloids is even more unusual among animals, namely their apparent ancient asexuality. Most other organisms which reproduce exclusively asexually have a short evolutionary history, and are thought likely to become extinct after not more than a few million years. However, bdelloids are estimated to have been asexual for tens of millions of years, perhaps as long as 80 MYr (Butlin, 2002; Birky, 2004; Mark Welch & Meselson, 2000). In over 300 years since bdelloids were first described, no evidence for males or meiosis has ever been found. Moreover, genetic evidence is consistent with a lack of meiotic recombination since genes that were alleles in a sexual ancestor exhibit high sequence divergence.
Bdelloid rotifers seem unable to produce trehalose (Lapinski & Tunnacliffe, 2003; Caprioli et al. 2004), the disaccharide often associated with anhydrobiosis in nematodes and yeast, suggesting that novel mechanisms are employed by these animals to withstand desiccation stress. We have recently shown that bdelloids, like most desiccation-tolerant organisms, contain LEA proteins, but it is likely that they have developed multiple adaptations to withstand drying.
Bdelloid Rotifer Research Topics:
Birky Jr, C. W. (2004) Bdelloid rotifers revisited. Proc Natl Acad Sci USA 101: 2651-2652.
Butlin, R. (2002) Evolution of sex: The costs and benefits of sex: new insights from old asexual lineages. Nat Rev Genet 3: 311-317.
Caprioli, M., Krabbe Katholm, A., Melone, G., Ramløv, H., Ricci, C. and Santo, N. (2004) Trehalose in desiccated rotifers: a comparison between a bdelloid and a monogonont species. Comp Biochem Physiol A Mol Integr Physiol. 139: 527-532
Clegg, J. S. (2001) Cryptobiosis--a peculiar state of biological organization. Comp Biochem Physiol B Biochem Mol Biol. 128: 613-624.
Crowe J. H., Hoekstra, F. A. and Crowe, L. M. (1992) Anhydrobiosis. Annu Rev Physiol. 54: 579-599.
Lapinski, J. and Tunnacliffe, A. (2003) Anhydrobiosis without trehalose in bdelloid rotifers. FEBS Lett. 553: 387-390.
Mark Welch, D. and Meselson, M. (2000) Evidence for the evolution of bdelloid rotifers without sexual reproduction or genetic exchange. Science 288: 1211-1215.
McGee, B. K. (2006) Hydrophilic proteins in the anhydrobiosis of bdelloid rotifers. Ph.D. thesis, Institute of Biotechnology, University of Cambridge.
Pouchkina-Stantcheva, N. N. and Tunnacliffe, A. (2005) Spliced-leader RNA mediated trans-splicing in phylum Rotifera. Mol. Biol. Evol. 22: 1482-1489.
Wheelbase - A database of rotifer biology with links to other rotifer sites.
Rotiferbase - A collection of cDNA sequences from Philodina sp.: library from Pouchkina-Stantcheva & Tunnacliffe (2005); sequences by Prof. Mark Blaxter's laboratory.
|Animal Magic.pdf - Overview of anhydrobiosis and rotifer research in the Tunnacliffe lab. Reproduced from the Pembroke College magazine, Martlet, with permission. |
|Podcast - Canadian Broadcasting Corporation interview with Dr. Alan Tunnacliffe.|