Domains of Life: Protists
DNA-based approaches have long been used to diagnose protistan diversity. Much of this work has employed sequence diversity in 18S rDNA to diagnose major protistan lineages (Cavalier-Smith 2002). However, this gene does not evolve rapidly enough to diagnose closely allied species. Mitochondrial genes, including COI, present a better option because their rates of evolution are much higher. Indeed, Ehara et al. (2000) have shown that COI diversity is substantial among protistan lineages, while Lynn and Strueder-Kypke (2003) have actually established that COI is very effective in discriminating species of Tetrahymena. A barcoding system based on COI will not provide a universal solution to protistan identifications because anaerobic species lack mitochondria (Henze and Martin 2003). However, specialized diagnostic approaches can be developed to probe protistan diversity in these settings.
References
- Cavalier-Smith, T. 2002. The phagotrophic origin of eukaryotes and phylogenetic classification of protozoa. Int. J. Syst. Evol. Microbiol. 52: 297-354.
- Ehara, M., Y. Imaga, K. Kazuo, I. Watanabe and T. Ohama. 2000. Phylogenetic analysis of diatom coxI genes and implications of a fluctuating GC content on mitochondrial code evolution. Curr. Genet. 37: 29-33.
- Henze, K. and W. Martin. 2003. Essence of mitochondria. Nature 426: 127-128.
- Lynn, D. H. and M. Strueder-Kypke. 2003. Cytoplasmic genes and evolution of species of Tetrahymena: evidence from cytochrome c oxidase I. Ciliate Molecular Biology, FASEB Conference, Vermont.