The evolution of stramenopiles and alveolates as derived by "substitution rate calibration" of small ribosomal subunit RNA.

The substitution rate of the individual positions in an alignment of 750 eukaryotic small ribosomal subunit RNA sequences was estimated. From the resulting rate distribution, an equation was derived that gives a more precise relationship between sequence dissimilarity and evolutionary distance than hitherto available. Trees constructed on the basis of evolutionary distances computed by this new equation for small ribosomal subunit RNA sequences from ciliates, apicomplexans, dinoflagellates, oomycetes, hyphochytriomycetes, bicosoecids, labyrinthuloids, and heterokont algae show a more consistent tree topology than trees constructed in the absence of "substitution rate calibration." In particular, they do not suffer from anomalies caused by the presence of extremely long branches.