Molecular Biology and Evolution, Vol 11, 672-683, Copyright © 1994 by Society for Molecular Biology and Evolution
D Zhu, BG Jamieson, A Hugall and C Moritz
The nucleotide sequences of segments of the cytochrome b gene (351 bp), the
tRNA(Pro) gene (49 bp), and the control region (approximately 313 bp) of
mitochondrial DNA were obtained from 26 fish representing different
populations and species of Melanotaenia and one species of Glossolepis,
freshwater rainbow fishes confined to Australia and New Guinea. The purpose
was to investigate relative rates and patterns of sequence evolution.
Overall levels of divergence were similar for the cytochrome b and tRNA
control-region sequences, both ranging from < 1% within subspecies to
15%-19% between genera. However, the patterns of sequence evolution
differed. For the cytochrome b gene, transitions consistently exceeded
transversions, the bias ranging from 4.2:1 to 2:1, depending on the level
of sequence divergence. However, in the control-region sequence, a bias
toward transitions (2:1) was observed only in comparisons between very
similar sequences, and transversions outnumbered transitions in comparisons
of divergent sequences. Graphic comparisons suggested that the control
region was saturated for transitions at relatively low levels of sequence
divergence but accumulated transversions at a greater rate than did the
cytochrome b sequence. These distinct patterns of base substitution are
associated with differences in A+T content, which is 70% for the tRNA
control- region segment versus 50% for cytochrome b. A test for skewness in
the distribution of lengths of random trees indicated that both segments
contained phylogenetic signal. Parsimony analyses of the data from the two
regions, with or without weighting schemes appropriate to the respective
patterns of sequence evolution, identified the same five groupings of
sequences, but the relationships among the groups differed. However, in
most cases the branches uniting different combinations of groups were
poorly supported, and the differences among topologies were insignificant.
Considering the observed patterns of base substitution and the results of
the phylogenetic analyses, we deduce that both the control region and
cytochrome b are appropriate for population genetic studies but that the
control region is less effective than cytochrome b for resolving
relationships among divergent lineages of rainbow fishes.
ORIGINAL ARTICLE
Sequence evolution and phylogenetic signal in control-region and cytochrome b sequences of rainbow fishes (Melanotaeniidae)
Department of Zoology, University of Queensland, Brisbane, Australia.
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