Zhu, D., Jamieson, B.G.M., Hugell,
A. and Moritz, C.
1994d. Sequence evolution and phylogenetic signal in control-region and
cytochrome b sequences of rainbow fishes (Melanotaeniidae). Molecular
Biology and Evolution 11, 672-683.
The nucleotide sequences of segments of the
cytochrome b gene (351 bp), the tRNA-Pro gene (49 bp), and the control
region (
apprx 313 hp) 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 lt 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.