Molecular Biology and Evolution, Vol 16, 67-82, Copyright © 1999 by Society for Molecular Biology and Evolution
DJ Funk
If a gene tree is to be judiciously used for inferring the histories of
closely related taxa, (1) its topology must be sufficiently resolved and
robust that noteworthy phylogenetic patterns can be confidently documented,
and (2) sampling of species, populations, and pertinent biological
variation must be sufficiently broad that otherwise misleading sources of
genetic variation can be detected. These principles are illustrated by the
complex gene tree of Neochlamisus leaf beetles that I reconstructed using
90,000 bp of cytochrome oxidase I (COI) and 16S mitochondrial DNA (mtDNA)
sequences from over 100 specimens. Cytochrome oxidase I haplotypes varied
up to 25.1% within Neochlamisus and up to 11.1% within the gibbosus species
group, while exhibiting very low A + T bias for insect mtDNA (63%), low
transition saturation, and conservative patterns of amino acid variation.
16S exhibited lower sequence divergences and greater A + T bias and
transition saturation than COI, and substitutions were more constrained in
stems than in loops. Comparisons with an earlier study of Ophraella leaf
beetles highlighted conservative and labile elements of molecular evolution
across genes and taxa. Cytochrome oxidase I parsimony and neighbor-joining
analyses strongly supported a robust mtDNA genealogy that revealed the
monophyly of Neochlamisus and of the gibbosus species group.
Phylogeographic relationships suggested that the eastern U.S. gibbosus
group derives from southwestern velutinus group ancestors. Haplotypes from
individual velutinus group species clustered monophyletically, as expected.
However, haplotypes from each of several gibbosus group taxa were
polyphyletically distributed, appearing in divergent parts of the tree. 16S
provided a less-resolved gibbosus group topology that was congruent with
the COI tree and corroborated patterns of mitochondrial polyphyly. By
subsampling haplotypes corresponding to particular species, populations,
and ecological variants of gibbosus group taxa, I demonstrate that
recovered topologies and genetic distances vary egregiously according to
sampling regime. This study thus documents the potentially dire
consequences of inadequate sampling when inferring the evolutionary history
of closely related and mitochondrially polyphyletic taxa.
ORIGINAL ARTICLE
Molecular systematics of cytochrome oxidase I and 16S from Neochlamisus leaf beetles and the importance of sampling
Department of Ecology and Evolution, State University of New York, Stony Brook, USA. funkd@u.arizona.edu
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