The Rates of Molecular Evolution in Rodent and Primate Mitochondrial DNA |
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Authors: | Daniel M Weinreich |
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Institution: | (1) Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA, US |
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Abstract: | A higher rate of molecular evolution in rodents than in primates at synonymous sites and, to a lesser extent, at amino acid
replacement sites has been reported previously for most nuclear genes examined. Thus in these genes the average ratio of amino
acid replacement to synonymous substitution rates in rodents is lower than in primates, an observation at odds with the neutral
model of molecular evolution. Under Ohta's mildly deleterious model of molecular evolution, these observations are seen as
the consequence of the combined effects of a shorter generation time (driving a higher mutation rate) and a larger effective
population size (resulting in more effective selection against mildly deleterious mutations) in rodents. The present study
reports the results of a maximum-likelihood analysis of the ratio of amino acid replacements to synonymous substitutions for
genes encoded in mitochondrial DNA (mtDNA) in these two lineages. A similar pattern is observed: in rodents this ratio is
significantly lower than in primates, again consistent only with the mildly deleterious model. Interestingly the lineage-specific
difference is much more pronounced in mtDNA-encoded than in nuclear-encoded proteins, an observation which is shown to run
counter to expectation under Ohta's model. Finally, accepting certain fossil divergence dates, the lineage-specific difference
in amino acid replacement-to-synonymous substitution ratio in mtDNA can be partitioned and is found to be entirely the consequence
of a higher mutation rate in rodents. This conclusion is consistent with a replication-dependent model of mutation in mtDNA.
Received: 24 September 1999 / Accepted: 18 September 2000 |
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Keywords: | : Molecular clock — Mitochondrial — DNA — Mammals — Neutral theory — Mildly deleterious theory — Maximum likelihood |
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