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Dramatically elevated rate of mitochondrial substitution in lice (Insecta: Phthiraptera)
Kevin P Johnson1, Robert H Cruickshank, Richard J Adams
1Illinois Natural History Survey, 607 East Peabody Drive, Champaign 61820, USA. kjohnson@inhs.uiuc.edu
Molecular Phylogenetics and Evolution
|February 5, 2003
Summary
Mitochondrial genes in lice evolve over 100 times faster than nuclear genes, a significantly higher rate than previously estimated. This finding highlights the impact of gene location and evolutionary models on substitution rate calculations.
Area of Science:
- Evolutionary biology
- Genomics
- Molecular evolution
Background:
- Estimating relative substitution rates between mitochondrial and nuclear genes in insects is challenging.
- Previous studies suggested mitochondrial genes evolve 2-9 times faster than nuclear genes in insects.
Purpose of the Study:
- To develop and apply novel methods for estimating relative substitution rates incorporating multiple substitutions.
- To investigate the relative substitution rates between mitochondrial and nuclear genes in lice (Phthiraptera).
Main Methods:
- Utilized a modification of copath analysis (branch length regression) for rate comparisons.
- Employed maximum likelihood models to correct for multiple substitutions.
- Estimated and compared codon-specific rates between mitochondrial (COI) and nuclear (EF-1alpha) genes.
Main Results:
- Mitochondrial COI genes in lice exhibit relative synonymous substitution rates several hundred times higher than nuclear EF-1alpha genes (>100x).
- This rate is substantially higher than previous estimates for any organism group.
- Comparisons in aphids yielded lower relative rates, indicating the extreme estimate is specific to lice and not solely method-driven.
- Taxon sampling and model complexity influenced the relative rate estimates.
Conclusions:
- Lice exhibit an exceptionally rapid rate of mitochondrial DNA evolution compared to nuclear DNA.
- Novel methods accounting for multiple substitutions reveal higher relative rates.
- Taxon sampling and model choice are critical factors in accurately estimating evolutionary rates.