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Not Bats, but Birds: Nuclear and mtDNA Give Different Rates
This paper has caught my eye as I sought to elaborate on different gene
evolution rates and the possibility of using mtDNA to definitely correlate
mutation rate and therefore lineage divergence timing. It's a modern
analogue, and it goes back only to the Pleistocene, but you'll get the
Saetre, G.-P.; Borge, T.; Lindell, J.; Moum, T.; Primmer, C.R.; Sheldon,
B.C.; Haavie, J.; Johnsen, A.; and Ellegren, H. 2001. Speciation,
introgressive hybridization and nonlinear rate of molecular evolution in
flycatchers. _Molecular Ecology_ 10 (3): 737-749.
"Evolutionary history of Muscicapidae flycatchers is inferred from nuclear
and mitochondrial DNA (mtDNA) sequence comparisons and population genetic
analysis of nuclear and mtDNA markers. Phylogenetic reconstruction based
on sequences from the two genomes yielded similar trees with respect to
the order at which the species split off. However, the genetic distances
fitted a nonlinear, polynomial model reflecting diminishing divergence
rate of the mtDNA sequences compared to the nuclear DNA sequences. This
could be explained by Haldane?s rule because genetic isolation might
evolve more rapidly on the mitochondrial rather than the nuclear genome in
birds. This is because hybrid sterility of the heterogametic sex
(females) would predate that of the homogametic sex (males), leading to
sex biased introgression of nuclear genes. Analyses of present hybrid
zones of pied (*Ficedula hypoleuca8) and collared flycatchers (*F.
albicollis*) may indicate a slight sexual bias in rate of introgression,
but the introgression rates were too low to allow proper statistical
analyses. It is suggested, however, that the observed deviation from
linearity can be explained by a more rapid mutational saturation of the
mtDNA sequences than of the nuclear DNA sequences, as supported by
analyses of third codon position transversions at two protein coding mtDNA
genes. A phylogeographic scenario for the black and white flycatcher
species is suggested based on interpretation of the genetic data obtained.
Four species appear to have diverged from a common ancestor relatively
simultaneously during the Pleistocene. After the last glaciation period,
pied and collared flycatchers expanded their breeding ranges and
eventually came into secondary contact in Central and Eastern Europe and
on the Baltic Isles."
mtDNA and Nuclear sampling provide different rates of evolution and
mutation. This paper is online at:
One may also wish to check out other of Primmer's publications by going
and clicking on the left at "Publications & Data."
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
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