Résumé
Mitochondrial DNA remains one of the most widely used molecular markers to
reconstruct the phylogeny and phylogeography of closely related birds. It
has been proposed that bird mitochondrial genomes evolve at a constant
rate of ~0.01 substitution per site per million years, that is that they
evolve according to a strict molecular clock. This molecular clock is
often used in studies of bird mitochondrial phylogeny and molecular
dating. However, rates of mitochondrial genome evolution vary among bird
species and correlate with life history traits such as body mass and
generation time. These correlations could cause systematic biases in
molecular dating studies that assume a strict molecular clock. In this
study, we overcome this issue by estimating corrected molecular rates for
birds. Using complete or nearly complete mitochondrial genomes of 475
species, we show that there are strong relationships between body mass and
substitution rates across birds. We use this information to build models
that use bird species’ body mass to estimate their substitution rates
across a wide range of common mitochondrial markers. We demonstrate the
use of these corrected molecular rates on two recently published data
sets. In one case, we obtained molecular dates that are twice as old as
the estimates obtained using the strict molecular clock. We hope that this
method to estimate molecular rates will increase the accuracy of future
molecular dating studies in birds.