Résumé
Reconstructing the ancestral characteristics of species is a major goal in
evolutionary and comparative biology. Unfortunately, fossils are not
always available and sufficiently informative, and phylogenetic methods
based on models of character evolution can be unsatisfactory. Genomic data
offer a new opportunity to estimate ancestral character states, through:
(i) the correlation between DNA evolutionary processes and species
life-history traits, and (ii) available reliable methods for ancestral
sequence inference. Here we assess the relevance of mitochondrial DNA –
the most popular molecular marker in animals – as a predictor of ancestral
life-history traits in mammals, using the order of Cetartiodactyla as a
benchmark. Using the complete set of 13 mitochondrial protein-coding
genes, we show that the lineage-specific nonsynonymous over synonymous
substitution rate ratio (dN/dS) is closely correlated with the species
body mass, longevity and age of sexual maturity in Cetartiodactyla, and
can be used as a marker of ancestral traits provided that the noise
introduced by short branches is appropriately dealt with. Based on
ancestral dN/dS estimates, we predict that the first cetartiodactyls were
relatively small animals (around 20 kg). This finding is in accordance
with Cope's rule and the fossil record but could not be recovered via
continuous character evolution methods.