Complete mitochondrial genomes from four subspecies of common chaffinch (Fringilla coelebs): New inferences about mitochondrial rate heterogeneity, neutral theory, and phylogenetic relationships within the order Passeriformes

► We analyzed 33 mitochondrial protein-coding genomes within the order Passeriformes. ► Mitochondrial rate heterogeneity due to mutational pressure exists for birds. ► Positive selection is implicated, especially for the complex I NADH genes. ► A Bayesian phylogeny identifies Muscicapoidea and Passeroidea as sister taxa.