MULTIPLE INDEPENDENT ORIGINS OF MITOCHONDRIAL GENE ORDER IN BIRDS

Mitochondrial genomes of all vertebrate animals analyzed to date have the same 37 genes, whose arrangement in the circular DNA molecule vari es only in the relative position of a few genes. This relative conserv ation suggests that mitochondrial gene order characters have potential utility as phylogenetic markers for higher-level vertebrate taxa. We report discovery of a mitochondrial gene order that has had multiple i ndependent originations within birds, based on sampling of 137 species representing 13 traditionally recognized orders. This provides eviden ce of parallel evolution in mitochondrial gene order for animals. Our results indicate operation of physical constraints on mitochondrial ge ne order changes and support models for gene order change based on rep lication error. Bird mitochondria have a displaced Or (origin of light -strand replication site) as do various other Reptilia taxa prone to g ene order changes. Our findings point to the need for broad taxonomic sampling in using mitochondrial gene order for phylogenetic analyses. We found, however, that the alternative mitochondrial gene orders dist inguish the two primary groups of songbirds (order Passeriformes), osc ines and suboscines, in agreement with other molecular as well as morp hological data sets. Thus, although mitochondrial gene order character s appear susceptible to some parallel evolution because of mechanistic constraints, they do hold promise for phylogenetic studies.