Abstract
Hummingbirds in flight exhibit the highest metabolic rate of all vertebrates. The bioenergetic requirements associated with hovering flight raise the possibility of positive selection upon proteins encoded by hummingbird mitochondrial DNA. Here, we have identified a non-conservative change within the mitochondria-encoded cytochrome c oxidase subunit I (COI) that is fixed within hummingbirds, yet exceedingly rare among other metazoans. This unusual change can also be identified in several nectarivorous hovering insects, hinting at convergent evolution linked to diet or mode of flight. We performed atomistic molecular dynamics simulations using bovine and hummingbird models, and our findings suggest that COI amino acid position 153 provides genetic control of D-channel hydration and activity. We discuss potential phenotypic outcomes for the hummingbird that are linked to this intriguing instance of positive selection upon the mitochondrial genome.