The mitochondria is the cellular seat of bioenergetics. Its presence in our primordial ancestors enabled the appearance of complex, multicellular life. Without the vast, sustainable ATP output made possible by this organelle, the metabolic demands of intricate behaviors, high performance locomotion and higher order brain function would not have emerged.

While much mitochondrial biology is highly conserved across the eukaryotes our knowledge in the ‘higher’ organisms is largely based on a restricted number of vertebrate species, dominated by mammals. These include inbred laboratory rodents, and immortalized human and rodent cell lines. Inborn errors of metabolism, lifestyle diseases, thermogenesis and athletic performance have all been major foci. Insights have also been generated by work on the nematode C. elegans and the fruit fly D. melanogaster.

The rationale for compiling this Research Topic is to promote the bird world’s capacity for generating fresh mitochondrial perspectives. For example, the evolution of flight has clearly placed bioenergetic demands on the pectoralis muscle responsible for wing flapping. Extreme performers such as Amethyst Woodstar hummingbirds (Calliphlox amethystina) possess a wing beat frequency of 80 beats per second! Arctic terns (Sterna paradissea) undertake an annual round trip of 70,900 km, the largest documented migration in the animal world; Bar-headed geese (Anser indicus) traverse the Himalayas at ultra-high altitude. Wild birds of this nature offer unparalleled opportunities to explore what is bioenergetically possible, and to ask the question: where exactly do the limits of physiology lie?

Compared to similarly sized mammals, some birds have exceptional longevity. This is thought to be a product, at least in part, of adapted mitochondrial function. A captive Major Mitchell Cockatoo (Lophocroa leadbeateri) lived to at least 82 years old. These exemplar avian models all bring to mind August Krogh’s famous contention that for every biological question there is an ideal animal upon which we can study it.

Moreover, like their mammalian counterparts, some birds have been selected for domestication - not only for agricultural production but also as companion animals. Comparison of the selected birds to their wild ancestors provides an ideal resource for uncovering the genomic basis of complex phenotypes. Pre-eminent among the domesticated birds are the Galliformes (including chickens and turkeys) which have been subject to very intensive genetic selection (and allied management practices) to modify bioenergetics and sustain prolific production.

From a mitochondrial perspective the domestic birds are a wealth of information. For example, the breast muscle of modern broilers Gallus gallus domesticus is unique among the vertebrates, being composed exclusively of very low mitochondrial content type IIB muscle fibers. This may help explain the birds’ status as one of the most efficient feed converters in the animal world; indeed, some producers are now finding elite broilers can transform just 1.38 kg of dry feed into 1 kg of wet weight gained.

We welcome a range of article types on mitochondrial biology as it applies to bird physiology. All avian species and tissues will be given consideration, as will aspects of function that lie beyond bioenergetics.

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Frontiers in Physiology

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