With a fossil record dating to the start of the Mesozoic era, approximately 250 million years ago, the tuatara (Sphenodon punctatus) is the sole extant representative of the reptilian order Rhynchocephalia. This unique reptile has an unusually long life span, with numerous individuals verifiably older than 100 years. The tuatara's survival success and longevity have been attributed to a number of remarkable genetic and biomolecular features, including specific genes and associated proteins that confer protection against aging, cell deterioration, and infectious diseases. Other distinctive genes and proteins provide tuataras with the ability to tolerate cold temperatures and still maintain high metabolic and physical activities, which is unusual for a reptile. Recent investigations also have identified another genetic feature that may provide tuataras with a singular adaptive advantage—specifically, the coexistence of two complete mitochondrial DNA sequences, or mitochondrial genomes (mitogenomes). No other vertebrate species has been found with two mitogenomes; in fact, bivalvian mollusks are the only other known animals possessing a pair of mitogenomes. See also: Adaptation (biology); Aging; Bivalvia; Gene; Genomics; Mesozoic; Metabolism; Mitochondrial DNA; Protein; Reptilia; Rhynchocephalia
Mitochondria are eukaryotic cellular organelles that produce energy through biochemical reactions. These organelles are essential for metabolism and contain their own small circular genome, typically only maternally inherited. Thus, possessing two divergent, yet entire, mitogenomes may provide tuataras with an enhanced ability to thermoregulate and sustain their metabolism, which would be an especially advantageous adaptation for any cold-blooded animal living in cool-temperature environments. With these mitogenomes bestowing greater metabolic flexibility, scientists suggest that the coexistence of two mitogenomes may be among the chief reasons for why tuataras have the lowest known optimal body temperature of any reptile—namely, 16–21°C (61–70°F). Molecular analyses and sequencing indicate that the two mitogenomes differ from each other by approximately ten percent. Researchers surmise that the divergent sets of genes contained within the two mitogenomes complement each other and, together, direct the production of specific transmembrane proteins that are linked to temperature sensitivity and regulation of body temperature. See also: Biological oxidation; Eukaryota; Mitochondria; Temperature adaptation in animals
Native to New Zealand and originally found throughout the two main New Zealand islands, tuataras are facing modern-day threats to their existence in the wild as a result of habitat destruction, climate change, and invasive species. Presently, tuataras live predominantly on about 30 small islets located off the main New Zealand coast. The ability of tuataras to survive hundreds of millions of years and through relatively harsh environmental conditions indicates a great degree of survival fitness. The discovery of two mitogenomes in the tuatara may thus furnish a genetic explanation for the life-span longevity of this animal on an individual basis and the species' overall perseverance on an evolutionary scale. See also: Endangered species; Evolution; Invasive species; New Zealand
