Tuataras are lizard-like reptiles endemic to New Zealand, and their closest relatives are an extinct group of reptiles from the time of the dinosaurs. Tuataras exhibit several unusual characteristics that distinguish them from lizards, including a lifespan of up to 100 years, resistance to many diseases, and a unique tolerance to cold climates. This reptile’s list of unique traits grew even further thanks to a recent finding by an international team of researchers regarding its mitochondrial DNA. Mitochondria are energy factories within cells, and they have their own set of genes that help them function. Many studies have shown that mitochondrial DNA is important in aging, metabolism, cancer, and neurodegenerative diseases. Since mitochondrial DNA is typically only inherited from the mother, we expect organisms to have only one copy, but research into tuataras revealed an unexpected finding.

As the tuatara is a taonga, or special treasure, in Maori culture, the researchers first received the blessing of the Maori people to sample the reptile’s blood. Upon sequencing the mitochondrial genome of a male tuatara, the researchers discovered that it carries two distinct mitochondrial genomes. This is the first evidence of co-existing separate mitochondrial genomes in a vertebrate, with mollusks as the only other organism found with this trait. The two genomes differed by 10.4 percent (as a reference, human and chimpanzee mitochondrial genomes differ by 8.9 percent), which suggests a 7-8 million year divergence between them. A large set of genetic changes between the two genomes was found in genes involved in metabolism, which can help organisms adjust to extreme temperatures.

Thus, the extra set of mitochondrial genes might give the tuatara an adaptive advantage in how its metabolism tolerates cold environments. This finding opens the need for further studies into whether females also carry two mitochondrial genomes and if the copies are inherited from both the mother and father. Furthermore, how this duplicated mitochondrial genome works in an animal that ages slowly in a cool climate might give insight into how mitochondrial genomes function in humans. The advancement and ease of deep sequencing technology may even lead to the discovery of more species with this unique genetic makeup in the future.

Dr. Neil Gemmell is a Professor in the Department of Anatomy and the Chair for AgResearch Centre for Reproduction and Genomics at the University of Otego in New Zealand. Dr. Robert Macey is the Director of the Peralta Genomics Institute in Oakland, CA.

Managing Correspondent: Lauren Davancaze

Press Articles: “Lizard-like tuatara carry two distinct mitochondrial genomes,” ScienceNews

Original Journal Article: “Evidence of two deeply divergent co-existing mitochondrial genomes in the Tuatara reveals an extremely complex genomic organization,” Communications Biology

Image Credit: Bernard Spragg (Flickr)

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