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Intriguing Finds About the Lizard that Isn’t

Brother Island Tuatara
Alizada Studios/Shutterstock

The tuatara. Is it more like a bird/crocodile/turtle, or is it more of a lizard/snake? Scientists have never quite been able to agree, but after sequencing its genome with permission from the Māori tribe Ngātiwai, the question has been answered—and some other surprise findings were uncovered.

Living Fossils

While tuatara (there is no “s” in the Maori language, so “tuatara” is the plural form of the animal’s name) certainly look like lizards, they are actually living fossils—the last surviving descendants of an order known as Sphenodontia. But the similarity to lizards is not a coincidence. Through genetic sequencing, researchers from the University of Otago (UO) have finally proved that the animal split from the ancient ancestor of lizards and snakes about 250 million years ago. The fact that it has existed on Earth for such a long period allows researchers to peer back into the past by examining its biology.

“The tuatara is an iconic species, both for the Māori and for biologists,” said Paul Flicek, Associate Director of UO and at EMBL’s European Bioinformatics Institute (EMBL-EBI) Services. “It has a unique biology and its basic body shape hasn’t changed much over evolutionary time, so it’s a precious species for us to understand what the common ancestor of lizards, snakes, and tuatara was like.”

In addition to learning more about the evolutionary tree, the researchers also undertook their work to protect the ever-dwindling numbers of tuatara in New Zealand, where they were once plentiful until the first human arrivals to the islands brought rats and other predators with them about 800 years ago. 

To work with the tuatara, the researchers partnered with the Ngātiwai. This tribe holds kaitiakitanga (guardianship) over the tuatara that live in the far northern islands of New Zealand.

So, what did they find once the genome was sequenced? 

For starters, they found that the tuatara have larger genomes than humans, but that 64% of the genome consisted of repetitive DNA sequences that seemed to have no function. These repeats matched mammalian DNA more closely than it did reptilian, making the animal’s genome unique. 

“Overall, the repeat architecture of the tuatara is—to our knowledge—unlike anything previously reported, showing a unique amalgam of features that have previously been viewed as characteristic of either reptilian or mammalian lineages,” write the researchers in a paper published in the journal, Nature.

More intriguingly, they discovered genetic information tied to the tuatara’s longevity; the animal can live more than 100 years, making it the longest-lived reptilian after the turtle. The probable reason for this is the fact that their genome encodes 26 molecules known as selenoproteins, which have been linked to protection against reactive oxygen species, of which free radicals are a sub-category. The human genome only encodes for 25 of them by comparison.

More Genetic Gems

Another finding of note is the fact that even though the adult tuatara is nocturnal, it has a strong diurnal color-vision system, thanks to “one of the lowest rates of visual-gene loss known” for any mammal, bird or reptile, write the researchers. This might be because young tuatara are active during the day (in part to avoid being cannibalized by adult tuatara at night) and need to see color to avoid predators. 

Additional genetic sequences were uncovered that shed light on the tuatara’s ability to function at the lowest body temperatures of all reptiles; those that provide a window into how the temperature at which eggs are raised determine the sex of the creatures; and those that provided insight into the animal’s strong sense of smell.

“Very early on, it became clear that a primary goal for us all was to develop new knowledge that would improve the conservation of this species, says Neil Gemmell, professor and team leader at the University of Otago. “We agreed to partner together with Ngātiwai to achieve that aim, whilst also looking for opportunities to share other benefits that might derive from the research. It was an informed partnership that I believe was an important enabling element for the project’s success, which extends well beyond the scientific achievement of sequencing the genome.”