A tuatara may look like your average lizard, but it’s not. The reptiles are the last survivors of an ancient group of reptiles that flourished when dinosaurs roamed the world. Native to New Zealand, tuatara possess a range of remarkable abilities, including a century-long life span, relative imperviousness to many infectious diseases and peak physical activity at shockingly low temperatures for a reptile. Now, scientists are figuring out how, thanks to the first-ever deciphering, or sequencing, of the tuatara’s genetic instruction book.
The research reveals insights into not only the creature’s evolutionary relationship with other living reptiles but also into tuatara longevity and their ability to withstand cool weather, researchers report August 5 in Nature.
Technically, the tuatara (Sphenodon punctatus) are rhynchocephalians, an order of reptiles that were once widespread during the Mesozoic Era, 66 million to 252 million years ago. But their diversity waned over millions of years, leaving the tuatara as the last of their line (SN: 10/13/03). The reptiles have long been of scientific interest because of their unclear evolutionary relationship with other reptiles, as they share traits with lizards and turtles as well as birds.
Tuatara were once found throughout New Zealand, but now survive in the wild mainly on offshore islands and are considered a vulnerable species. The reptiles have suffered from habitat loss and invasive species such as rats, and are especially imperiled by a warming climate (SN: 7/3/08).
This peril — combined with the tuatara’s cherished status as a taonga, or special treasure, to the Indigenous Maori people — led researchers to prioritize compiling the reptile’s genome, or genetic instruction book.
In 2012, Neil Gemmell, an evolutionary biologist at the University of Otago in Dunedin, New Zealand, and an international team of researchers began to assemble the tuatara genome, in close partnership with the Indigenous Ngātiwai people. The Ngātiwai are considered kaitiaki, or guardians, of the tuatara and were intimately involved in decisions regarding the use of genetic data from the project.
The tuatara’s genome is huge, about 5 gigabases, or some 5 billion DNA base pairs in length, the researchers found. That’s about two-thirds bigger than humans’ and is “unusually large” for a reptile, says Giulia Pasques, an evolutionary biologist at the University of Colorado Boulder who was not involved with the research. Lizard and snake genomes are usually around 2 gigabases, she says. Bird genomes may be half that size.
Based on the genetic analyses, the researchers confirmed that the tuatara is more closely related to snakes and lizards than to crocodilians, birds or turtles. The researchers estimate that the tuatara and their ancestors diverged from snakes and lizards about 250 million years ago, meaning the group predates even the oldest dinosaurs.
The team identified genes possibly involved in the tuatara’s biological quirks including their long lives, which are the longest of any other reptiles besides tortoises. Tuatara have many genes involved in producing selenoproteins, which help protect against aging and cellular deterioration, and have more of these genes than humans do. Such insights may eventually have useful applications for human biology, says coauthor Matthieu Muffato, a comparative genomicist at the European Bioinformatics Institute in Hinxton, England.
Tuatara also appear to have an unusually high number of TRP genes, which are involved in making proteins tied to temperature sensitivity and regulation of body temperature. Those genes may be behind the reptiles’ tolerance of cool temperatures, the researchers say. Tuatara have the lowest known optimal body temperature of any reptile, from 16° to 21° Celsius.
Although the new research goes a long way to dispelling some of the mystery surrounding the tuatara, there is much to learn about these scaly enigmas. “Publishing the tuatara genome is like uncovering an ancient book,” Muffato says. “We have started analyzing it, and started decoding some of the genetic information, but we are still a long way off from understanding the complete genome.”
sciencenews.org, 5 August 2020
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