Dinosaur relative's genome linked to mammals: Curious genome of ancient reptile

Date:
August 5, 2020
Source:
Northern Arizona University
Summary:
Biologists have sequenced the genome of the tuatara, a lizard-like
creature that lives on the islands of New Zealand.



FULL STORY ==========================================================================
A lizard-like creature whose ancestors once roamed the Earth with
dinosaurs and today is known to live for longer than 100 years may hold
clues to a host of questions about the past and the future.


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In a study published Aug. 5 in Nature, an interdisciplinary, international
team of researchers, in partnership with M?ori tribe Ng?tiwai, sequenced, assembled and analyzed the complete genome of the Sphenodon punctatus,
or the tuatara, a rare reptile whose ancestors once roamed the earth
with dinosaurs. It hasn't changed much in the 150 million to 250 million
years since then.

"We found that the tuatara genome has accumulated far fewer DNA
substitutions over time than other reptiles, and the molecular clock
for tuataras ticked at a much slower speed than squamates, although
faster than turtles and crocodiles, which are the real molecular
slowpokes," said co-author Marc Tollis, an assistant professor in the
School of Informatics, Computing, and Cyber Systems at Northern Arizona University. "This means in terms of the rate of molecular evolution,
tuataras are kind of the Toyota Corolla -- nothing special but very
reliable and persistently ticking away over hundreds of millions of
years." Tuatara have been out on their own for a staggering amount
of time, with prior estimates ranging from 150-250 million years, and
with no close relatives the position of tuatara on tree of life has long
been contentious. Some argue tuatara are more closely related to birds, crocodiles and turtles, while others say they stem from a common ancestor shared with lizards and snakes. This new research places tuatara firmly
in the branch shared with lizards and snakes, but they appear to have
split off and been on their own for about 250 million years -- a massive
length of time considering primates originated about 65 million years
ago, and hominids, from which humans descend, originated approximately
six million years ago.

"Proving the phylogenetic position of tuatara in a robust way is exciting,
but we see the biggest discovery in this research as uncovering the
genetic code and beginning to explore aspects of the biology that makes
this species so unique, while also developing new information that will
help us better conserve this taonga or special treasure," said lead
author Neil Gemmell, a professor at the University of Otago.

One area of particular interest is to understand how tuataras, which can
live to be more than 100 years old, achieve such longevity. Examining
some of the genes implicated in protecting the body from the ravages of
age found that tuatara have more of these genes than any other vertebrate species thus far examined, including humans. This could offer clues into
how to increase humans' resistance to the ailments that kill humans.



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But the genome, and the tuatara itself, has so many other unique features
all on its own. For one, scientists have found tuatara fossils dating
back 150 million years, and they look exactly the same as the animals
today. The fossil story dates the tuatara lineage to the Triassic Period,
when dinosaurs were just starting to roam the Earth.

"The tuatara genome is really a time machine that allows us to understand
what the genetic conditions were for animals that were vying for world supremacy hundreds of millions of years ago," he said. "A genome sequence
from an animal this ancient and divergent could give us a better idea
about what the ancestral amniote genome might have looked like."
While modern birds are the descendants of dinosaurs, they are less
suitable for this type of research because avian genomes have lost a significant amount of DNA since diverging from their dinosaur ancestors.

But the tuataras, which used to be spread throughout the world, have
other unusual features. Particularly relevant to this research is the
size of its genome; the genome of this little lizard has 5 billion bases
of DNA, making it 67 percent larger than a human genome. Additionally,
tuataras have temperature- based sex determination, which means the ratio
of males to females in a clutch of eggs depends on the temperatures at
which they are incubated. They also have a pronounced "third eye" -- a
light sensory organ that sticks through the top of their skulls. Mammals' skulls have completely covered the third eye, though they still contain
the pineal gland underneath, which helps maintain circadian rhythms.

The tuatara also is unique in that it is sacred to the M?ori
people. This research, for all the scientific knowledge that came from
it, was groundbreaking for its collaboration with the Indigenous New Zealanders. The purpose was to ensure the research aligned with and
respected the importance of the tuatara in their culture, which has
never been done before in genomic research.

"Tuatara are a taonga, and it's pleasing to see the results of this
study have now been published," Ng?tiwai Trust Board resource management
unit manager Alyx Pivac said. "Our hope is that this is yet another
piece of information that will help us understand tuatara and aid in
the conservation of this special species. We want to extend a big mihi
to all of those who have been involved in this important piece of work."
With the genome now sequenced, the international science community has a blueprint through which to examine the many unique features of tuatara
biology, which will aid human understanding of the evolution of the
amniotes, a group that includes birds, reptiles and mammals.


========================================================================== Story Source: Materials provided by Northern_Arizona_University. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Neil J. Gemmell, Kim Rutherford, Stefan Prost, Marc Tollis,
David Winter,
J. Robert Macey, David L. Adelson, Alexander Suh, Terry Bertozzi,
Jose' H. Grau, Chris Organ, Paul P. Gardner, Matthieu Muffato,
Mateus Patricio, Konstantinos Billis, Fergal J. Martin, Paul
Flicek, Bent Petersen, Lin Kang, Pawel Michalak, Thomas R. Buckley,
Melissa Wilson, Yuanyuan Cheng, Hilary Miller, Ryan K. Schott,
Melissa D. Jordan, Richard D. Newcomb, Jose' Ignacio Arroyo,
Nicole Valenzuela, Tim A. Hore, Jaime Renart, Valentina Peona,
Claire R. Peart, Vera M. Warmuth, Lu Zeng, R. Daniel Kortschak,
Joy M. Raison, Valeria Vela'squez Zapata, Zhiqiang Wu, Didac
Santesmasses, Marco Mariotti, Roderic Guigo', Shawn M. Rupp,
Victoria G.

Twort, Nicolas Dussex, Helen Taylor, Hideaki Abe, Donna M. Bond,
James M.

Paterson, Daniel G. Mulcahy, Vanessa L. Gonzalez, Charles
G. Barbieri, Dustin P. DeMeo, Stephan Pabinger, Tracey Van Stijn,
Shannon Clarke, Oliver Ryder, Scott V. Edwards, Steven L. Salzberg,
Lindsay Anderson, Nicola Nelson, Clive Stone. The tuatara genome
reveals ancient features of amniote evolution. Nature, 2020; DOI:
10.1038/s41586-020-2561-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200805124044.htm

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