Genomic secrets of a rare reptile

Scientists have sequenced the genome of the tuatara – a rare reptile found only in New Zealand whose ancestors roamed the Earth with dinosaurs.

It is 67% bigger than the human genome, they say, and the genomic architecture is unlike anything previously reported.

The project was an international collaboration led by NZ’s University of Otago in collaboration with local iwi (Māori indigenous tribe) Ngātiwai.

The findings – which they hope will further understanding of the evolution of the amniotes, a group that includes birds, reptiles and mammals – are reported in the journal Nature.

With no close relatives, the position of tuatara on the tree of life has long been contentious.

The new research places it firmly in the branch shared with lizards and snakes, but it appears to have split off and been its own species for around 250 million years – an enormous amount of time, the researchers say, given primates only originated around 65 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,” says Otago geneticist Neil Gemmell, the paper’s lead author.

Analysis in Australia by David Adelson from the University of Adelaide and Terry Bertozzi from the South Australian Museum revealed that the tuatara’s genomic architecture is half-way between a mammal’s and reptile’s.

They demonstrated that some sequences of its DNA that move or jump location, referred to as jumping genes, are most similar to those found in platypus while others are more similar to those in lizards.

“The tuatara genome contained about 4% jumping genes that are common in reptiles, about 10% common in monotremes – platypus and echidna – and less than 1% common in placental mammals such as humans,” says Adelson.

“This was a highly unusual observation and indicated that the tuatara genome is an odd combination of both mammalian and reptilian components.”

Also of interest is how tuatara can live to be more than 100 years of age. Examination of 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.

Tuatara also don’t appear to get many diseases, so looking into what genetic factors might protect them is another point of focus, says Gemmell, as are genetic aspects that underpin its vision, smell and temperature regulation.

“Further functional exploration will refine our understanding of these unusual facets of tuatara biology, and the tuatara genome itself will enable many future studies to explore the evolution of complex systems across the vertebrates in a more complete way than has previously been possible,” the researchers write in their paper.