Small locusts hop among the dry leaves at the bottom of the zoo enclosure. They're a snack for one of New Zealand's special reptiles.

Or they're supposed to be. The unimpressed snacker, a tuatara, ignores the locusts.

"He's used to much bigger ones" says Chye-Mei Huang, Auckland Zoo ectotherm keeper.

Chye-Mei is responsible for looking after the cold-blooded animals, more technically known as ectotherms. These are animals whose regulation of body temperature depends on external sources, such as sunlight or a heated rock surface. And that includes the oddball New Zealand native, the tuatara.

Life in the slow lane

"A lot of people often ask us if they're real because they do spend a lot of time sort of sitting around and resting. If they don't need to do anything they won't, which I think is quite sensible of them," says Chye-Mei.

Eating and keeping their body temperature just right are a tuatara's two main occupations.

"Most of the time when you see them moving around, they'll be heading towards a basking spot." When they get too warm, they'll retreat into their burrows.

Tuatara are adapted to cooler climates. They are active at body temperatures from around 5°C to 30°C.

They are also long lived. In captivity, they can live to more than 100 years in age. Henry, one of the Southland Museum's resident tuatara in Invercargill, is estimated to be over 100 years old, possibly as old as 130 years.

Tuatara are the only remaining species of an ancient order of reptiles. The others died out 65 million years ago, in the extinction event that also wiped out the dinosaurs. And it seems that tuatara have changed little since that time, which means they often get given the nickname 'living fossils'.

Henry the tuatara at Southland Museum in 2018. Photo: Ellen Rykers

When humans arrived in Aotearoa, tuatara came under intense pressure - in particular from predation by rats. They became extinct on mainland Aotearoa, while some survived on a few offshore islands.

Where are the tuatara now?

Tuatara persisted on 32 offshore islands. Since 1995, as part of a conservation plan to have back-up populations, they've have been translocated to some other islands and five mainland fenced sanctuaries, bringing the number of populations to 47.

A tuatara at Auckland Zoo. Photo: Claire Concannon / RNZ

The vast majority of wild tuatara are found on Takapourewa Stephens Island, at the tip of the Marlborough Sounds. It was from here that 70 tuatara were translocated in 2005, gifted by their kaitiaki Ngāti Koata to Zealandia ecosanctuary in Wellington.

Despite concerns about the presence of mice, the translocation worked. The tuatara thrived and began breeding. Today, tuatara are found on the mainland in fenced ecosanctuaries that span the country - Zealandia in Wellington, Orokonui in Dunedin, Sanctuary Mountain Maungatautari in the Waikato, Cape Sanctuary in Hawke's Bay and Te Kurī a Paoa Young Nick's Head just south of Gisborne.

It's these ecosanctuaries that University of Auckland PhD candidate Cam Hoffbeck has been travelling to for her research field work.

The tuatara gut microbiome

While tuatara are interesting creatures by themselves, it's the interaction between these prehistoric-looking reptiles and the community of bacteria that live inside them that fascinates Cam.

Just like our gut microbiome, microbes living in a tuatara's tum help them digest their food and keep them healthy and well. Cam was curious: had the tuatara microbiome changed significantly between the those in the wild on Takapourewa and those in ecosanctuaries and zoos?

Surprisingly, the types of microbes weren't different between island and mainland tuatara. There was, however, a statistically significant difference in the relative abundance of different bacteria, albeit a small effect.

This is the first time the tuatara microbiome had been investigated. In the absence of any other information, Cam says, "it's reassuring that our current conservation practices aren't interfering with the tuatara gut too much."

A change in diet didn't seem to disrupt this stable bacterial community either. When Cam put several captive tuatara on a four-week diet of crickets alone, she didn't see much of a shift. Maybe their gut bacteria also choose to live in the slow lane.

While a tuatara 'stool' sample would be the best material for her to work on, turns out tuatara don't poo all that often. Instead, Cam uses cloacal swabs. (The cloaca is the shared reproductive and excretory opening in reptiles and birds.) She uses DNA sequencing techniques to look for different bacteria and their quantities in these swabs.

Cam Hoffbeck, PhD candidate, at the Auckland Zoo tuatara display. Photo: Claire Concannon / RNZ

What she finds is very different to human or other mammals' gut bacteria - which you'd expect for a reptile. But the tuatara microbiome also looks quite different compared to other reptiles too.

"Their closest living relatives would be the squamates - so that's things like skinks and geckos and snakes - but it didn't even look remotely similar to those. There's basically a completely different set of dominant bacteria occurring in the tuatara gut," she says.

Working with the Zealandia population of tuatara, Cam has investigated seasonal changes in tuatara gut bugs. Generally slow in nature, tuatara take things to the next level in winter, going into a state of torpor - effectively a temporary hibernation.

As tuatara move into summer, the microbiome shifts, suggesting that seasonal changes in temperature might have a role to play.

Future investigations will look deeper into this microbiome summer seasonal change and focus in on the functions of some of the bacteria.