Health & Science
A walk on the wild side
by Veronika Meduna
Three Auckland students have learnt firsthand how biologists “dial up the sex” of tuatara eggs.
An eye-to-eye encounter with a tuatara is like looking back through more than 200 million years of natural history.
And so it was for three Auckland high school students when the Victoria University biologists who study these ancient reptiles recently escorted the girls to the home of the tuatara, rugged Stephens Island at the tip of the Marlborough Sounds, to let them get up close and personal.
Monique Higgins, Eileen Gallagher and Jenny Suo entered the Royal Society’s Big Science Adventures competition with a documentary about amateur astronomer Jennie McCormick, who had recently discovered a planet. Their prize for winning the science-video competition was a field-trip to the tuatara sanctuary to film the work of researchers studying the ecology of these last survivors of a group of reptiles that roamed the Earth at the same time as dinosaurs.
Thousands of tuatara live on Stephens Island, sharing the 150 hectares of steep and windswept slopes with fairy prions and diving petrels, which come to nest, and other endangered wildlife. “We think there are at least 20,000 tuatara here, but no one’s ever counted them,” ranger Clare Allen told the team.
“Probably the most endangered wildlife that we know of here is the [native Stephens Island] frog, which lives in a very small area on the summit rocks. We’ve got a protective fence around that two-acre area to keep the tuatara out because they eat these little frogs.”
Stephens Island has always been free of rodents, and the last of the lighthouse keepers’ cats were removed decades ago, making the island a stronghold for the tuatara population and for research.
“This is not the only place where tuatara survived,” says Sue Keall, one of the Victoria University biologists who accompanied the Pakuranga College team during their week-long excursion. “They did survive on just over 30 offshore islands, but not the mainland. They are extinct there as far as we know, but Stephens Island is most definitely the largest population. We have more tuatara here than on all the other islands put together.”
The island’s population has allowed researchers to observe tuatara courtship, mating, nesting and breeding behaviour, and led to discoveries such as the effect of temperature on the sex of hatchlings. “From that kind of research, we’ve been able to develop techniques that can be used for conservation. One of the really valuable techniques has been learning how to incubate tuatara eggs. By doing that, we’ve been able to take eggs from nature, incubate them in the lab and get a much higher success rate of hatching. If we look after those young ones for maybe five years until they are a robust size, they can be returned to nature,” says Keall.
Back at Victoria University, conservation biologist Nicky Nelson explains that a “room of former glory” once held more than 300 young tuatara, which have all been returned to the wild. Now it’s home to hatchlings from eggs taken from Stephens Island as part of a paternity study to work out the genetic relationships in the offspring.
In the incubation room “it’s dial up the sex”, says Nelson. Two large incubators set at 20˚ and 23˚C respectively hold ice-cream boxes with tiny soft eggs, weighing just a few grams, ready to hatch into female or male tuatara.
“Tuatara have temperature-dependent sex determination,” says Nelson. “Twenty degrees produces girls and we have 23 degrees for boys. The difference is actually even less than 1˚Celsius, but we operate at these two temperatures because then we can be sure that we get a hundred percent boys or girls.”
Recent studies on Stephens Island have shown a slight bias towards males in the wild population, and Keall says one of the challenges for tuatara researchers is “to determine whether the reptiles will be able to adapt to the global-warming challenge”.
The Pakuranga team returned home with a conservation story-line, hours of footage and the experience of visiting a place few people get to see. They were the first of six groups of students to travel to some of New Zealand’s most remote places last month as a reward for their winning entries in the Royal Society competition.
The itineraries of the five other teams included an exploration of the volcanic hot-spots in the central North Island and White Island, a trip to study the population genetics of whales and dolphins in the Bay of Islands and the marine food chain in Fiordland, a geological excursion to the Chatham Islands, and a stint of planet-hunting at the snowed-in Mt John Observatory.
With the field-trips now behind the teams, they are using the school holidays to produce their next documentary – and hope for the top reward, an expedition to join science projects in Antarctica.
Email: science4@ paradise.net.nz
