Professor Alison Cree is a reproductive biologist, working in the Department of Zoology at the University of Otago. A key focus of her research is the effect of temperature on New Zealand’s native reptiles.
Alison recently led a project investigating the viability of translocating tuatara to Orokonui Ecosanctuary. The research work carried out by Anne Besson, one of Alison’s PhD students, was an important part of this project.
Tuatara were once widespread in New Zealand. Fossil evidence suggests that this unique, endemic reptile previously lived as far south as Bluff. Since human arrival and the introduction of mammalian predators, tuatara have become restricted to a few dozen offshore islands in Cook Strait and northern New Zealand.
Orokonui Ecosanctuary is a new ‘mainland island’ situated close to Dunedin. Mammalian predators have been eradicated, and a predator-proof fence surrounds the sanctuary. A proposal to translocate tuatara from an island in Cook Strait required further research to see if the cooler temperatures in Otago would affect the success of the translocation.
Temperature effect on sex determination in tuatara
Sex determination is the process by which a new embryo becomes a male or a female. In many animals, the sex of the young is determined by a specific chromosome in the father’s sperm. For some reptiles, including tuatara, things work a little differently!
Tuatara have a system called temperature-dependent sex determination. In this system, the sex of the new organism is still undecided when the egg and sperm meet. Tuatara lay their eggs in soil, and the temperature of the surrounding soil determines the sex of the offspring – warmer temperatures produce males and cooler temperatures produce females.
Translocation and soil temperature
Anne Besson’s PhD research investigated how tuatara might respond to the cooler temperatures in Otago. The most important research question that Anne and Alison hoped to answer was whether the soil temperatures at Orokonui Ecosanctuary would be warm enough for the eggs. In particular, they wanted to know whether the soil temperatures would be warm enough to produce both males and females at the end of the egg incubation process.
Anne used special data loggers that she buried in the soil. These miniature pieces of equipment, about the size of a 50 cent coin, can record the soil temperature over long periods and store the information. This information can then be transferred to a laptop and analysed. Anne used data loggers at a number of sites in Otago to see how the soil temperatures compared with temperatures that tuatara eggs experience in their natural habitat on Stephens Island in Cook Strait.
Nature of Science
Scientific investigation often uses sophisticated pieces of equipment to capture data that can then be analysed and interpreted using a computer.
Disappointingly, Anne’s initial results did not find any sites warm enough to ensure that some males would hatch. However, the following year, the research team recorded warmer temperatures at some sites. This raises optimism that both sexes can be produced at the sites, but longer-term monitoring is required.
Tuatara on the move
In March 2009, 15 juvenile tuatara were moved to Orokonui Ecosanctuary. The tuatara were placed into a secure, outdoor rearing enclosure so they could be closely monitored. Ecosanctuary staff and university researchers are in consultation with the Department of Conservation and iwi, including Ngāti Koata and Ngāi Tahu, regarding the possibility of future translocations and the eventual free release of tuatara within the sanctuary.