Education:Stories from the Field
Tuataras and temperature
Like some other reptiles, such as alligators, tuataras have temperature-dependent sex determination. This means that the temperature the eggs are incubated at determines the sex of the young. It has been found that just one degree centigrade of difference can change the young from all females to all males. Since higher temperatures cause the young to become males, there is some concern about the effects global warming could have on the survival of populations of these unique animals.
In 2002 Dr. Nicola Nelson, a Millennium Postdoctoral Fellow with the San Diego Zoo's CRES began following female tuataras at the main rookeries (communal nesting areas) on Stephens Island in New Zealand. Each night she recorded data on where tuataras were building their nests. As soon as a female laid her eggs and covered them, Dr. Nelson put a small device next to the eggs that measured and recorded the temperature in the nest every hour for the next 13 months, the length of time it takes tuatara young to develop. With this temperature information, Dr. Nelson hoped to determine the sex of the hatched young.
Comparing the nest temperatures to the air temperature, Dr. Nelson wanted to see how changes in air temperature affect the nest temperatures and thus the sex ratios of the young. By December 2003 she had approximately 900 females tagged and 90 nests marked with data loggers. Current data analyzed from 46 nests suggests an even sex ratio: 50 percent female and 50 percent male. This is excellent news and will have important implications for the future of tuatara conservation.
