Tuatara Sex Debate

by Kirsty Macnicol and NZPA

Reprinted from Notes from NOAH, the newsletter of the Northern Ohio Association of Herpetologists, Vol.29, No2, December 2001.
Originally published in the Southland Times.

A new theory that tuatara might have four sexes instead of the usual two has drawn a cautious interest from Invercargill tuatara curator Lindsay Hazley. The theory has been put forward by molecular genetics researchers from Massey, Victoria, and Sydney Universities investigating how sex is determined in tuataras.

The “miniature dinosaur” is the only surviving member of an ancient line of creatures stretching back 225 million years to the Mesozoic era. The tuatarium at Southland Museum and Art Gallery is the only place in the world where tuatara are bred in captivity.

Those studying tuatara have known for about five or six years that incubation temperatures can determine sex. Eggs incubated at 22°C produced mostly males, at 18°C would produce mainly females, while at the pivotal point in the middle it could go either way. But Dr. Stephen Sarre, of Massey University, said studies of tuatara DNA showed there appeared to be differences in the genetic makeup of males and females. If the difference was found to be significant, this would indicate the sex of tuatara was determined not only by temperature during incubation, but also by genetics and the interplay between the two.

“A study of tuatara chromosomes published in the 1960s did not show obvious sex chromosomes, like X and Y that humans have, so it has been assumed their sex is not determined by genetics,” he said. “But if we find that there is a significant difference between male and female DNA, and that sex can be determined by temperature during incubation, then this would imply they could have four sexes,” Dr. Sarre said.

There would be males that are genetically male and look male; males that are genetically male, but look like females, genetic females that look like females, and genetic females that look like males. Dr. Hazley said it was an interesting theory but it would take several years before those eggs incubated in controlled temperatures reached sexual maturity to determine what effect it had on breeding.

Tuatara have no copulatory organs, so it usually takes up to eight years to determine their sex. Even then, Dr. Hazley said he had been fooled – an Edward had to become Edwina and a Charles became Charleen.

The new theory suggested breeders might be making a mistake by artificially altering incubation temperatures to determine sexes, Mr. Hazley said. “We might have a whole lot of gay tuatara.” However, he believed the possibility was remote.

Temperatures change in nature. The only difference is that artificial incubation temperatures remain constant. Nevertheless, he was interested in hearing the final analysis.

Two years ago, Mr. Hazley hatched 13 eggs at 22°C in the hope of raising mainly males, last year he got 12 successful hatchlings at 18°C (female), while in February, 15 tuatara were born after being incubated at the midway point of 21°C. It would likely be 2003 before he could start drawing conclusions from those hatchings. The Southland museum had 64 tuatara – 50 of which were bred by Mr. Hazley.

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