Transgender Dragons

Now and again there’s a report in the media which raises questions about gender determination – not in humans but in animals. In December there were reports that a lizard in an Australian aquarium had changed from female to male at the beginning of last year and scientists don’t know how or why.

Gender switching is not uncommon outside our hominid family. In fact it is well documented among reptiles and fish, including lizards and even crocodiles. Several years ago I wrote about gender-switching in chickens which may have led to the origin of stories about the legendary creature the basilisk or cockatrice. The gender determination process in lizards is similar, especially in several species that are named after another legendary creature, the dragon.

Like chickens and birds lizards’ chromosomes are given the names ZZ, which normally indicates a male lizard, and ZW, which normally indicates a female lizard. High environmental temperatures seem to trigger a sex change in embryos in pre-hatched eggs. It is the temperature of the eggs that determines whether the ZZ embryo of a male lizard develops into a female before it hatches. These female lizards with ZZ male chromosomes are even capable of producing normal offspring, all of them normal ZZ males.

In 2015 this type of gender determination was studied in a species of lizard called the central bearded dragon. This dragon lives in the tropical regions of Australia and despite their monstrous name they are no bigger than a domestic cat. Researchers found that around 10% of the dragons they examined were females with ZZ male chromosomes and no ZW female chromosomes. It was the first time that genetic gender differences of these lizards had been found in the wild.

But what is puzzling biologists is that one species of lizard closely related to the central bearded dragon called the Boyd’s forest dragon has unexpectedly changed sex from female to male in adulthood. The dragon in question lives in the Sea Life aquarium in Melbourne, where she had been given the name Doris.

Doris had lived as the aquarium for the past 6 years and has laid many eggs and produced many young. She lived in a tropical forest exhibit with two other Boyd’s forest dragons, a male and a female. Sadly the male dragon, called Old Mate, died in 2019 and the two female dragons were transferred to a new tropical exhibit in early 2020. Shortly afterwards Doris began exhibiting behaviour that was not typical for her gender. She began to eat regularly. Female Boyd’s forest dragon’s usually only binge eat in one short period prior to laying eggs, but Doris was eating like a male dragon. Then Doris started to change skin colour and develop a more prominent crest and she began to grow larger, just like a male dragon.

Doris the Boyd’s forest dragon.
Photo from the Sea Life Aquarium’s Facebook page.

These changes were noticeable to the aquarium staff particularly the reptile keeper Tom Fair (who is openly gay, by the way, but that’s not relevant to this story). The animals at the aquarium are given a medical check regularly and during one of them Tom took Doris to the aquarium vet. An ultrasound confirmed that Doris was a female dragon. Ovaries and underdeveloped eggs were detected. Then, a month later at the next check Doris was given another ultrasound. This time there were no ovaries and no eggs, and instead Doris had developed testicles. Doris was now a male dragon.

Scientists are both mystified and sceptical. Adult reptiles had not been known to change gender before. As explained above sex changed has only been found in embryos in unhatched eggs. The only other species known to change sex in adulthood is the clownfish (yes, the same fish as Marlin in “Finding Nemo” – I wonder if Disney will ever make a sequel about Marlin as an adult suddenly changes sex. I doubt it – you know how prudish the American are on these subjects).

There are several tentative theories about how Doris (I suppose we should start calling him Boris now) changed gender. A lot of research and observation will have to be done before any proper theory can be formulated. Over a year later scientists are no nearer to providing an answer. Until we know for sure that Doris won’t or can’t change back he goes down in history as the world’s first transgender dragon.