A new study comes to suggest that bearded dragons change their sex in dependance to the temperature at which the eggs are hatched.
What was previously held true about sex determination in the bearded dragon was entirely connected to chromosomes. Two Z chromosomes indicate that the lizards are male, while a Z chromosome and a W chromosome indicate the lizard develops into a female.
Nonetheless, if the temperature at which the eggs are hatched is above the normal limits at which the bearded dragons develop, then a whole new process takes shape.
All it takes is a 34 degrees Celsius temperature and the chromosome determination is useless. In a batch of eggs, if half bear the genetically male chromosomes combination, ZZ, they will still hatch as females.
Clare Holleley, researcher from the University of Canberra unraveled this phenomenon is the wild. Collecting a few wild ZZ females, she proceeded to breed them with the ZZ males. With all the Z chromosomes, it was expected that the hatchlings would be male.
It wasn’t the case. At the temperature of 34 degrees Celsius, all hatches were in fact female. Turn the thermostat a few degrees lower and the hatches are entirely males.
This shift in reproduction is the produce spanning only one generation. The bearded dragons’ genes headed way to the increasingly warming global temperature to control sex determination.
For humans and other mammals, as well as insects, females of the species usually present a pair of identical chromosomes, XX. At the same time, males have a combination of XY.
For reptiles and birds, the situation is different. Males present a pair of identical chromosomes, ZZ, while females differ with a ZW pairing.
The phenomenon observed in the bearded dragons is not new. Some reptiles rely entirely on temperature to decide the sex of the hatchlings. Turtles follow a similar pattern to that observed in the bearded dragons, while crocodile eggs hatch as males at higher temperatures and females at lower temperatures.
Scientifically these two ways of determining sex in an individual are known as genetic sex determination or GSD and temperature sex determination or TSD. In 2007 it was discovered that GSD and TSD are by no means mutually exclusive.
To confirm the finding, Clare Holleley and her team captured 131 bearded dragons in eastern Australia. Of these, 11 specimens were ZZ females. Their eggs bore no determination by chromosomes.
When incubated at a maximum of 30 degrees Celsius, the hatchlings were all males. Above 34 degrees the hatchlings of the ZZ females turned out females. In between, the results were mixed. The study spanned one generation of bearded dragons, bred under laboratory conditions.
Throughout, the W chromosome was entirely wiped out.
If this were to happen in the wild, the researchers say, the species would be left with only females, possibly leading the bearded dragon to extinction.
Cases have been observed before where adaptation to climate and an evolving habitat drive adaptive change in the species, yet, bearded dragons haven’t witnessed such a raise in global temperatures ever before.
Image Source: dragonspictures.info