How heat can rewrite the destiny of a bearded dragon

In the bearded dragon, sex isn’t determined by chromosomes alone. These lizards can hatch male or female depending not just on their DNA, but also on the temperature of their nest.

This rare phenomenon has made the bearded dragon a focus for scientists exploring how sex is determined in vertebrates.

Now, two separate studies have built nearly complete reference genomes of the central bearded dragon, Pogona vitticeps.

The research provides the clearest look yet at what makes a male a male – and why sometimes, a genetically male dragon hatches as a female.

The bearded dragon’s genetic switch

The new research comes from scientists at the University of Canberra in Australia and Zhejiang University in China. Both groups independently sequenced the bearded dragon genome, using different technologies and approaches.

The teams landed on the same key insight: a likely master sex-determining gene hiding in the dragon’s Z chromosome.

Unlike humans, where sex is determined entirely by chromosomes, bearded dragons follow a ZZ/ZW system. Males are ZZ and females are ZW.

But high temperatures during egg incubation can flip the switch – turning a genetic male (ZZ) into a fully functional female. That rare flexibility in vertebrates has made these lizards essential for studying how environment and DNA interact.

With the help of advanced sequencing tools, both teams zoomed in on one region of the genome they believe controls this entire process.

Two genomes, one big answer

The first study used a combination of DNBSEQ short-reads and long-reads from the new CycloneSEQ nanopore sequencer. It’s the first time this technology has been used to sequence an animal genome.

The second project, focused on a female lizard, used a mix of PacBio HiFi, ONT ultralong reads, and Hi-C sequencing.

By analyzing different animals (one male, one female) and utilizing different technology, the teams created genomes that complement each other.

Together, the genomes help fill in gaps and confirm shared findings – like the identification of roughly 124 million base pairs of previously missing sequence, including genes and regulatory elements.

Bearded dragon sex gene

Thanks to these advanced methods, the scientists were able to assemble nearly the full genome – 1.75 billion base pairs in each case – down to the telomeres.

The researchers also mapped the Z and W chromosomes in detail, including a key “pseudo-autosomal region” (PAR) where the sex chromosomes pair and recombine.

Most importantly, both teams pinpointed the same region of the genome as the likely home of the sex-determining gene. Within that region, one gene stood out: Amh, or Anti-Müllerian hormone.

The hormone – along with its receptor Amhr2 and another gene, Bmpr1a – were identified as strong candidates for controlling sex.

Expression analysis showed that Amh is far more active in developing males, suggesting it could be the master regulator. The twist? Bearded dragons also have autosomal (non-sex chromosome) versions of these genes, meaning they might act together in a network, not just through the sex chromosomes.

A milestone for reptile genetics

Until now, no reptile had a clearly identified master sex-determining gene like mammals (Sry) or birds (Dmrt1). This discovery may be the closest we’ve come in reptiles.

Arthur Georges, senior author on the second paper, explained that the new genome assemblies will fuel rapid progress in many research areas. They open the door to studies on cranial and brain development, behavior, and how genes interact with one another as well as with the environment.

Georges added that the bearded dragon now offers a strong squamate model for comparison with more traditional model species, including mice, humans, and birds.

Sex determination in bearded dragons

Qiye Li, senior author on the first paper, explained why the bearded dragon was the first animal genome sequenced using the new technology.

“We decided to start working on the bearded dragon genome last year as the first animal genome for this new sequencer because it was the Year of the Dragon in China,” said Li.

“The two reference genomes, derived from opposite sex and generated by different technologies, are indeed complementary to each other.”

“I am excited that both genomes pinpoint the key role of AMH signaling in sex determination in this species. But how did the sex chromosomes arise? We anticipate that additional high‑quality genomes from related species will further elucidate the evolutionary origin of the ZW system and complete the story.”

A webinar with the two lead authors will take place on August 26 at 10:00 AM UTC, offering a chance for researchers and the public alike to ask questions and learn more about what’s next for this fascinating species.

The research was published in the journal GigaScience.

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