The central bearded dragon is also called the inland bearded dragon. It is one of the species of agamid lizard found in a wide range of arid to semi-arid regions of Australia’s eastern and central parts. An adult male bearded dragon can bite more forcefully if compared to a female bearded dragon. This is because of the difference in head dimensions.
Embryos of Bearded Dragons become females either by Sex Chromosomes or Hot Temperatures
Now the interesting part is, to become a female lizard, the embryos of the bearded dragon use two different sets of genes, one of which is activated obviously by sex chromosomes, and another one is activated by high temperatures during evolution. In April 2021, Sarah Whiteley and Arthur Georges of the University of Canberra published this new research on the bearded dragon, in the journal PLOS Genetics.
It has been observed that the sex of developing embryos depends on the surrounding temperature in most reptiles and fishes. This incidence was discovered in the 1960s and called temperature-dependent sex determination. Despite intense research for a century, the scientists do not know the molecular details about how it happens?
Researchers calibrated the biochemical pathways that are required to make a female in their new study. For this study researchers used the phenomenon in bearded dragons. Thus in male bearded dragons, there are ZZ sex chromosomes while in female ones there are ZW sex chromosomes. If there is a high temperature in the surrounding then it can override the ZZ sex chromosome which will cause the male lizard to develop as a female.
Sex reversals due to high temperature
A study in the year 2015 showed that high-temperature incubation of eggs leads to the transformation of genetically male bearded dragons into female ones. Sex determination is apprized genetically as told earlier that Males have ZZ as sex chromosomes, females have ZW. However, when their eggs are hatched at temperatures above 32 °C (90 °F) some genetic males are born as female bearded dragons.
These females are more fertile, and it has been observed that they will produce more eggs than ZW females. Despite this sex reversal, ZZ females are similar to ZZ males as per tail length and boldness. However, during their younger period, adults sex-reversed ZZ females remain behind in larger head and greater bite force of ZZ males and thus tend to become closer to ZW females.
Whiteley and Georges in their study compared which genes were turned on during development in bearded dragons when ZW chromosomes compared to ZZ animals and exposed to high temperature. They discovered that at the initial stages, in two types of females different sets of genes were active, but ultimately the pathways converged to produce ovaries. This finding is in support of recent researches stating that the ancient signaling processes inside the cell help to translate high temperature into sex reversal.
Whiteley said that “the most exciting part of this work is the discovery that the mechanism involves universal and highly conserved cellular processes, signaling about pathways, and epigenetic processes of chromatin modification. This new knowledge about bearded dragons brings us closer to understanding how temperature can determine sex, thus it is a very exciting time to be in biology.”