One of the varieties of clownfish , Amphiprion bicinctus , is monogamous and sequential protandric hermaphrodite . This means that all the fry of these fish are male but have the ability to become female when the hierarchical situation in the group allows it. The eldest specimen of the clan becomes the dominant female of the matriarchy, which is how their society is configured. Then they lay eggs in an elliptical shape, demersal and attached to the substrate, which the males are in charge of oxygenating until the fry are born. Within a week, the fry become independent from their parents.
In reality, among reef fish species, a specimen changing sex after reproducing several times is not a novelty. But the process of sequential hermaphroditism was a molecular mystery to scientists. Among these clownfish ( Amphiprion bicinctus ), it is common for an adult male and female to cohabit with several fry. When the female disappears, the male alters his hormonal levels and his behaviors and transforms into a female to restore the previous balance. This produces populations that are more resistant to changes in the environment and stimulates their reproductive capacity.
Recently, scientists from the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have studied this phenomenon and have identified changes in gene expression within the brain and gonads that lead to the process of sequential hermaphroditism. To do this, they compared the profiles of genetic activity in adult males and females and in males at various stages of their life process. After being separated from a female for two weeks, the expression of genes in the brains of the males changed markedly as heralding the beginning of the sex change. The study, published in Scientific Reports , has served to identify numerous molecular sequences capable of fine-tuning and controlling the proportion of each sex in a population of fish, according to Timothy Ravasi, of the KAUST Environmental Epigenetics Program.
A key candidate is a gene that encodes an enzyme called aromatase, responsible for a critical step in estrogen biosynthesis. This enzyme was highly expressed in the brains and gonads of fish that adapted to alterations of sex. In addition, the team of scientists discovered that many other genes can interact with aromatase to manage the degeneration of the testes and the development of the ovaries . Based on these findings, the scientists want to study the influence of environmental factors, and especially climate change , in this adaptive process of sex changes .
