How many animals can change their sex

This is how wrasses change their gender

Most blue-headed Junckers start their lives as females. But depending on their social environment, they can change their gender.

The fish live in social groups with a dominant male. The male has a striking blue head and protects his harem of yellow colored females. When that male leaves the group or dies, the largest female in the group begins to transform into a male within minutes. The still female behaves more aggressively and mates just like a male otherwise does. In addition, his body changes and his head turns blue.

How does the sex change take place?

The scientists from New Zealand have found that the genes themselves do not change - the DNA remains as it is. But a new decision is made as to which genes are read and which are not. For example, when a certain gene is read off, aromatase is created. This is an enzyme that is needed for the production of estrogen - so it is responsible for ensuring that the fish has female sex hormones. As long as the fish remains a female, the corresponding gene is read and the fish produces the hormone.

The gender genes are selected differently

If the fish now becomes male, this gene is marked. It gets a “please do not read” sticker, so to speak. But with it no more estrogen can be produced either.

This triggers a kind of chain reaction - many different genes in the fish are marked; the pattern of which genes are read and which are not changes. And massive.

The female fish develops testicles and sperm

The body of the female fish is completely transformed: the female becomes larger and has a blue head. But the ovaries also recede and fully functional testicles develop instead. The female is reprogrammed to become a male. And all of this in just 10 to 20 days!

Stress is believed to be the trigger for sex reassignment

The trigger for this transformation has long been unknown - in the journal "Science Advances" the researchers report that an increased stress level could be the trigger. When the male leaves the group, it causes a lot of social stress in the Pisces women - the starting signal for the renovation.

Males can become females too

In a previous study, scientists found that the sex of the blue-headed Juncker and many other wrasse depends on how many other animals of the species lived in the same area. If the number is low, the likelihood that males will become females is significantly higher. On the other hand, if there are many fish, females become males. In the journal Proceedings of the Royal Society: Biological Sciences, the researchers wrote that this shows that sex, unlike in mammals or birds, is not genetically predetermined.