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The bluehead wrasse is a fish that lives in small social groups in coral reefs in the Caribbean. Only the male has a blue head—signaling his social dominance over a harem of yellow-striped females.
If this male is removed from the group, something extraordinary happens: the largest female in the group changes sex to become male. Her behavior changes within minutes. Within ten days, her ovaries transform into sperm-producing testes. Within 21 days she appears completely male.
Wrasse - Change - Sex - Evolution - System
But how does the wrasse change sex, and why did evolution select this system?
Also, given that fish share sex-determining genes with mammals, would an understanding of this provide new insight into how sex works in humans and other animals?
How does the transformation happen?
The trigger for sex change in the bluehead wrasse and some other species is social. When the male fish is removed, the largest female immediately senses his absence and adopts full male breeding behaviors the same day.
Cue - Translates - Action - Bit - Mystery
How this social cue translates into molecular action remains a bit of a mystery, but it probably involves stress. High levels of the stress hormone cortisol are associated with temperature-based sex determination in other fish and reptiles. Cortisol probably alters reproductive function by impacting sex hormone levels.
Stress could be the unifying mechanism that channels environmental information into a change in sex.
Research - Changes - Activity - Bluehead - Wrasse
Our research traced changes in the activity of all 20,000-odd bluehead wrasse genes during the female to male transformation.
Unsurprisingly, we found the gene that produces the female hormone (estrogen) rapidly shuts off, and genes responsible for making male hormones (androgens) are turned on.
Hundreds - Genes - Genes - Egg - Components
Hundreds of other genes required for being female (including genes that make egg components) also progressively shut down, while genes required for maleness (including genes that make sperm components) turn on.
We also noticed changes in the activity of developmentally important genes whose roles in sex...
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