Most bluehead wrasses begin life as females, but can change sex sometime later to become males - a process that takes just 10-21 days from start to finish.
Caption: A female becomes a male: a transitioning bluehead wrasse (darker colouration) establishes dominance and begins courting females (yellow colouration).
Functional sex change is widespread in marine fishes, appearing in 27 families. Among the most outstanding, and well-studied, example of sex change is the bluehead wrasse (Thalassoma bifasciatum), a small coral reef fish that undergoes rapid and complete female-to-male sex reversal in response to a social cue.
Sex change in 10 days
"When a dominant male is lost from a social group, the largest female transforms into a fertile male in 10 days flat", says Dr Erica Todd, co-author of a study at University of Otago.
Females begin this transformation within minutes, first changing colour and displaying male-like behaviours. Her ovaries then start to regress and fully functional testes grow in their place.
"How this stunning transformation works at a genetic level has long been an enigma,"
- Dr Erica Todd
"Our study reveals that sex change involves a complete genetic rewiring of the gonad. We find that genes needed to maintain the ovary are first turned off, and then a new genetic pathway is steadily turned on to promote testis formation."