At New Scientist, "Zoologger" has a post up on the transsexual abilities of the hawkfish (species Cirrhitichthys falco), which is found off Kuchino-Erabu Island in southern Japan. As the post notes, transitioning in fish occurs in many species - but this one reverses the process. (Even this ability is not unique though - see Joan Roughgarden, " Evolution's Rainbow ").
When it comes to selecting mates, hawkfish keep their options open. The flamboyantly coloured reef dwellers start life as females but can transform into males after maturing. Many marine animals do this, but these fickle fish have a rare trick up their fins: they can change back when the situation suits.
Tatsuru Kadota and colleagues from Hiroshima University in Higashi-Hiroshima, Japan, have observed reverse sex changes in wild hawkfish for the first time in the subtropical reefs around Kuchino-Erabu Island in southern Japan.
Hawkfish live in harems, with one dominant male mating with several females. Kadota's team studied 29 hawkfish and found that when it comes to sex change, the size of the harem matters.
If a male hawkfish took on many females, one of the two largest females would change sex and take over half of the harem, mating as a male. Conversely, if that new male hawkfish lost a few females to other harems and was challenged by a larger male, it reverted to mating as a female, instead of wasting precious energy fighting a losing battle. "The ability to undergo bidirectional sex change maximises an individual's reproductive value," Kadota says.
A reader, Mario, has shared a link to a fascinating story about a domestic hen that transitioned to a cockerel, after an injury. I've known about transitioning in fish species for years, but this is the first time I've come across an instance in birds.
Bagemihl, Bruce: Biological Exuberance: Animal Homosexuality and Natural Diversity
Roughgarden, Joan: Evolution's Rainbow: Diversity, Gender, and Sexuality in Nature and People,
- Transsgendered Fish: He's Not Making This Up!
- Exclusive Homosexuality Unnatural?
- Natural Law, Natural Sex, Natural Families
- Africa's Female Kings and Husbands
- Gay (Wild)life