2003 CRC Reef Marine Science Journalism Prize

The 2003 CRC Reef Marine Science Journalism prize was awarded to Bridget Green of James Cook University, Townsville, for her story about ‘Reef Transvestites’.

The award was presented by Minister for Science The Hon Peter McGauran at the opening of the Australian Science Festival in Canberra in August 2003.

The Dorothy Paramore Highly Commended Award was won by Melissa Lyne of the University of Tasmania. To read Melissa's story go to: http://www.reef.crc.org.au/postgraduate/paramoreaward2003.html

Reef transvestites. Sex and the Science of Sex Change.

By Bridget Green

Internet sex can be surprising, educational and somewhat fishy. A quick Google search for ‘sex change’ introduces the net surfer to an assortment of operation choices, pre-and post- op photos, support groups and discussions for humans interested in transvestism. There is also a small reference to a family of tiny residents of the Great Barrier Reef, the unusual and very sexually labile gobies.

Confused, kinky, licentious? No, just practical, well adapted and highly evolved to life on the reef as a small and vulnerable fish.

Multi-coloured coral-dwelling gobies like it both ways, the trans-transsexuals of the marine world can quickly and with little fuss undergo multiple gender reassignments, or sex changes. Fullbright scholar and coral reef marine scientist from James Cook University, Dr Philip Munday, has spent three years investigating the sexy duality of these tiny coral dwelling fishes.

“Gobies are the first species we’ve found on the Great Barrier Reef that can change sex from female to male and then back to female again if their living arrangements require it,” explains Dr Munday.

Similar to their human counterparts, gobies do this to optimise their relationships. But for a goby the sex change increases rather than removes their reproductive capacity.

Gobies live in monogamous pairs within the branches of their host coral, protected from larger predators by the fence-like labyrinth of calcium carbonate branches of the living coral. Leaving the relative safety of these coral branches to find a partner in the unprotected waters between coral outcrops is a risky business. Staying put and being adaptable is much simpler. Big picture evolutionary theory suggests that for all species the raison d’etre is to reproduce. And so for these small gobies, the ability to change sex in both directions brings partnership, a functional reproductive mate and a fulfilment of evolutionary reproductive requirements.

While sex change is not uncommon in reef fish, with hundreds of species able to undergo gender reassignment once during their lives, sex change in both directions, that is bi-directional sex change, is highly unusual and so far only known from a few species.

Most sex-changing fishes, such as coral trout and red throat emperor, start life as a female and turn into a male as they grow larger; there are more benefits available to big boys, such as having a harem and fertilising many females at once. A few, mainly monogamous fishes like clownfish, will start life as a male and turn into a female.

What makes gobies so unusual is that their gender reassignment works both ways, so they need never be stuck for a date. If their mate leaves them or dies, they can simply court the next homeless fish that comes along, regardless of its current sexuality, because soon enough one of them will make the switch and become a serviceable sexual partner. In fact, this amazing and complex reorganisation of their sexuality and gonad structure happens in less than 30 days. According to one Google female- to male- transsexual, human gender reassignment can bring about ‘two years of hormones and anxiety’.

Dr Munday discovered the strange and yet-so-practical sex habits of coral-dwelling gobies on the Great Barrier Reef after orchestrating a veritable swingers club in the waters surrounding Lizard Island Research Station. In scientific terms this translates to a group of controlled experiments where Dr Munday partner-swapped 25 pairs of gobies into homosexual pairs, both male-male, and female-female pairs. While the gobies accepted these changes to their living arrangements, they were not passive conformists. In many cases, one of the newly formed pair very quickly shuffled their gonads, changing sex and so forming reproductively active female-male pairs.

Most surprising of all is that despite popular theory, this sex-change operation comes at little or no energetic cost to the fishes.

“The relatively low cost of sex change compared to the likely costs of searching for a mate of the correct sex, appears to explain the evolution of bi-directional sex change in coral-dwelling gobies”, writes Dr Munday in the scientific journal Marine Biology.

It appears the benefits derived from switching teams so readily far override the costs of reorganising gonads and the mating ‘down-time’ during the change and through the recovery.

Bi-directional sex-change capabilities also reduce the likelihood of eternal widow-hood upon the loss of a partner.

The goby’s open sexuality does not extend to menage a trois. Three’s a crowd for this highly territorial fish where all available residential corals are occupied by couples that vigorously defend their prize coral real estate against intruders, which includes lonely gobies looking for a threesome. For mature adult fish the roving singles game is tough, as there are no singles bars to cruise, and mating success depends on owning coral real estate. All the good mates are taken and these committed monogamous couples live in all the best homes on the Reef. Moving from coral to coral is a risky business when you are only a few centimetres long, and so staying at home welcoming homeless singles and changing sex appears to be the safest option of finding a new mate.

The apparent simplicity of this sex-change may lie in the hormonal system of these fish. Dr Munday’s most recent research shows that the female gobies of the species Gobiodon histrio have the same amount of testosterone as the males, even when they have fully functioning female gonads. This is extremely fishy. Steroids in humans have a much more pronounced effect on the human body. In humans, in broad terms, oestrogen is responsible for secondary sexual characteristics such as breast growth and high voices while testosterone is responsible for deep voices, facial hair and testicles. Too much of either will affect reproductive viability, illustrated by the male contraceptive pill which is basically a super-large dose of testosterone, reducing a human male’s sperm count to zero. Gobies are therefore very unusual in that both sexes have similar quantities of testosterone and oestradiol and have perfect sexual function without displaying any fishy secondary sexual characteristics, such as size or colour change.

As Dr Munday’s research continues to unravel the unusual and yet how-so-convenient sex lives of these tiny coral dwelling fish, medical doctors in a parallel world above the waves, investigate procedures and drugs that could simplify gender reassignment in humans. Maybe in a parallel universe, the secrets of coral dwelling gobies and their simply gender reassignment will benefit people in medical science!?