Most of the stories we see in the news about “sex change chemicals” in the environment focus on male animals turning into females, with the blame often being placed on the use of contraceptives by human women. But all sorts of things can happen in the weird and wonderful world of biology. Here is a story to redress the balance.
Murex is a genus of carnivorous sea snails with impressively spiny shells. Different species are found in many places in the world, but the Mediterranean varieties are particularly famous for being the source of Tyrian Purple, the expensive dye that was beloved of Roman emperors and other potentates of ancient times. While the snails are no longer harvested to make dye, they are still eaten by people around the Mediterranean. Sicily was noted for its fisheries, until now.
According to a study by Italy’s Institute for Environmental Protection and Research (ISPRA in Italian), populations of Murex around the Sicilian coast face extinction because all of the female snails have turned into males. The culprit is apparently a chemical called TBT which used to be used in anti-fouling paints. It was banned in 2001, but has yet to be totally phased out. A report in an Italian newspaper explains:
The exact mechanism behind the transexual molluscs is still being studied. A handful of Italian researchers are at the cutting edge. One of them, Antonio Terlizzi of Lecce University, explained that TBT boosts the production of testosterone in the female murexes, making them sterile and eventually turning them into males.
”It’s a little bit like all those women shot-putters with moustaches you used to see a few years ago,” he said.
Um, quite. So eating Sicilian sea snails might not be a good idea right now.
We used to have chickens when we lived in Las Vegas. After giving away the males, one of our hens started becoming a rooster. It was fascinating and caused me do to some research on chickens. Sure enough, they change gender when there is too much of one or the other. With my chicken, it was some sort of internal switch, I suppose. She was accepted as a rooster to the other hens and she did everything a rooster does except fertilize eggs. She laid eggs herself.
Sea life seem to have an easier time switching genders. No problem with them being able to fit in either.
Generally the simpler the animal, the easier it is for it to swap genders. Chickens are pretty high up the evolutionary ladder though. I’m impressed, and am wondering about the mechanism.
I believe the chicken change is something about pecking order (literally – it’s where the phrase comes from). The “top hen” takes on the male role and male hormones increase, which results in physical changes.
Many fish species have both male and female internal organs, but when they’re small the male organs are the only ones to mature. As the fish grows, the female organs mature, creating a hormonal chain reaction that may change their color and many other things. All of the fish in some species do this. This happens much more frequently with marine species, particularly reef species. By the time the female organs are mature, the male organs have atrophied and are usually fully resorbed into the body – mostly if not completely.
Bob:
That much I could pretty much guess (and indeed knew about fish). But what intrigues me is how the “top hen” knows to undergo those physical changes. It suggests that something in the social environment of the hens is triggering a physical change in their bodies.
This isn’t just academic interest. In Rainbow Bridge Gwyneth Jones has a Chinese general state that the infanticide of girl children under the One Child policy “caused” a significant increase in the number of male-to-female transsexuals in China. I assumed at the time that Jones was suggesting that MtFs are simply men who find it impossible to get laid as men and decide to try their luck on other side, but if she knew about the chicken thing perhaps she had a biological mechanism in mind.
Apparently the chicken change has only made it into the news (online) a couple of times. Once in India and once in the UK, but like Mo say’s it’s a widely known phenomenon in egg production houses (but still 1:10,000)
Dunno. Here’s what I found, just for fun. Oh, and the Chinese General – HA, not even hardly likely.
Damaged Ovary theory:
http://www.hemmy.net/2006/04/24/sex-change-chicken-baffles-animal-experts/
and
http://www.worldpoultry.net/news/from-georgina-to-george-%E2%80%93-chicken-changes-sex-id3251.html
“Soaring Testosterone Levels” theory (which can result from damages ovary)
http://www.mirror.co.uk/news/top-stories/tm_objectid=16963028&method=full&siteid=94762-name_page.html
and
“Yes a type of sex reversal does occur in poultry. Both a right and left ovary start to develop in the embryo but between day 7 and 9 of incubation the right gonad ceases to continue development. If in the adult, the left ovary is removed or fails to function the right gonad hypertrophies to become a testis-organ and thus “a male’ instead of what was a hen.” From: http://www.angelfire.com/oh/ZebraDirectory/faq.html
Thanks, that sounds a lot more plausible.