Posted on 05/23/2007 11:21:54 AM PDT by DogByte6RER
Scientists: Hammerhead has 'virgin birth' in zoo's shark tank
By David Fleshler
South Florida Sun-Sentinel
May 23, 2007
A hammerhead shark captured in Florida Bay gave birth without sex, according to scientists who said they used genetic analysis to account for the mysterious appearance of a pup in a tank of female sharks.
The research was to be published today in the British journal Biology Letters.
The phenomenon, known among biologists as a "virgin birth," had been observed before among some snakes, lizards and birds, but never a shark, the scientists say.
The issue arose in late 2001 at a zoo in Omaha, Neb., when a worker noticed a baby shark swimming in a tank that contained only females. The three female bonnetheads, a small species of hammerhead, had been caught as juveniles. Three years later, the pup appeared.
The zoo's scientists advanced possible explanations -- someone dropped the baby shark in the tank as a hoax; a different fish species in the tank somehow fertilized the female; or one of the females had stored sperm from a previous encounter with a male.
But in the article, a team of scientists from Nova Southeastern University, the University of Miami, Queen's University Belfast and the Henry Doorly Zoo of Omaha report that a genetic analysis proved the pup was the offspring of one of the females only and contained no paternal genetic material.
"It now appears that at least some female sharks can switch from a sexual to a non-sexual mode of reproduction in the absence of males," said Mahmood Shivji, a biologist at Nova's Guy Harvey Research Institute, and one of the study's authors.
(Excerpt) Read more at sun-sentinel.com ...
Is the stringray's name "Pontius Pilate" by chance?
Very interesting...
Was it the jewfish?....../s
'Virgin brith' of hammerhead A hammerhead shark caught in Florida Bay gave birth to this pup without sex, the first such case established among sharks and rays. Nova Southeastern University biologist Mahmood Shivji analyzed the pup's genes and established that they contain no paternal DNA, only DNA from a female shark. (Photo courtesy Lee Simmons)
That looks more like a shovelnose shark.........
If it had not been killed, I would have guessed the AntiChrist. Makes perfect sense that he’d be born to a virgin shark.
Was John Edwards, notorious PI lawyer, anywhere near the tank in the last few months?
Rosie O’Donnell and other lesbians should be interested in this research. It sounds as if there could be natural ways for a female to have children without having a man in the picture.
I have read that in some species of fish, self-changing of gender, including all the reproductive characteristics, is more common than rare.
Humans have done and do this. Once or twice in ancient Israel and often nowdays in the Middle East.
Or maybe it’s those estrogens and other female hormones from birth control pills entering rivers and streams via the toilet, that’s causing male fish to develop ovaries.
http://www.canada.com/montrealgazette/news/story.html?id=1a624943-4a0e-4358-b5c4-a0f887cbe480
Pumped full of estrogen, fish are too confused to mate
Hormone flushed into rivers, lakes. Feminized male minnows grew ovary-type tissue and produced eggs, researchers say
TOM SPEARS, CanWest News Service
Published: Tuesday, May 22, 2007
Estrogen that goes down Canadian toilets - some naturally from women, some from the Pill - is enough to make entire fish species too feminine to reproduce, a seven-year Canadian study shows.
Fish scientist Karen Kidd dripped small amounts of estrogen into a clean lake in northwestern Ontario over several years, just as if urine with the female hormone were running in via sewage from a nearby city.
This constant hormone bath made male minnows produce eggs in unnatural, part-female sex organs.
And even after she stopped adding estrogen and the water turned clean again, the minnows almost completely disappeared for several years.
Even small concentrations of estrogen can decimate wild fish populations, the University of New Brunswick biology professor concludes, even at levels found in some Canadian waters. She wouldn’t name individual rivers.
And while the minnows were prone to fast extinction because of their short lifespan (about two years), she says bigger fish like trout or pike might also be hurt if they are exposed for long enough.
The first dramatic news of “feminized” fish came from British rivers in the 1990s where male fish near sewage plants were producing eggs and carrying reproductive organs that were partly female.
“A lot of follow-up studies showed it was the natural estrogens that women excrete and then the synthetic estrogens in birth control pills that were the main causes of feminization in male fish,” Kidd said.
“The Pill is one of the most heavily prescribed pharmaceuticals in the world. There are over a million women on it in Canada.”
She chose to conduct her experiment in an unpolluted lake with healthy fish to learn what damage estrogen would cause.
Male minnows in water with estrogen just stopped looking male. Where they should have distinct colours and bumps at spawning time, they didn’t have any visible sign of maleness.
“And then when you opened them up, their testes were much smaller than they should have been” - about one-third the normal size. By the third year of adding estrogen to the lake, the testes had ovary-type tissue, and were producing eggs - a condition called “intersex.”
It’s exactly what scientists had seen in the wild. The achievement is in reproducing this effect in a previously clean lake, proving that estrogen is the cause.
Meanwhile, the female fish produced eggs more slowly.
The Kidd team found these effects early, but continued the study for several years to see what would happen. And the whole minnow population crashed.
“That was the big question: What does it mean for the fish population? We’ve shown that it has profound effects on the fathead minnow.”
If minnows don’t sound very exciting, Kidd notes they are a staple source of food for bigger fish across North America, right up to lake trout and northern pike. Killing the minnows in a lake is like taking wheat or rice out of the human food supply.
The last estrogen went into the lake in 2003.
Since then, bacteria and sunlight have broken down the estrogen and the water quickly returned to normal. The minnow population, however, took a further two years to recover.
© The Gazette (Montreal) 2007
My understanding of this issue this that the offspring is, with one exception, always female. I noticed the article did not mention the sex of the “pup.”
Or adoption.
A ‘virgin birth’ then a murder?
It’s a SIGN!!!
Stingrays are trying to establish their street cred. First they knocked off Steve Irwin, now the Jesus shark...
Nature finds a way.
Estrogen itself still might be a factor "in the wild", and in the oceans there might be some set of environmental signals - recognized by a school of fish - from which the production and release of estrogen is raised, or lowered within the school itself (changing the concentration of estrogen in the local environment of the school), providing the hormonal trigger for the "sex" change.
Interesting article. Just now hearing of it.
http://www.foxnews.com/story/0,2933,286523,00.html?sPage=fnc/scitech/naturalscience
http://www.usatoday.com/tech/science/2007-06-25-2630843731_x.htm
It is called Parthenogenesis. There is a lizard that are all “clones” from the original parthinogenic female founder. They simulate mating to get the hormones going but no genetic material is exchanged.
And many fish do change sex. They usually start as male, then turn female when they get large enough to devote resources to developing a clutch of eggs; but I don't think this is common in sharks.
“Is anyone here a Marine Biologist?” (besides George Castanza?)
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