Ga percaya. That's all
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From: A. Dharmawan <[EMAIL PROTECTED]>
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Sent: Friday, October 10, 2008 22:31:39
Subject: [is-lam] Kelahiran Tanpa Ayah...bukan suatu kemuskilan di Alam...
DNA test proves it -- baby shark has no father
* Story Highlights
* Pup carried by a female blacktip shark contains no male genetic
material
* Scientist: "This is something female sharks of many species can do
on occasion."
* Virgin birth has been proven in some bony fish, amphibians,
reptiles, birds
* Virginia aquarium case is nation's second; first was in Nebraska
RICHMOND, Virginia (AP) -- Scientists have confirmed the second case of a
"virgin birth" in a shark.
In a study reported Friday in the Journal of Fish Biology, scientists said DNA
testing proved that a pup carried by a female blacktip shark in a Virginia
aquarium contained no genetic material from a male.
The first documented case of asexual reproduction, or parthenogenesis, among
sharks involved a pup born to a hammerhead at an Omaha, Nebraska, zoo.
"This first case was no fluke," Demian Chapman, a shark scientist and lead
author of the second study, said in a statement. "It is quite possible that
this is something female sharks of many species can do on occasion."
The scientists cautioned that the rare asexual births should not be viewed as
a possible solution to declining global shark populations. The aquarium sharks
that reproduced without mates each carried only one pup, while some species
can produce litters of a dozen or more.
"It is very unlikely that a small number of female survivors could build their
numbers up very quickly by undergoing virgin birth," Chapman said.
The medical mystery began 16 months ago after the death of Tidbit, a blacktip
shark that had lived for eight years at the Virginia Aquarium & Marine Science
Center in Virginia Beach. No male blacktip sharks were present during her
eight years.
In May 2007, the 5-foot, 94-pound shark died after it was given a sedative
before undergoing a yearly checkup. The 10-inch shark pup was found during a
necropsy, surprising aquarium officials. They initially thought the embryonic
pup was either the product of a virgin birth or a cross between the blacktip
and a male of another shark species -- which has never been documented,
Chapman said.
Tidbit's pup was nearly full term, and likely would have been quickly eaten by
"really big sand tiger sharks" that were in the tank, Chapman said in a
telephone interview from Florida.
That is what happened to the tiny hammerhead pup in the Omaha case.
"By the time they could realize what they were looking at, something munched
the baby," he said of aquarium workers. The remains of the pup were used for
the DNA testing.
Virgin birth has been proven in some bony fish, amphibians, reptiles and
birds, and has been suspected among sharks in the wild.
The scientists who studied the Virginia and Nebraska sharks said the newly
formed pups acquired one set of chromosomes when the mother's chromosomes
split during egg development, then united anew.
Absent the chromosomes present in the male sperm, the offspring of an asexual
conception have reduced genetic diversity and, the scientists said, may be at
a disadvantage for surviving in the wild. A pup, for instance, can be more
susceptible to congenital disorders and
diseases.
The scientists said their findings offer "intriguing questions" about how
frequently automictic parthenogenesis occurs in the wild.
"It is possible that parthenogenesis could become more common in these sharks
if population densities become so low that females have trouble finding
mates," said Mahmood Shivji, one of the scientists and director of the Guy
Harvey Research Institute at Nova Southeastern University in Florida.
The DNA fingerprinting techniques used by the scientists are identical to
those used in human paternity testing.
Chapman, who is with the Institute for Ocean Conservation Science at Stony
Brook, was assisted in the study by Beth Firchau of the Virginia Aquarium.
Chapman and Shivji were on the team that made the first discovery of virgin
birth involving the Nebraska shark.
.
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