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Female hammerhead sharks fertilize own eggs


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#1    Owlscrying

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Posted 23 May 2007 - 03:21 AM

May 22

DUBLIN, Ireland —  Female sharks can fertilize their own eggs and give birth without sperm from males, according to a new study of the asexual reproduction of a hammerhead in a U.S. zoo.

The joint Northern Ireland-U.S. research, analyzed the DNA of a shark born in 2001 in the Henry Doorly Zoo in Omaha, Neb. The shark was born in a tank with three potential mothers, none of whom had contact with a male hammerhead for at least three years.

The baby was killed within hours of its birth by a stingray in the same tank. Analysis of its DNA found no trace of any chromosomal contribution from a male partner.

Shark experts said this was the first confirmed case in a shark of parthenogenesis, which is derived from Greek and means "virgin birth."

Asexual reproduction is common in some insect species, rarer in reptiles and fish, and has never been documented in mammals. The list of animals documented as capable of the feat has grown along with the numbers being raised in captivity _ but until now, sharks were not considered a likely candidate.

The findings were really surprising because as far as anyone knew, all sharks reproduced only sexually by a male and female mating, requiring the embryo to get DNA from both parents for full development, just like in mammals.

The lack of any paternal DNA in the baby shark ruled out this possibility.

This phenomenon has now been demonstrated in all major vertebrate groups except for mammals. Birds do it, reptiles do it, amphibians do it, fishes do it, and now sharks are known to do it.

The power to self-impregnate represents an evolutionary strategy to keep the population and species going when all else fails. Genetically, it's a last resort tactic because it leads to genetic uniformity, and eventually that will catch up with the population and make it less fit.

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#2    glorybebe

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Posted 23 May 2007 - 03:26 AM

Quote

May 22

DUBLIN, Ireland —  Female sharks can fertilize their own eggs and give birth without sperm from males, according to a new study of the asexual reproduction of a hammerhead in a U.S. zoo.

The joint Northern Ireland-U.S. research, analyzed the DNA of a shark born in 2001 in the Henry Doorly Zoo in Omaha, Neb. The shark was born in a tank with three potential mothers, none of whom had contact with a male hammerhead for at least three years.

The baby was killed within hours of its birth by a stingray in the same tank. Analysis of its DNA found no trace of any chromosomal contribution from a male partner.

Shark experts said this was the first confirmed case in a shark of parthenogenesis, which is derived from Greek and means "virgin birth."

Asexual reproduction is common in some insect species, rarer in reptiles and fish, and has never been documented in mammals. The list of animals documented as capable of the feat has grown along with the numbers being raised in captivity _ but until now, sharks were not considered a likely candidate.

The findings were really surprising because as far as anyone knew, all sharks reproduced only sexually by a male and female mating, requiring the embryo to get DNA from both parents for full development, just like in mammals.

The lack of any paternal DNA in the baby shark ruled out this possibility.

This phenomenon has now been demonstrated in all major vertebrate groups except for mammals. Birds do it, reptiles do it, amphibians do it, fishes do it, and now sharks are known to do it.

The power to self-impregnate represents an evolutionary strategy to keep the population and species going when all else fails. Genetically, it's a last resort tactic because it leads to genetic uniformity, and eventually that will catch up with the population and make it less fit.

go


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#3    War-Junkie

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Posted 24 May 2007 - 12:12 AM

so marry was a shark

Edited by War-Junkie, 24 May 2007 - 12:13 AM.





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