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In shark maternity wards, males optional

Published May 23, 2007


DUBLIN, Ireland - Female sharks can fertilize their own eggs and give birth without sperm from males, according to a study of the asexual reproduction of a hammerhead that was captured in Florida Bay.

The joint Northern Ireland-U.S. research, being published today by the British journal Biology Letters, analyzed the DNA of a shark born in 2001 at a zoo in Omaha, Neb. The shark was born in a tank with three potential mothers, none of which had contact with a male hammerhead for at least three years.

Analysis of the baby shark's DNA found no trace of 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, " said marine biologist Paulo Prodohl of Queen's University of Belfast, Northern Ireland, a co-author of the report.

Before the study, many shark experts had presumed that the Nebraska birth involved a female shark's well-documented ability to store sperm for a lengthy time. But a genetic analysis proved the pup was the offspring of one of the females only and contained no paternal genetic material.

"Yes, indeed this is a virgin birth, " said the report's co-author, Mahmood Shivji of the Guy Harvey Research Institute at Nova Southeastern University in Fort Lauderdale.

Bob Hueter, director of the Center for Shark Research at the Mote Marine Laboratory in Sarasota, who wasn't involved in the project, noted that sharks have been on Earth longer than other species higher up the evolutionary chain that have also demonstrated this ability, such as lizards and birds. "This finding is new and definitely unexpected, " he said.

Information from the Washington Post and South Florida Sun-Sentinel was used in this report.

[Last modified May 23, 2007, 02:15:15]

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