Scientists: Hammerhead has 'Virgin Birth' in Zoo's Shark Tank

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 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.

It was only said half in jest so I thought the ‘Costanza’ part was a necessary adjunct for those who might not catch the reference.

That was a very funny show and for not having watched it that much I seem to always run across things that remind me of the episodes I have seen.

Anyway virgin birth is no big deal in the animal kingdom, it is however a very interesting finding that some sharks are apparently capable of Parthenogenesis.

Quoting from one of the other articles; [I want to find out what the DNA results were, but haven’t come up w/ that yet and hope to visit vmsm.com when time permits.]

When George performed the necropsy on the shark, he realized that the surprise pregnancy could have been a factor in the shark’s reaction to sedation. The shark also was under stress from being handled and from having been bitten recently by another shark, he said.

If Tidbit had not died, he said, the pup might never have been discovered.

Tidbit did not appear pregnant, and since employees had no reason to believe she could be pregnant, they would not have been watching for a pup. So another shark could have eaten the pup without employees ever noticing.

George is not sure which scenario, crossbreeding or asexual reproduction, is more important scientifically.

The joint Northern Ireland-U.S. research that analyzed the DNA of a hammerhead shark born in 2001 in Nebraska was published in the Royal Society journal Biology Letters on the day before Firchau was bitten.

Asexual reproduction is common in some insect species, rarer in reptiles and fish, and has never been documented in mammals. Until now, sharks were not considered a likely candidate.

And if the pup turns out to be the result of crossbreeding, that will be interesting because sharks are not known to do that, said Heather Thomas, aquarist at the John G. Shedd Aquarium in Chicago.

“Either way, it’s going to be very interesting,” George said.

http://www.iht.com/articles/ap/2007/06/24/america/NA-GEN-Shark-Mystery.php

What I found, inconclusive as it is:

[snip] ... the first-ever shark bite at the facility.

Tidbit apparently had reacted badly to the sedatives used by the vets, and she died several hours after the attack.

When they did a necropsy after Tidbit died, they discovered she was with pup.

Curators were baffled, Candler said.

The aquarium put out a news release, raising the possibility that it was a rare instance of asexual reproduction.

Just a month earlier, scientists in a Nebraska zoo had confirmed that a female hammerhead shark had given birth without mating with a male.

A Florida-based researcher offered to take on the mystery, Candler said. The aquarium sent samples of the DNA from Tidbit and the 1-pound fetus found in her uterus.

The researcher will run multiple DNA tests on both, and if they all come up confirming only one source of genetic materials, it will prove Mom pulled the pregnancy off alone, Candler said.

If not, there’s the possibility Tidbit crossed the genetic line and mated with another species. The world is full of mules and wolf/dog hybrids, after all.

The researcher, however, had to leave the country before finishing the testing, Candler said.

“Unfortunately, it’s not like on ‘CSI,’ where you have DNA results back in 10 seconds,” she added. [end snip]

http://hamptonroads.com/node/450019

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