Sharks continue to fascinate experts

It was recently confirmed that a female blacktip shark from the Virginia Aquarium & Marine Science Center in Virginia Beach carried a shark pup with no genetic material from a male shark. This is the second case in which scientists have used DNA testing to verify a “virgin birth” of a shark,  the first was reported from a bonnethead shark in Omaha, Nebraska. Shark experts at the National Aquarium are familiar with the studies, but are still very intrigued with the findings.

Fishes Research Specialist at the National Aquarium, Alan Henningsen, believes that this type of birth could be more common in the wild then once thought, and could be in response to declining populations and the reduced encounters with mates. However, these theories are not testable in the wild.

Another of our shark experts, Andy Dehart, agrees with others in saying that this finding will not be a fix for the falling shark population. In both cases of parthenogenesis in aquariums there was only one pup. Bonnethead liters are usually 6-8 pups and blacktips generally have 2-4 pups. It is likely these events happened as a survival instinct due to the lack of a male, but even in extreme cases if this were happening in the wild it would not be a successful way for shark populations to reestablish themselves. 

So how can this be true? Scientists confirmed shark parthenogenesis, the process that allows females of some species to produce offspring without sperm, last week from DNA test results. The mother blacktip shark, Tidbit, died last year during a routine yearly checkup. During her necropsy (a shark autopsy), a 10-inch, almost full term shark pup was found.

Tidbit arrived to the Aquarium before reaching sexual maturity, and in her eight years there she had never been in a tank with a male shark. Scientists tested DNA of the mother and baby to verify that the shark was in fact able to produce her own pup without a fertilizer present. In their studies, scientists discovered that Tidbit’s DNA was almost exactly the same as the pup’s, it was just set up in a different order. It was decided that not only did the pup have Tidbit’s DNA, but it had a second set of the same copied DNA.

There have been no confirmed asexual births from any sharks at the National Aquarium, but that there have been successful births of sandbar sharks from females that arrived when pregnant, as well as bonnethead sharks that mated while at the Aquarium.

What’s truly fascinating is that until the case in Omaha, no one thought this was possible in a higher vertebrate like a shark. Nature certaintly is amazing, and there is still much we need to learn about the species that seem so common to us.

For more information about our sharks and how to visit them, click here.


2 Responses to “Sharks continue to fascinate experts”

  1. 1 Sarah October 21, 2008 at 4:40 pm

    Wouldn’t it be interesting to see what cues parthenogenesis in these animals? Is it a lack of exposure to males (and maybe any pheromones they release)? How does this secondary system get put into drive?? Its just such a cool alternative to actually switching sexes (like clownfish say) or carrying around both sets of reproductive tissue as hermaphrodites.


  2. 2 New Aquarium Blog November 2, 2008 at 10:39 pm

    Sharks, one of the best ones in a aquarium !

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