Retrospectacle: A Neuroscience Blog

i-33f3bb78b33bd15b77ba3733340a0447-hammerhead.jpg In a really astounding discovery, it was confirmed that a 2001 birth by a female Hammerhead shark was achieved in the complete absence of males, in a process called parthenogenesis. While at first it was believed that the female shark mated before being captured, and stored the sperm for three years (ew), testing on the resulting offspring showed that their DNA only matched the mother and showed no evidence of a father. This phenomenon, while seen in some other vertebrates like birds and amphibians, has never been demonstrated in such a major vertebrate line as sharks. Mammals are now the only major vertebrate group that has yet to show evidence of parthenogenesis.

Co-author Dr Mahmood Shivji, who led the Guy Harvey Research Institute team, said: “We may have solved a general mystery about shark reproduction – our findings suggest that parthenogenesis is the likely explanation behind the anecdotal but increasing observations of other species of female sharks reproducing successfully in captivity despite not having contact with males.

“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.”

During parthenogenesis, a female organism’s eggs develop without fertilization. This likely evolved as a mechanism to ensure population persistence in the absence of a fertile male (sharks are often solitary for long stretches, and the sea is a big place.) However, the process does have drawbacks, ie the reduction of genetic diversity in populations.

The study is published in Biology Letters. (Chapman et al. 2007. Virgin birth of a hammerhead shark. Biology Letters. doi:10.1098/rsbl.2007.0189)

Comments

  1. #1 Linzel
    May 23, 2007

    All I can say is COOL!
    Maybe baby Jesus was female?! That would explain the virgin birth hypothesis. :)

  2. #2 Science Avenger
    May 23, 2007

    Mammals are now the only major vertebrate group that has yet to show evidence of parthenogenesis.

    Oh Shelley, you had to say it. Ever been quotemined? The creationists are coming…

    However, the process do have drawbacks, ie the reduction of genetic diversity in populations.

    Love the ebonic typo, but I digress…

    More specifically, it has the drawback of potentially eliminating males entirely. I’m no biologist, but I presume parthenogenesis does not come with the ability to produce a “Y” chromosome.

    I’ll do my tongue in cheek impersonation of a creationist here and say this science issue has horrible philosophical implications that must be considered! The day a human female manages this feat is the day the gals finally prove they don’t need us.

    Hmmm, there’s fertile ground for a good political mind experiment there. If the world is populated with nothing but women, would gay marriage still be immoral to those that fight against it now? It certainly blows away all their family values arguments about stable home environments.

  3. #3 nancy
    May 24, 2007

    actually there’s a few species whose members are all females.

  4. #4 tb
    May 24, 2007

    I think there’s really only one important question here:

    Did they rename the baby shark Jesus?

  5. #5 Charlie (Colorado)
    May 24, 2007

    No wonder they look cranky.

  6. #6 AgnosticOracle
    May 24, 2007

    The Evangelical Church of the Selachimorpha may have been right all along. =)

  7. #7 Science Avenger
    May 24, 2007

    Really Nancy? Someone please direct me to a few links. I knew the vast majority of some species were female (eg ants), but ALL female?

    There’s a sci-fi theme with a lot of appeal to teenaged boys in there somewhere.

  8. #8 Cameron
    May 25, 2007

    Virgin turkeys (the bird parthenogensis example I’m aware of) give birth to only males. Females have an extra chromosome which I assume they drop in parthenogenesis. Obviouslly wouldn’t work in humans. It’s interesting that rates increase upon exposure to sperm that’s been irradiated.

  9. #9 CCP
    May 25, 2007

    Parthenogenetic birds are male because birds have a ZW-type sex determination system–in contrast to mammals, two identical sex chromosomes make a male and two different ones make a female.
    There are all-female species of whiptail lizards (Cnemidophorus uniparens for example, though it might not be Cnemidophorus any more), worm snakes, and even an all-female class of rotifers, the bdelloids.

  10. #10 drcharles
    May 28, 2007

    very interesting stuff. I wonder if there’s ever been a case of this outside the bible in humans. the virgin birth 2007 years ago was hardly a controlled, male-less situation. this post ties into an article in newsweek last week about gender:
    http://www.msnbc.msn.com/id/18618970/site/newsweek/