Scientists reported on Friday that a female blacktip shark, dubbed “Tidbit”, who resided in a Virginia Beach aquarium without any male companion, gave birth to a pup through Parthenogenesis. Unfortunately both she and her pup died in the process due to complications in May 2007.

To check if there was indeed no father, scientists performed genetic testing on the remains of both Tidbit and her pup, which are identical to human paternity tests. The result shocked them: there was no trace of a father’s DNA in the pup; the only one present was its mother’s.

Parthenogenesis, which is often encountered in the wild among vertebrates but (almost) never in humans or other mammals, and up to this point it hadn’t been encountered in sharks either.

The process, a sort of asexual reproduction happens when the egg cell of the female is fertilized by one of the three “polar bodies” generated along with the egg, who although identical with the egg itself sometimes act like sperm, fertilizing it. The result, although having a single source of DNA, is not a clone of its mother due to genetic material combining differently. However unless a species is designed to reproduce that way – most lower plants, certain lizards, aphids and the like – freak occurrences like in the case of Tidbit here are detrimental to a species’ genetic diversity. Much like in the case of incest between first-degree relatives, the offspring who do survive are much more prone to congenital defects and a weakened immune system.

Theories as to why the event happened tend to either imply a freak occurrence/aberrant egg, or a physiological reaction to the absence of a male. Testing done by Demian Chapman, a shark scientist with the Institute for Ocean Conservation Science at Stony Brook University in New York State, who was responsible for establishing Tidbit’s parthenogenesis, also proved that the same happened to a hammerhead shark at a zoo in Omaha in 2002. Unfortunately the pup was lost in this case as well, due to it being eaten shortly after its birth. However the recurrence of the event makes Chapman give credence to the second theory.

"It tells us that the original case we documented last year was not some fluke of nature. This is something that might be more common than we think it is, and widespread among sharks," Chapman said in an interview.
Indeed, the biological mechanism, if it is something more common than previously observed, probably developed as a safety for when shark populations became so low that males weren’t able to find enough females. Not to mention that shark sex can become quite violent.

There’s little hope however to use the “immaculate conception” method to boost shark population in dwindling species; both documented cases only carried one pup while most regular impregnations result in a full litter of 12 pups or more.