Wednesday, 7 March 2012

Virgin Birth by Shark

Scientist have found a case of a birth by a Shark
without having sex with male. This is the second ever case of Virgin Birth in a Shark. This has proved that female sharks have a capability by which they can reproduced without mating.

Team Of Scientist 

The team of scientist that carried out this research consists of Dr. Demian Chapman , shark scientist with the Institute for Ocean Conservation Science at Stony Brook University, Beth Firchau, Curator of Fishes for the Virginia Aquarium & Marine Science Center, and Dr. Mahmood Shivji, Director of the Guy Harvey Research Institute and Professor at Nova Southeastern University in Florida.

They have proven that offspring of a female blacktip shark named Tidbit contained no genetic material in its DNA from a father. Tidbit is in Virginia Aquarium in Norfolk Canyon Aquarium for eight years since shortly after her birth in the wild.

First Reporting of Virgin Birth

Chapman and Shivji were a part of team that reported a virgin birth in a female shark in May 2007. That shark at Omaha, Nebraska zoo had not been in contact with male shark for atleast 3 years. This news captured global media and scientific attention, when it was published in journal Biology Letters.


Parthenogenesis is the technique used for DNA fingerprinting in human paternity testing. The same technique was used to prove both cases of Virgin Birth in sharks.

Scientific Point of View

According to Chapman, "Sharks' ability to reproduce alone should not be viewed as an adequate replacement for normal sexual reproduction". The Blacktip and Hammerheadsharks that reproduced without mating both only produced one pup, rather than an entire litter. Shark litters normally contains few to more than a hundred shark pups, depending upon the species.
This case can't stop us worrying from decreasing of shark population due to overfishing.

According to Chapman, "It is very unlikely that a small number of female survivors could build their numbers up very quickly by undergoing virgin birth."

Shark Birth

How It Was Discovered?

Tidbit was an Atlantic blacktip shark who had just reached sexual maturity according to the biologists of Virginia Aquarium. Curators and biologists never observed her reproductive behavior or any signs of breeding in her. Unfortunately, Tidbit died due to some reasons and they did Autopsy (a necropsy for animal) on her as a usual procedure. During Autopsy they found that she was pregnant.

According to Firchau, "There were no male blacktips in the tank for the past eight years!"

Virgin Birth: Parthenogenesis

The phenomenon of "virgin birth" occurs when a baby is conceived without male sperm having first fertilized the female's eggs. This phenomenon has been proven in some bony fish, amphibians, reptiles, and birds. The Parthenogenesis seen in these sharks is known as Automictic Parthenogenesis. In this type, the newly forming pup acquires one set of chromosomes when the mother's chromosomes split during egg development. But instead of uniting with similarly split chromosomes from sperm, as occurs in sexual reproduction, the mother's set is paired with a copy of itself. However this may results in offspring of reduced genetic diversity who may be at a disadvantage for surviving in the wild.

A Big Question

This phenomenon of Parthenogenesis in Blacktip sharks give rise to many questions. First of them is, "Is it possible that Parthogenesis would become more common in Sharks as females have trouble in finding mates?" As we all know that population of sharks have decreased in past 20 years due to overexploitation, mainly to supply the shark fin markets.

These two cases were revealed but actually there have been nearly a dozen reports of suspected virgin births in sharks in recent years. Scientists assumed that these cases were the result of long-term sperm storage by females after mating with males.

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