Introduction
Hammerhead Sharks are such fascinating creatures although they can become monsterous in size and if you encounter them in the deep blue sea you can be assured that they will make you tremble. They are not the best looking creatures but they have very special characteristics that will blow your mind. They are easy to spot if looking for them. With their wide flat heads and eyes that sit on the ends of each side, these "odd balls" are good hunters and can pick up movement and vibrations with all the nerves that are in the hammered shaped head.
What makes these mammals a subject of interest is that they are the first recorded to ever give birth without having an encounter with another male shark present. Although they are known for storing sperm for several months, scientific evidence has proven that was not the case. Can you imagine reproducing without having sexual intercourse? Mammals have never been recorded to reproduce without sexual encounters from male and female. How is it possible? What had to have taken place for this mammal to reproduce without male sperm? Even more important what will happen to genetic diversity if this continues?
What makes these mammals a subject of interest is that they are the first recorded to ever give birth without having an encounter with another male shark present. Although they are known for storing sperm for several months, scientific evidence has proven that was not the case. Can you imagine reproducing without having sexual intercourse? Mammals have never been recorded to reproduce without sexual encounters from male and female. How is it possible? What had to have taken place for this mammal to reproduce without male sperm? Even more important what will happen to genetic diversity if this continues?
Asexual Reproduction
"Hammerheads normally have sexual encounters with male sharks and give birth to active pups and can have up to forty pups per litter states Prager(Prager, H. p.103). In 2007 the first documented asexual reproduction in sharks occured in a zoo in Nebraska. A female hammerhead shark gave birth without having any encounters with a male shark. Many scientist thought that because hammerheads are known to store sperm than it must have been a legitimate birth but debated whether the shark had stored the sperm for three years, which was the length of time in captivity when the birth took place. Investigating further it was discovered that this was indeed a case of asexual reproduction.
Asexual reproduction is not uncommon in other vertebrates such as reptiles and insects but this was the known case of a shark. Pogatchnik stated, "Shark experts said this was the first confirmed case in shark of parthenogensis, which is derived from Greek and means "virgin birth". He also claims that "asexual reproduction is common in some insect species, rarer in reptiles and fish and has never been documented in mammals. "Sharks where not considered a likely candidate" (Pogatchnik).
Researchers took DNA samaples from both the pup and mother to come to terms with this rare and peculiar occurence. The results showed that this was indeed a parthenogensis birth. Fountain said, "No male DNA was found in the female baby shark". "The female shark's own genetic material combined during the process of cell division that produces the egg. A cell called the secondary oocyte, which contains half the female chromosomes and normally becomes the egg, fused with another cell called the secondary polar body, which contains the identical genetic material", explains Fountain.
This is where the complication comes. In order for diversity to continue genes must be passed on to each generation of offspring. I marvelled at the thought of a mammal being able to reproduce without a male present but how does it affect the newborn. Fountain states, that "Through parthenogensis, the offspring will be less genetically diverse, making the species more susceptible to disease and other problems". Maybe this has been happening in other species over the years but now that scientists are aware and know what to look for this can be the solution to unanswered questions.
Asexual reproduction is not uncommon in other vertebrates such as reptiles and insects but this was the known case of a shark. Pogatchnik stated, "Shark experts said this was the first confirmed case in shark of parthenogensis, which is derived from Greek and means "virgin birth". He also claims that "asexual reproduction is common in some insect species, rarer in reptiles and fish and has never been documented in mammals. "Sharks where not considered a likely candidate" (Pogatchnik).
Researchers took DNA samaples from both the pup and mother to come to terms with this rare and peculiar occurence. The results showed that this was indeed a parthenogensis birth. Fountain said, "No male DNA was found in the female baby shark". "The female shark's own genetic material combined during the process of cell division that produces the egg. A cell called the secondary oocyte, which contains half the female chromosomes and normally becomes the egg, fused with another cell called the secondary polar body, which contains the identical genetic material", explains Fountain.
This is where the complication comes. In order for diversity to continue genes must be passed on to each generation of offspring. I marvelled at the thought of a mammal being able to reproduce without a male present but how does it affect the newborn. Fountain states, that "Through parthenogensis, the offspring will be less genetically diverse, making the species more susceptible to disease and other problems". Maybe this has been happening in other species over the years but now that scientists are aware and know what to look for this can be the solution to unanswered questions.
Why They Matter
Sharks have been around for millions of years and are known to be one of the longest surviving creatures from pre-historic times. There are movies created and documentaries that enlighten humans on their magical underwater life. Here in Bermuda shark oil is collected from the shark and stored in a glass bottle which is hung outside of peoples homes. Many of our elders say that the sharks oil is like a weather forcaster for the island's fisherman. They say that if the oil was cloudy bad weather is coming and if it was clear it was going to be a good day. I made observations for myself and most times the sharks's oil was right; whether or not this is a known fact about the oil I certainly head down to my Nana's house to find out if it will be a nice day to have picnic or go beaching especially during hurricane season. Sharks have also proven themselves to be useful in the medicine world also. Prager states, that sharks are being used as biomedical models to better understand how kidneys function and respond to diuretics, and to learn more, about the rejection of organ transplants". Some may also eat the hammerhead shark in chowders, soups, but here in Bermuda one of the traditional dishes is "Hash Shark". If they are not being eaten by other sharks or humans they are being killed for bragging rights and hung on walls as a display. There are some countries that have put protection plans in place which is needed because the hammerhead species is already an endanger species and although the asexual reproduction will "ensure that the species will survive it will also come with a cost: a loss of genetic diversity" (Fountain).
References
Fountain, Henry. The New York Times. Published May 23, 2007. Female Shark Reproduced Without Male DNA, Scientist Say. http://www.nytimes.com/2007/05/23/science/23shark.html?_r=1&
Hammerhead Shark, Cocos Island, Costa Rica. Retrieved from: http://ocean.si.edu/ocean-photos/hammerhead-shark-cocos-island-costa-rica-0
Monster hammerhead shark heads to Queensland. Photos retrieved from: http://www.couriermail.com.au/news/queensland/monster-hammerhead-shark-heads-to-queensland/story-e6freoof-1225853776227
Pogatchnik, Shawn. Ap Associated Press. Updated 5/22/2007 7:27:49 PM ET. http://www.nbcnews.com/.../t/female-shark-capable-virgin-birth
Prager, Ellen. Sex, Drugs, and Sea Slime. Chicago and London 2011
Sharks in hot Water. Photos retrieved from: http://www.abc.net.au/science/features/sharksoup/
http://mp3skull.com/mp3/jaws_theme_song.html
Hammerhead Shark, Cocos Island, Costa Rica. Retrieved from: http://ocean.si.edu/ocean-photos/hammerhead-shark-cocos-island-costa-rica-0
Monster hammerhead shark heads to Queensland. Photos retrieved from: http://www.couriermail.com.au/news/queensland/monster-hammerhead-shark-heads-to-queensland/story-e6freoof-1225853776227
Pogatchnik, Shawn. Ap Associated Press. Updated 5/22/2007 7:27:49 PM ET. http://www.nbcnews.com/.../t/female-shark-capable-virgin-birth
Prager, Ellen. Sex, Drugs, and Sea Slime. Chicago and London 2011
Sharks in hot Water. Photos retrieved from: http://www.abc.net.au/science/features/sharksoup/
http://mp3skull.com/mp3/jaws_theme_song.html