Monday, June 17, 2013

Shark Clones : A story of Parthenogenesis ( inspired by presentation by Rob Stewart)

by Valzaby, This post originally appeared at Future Science Leaders.

At my school today, I had the wonderful opportunity of meeting Rob Stewart, a conservationist, filmmaker, writer and biologist. He is the creator of the documentary “Sharkwater” that came out in 2007 and his new movie “Revolution” is coming out in theaters soon. Rob’s passion is saving sharks and raising awareness to the world about other environmental issues and during his presentation he stated a great deal of surprising and terrifying facts. He spoke to our school about issues such as ocean acidification, marine species extinctions, tar sands and many other environmental problems that we are facing today. But one particular quote stuck to me the most and went something along these lines: “We have all the tools and the power to make our Earth sustainable and to save our life diversity from extinctions; some people simply choose to not use those tools in order to make a profit”.
Overall it was a very inspiring and motivational talk, and it made me realize that there are so many people out there that share the same passion for conservatism and sustainability as me, and that together, change is more possible than some may think. Here are the trailers for his two documentaries (the first one being critically acclaimed and winning many awards):
During his speech one particular fact about sharks sparked my curiosity. He mentioned that the reason sharks are not completely extinct as compared to other marine species, is because they have an adaptations that allows them to clone themselves in the event that their populations decline and there are not enough mates to be fertilized. Hearing this I decided to do some of my own research to further understand this intriguing ability.
This ability is called Parthenogenesis. This is a form of asexual reproduction, meaning that embryos grow and develop without fertilization of the first egg cell. The word itself originated from the Greek word “parthenos” which meant virgin and “genesis” meaning birth. In normal fertilization processes egg cells form after meiosis and are haploid (having ½ the chromosomes of the mother), but parthenogenesis offspring on the other hand are created diploid, meaning they have all the chromosomes necessary for normal development. Depending on the species the offspring can have anywhere from half to all of the mother alleles (meaning it could potentially be a clone). If they are full clones, the eggs cells are formed without meiosis.
The parthenogenic reproduction of sharks was first discovered in a zoo in Nebraska in 2001, when a small hammerhead shark gave birth to a baby shark, while living in a tank containing only females. Queen’s University Belfast, the zoo itself and the Southeastern University of Florida, tested the shark and found through its DNA that the reproduction was parthenogenic, because it matched the DNA of only one of the females in the tank. The pup also had no male DNA present, and only half of its mother’s DNA.
Later in 2002, in Belle Isle Aquarium in Detroit, two white-spotted bamboo sharks were born to a female shark that lived with another female. They hatched from eggs which are often laid by females but usually do not hatch without fertilization. This shocked the curator of the aquarium, as the eggs still hatched without a male present.
In 2008 parthenogenesis occurred once more, when lonely sharks gave birth to a pup without any contact whatsoever with a male shark. Also that year an Atlantic blacktip shark in Virginia gave birth to a pup without a mate.  A study then proved that this pup had no male genetic material.
Though it is a great way to reproduce if no mate is present, parthenogenesis in sharks does have its negative effects. First of all, it fails to increase genetic diversity amongst sharks, and creates offspring that may not be able to survive if the environment and their ecosystem were to change. So although it does aid the conservation effort of sharks, it decreases diversity which could be an issue for the future. Instead of relying on this adaptation they have, we as a species should be working on strategies to reduce our exploitation of this magnificent animal.
Because sharks have an XY sex-determination system, parthenogenesis only produces XX females, thus reducing the male population. So in order to create a male shark, the female sharks must physically come in contact with them. However if females continue to reproduce more and more and develop certain adaptations, who’s to say that they will even want to mate with a male shark in the future
It is dangerous to continue our actions (such as over-fishing and eating shark fin soup), because by doing so in one way or another, we are destroying a species that has been around millions of years.
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About this author: Currently a grade 12 high school student who is both ambitious and motivated, but loves to have fun. Interested in human biology, psychology, dramatic soap opera TV shows and fitness through dance, she is in general a very social and open person.

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