Tuesday, July 31, 2007

Fish Populations Controlled by Sex Changes

Florida has been inundated with invasive species. Since the 60's, Florida's rivers have been slowly filling with an Aquatic plants called Hydrilla. To combat the invader, Tilapia fish were brought in, along with two species of snail. Unfortunately, these exotics preferred the native species of vegetation over the Hydrilla, sending the biodiversity of Florida's rivers into further turmoil.
Now Juan Gutierrez, a bio-mathematician at Florida State University, thinks he can solve the problem. Gutierrez has developed a mathematical model of a population in which males carry two different sex chromosomes (XY) and females are XX. Unlike humans, the sex of a fish can be changed by exposure to different sex hormones. According to this week's Nature,
"By exposing genetic males to female hormones, or vice versa, it is therefore possible to create a male that is genetically XX, or a female that is XY or even YY. Such individuals, with the genetics of one sex but the physical characteristics of the other, are referred to as carriers of 'Trojan sex chromosomes'."
After simulated generations with the model, it was shown that when there was an introduction of YY females, the subsequent offspring were predominantly male, and that this male dominance only strenghtened with each new cycle. Eventually there were only males left in the population.
Gutierrez stresses that this only a model, and further study will have to be made to determine if this technique would truly work in a real environment. However, the potential could be the final solution to the problem, as this is not introducing genetically modified organsims or new potentially invasive exotics into the rivers.
I wonder if any thought has been given to whether introducing these altered fish runs the risk of increasing their fertility rates and creating a population explosion.
For the article in its entirety in news@Nature

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