Biologists have genetically mapped the sex chromosomes of several species of cichlid fish from Lake Malawi, East Africa, and identified a mechanism by which new sex chromosomes may evolve.
In research published in this week's issue of the journal Science, biologists Thomas Kocher, Reade Roberts and Jennifer Ser of the University of Maryland describe the genetic basis for two co-existing systems of sexual determination in cichlid fish from Lake Malawi.
"This study marries two evolutionary mysteries: the incredible diversity of fish in the lakes of East Africa and the genetic basis of sex determination," says Sam Scheiner, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research. "Simple genetic changes can lead to enormous biological diversity."
In nearly all mammals, the SRY gene determines the sex of offspring and is located on the Y chromosome, which is much smaller than the X chromosome.
But in many other animal groups, the genetic mechanism of sex determination evolves quite rapidly, and the differences between sex chromosomes are harder to observe.
Even sister species of fish may have entirely different sex determination systems. How and why the genetic mechanisms for such an ancient developmental distinction continue to evolve has remained a mystery.
The thousands of closely related cichlid fishes in the lakes of East Africa turn out to be an excellent model system for understanding how the mechanisms of sex determination evolve.
The East African cichlid fishes that inhabit Lakes Malawi, Tanganyika, and Victoria are known for their sexually distinct appearance--the males are generally conspicuous and brightly colored, making them more attractive to females, while the females are drab and brown, making them inconspicuous to predators.
One exception to the uniformly brown pigmentation among female cichlids is the "or
|Contact: Cheryl Dybas|
National Science Foundation