The method of foraging for food was a key factor influencing fish vision. Fish whose diets consist primarily of zooplankton were more likely to have UV sensitivity, which enables them to detect the presence of these small transparent aquatic organisms that absorb ultraviolet light. In contrast, cichlids in the murky waters of Lake Victoria expressed longer wavelength combination of opsin genes, regardless of what they ate.
This long wavelength combination matches the light that is best transmitted through the murky water. A few Lake Victoria fish at clearer sites turned on shorter wavelength genes, suggesting that opsin expression matches the light environment. Therefore opsin gene expression in both lakes is adaptively determined based on important ecological variables.
The authors also examined changes in the genetic sequence of these opsins that fine-tuned visual pigment sensitivity at the short and long-wavelength ends of the spectral range.
"When you get to the extremes of the light spectrum, there is no other gene that can be turned on or off, so the only way to extend the sensitivity is to change the gene structure itself," says O'Quin. Therefore, this study presents a model of sensory evolution in which both molecular genetic mechanisms work in concert.
For a copy of the paper go to: http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1000266
Previous work by Ole Seehausen, Karen Carleton, Nori Okada and colleagues (Nature, 455, 620-626, 2 Octobe
|Contact: Kelly Blake|
University of Maryland