Fish eyes...

It's been an unusually busy few days. Finally taking a few minutes to call attention to a few interesting things that have appeared recently. A paper that appeared in the December 21 edition of the Public Library of Science's open access biology journal, PLoS Biology, examines the manner in which gene coding sequence and gene expression interact to help produce the tremendous diversity seen in the rapidly evolving cichlids in the East African lakes. The work of Karen Carleton and her colleagues compares cichlids found in the clear waters of Lake Malawi to those found in more turbid Lake Victoria.

Cichlids have several genes that code for different opsins (light-sensitive protein receptors found in cone cells of eye) that can give them sensitivity to light ranging from ultraviolet to the red end of the spectrum. The genes are expressed to differing degrees in different species, resulting in an array of different visual systems. In the relatively clear waters of Lake Malawi, a wide range of opsins were expressed. This may result in closely related species using a dramatically different range of wavelengths. The difference is related to feeding behavior, with cichlids feeding largely on zooplankton relying more heavily on ultraviolet wavelengths. This apparently enables them to more easily detect their small, transparent prey. Those fish feeding on larger prey were more likely to use light of longer wavelengths. In the murkier waters of Lake Victoria, on the other hand, cichlids are more likely to use longer wavelengths of light, independent of feeding habits. This is likely due to the fact that the longer wavelengths is transmitted more readily through the turbid waters.

Another of those amazing "just-so stories" reminding us that the ways in which biodiversity can evolve is as diverse as the organisms themselves. Another interesting paper, by the way, in the same issue of PLoS Biology, which we'll look at it more detail later. Tristan Long and colleagues at UC-Santa Barbara have looked at a potential cost of male mate choice to highly fecund females. Since we'll be talking about mate selection later, we'll probably revisit this one.