Thursday, November 10, 2005

Evo-Devo and Cichlids

Added Later: Pharyngula has a fascinating post on the same subject. A must read!

The above is a picture of a cichlid. I have blogged about them before. A new studies illustrates the link between evolutionary development and embryonic development in the jaws of cichlid fishes. From Science Daily:

In a study illustrating the apparent linkages between the evolutionary development and embryonic development of species, researchers have uncovered the genetic elements that determine the structure and function of a simple biomechanical system, the lower jaw of the cichlid fish. In addition, they've shown that increasing expression of a particular gene in an embryo can lead to physical changes in the adult fish. The results appear in the November 11, 2005 issue of the Proceedings of the National Academy of Sciences.

Researchers predicted that functionally or developmentally related componets of the cichlid jaw would be controlled by the same set of genes. The researchers compared two species of cichlid from Lake Malawi:

One species had force modified jaws that are more adept at biting prey; the other had speed modified jaws, which are more accomplished at using suction to feed on plankton. Each jaw system is essentially a lever system made up of one out-lever and two in-levers.

The predator cichlid is the first picture above. Below is a picture of the plankton eating cichlid.

But when the researchers mapped the part of the genome that controlled the system they found that the levers were controlled by genes on different chromosomes (i.e. the short lever genes are on a different chromosome than the long gene). Or to phrase it another way:

“We were surprised to see that the genetic basis of components involved in opening the jaw is independent of the jaw-closing system,” said Streelman. (one of the researchers involved - afarensis)

Taking it a step further:

In another part of the study, researchers showed that the gene bmp4 is a major factor in controlling the jaw-closing system. When the team injected bmp4 protein into the developing embryos of another fish species, the zebrafish, they saw that the mechanical advantage (and thus the biting power) of the jaw increased.

The researchers sum up their work thusly:

"We've demonstrated that important functional differences operating in adult organisms are elicited by changes in early development. Our next goal is to understand the genetic bases underlying the differences between the simple biomechanical system of the lower jaw and complex systems of the anterior jaw in these fish."