Convergent evolution of molecules in electric fish
Weakly electric fish from South America (top) and Africa.
Images courtesy of Carl D. Hopkins and John Sullivan.
Having a set of extra genes gave fish on separate continents the ability to evolve electric organs.
South American and African groups of fish independently evolved the ability to generate and sense electric fields by modifying sodium channel proteins typically used in muscle contraction.
In humans and other vertebrates, serious muscular disorders, epilepsy and heart problems can be caused by mutations in sodium channel proteins. However, fish have two copies of many of their genes — and the duplicate sodium channel gene can mutate and evolve without harming the fish. Most fish have both genes in the muscle, but as the new electric organ was evolving, the sodium channel — by being lost from the muscle — became devoted to the electric organ, so twice, independently, the gene has been ‘lost’ from the muscle.
- “Functionally important parts of this molecule are changing in order to change the electrical discharge in the fish–changes that would be detrimental in a human muscle… When natural selection is acting to cause changes in a part of a molecule, you know it’s functionally important. Natural selection can start showing you the important parts of molecules.” – Dr. Harold Zakon
NB. The two species illustrated here also independently evolved curved jaws for bottom feeding.