Electric fish

Weakly electric fishes produce continuous wave-type electric organ discharges that are used for electrolocation and communication. Electrocommunication convergently evolved within the distantly related South American and African weakly electric fishes approximately 100 million years ago, enabling them to detect their environment and communicate with each other through the generation and sensation of electric signals. Most species use special muscle-derived electric organs to generate the necessary electric current. Members of the ghost knifefishes (family Apteronotidae)  have an electric organ derived from the axons of specialized spinal neurons (electromotorneurons). These eurons fire spontaneously and are the fastest-firing neurons known. Ghost knife fish discharge their electric organs in excess of 1 kHz. 

Today I came across a publication that looked into the evolution of these highly specialized organs. I must say I find this study very fascinating and very well executed. The colleagues show that a skeletal muscle–specific sodium channel gene duplicated in this lineage and, within approximately 2 million years, began expressing in the spinal cord, a novel site of expression for this isoform. Concurrently, amino acid replacements that cause a persistent sodium current accumulated in the regions of the channel underlying inactivation. Therefore, a novel adaptation allowing extreme neuronal firing arose from the duplication, change in expression, and rapid sequence evolution of a muscle-expressing sodium channel gene.

A must read ;-)