Evolution of Electric Organs

treeOf the few traits that have evolved multiple times in vertebrates, one of the most unique is the electric organ, which has evolved to produce electric fields for the purposes of communication, navigation, and in extreme cases, for predation and defense. To contrast with most other vertebrate traits, there have been six independent origins of electrogenesis (Fig. 1) occurring within extant vertebrates. The taxonomic diversity of electrogenic fishes is so profound, that Darwin considered the multiple origins of electric organs a difficulty to reconcile with his theory of natural selection. Though it has been 150 years since the publication of The Origin of Species, we still know remarkably little about the “steps by which these wonderous organs have been produced” despite their clear benefit as a model for understanding general principles of how complex vertebrate tissues may have repeatedly evolved.  Electric organ (EO) evolved independently in six different lineages of fish usually derived from skeletal muscle (SM) during development. Despite their shared developmental origin, electric organs and skeletal muscle are morphologically and physiologically distinct tissues.

Recently, in collaboration with the electric eel genome sequencing consortium, our laboratory has begun to examine the genomic basis of the convergent anatomical and physiological origins of these organs by assembling the genome of the electric eel (Electrophorus electricus) and by sequencing electric organ and skeletal muscle transcriptomes from three lineages that have independently evolved electric organs (including mormyrids, electric catfish, and several species of knife fishes). Our results indicate that, despite millions of years of evolution, and large differences in the morphology of electric organ cells, independent lineages have leveraged similar transcription factors and developmental and cellular pathways in the evolution of electric organs.