Electric fish are one of those marvels of nature that seem almost like a contrivance of science fiction, but which in fact are very real, capable of using muscles to produce electric fields that help them communicate, navigate, hunt, and ward off predators.
A research team led by Dr. Harold H. Zakon of the University of Texas at Austin, Dr. Michael R. Sussman of the University of Wisconsin-Madison, and Manoj Samanta of the Systemix Institute in Redmond, Washington have analyzed the electric eel genome and the genes of two other distantly related electric fish species. The same genes were recruited within the different species to make evolutionarily new structures that function similarly. identified the regulatory molecules involved in genetic and developmental pathways that have resulted in electric fish convert a simple muscle into an organ capable of generating a potent electrical field.
Their findings are published in a paper in the journal Science’s June 27, 2014 edition, entitled “Genomic basis for the convergent evolution of electric organs” (Science 27 June 2014: Vol. 344 no. 6191 pp. 1522-1525 DOI: 10.1126/science.1254432), coauthored by Drs. Zakon, Sussman, and Samanta, with Jason R. Gallant of Michigan State University, Lindsay L. Traeger and Jeremy D. Volkening, of the University of Wisconsin, Madison, Howell Moffett, Po-Hao Chen, and Carl D. Novina of the Dana-Farber Cancer Institute and Harvard Medical School, Boston, George N. Phillips Jr. of Rice University, Houston, TX, Rene Anandof The Ohio State University Wexner Medical Center, Columbus, Gregg B. Wells of Texas A&M University, College Station, TX, Matthew Pinch, Robert Gth, and Graciela A. Unguez of New Mexico State University, Las Cruces, and James S. Albert of University of Louisiana, Lafayette
The researchers note that little is known about the genetic basis of convergent traits that originate repeatedly over broad taxonomic scales, onserving that the myogenic electric organ has evolved six times in fishes to produce electric fields used in communication, navigation, predation, or defense.
The team has examined the genomic basis of the convergent anatomical and physiological origins of these organs by assembling the genome of the electric eel (Electrophorus electricus) and sequencing electric organ and skeletal muscle transcriptomes from three lineages that have independently evolved these muscular electric organs. Strictly speaking, these fish are not actually eels, but more closely related to catfish. They can reportedly produce electric fields of up to 600 volts, or about 100 volts per foot of fish length.
They report their results indicating 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.
Dr. Zakon says his lab at UT Austin studies a number of questions using weakly electric fish as their model organism. These fish live in murky waters, are nocturnally active, and generate weak electric fields around themselves from a specialized electric organ that is derived from muscle cells, sensing these electric fields, with specialized sensory receptors that can detect distortions caused in their own electric fields to locate nearby objects, and use their electric fields to broadcast electric signals other fish.
He observes that the electric organ discharge varies across species, is different in the two sexes, varies in each individual, is influenced by social factors and hormones, and may also show circadian variations. The discharges can be easily recorded in freely behaving animals. The circuitry for generating them is simple and many of the cells are accessible for electrophysiological analysis. Thus, the researchers can study dynamic biophysical events in excitable membranes from the level of freely behaving animals to the level of the ion channels themselves.
Dr. Zakon notes that his lab’s main research focus has been regulation of sodium and potassium currents in the electric organ by sex steroid hormones (which accounts for sex differences in the discharge) and phosphorylation (which accounts for circadian variations). A major new emphasis of the laboratory has been the molecular cloning of these ion channels to understand their regulation on the molecular level, and their evolution. Other projects include studies of the modulation of the electric discharge pattern by NMDA receptors in the brain, with behavioral studies of communication and social interaction in electric fish; understanding the molecular and developmental mechanisms whereby a differentiated muscle cell has evolved into a novel type of cell–an electric organ cell, a question Dr. Zakon says was first posed by Charles Darwin in the “Origin of Species.”
Dr. Michael Sussman initiated research on the origins of the electric organs in fish about a decade ago, and is cited observing recently that the fish are capable of making an electric organ using muscle only. Research in the Sussman lab at the University of Wisconsin-Madison Biotechnology Center focuses on two main goals: (1) Development of novel technologies for global characterization of biological systems, and (2) Application of traditional genetics and biochemistry as well as novel technology to better understand the role of plasma membrane proteins in eukaryotic cell differentiation, with emphasis on the two model eukaryotes, Arabidopsis and yeast.
Interviewed by NPR’s KTEP El Paso, Dr. Sussman characterizes a 6-foot-long electric eel as “basically a 6-inch fish attached to a 5-½-foot cattle prod… All of the intestines and the stomach and all that stuff is right close to the head, and the rest of the electric eel is an electric organ. It’s just a beautiful tissue,” also noting that output is about 100 volts per foot of eel.
Systemix Institute was founded by Dr. Manoj Pratim Samanta, who received his Ph.D. in Electrical engineering and conducted some of the pioneering research on nano-conductors. Dr. Samanta became interested in biological systems after noticing their similarities with digital computers in design and control. The Systemix Institute, under his guidance, is interested in understanding this similarity at the system level and in utilizing this knowledge to find cures of diseases.
Systemix Institute conducts state-of-the-art research in advanced genomics, took part in decoding the transcriptomes of many organisms in collaboration with leading groups from around the world, and their work has been covered by BBC news and published in several scientific journals.
University of Texas at Austin
University of Wisconsin-Madison
University of Texas at Austin
University of Wisconsin-Madison
For more on this topic see:
The shocking truth about electric fish: Sequencing electric eel genome