For many Europeans and North Americans, December brings out the festive traditions of the Christmas tree or tannenbaum, where evergreen trees often get decorated with electric lights, glowing and twinkling away into the night.
And at one researcher’s lab, fish are lending a hand in the tree lighting.
Professor Jason Gallant of Michigan State University studies a strange-looking group of fishes from African rivers called elephantfishes. Gallant keeps a few species of elephantfish at his laboratory, and recently turned over the light controls of his lab’s Christmas tree to these fish—which have the ability to produce electrical signals:
The species controlling these lights is Brienomyrus brachyistius, a species of elephantfish found in West and Central Africa, from the Democratic Republic of Congo north to Gambia.
Elephantfish got their funny name because many species have oddly shaped mouths, either stretched out in a long snout or equipped with a long appendage on their chin—both resembling an elephant’s trunk.
However, some species like Brienomyrus brachyistius have a stubby mouth and a squared-off head, somewhat resembling a sperm whale. So these species have been given a rather ridiculous sounding name—“baby whale”—by the tropical fish pet trade.
Their strange heads aside, elephantfish are also famous for having electric organs—highly specialized muscles which the fish use to discharge electricity in specific frequencies and signal patterns.
Jason Gallant’s research focuses on the genetics and evolution of these electric organs in elephantfish and in other unrelated fish like the electric eel (Electrophorus electricus). I asked Gallant to tell us more about his fish-activated Christmas tree lights, and what researchers are learning about the electric abilities of elephantfish.
Your fish-triggered tree lights are a great way to visualize the unusual way these elephantfish are equipped to sense and communicate with their world. Explain to us what we’re actually seeing when the lights flash on and off.
Weakly electric fish like elephantfish produce electric discharges for communication and navigation in their environments with a specialized organ called an electric organ. The electric organ is composed of many tiny cells called electrocytes. Each electrocyte produces a pulse is very much the same speed and voltage as the action potentials produced in the nerves and muscles of your body.
The electric organ is an organ with incredible precision and synchronization. When the fish’s nervous system instructs the electric organ to discharge, all of the cells do that simultaneously. The combined voltage of all these cells forms a weak electric field, which we can detect as pulses using our instruments.
The Christmas tree device we built monitors the water for each electrical pulse produced by the fish, then turns on an electronic switch hooked up to a normal household outlet where we plugged in the lights. So the fish are actually controlling the lights: each time the fish generates an electric pulse, the lights get switched on!
So do elephantfish send out electric signals to talk to each other? What might they be saying to each other? Or are they also using electricity to feel their way through their habitat, like a sonar scan?
Absolutely—the fish use the electricity in a manner analogous to “Morse code” to communicate with each other. The shape and timing of the waveform conveys information about the species and sex of the individual, whereas the sequence conveys information about social contexts—information like aggression, trying to court a mate, and the like.
- Click to listen to the amplified electric signals of the elephantfish Brienomyrus brachyistius (MP3 recorded by Jason Gallant; file hosted by National Public Radio)
This communication is facilitated by specialized receptor organs, called knollenorgans, which are specially wired to only receive electrical information coming from other fish—these receptors are effectively deaf to the fish’s own discharge, through a common nervous system trick called a corollary discharge.
The fish also use their electric discharges to navigate through their environments—the system works somewhat like sonar, but at the speed of light instead of sound! Electricity, unlike the acoustic information used by sonar is not reflected or refracted by objects, but rather is resisted or conducted by objects. In this sense, objects in the environment act like different types of “lenses”. The fish has a second array of electroreceptor cells, called mormyromasts, that detect distortions of the electric field as “bright and dark” spots over the surface of their body, giving an electrical readout of the environment. Admittedly, it is a strange sense for us very visual primates to imagine, but the fish are enormously acute and can discriminate tiny differences in objects with this sense.
Elephantfish are reported to have a large cerebellum compared to other fish. What’s the implication of these large brains?
Yes, the rumors are true—elephantfish have one of the largest vertebrate brains when scaled to body size because of their enormous cerebellums, which house the neural circuitry necessary to decode the electrical information they constantly send and receive.
Among the questions you are researching is how electric organs evolved in fish, especially since they are known in at least six widely unrelated groups of fish—torpedo rays, skates, elephantfish, catfish, electric eels, stargazers. How are these “muscle batteries” similar or different among these fishes, and why do think natural selection has encouraged these electric organs to evolve time and time again?
Great question! This is something that left Charles Darwin scratching his head.
Some fishes, like the torpedo ray and stargazer are only produce strong discharges, and the function is apparently to defend or kill potential prey. At his time, Darwin knew of these strongly electric fish, as well as the electric eel. But he was very bright and realized that there were all sorts of fishes that also had organs that resembled the organs of the strongly electric fish, but did not apparently produce electricity.
Nearly 100 years later, at the beginnings of modern neurophysiology, amplifier technology were common in the laboratory, and a bright fellow by the name of Hans Lissmann provided the first recording of Gymnarchus niloticus, a weakly electric fish. He provided the first clues into the solutions for this problem—fishes likely evolved (in the majority of cases) weakly electric discharges first.
- Click to listen to the amplified electric signals of the aba fish Gymnarchus niloticus (MP3 recorded by Jason Gallant; file hosted by National Public Radio)
Lissmann and others went on to demonstrate with clever experiments that the fishes used this ability for communication and navigation in their environments. Scientists now think (though there is little evidence to suggest it) that electric discharging abilities probably evolved from sound producing organs, and electroreception may have evolved second. In the electric eel, the 600 Volt killer pulse probably evolved following this.
Our lab’s research has been asking the question of “how” these fishes build their electric organs. In all cases, electric organs start out as humble skeletal muscle precursors, and then through additional (and unknown) developmental steps, become electric organs. So, we asked the question, “are all types of electric organs different from muscle in the same ways?”
As it turns out, there seems to be a set of 30 or so normally muscle related genes that are always expressed in the same fashion in every electric organ we’ve looked at to date. This suggests that there may be only one way to build a functioning electric organ from muscle, and that six groups have come up with this solution by natural selection independently. This may seem difficult to believe, but many researches have shown that convergent molecular evolution occurs readily in nature, though we are among the first groups to provide this evidence for such a complex organ.
You are also studying how electric signals in elephantfish can change as they evolve into different species. How do these species come to “speak” different signals?
This is also a great question—the short answer is we don’t know, but we’re working on it. Many groups of species, like the Paramormryops electric fish from Africa, the birds of paradise, Hawaiian crickets and Drosophilla flies, have evolved species at astonishing rates.
In almost all cases, they are accompanied by corresponding diversity in communication signals. Because we define a species in biology as populations that can interbreed and produce fertile, viable offspring, the speciation process is very much related to mating behavior.
Since communication signals are almost always utilized in facilitating mating, scientists have often wondered whether rapid evolution of communication signals might be sufficient to drive the speciation process itself. Elephantfishes in the genus Paramormyrops seem to be excellent candidates for such a process, though we are in the early stages of figuring this out. We have identified the major transitions of signal variation across populations of fishes, and the morphological and physiological changes that happen in the electric organ underlying these variations. We’re now trying to figure out what the genetic basis of these changes are.
At some point we experience an encounter with nature that hits us to the core. Was there a memorable experience in your life that helped steer your interests toward fish biology, and electric fishes in particular?
Sometime between first and fourth grade my fate was sealed. I’ve always kept fish and have been fascinated by them—but when I was in fourth grade, Jurassic Park came out, and I was astonished by this chemical called DNA which seemed like one of the most powerful chemicals on the planet.
After several amazing science teachers, I made it to college, and all it took was a very enthusiastic faculty member, who taught my first course in animal communication, to introduce me to electric fish, and the questions have basically ruled my life ever sense!
Thank you for your time, Jason!
FishBase Page: http://www.fishbase.org/summary/5208
Gallant, JR, LL Traeger, JD Volkening, H Moffett, PH Chen, CD Novina, GN Phillips, R Anand, GB Wells, M Pinch, R Güth, GA Unguez, JS Albert, HH Zakon, MP Samanta, MR Sussman. 2014. Genomic basis for the convergent evolution of electric organs. Science 344(6191): 1522-1525. doi: 10.1126/science.1254432
Gallant, J, M Arnegard, J Sullivan, CD Hopkins. 2011. Patterns of geographic signal variation and its morphological correlates in a mormyrid electric fish provide insights into evolution of electrogenic signal diversity. Journal of Comparative Physiology A 197(8):799-817. doi: 10.1007/s00359-011-0643-8
A Note: This post is the 42nd installment of a more than 32,000-part series, “Better Know a Fish”, and it is also being published on the final day of the U.S. television program “The Colbert Report”, which inspired this website’s name with its “Better Know a District” segments. Fans of the show will know that Stephen Colbert has done much to feature science and scientists on his program, so to that and to his great milestone, I tip my hat to Stephen—and his very hungry fish.
— Ben Young Landis