Neuroethology and Behavioral Ecology
of Communication in Electric Fish
My lab asks the question “How does a communication system
evolve?” We take an integrative approach, exploring communication
at every level, from the ecological forces that drive natural selection,
to the proteins that constitute the structures producing communication
signals. Our study organism is the South American electric fish we
call the “pinni”. Tiny cousins of the formidable electric
eel, electric fish have electric organs that generate low voltage
electric field pulses, the “Electric Organ Discharge” or “EOD”.
The electric organ is derived from myocytes (muscle cells) but functions
like an array of giant neurons (nerve cells).
Electric fish sense the distortion of their EODs produced by nearby
objects, and so can see in the dark, a short-range version of sonar
used by bats and dolphins. They also vary the EODs to communicate.
Males sing electric courtship songs to the females (played through
an audio amplifier, these sound like a faltering lawnmower).
Because the electric fish shares its electric signals with the outside
world and because it signals all the time to electrolocate, we view
the electric fish as the only vertebrate with a public nervous system.
Thus, the electric fish can reveal to an inquisitive scientist the
instantaneous inner workings of its neuroendocrine systems, most
components of which are extremely similar to those of all vertebrates
including ourselves. We take advantage of this unique window to explore
how a vertebrate translates changes in the social environment into
changes in the brain and body. Everybody knows, for instance, that
when a person is happy, she or he is healthier, and when our relationships
go sour, so goes our health. The electric fish are telling us how
this works. We change the fish’s social environment and observe
the changes in the electric signal. For instance, placing a social
fish by itself causes circadian rhythms in the magnitude and spectrum
of the EOD to diminish causing the EOD to lose its value as a communication
signal. We can restore the signal and its circadian rhythms to their
prior values, either by restoring the social environment, or by administering
sex steroids to the fish. Not surprisingly, the nature of the social
environment makes a big difference. The animals enhance their electric
signals the most in the presence of rivals they can dominate.
Recently, we have discovered that electric fish have borrowed components
of the neuroendocrine stress axis to regulate their EOD waveforms.
This works very well for them most of the time. But, the stress axis
is alive and well, so when the animal encounters a stressful situation,
the EOD is enhanced, raising energetic costs and making the animal
more conspicuous. If the stress is a social encouter, enhancing the
signal can benefit the signaler, but if the stress is caused by a
predator, enhancing the signal is precisely the worse thing to do.
Evolution is not perfect.