'Spooky Interactions', shocking adaptations discovered in electric fish
of Brazil's Amazon

Date:
December 9, 2020
Source:
New Jersey Institute of Technology
Summary:
Researchers have shown how a cave-adapted glass knifefish species
of roughly 300 living members (Eigenmannia vicentespelea) has
evolved from surface-dwelling relatives (Eigenmannia trilineata)
that still live just outside their cave door -- by sacrificing
their eyes and pigmentation, but gaining slightly more powerful
electric organs that enhance the way they sense prey and communicate
in absolute darkness.



FULL STORY ==========================================================================
A study of weakly electric fishes from a remote area of the Brazilian
Amazon Basin has not only offered a unique window into how an incredibly
rare fish has adapted to life in caves over tens of thousands of years,
it has also revealed for the first time that electric fish are able to
interact with each other over longer distances than known possible in
a way similar to AM radio.


==========================================================================
In findings published in the journal Frontiers, researchers have shown
how a cave-adapted glass knifefish species of roughly 300 living members (Eigenmannia vicentespelea) has evolved from surface-dwelling relatives (Eigenmannia trilineata) that still live just outside their cave door
-- by sacrificing their eyes and pigmentation, but gaining slightly
more powerful electric organs that enhance the way they sense prey and communicate in absolute darkness.

The study, which analyzed the fishes' electric-based communication and behavior, has detailed the discovery that weakly electric fishes tap
into a special channel for long-distance messaging via changes in the
amplitude of electrical signals sent to one another. Researchers have
adapted Einstein's famous quote on the theory of quantum entanglement -- "spooky interaction at a distance" -- to describe how the weakly electric fishes perceive these social messages, altering each other's behavior
at distances up to several meters apart.

Of the nearly 80 species of cavefish known today to have evolved from
surface- dwelling fish, all have developed sensory enhancements of some
kind for enduring cave life, commonly adapting over millions of years
while losing sensory organs they no longer need in the process.

However, biologists have questioned how weakly electric fishes, which use
their electrical senses for navigating the dark and murky conditions of
the Amazon River, might also adapt -- either evolving heightened electric senses to see and communicate in absolute darkness, or by powering down
their electric fields to save on energetic cost when most caves have
few food resources.

"One of the big questions about fish that successfully adapt to living in
caves is how they adapt to life without light," said Eric Fortune, lead
author of the study and biologist at New Jersey Institute of Technology
(NJIT). "My colleagues were split between two groups ... one group that predicted that the electric fields of the cavefish would be weaker due
to limited food supplies, and another that bet that the electric fields
would be stronger, allowing the fish to use their electric signals to
see and talk more clearly in the complete darkness of the cave.



==========================================================================
"It seems that using their electric sense to detect prey and communicate
with each other is quite valuable to these animals; they have greater
electric field strengths. Interestingly, our analysis of their electric
fields and movement shows that they can communicate at distances of
meters, which is quite a long way for fish that are around 10cm in
length." "Nearly all research of cavefish species until now has been
limited to behavioral experiments in labs, and that is why this study
is special," said Daphne Soares, NJIT associate professor of biology
and co-author on the study.

"This is the first time we've been able to continuously monitor the
behavior of any cavefish in their natural setting over days. We've gained
great insight into their nervous system and specialized adaptations for
cave life, but it's just as exciting to learn how sociable and chatty
they are with each other ...

it's like middle school." Spooky Interactions & Shocking Adaptations
For the investigation, NJIT and Johns Hopkins researchers teamed with
biologist Maria Elina Bichuette from the Federal University of Sa~o
Carlos, who began studying the two groups of fish nearly two decades
ago in the remote Sa~o Vicente II Cave system of Central Brazil's Upper Tocantins river basin.

Over several days, the team applied a customized electric fish-tracking technique involving placing electrode grids throughout the fishes' water habitats to record and measure the electric fields generated by each fish, allowing the team to analyze the fishes' movements and electricity-based
social interactions.



==========================================================================
The researchers were able to track more than 1,000 electrical-based
social interactions over 20-minute-long recordings taken from both
surface and cavefish populations, discovering hundreds of specialized long-distance exchanges.

"When I began studying these fishes, we could watch behavior associated
with these fishes' unique and specialized morphology, but in this project,
it was fascinating to apply these new technical approaches to reveal just
how complex and refined their communication could be," said Bichuette.

"Basically, our evidence shows that the fishes are talking to each
other at distance through electricity using a secret hidden channel,
amplitude modulations that emerge through the summation of their electric signals. It is not unlike how an AM radio works, which relies on amplitude modulations of a radio signal." said Fortune.

The recordings also showed that strengths of electric discharges in the cavefish were about 1.5 times greater than those of surface fish despite
coming at a cost of up to a quarter of their overall energy budget. The
team conducted CT scans of both species, showing that the cavefish
also possess relatively larger electric organs than their stream-mates,
which could explain the source of the cavefishes' extra electrical power.

Another consequence of trading their eyes and surface life for heightened electrosensory perception is that the cavefish were more social and
territorial at all hours. Unlike their freely-foraging surface relatives
that sleep during the day and forage at night, the cavefish lacked a
day-night cycle.

For now, the discovery of the fishes' AM radio-style distant interactions
is noted by Fortune as the first of its kind reported among electric
cavefish, though he says similar phenomena is now being reported in
some other species as well, recently by researchers in Germany who have observed a form of long- distance electrical communication among a group
of fish known as Apteronotus.

Fortune says the finding could have implications for the field of
neurobiology, where weakly electric fish is a unique and powerful model
for exploring the nature of the brain-body connection in other animals including humans.

"Electric fish are great systems for understanding the neural basis
of behavior, so we have been studying their brains for decades,"
said Fortune.

"These new data are forcing a reexamination of the neural circuits used
for the control of behavior of these fishes."

========================================================================== Story Source: Materials provided by
New_Jersey_Institute_of_Technology. Original written by Jesse
Jenkins. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Eric S. Fortune, Nicole Andanar, Manu Madhav, Ravikrishnan
P. Jayakumar,
Noah J. Cowan, Maria Elina Bichuette, Daphne Soares. Spooky
Interaction at a Distance in Cave and Surface Dwelling Electric
Fishes. Frontiers in Integrative Neuroscience, 2020; 14 DOI:
10.3389/fnint.2020.561524 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/12/201209140336.htm

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