Featured Research

from universities, journals, and other organizations

AC or DC? Two newly described electric fish from the Amazon are wired differently

Date:
August 28, 2013
Source:
Pensoft Publishers
Summary:
Two new species of weakly electric fishes from the Amazon with some unusual characteristics. Often collected together and so similar in many respects that they have been mistaken for a single species, the two species differ most notably with respect to their electric organs and electric signals.

This is an image of the two new species with their electric organ discharges (EODs). Brachyhypopomus walteri (top) has a longer, thinner tail and produces an EOD with both positive and negative phases. Brachyhypopomus bennetti (bottom) has a shorter, thicker tail and produces monophasic EODs.
Credit: John P. Sullivan; CC-BY 3.0

Much as human siblings can have vastly different personalities despite their similar resemblance and genetics, two closely related species of electric fish from the Amazon produce very different electric signals. These species, new to science, are described in the open access journal ZooKeys by Drs. John Sullivan of Cornell University in Ithaca, New York, Jansen Zuanon of the National Amazonian Research Institute in Manaus, Brazil and Cristina Cox Fernandes of the University of Massachusetts, Amherst.

The two new species are bluntnose knifefish, genus Brachyhypopomus, that live under rafts of unrooted grasses and water hyacinth along the margins of the Amazon River called "floating meadows." These are weakly electric relatives of South America's famous electric "eel" (not a true eel) that can produce strong electric discharges of hundreds of volts. By contrast, these weakly fishes produce pulses of only a few hundred millivolts from an organ under the body that extends out onto a filamentous tail. Nearby objects in the water create distortions to the electric field that are sensed by receptor cells on the fishes' skin. In this way, they are able to "electrolocate" through their complex aquatic environment at night. Their short electric pulses, too weak to be sensed by touch, are also used to communicate the sender's species identity and gender to other electric fishes.

"The most striking differences between these two similar species have to do with their electric organs and their electric organ discharges, or EODs," says lead author John Sullivan, Curatorial Affiliate at the Cornell University Museum of Vertebrates. "If it weren't for these traits, we undoubtedly would have thought they were a single species. The one we are calling Brachyhypopomus bennetti has a huge electric organ, a short, fat tail, and produces a monophasic EOD; the other one that we're calling Brachyhypopomus walteri has a more typical electric organ, a long thin tail, and a more typical biphasic EOD."

It turns out the monophasic EOD of the new species Brachyhypopomus bennetti is highly unusual. Most species of this kind of knifefish produce EOD waveforms with both a positive and negative phase to them, as viewed on an oscilloscope: essentially alternating current. In this way, there is no net positive or negative current generated by the signal. "All of this fish's relatives, including its newly described sister species, have biphasic EODs," says Sullivan. "For that reason we know that this trait evolved in this species' lineage. The interesting question is why."

One widely accepted idea is that the biphasic EOD with its reduced amount of direct current (DC) is an adaptation to hide from predatory fish, like catfishes and electric eels, that are equipped with a type of electroreceptor that are sensitive to DC. So why would one species seemingly court danger by evolving a monophasic EOD?

The only other electric fish in the Amazon with a similar monophasic EOD is the fearsome electric eel. This fish has both a weak EOD used for electrolocation and communication as well as a much more powerful EOD used to stun prey and for defense. A theory proposed by Dr. Philip Stoddard of Florida International University contends that, in much the same way that the Viceroy butterfly -- a species tasty to birds -- evolved wing color patterns to mimic the distasteful Monarch butterfly, the harmless B. bennetti 's EOD waveform evolved to mimic that of the electric eel, a species electroreceptive predatory fishes may have learned to avoid.

In this paper, the authors suggest an additional possible benefit of of B. bennetti's monophasic EOD. Unlike biphasic species, B. bennetti's EOD waveform is largely unaffected after their tails are partially bitten off by predators, a common type of injury in this species. They suggest that this species' preference for floating meadow habitat near river channels may put them at particularly high risk of predation and 'tail grazing' by other fishes.

The authors show that the EOD waveforms of Brachyhypopomus species with biphasic EODs are severely altered after such injuries, whereas those of B. bennetti are not. "Any change to the EOD waveform likely impairs electroreception and communication and the monophasic EOD waveform may have been favored by natural selection in a species that suffers a lot of tail injuries," says Sullivan. "Selection for both EOD stability and mimicry of electric eels could be going on simultaneously…both hypotheses make predictions that should be tested," said Sullivan.


Story Source:

The above story is based on materials provided by Pensoft Publishers. The original story is licensed under a Creative Commons License. Note: Materials may be edited for content and length.


Journal Reference:

  1. John Sullivan, Jansen Zuanon, Cristina Cox Fernandes. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 2013; 327: 1 DOI: 10.3897/zookeys.327.5427

Cite This Page:

Pensoft Publishers. "AC or DC? Two newly described electric fish from the Amazon are wired differently." ScienceDaily. ScienceDaily, 28 August 2013. <www.sciencedaily.com/releases/2013/08/130828103440.htm>.
Pensoft Publishers. (2013, August 28). AC or DC? Two newly described electric fish from the Amazon are wired differently. ScienceDaily. Retrieved April 19, 2014 from www.sciencedaily.com/releases/2013/08/130828103440.htm
Pensoft Publishers. "AC or DC? Two newly described electric fish from the Amazon are wired differently." ScienceDaily. www.sciencedaily.com/releases/2013/08/130828103440.htm (accessed April 19, 2014).

Share This



More Plants & Animals News

Saturday, April 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Vermont Goat Meat Gives Refugees Taste of Home

Vermont Goat Meat Gives Refugees Taste of Home

AP (Apr. 18, 2014) Dairy farmers and ethnic groups in Vermont are both benefiting from a unique collaborative effort that's feeding a growing need for fresh and affordable goat meat. (April 18) Video provided by AP
Powered by NewsLook.com
First Ever 'Female Penis' Discovered In Animal Kingdom

First Ever 'Female Penis' Discovered In Animal Kingdom

Newsy (Apr. 18, 2014) Not only are these newly discovered bugs' sex organs reversed, but they also mate for up to 70 hours. Video provided by Newsy
Powered by NewsLook.com
Little Progress Made In Fighting Food Poisoning, CDC Says

Little Progress Made In Fighting Food Poisoning, CDC Says

Newsy (Apr. 18, 2014) A new report shows rates of two foodborne infections increased in the U.S. in recent years, while salmonella actually dropped 9 percent. Video provided by Newsy
Powered by NewsLook.com
The Great British Farmland Boom

The Great British Farmland Boom

Reuters - Business Video Online (Apr. 17, 2014) Britain's troubled Co-operative Group is preparing to cash in on nearly 18,000 acres of farmland in one of the biggest UK land sales in decades. As Ivor Bennett reports, the market timing couldn't be better, with farmland prices soaring over 270 percent in the last 10 years. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins