(Press-News.org)
AUDIO:
Amplified electric pulses were recorded at Biroudou Creek in southeastern Gabon. Each click represents a single electric-organ discharge, which is about one millisecond long. Several fish can be heard in...
Click here for more information.
Bruce Carlson stands next to a fish tank in his lab, holding a putty colored Radio Shack amplifier connected to two wires whose insulation has been stripped. At the bottom of the tank a nondescript little fish lurks in a sawed-off section of PVC pipe.
Carlson sticks the two bare wires into the tank. Suddenly we hear a rapid-fire pop, pop, pop, pop, pop, pop. The pops, which are surprisingly loud, sound rather like the static on an old-fashioned tube radio tuned between stations.
"When there are many fish in a tank," Carlson says, "it sounds like a frying pan".
Carlson, PhD, assistant professor of biology in Arts & Sciences, is studying the African family of weakly electric fishes called the Mormyridae, or mormyrids.
Each fish in this family has an electric signal distinctive to its species, but also, to its sex, dominance status and even its individual identity.
The shape of the discharge is the fish's "face," says Carlson. "It's how they recognize one another."
The sensory pathway that detects and analyzes the electric discharges in the Mormyridae had been well studied, but only in two or three species, Carlson says, and the family has more than 200. Given its diversity Carlson asked whether changes in electrical communication might have influenced rates of speciation.
Three anatomical advances underlie the ability to send and receive diverse electrical signals: cells able to produce different discharges, a global distribution of the sensors that detect the discharges' shape, and a more complex signal-processing area of the brain to analyze them.
In 2008 the National Science Foundation awarded Carlson a grant to travel to Gabon (where many mormyrid species are found) to study the mormyrid brain, and how brain anatomy maps onto the evolutionary tree of the fishes.
His team found that changes in brain anatomy and the resulting ability to fully exploit electric signal space did indeed lead to rapid speciation, a result published in the April 29 issue of Science.
The electric organ
Each pop is one discharge of an electric organ located at the base of a fish's tail. The organs consist of stacks of disk-like cells called electrocytes, "pretty much like watch batteries in series," says Carlson.
The electrocytes all fire action potentials simultaneously, and so their tiny action potentials sum to produce a discharge that is typically about a few volts.
"These signals don't propagate as electromagnetic waves," Carlson explains. "Instead they exist as an electrostatic field, just like you'd get by sticking a battery in the water.
"That's why these fish are so good at recognizing pulses with different shapes," he says. Waves are distorted during transmission, so that their fine temporal structure is smeared.
"The discharges are not distorted. They get weaker with distance, but their temporal structure stays the same. That's one reason mormyrids evolved to be exquisitely sensitive to small timing differences in electric signals," Carlson explains.
Detecting the pulse
Weakly electric fish have several types of electroreceptors but the ones important for communication are called knollenorgans, from the German word "Knolle," or tuber, because they consist of bulbous cells buried just under the fish's skin.
The knollenorgans respond to a voltage rise, firing a time-locked spike in response to outside positive-going voltage changes.
The knollenorgans on one side of a fish's body respond to the start of a discharge and those on the opposite side respond to the end of a discharge. This lets a fish recognize a species-specific discharge by comparing the intervals between spikes coming from opposite sides of its body.
The spike time comparison occurs within the central nervous system, in a part of the brain called the extero-lateral nucleus, or EL.
Signal processing
When we began our work, the "standard anatomy" for the "mormyrid" brain—what you'd find if you looked in a textbook-- says Carlson, was a two-part EL, with separate nuclei, or clumps of cells, in the anterior and posterior portions.
"We collected lots of brains in Gabon, and two collaborators, Saad Hasan, a former undergraduate at Washington University, who is now a medical student at Cornell, and Derek Miller, who is an undergraduate at Washington University, did all the histology on the brains.
"In addition to the standard anatomy, we were amazed to see another anatomy, where the EL is substantially smaller and not split into two portions.
"All the fish we looked at either had the large EL that was divided into anterior and posterior halves, or they had the small undifferentiated EL.
Working with collaborator Matthew Arnegard, PhD, a postdoctoral fellow at the Fred Hutchinson Cancer Research Center in Seattle, WA, the scientists mapped the brain anatomy onto a phylogenetic tree (an evolutionary tree based on the similarity of DNA sequences), and they could see that there were two equally parsimonious ways to reconstruct the fishes' evolutionary history.
Either the complex brain was ancestral and the simpler brain evolved twice or the simpler brain was ancestral and the complex brain arose twice. To solve this riddle, they did what evolutionary biologists do, which is look at the "next outgroup member," the closest related fish that's not part of the Mormyridae family.
This fish has an area in the midbrain that is similar to a small, undifferentiated EL. This suggested the EL brain was probably the ancestral brain, and the more complex divided ELa/ELp evolved twice, once within the subfamily Mormyrinae and once within the subfamily Petrocephalinae.
Did fancy anatomy lead to rapid diversification?
If a communication system is to promote species diversity it must have both the capacity to create new signals (flexible stalk morphology) and the ability to distinguish those new signals from other signals (the broad distribution of knollenorgans and the complex brain).
"The only fish that have all three is a group of mormyrids we ended up calling Clade A for simplicity's sake," Carlson says.
To test the importance of these traits on signal divergence we analyzed the discharges of fish collected in two locales: the Ivindo River of Gabon, home to the largest known assemblage of the subfamily Mormyrinae; and Odzala National Park in the Republic of the Congo, home to the largest known assemblage of the subfamily Petrocephalinae.
"Statistical analysis showed us that the rate of signal divergence in Clade A was 10 times higher than among other fish within the Mormyridae," Carlson says. Further analysis by collaborator Luke Harmon, PhD, assistant professor of biology at the University of Idaho, revealed that the number of species in clade A has been increasing three to five times faster than the number of species in other mormyrid lineages.
In other words, the fancier the fishs' communication kit, the more likely it was to come up with new electric discharges and new species that identified one another by those discharges.
Putting it to the test
It all worked out statistically and logically but was it what the fish actually experienced?
"After all," says Carlson, "this sensory world is totally foreign to us. I've worked with these fish a long time, so I can tell a few of the discharges apart by ear. But for the most part I need an oscilloscope to see the differences.
Can the Clade A fish tell the difference between discharges? To test them, Carlson ran behavioral playback experiments on fish caught in Gabon.
"A fish would be going pop, pop, pop and we'd pulse it. Depending on the fish, it would either discharge more rapidly, brrrrrrrrr, or stop discharging altogether.
"But if we repeated the stimulus again and again the fish would stop responding. Once it stopped responding, we hit it with a phase-shifted version of the same pulse. If the fish could tell the difference, the discharge rate or pause duration would increase. If it couldn't tell the difference, there would be no change.
The experiments showed that mormyrid fish in Clade A were able to distinguish among pulses, but other mormyrids (those with the EL brain) were not.
Did the evolution of a fancy signal-processing brain drive speciation in the Mormyridae? "It's always difficult with evolutionary studies to say that any one trait is the cause or the trigger for another," Carlson says. "But in this case we were able to show that the complex signal-processing brain evolved before a burst of speciation, that signal variation was higher among fishes with that brain, and that these fishes could distinguish among subtly different pulses, whereas others could not.
"Together it adds up to a strong case for brain evolution triggering increased diversification."
INFORMATION:
Jump in communication skills led to species explosion in electric fishes
A novel way to ramp up biodiversity
2011-04-29
ELSE PRESS RELEASES FROM THIS DATE:
Mutations in single gene may have shaped human cerebral cortex
2011-04-29
The size and shape of the human cerebral cortex, an evolutionary marvel responsible for everything from Shakespeare's poetry to the atomic bomb, are largely influenced by mutations in a single gene, according to a team of researchers led by the Yale School of Medicine and three other universities.
The findings, reported April 28 in the American Journal of Human Genetics, are based on a genetic analysis of in one Turkish family and two Pakistani families with offspring born with the most severe form of microcephaly. The children have brains just 10 percent of normal size. ...
Unlock Advantage Provides Simple Instructions With Requested Blackberry and Nokia Unlock Codes
2011-04-29
Unlock Advantage specializes in providing unlock phones along with hassle-free instructions. Whether your phone is a Nokia E7, a Blackberry Style 9670, or any other of hundreds of models, Unlock Advantage can help you get maximum benefit out of your cell phone.
Everything looks crystal clear on the high-quality 4" touch screen on your Nokia E7 cell phone. Some of your advanced mobile features on this sleek phone include real-time push e-mails with Mail For Exchange and effortless access to both your work and private e-mail accounts from the same view. You can also ...
Video captures cellular 'workhorses' in action
2011-04-29
VIDEO:
Thread-like actin filaments, strong as commercial plastic, are the muscular workhorses of our cells -- pushing on membranes to move cells to the proper location within tissues and applying pressure...
Click here for more information.
Scientists at Yale University and in Grenoble France have succeeded in creating a movie showing the breakup of actin filaments, the thread-like structures inside cells that are crucial to their movement, maintenance and division.
Actin ...
BU researchers probe link between theta rhythm and ability of animals to track location
2011-04-29
In a paper to be published today [April 29, 2011] in the journal Science, a team of Boston University researchers under the direction of Michael Hasselmo, professor of psychology and director of Boston University's Computational Neurophysiology Laboratory, and Mark Brandon, a recent graduate of the Graduate Program for Neuroscience at Boston University, present findings that support the hypothesis that spatial coding by grid cells requires theta rhythm oscillations, and dissociates the mechanisms underlying the generation of entorhinal grid cell periodicity and head-direction ...
LeFluer Transportation Engages Compliance Safety Systems Driver File Services
2011-04-29
Compliance Safety Systems announced today that the LeFluer Transportation Corp. of Ridgeland, Mississippi has engaged the services of Compliance Safety Systems for their Electronic Driver File capabilities. This new relationship will allow LeFluer Transportation Corp. to take advantage of creating a paperless driver file record keeping process that Compliance Safety Systems, (CSS), provides for employers. LeFluer Transportation is moving to electronic employee files to help them to have better control and review of these documents from remote locations.
About LeFluer ...
Fluctuations before the fall: Predicting and preventing environmental collapse
2011-04-29
(Millbrook, N.Y.) By closely monitoring environmental conditions at a remote Wisconsin lake, researchers have found that models used to assess catastrophic changes in economic and medical systems can also predict environmental collapse. Stock market crashes, epileptic seizures, and ecological breakdowns are all preceded by a measurable increase in variance—be it fluctuations in brain waves, the Dow Jones index, or, in the case of the Wisconsin lake, chlorophyll.
In a paper published this week in the journal Science, a team of ecologists is the first to show that by paying ...
Precise Air Systems, Inc. Has Been Providing Services for HVAC in Los Angeles Since 1975 and Offers Tips for Running Your Air Conditioner Efficiently
2011-04-29
When the temperatures heat up dramatically, the air conditioner runs nonstop, putting a huge burden on the cooling system. It could help save money on energy costs and reduce your need for air conditioning repair in Los Angeles if you run your air conditioner efficiently. Precise Air Systems, Inc. provides helpful tips:
- Set your thermostat at 78 degree Fahrenheit and leave it there. Moving the thermostat to a lower temperature setting won't get your home to 78 degree any faster.
- Keep your blinds and curtains closed to keep the direct rays of the sun from entering ...
Clinical trial recommends new antibiotic for treating typhoid in low income countries
2011-04-29
A large clinical trial comparing treatments for typhoid has recommended the use of gatifloxacin, a new generation and affordable antibiotic. The results of the trial in Kathmandu, Nepal, funded by the Wellcome Trust and the Li Ka Shing Foundation, are published today in the Lancet Infectious Diseases.
Typhoid – also known as 'enteric fever' – is characterised by a high fever and diarrhoea. It is transmitted through the ingestion of food or drink contaminated by the faeces or urine of infected people. It causes an estimated 26 million infections each year and over 200,000 ...
Concern over 'excessive' doses of thyroid drugs for older patients
2011-04-29
Many older adults may be taking "excessive" doses of drugs for thyroid problems which can lead to an increased risk of fractures, finds a study published on bmj.com today.
The study raises concern that treatment targets may need to be modified in the elderly and that regular dose monitoring remains essential even into older age.
Levothyroxine is a synthetic form of thyroxine (thyroid hormone) and is widely used to treat an underactive thyroid gland (hypothyroidism).
Most hypothyroid patients are diagnosed in early or middle adulthood but, as people age, their thyroxine ...
Electrical oscillations found to be critical for storing spatial memories in brain
2011-04-29
Biologists at UC San Diego have discovered that electrical oscillations in the brain, long thought to play a role in organizing cognitive functions such as memory, are critically important for the brain to store the information that allows us to navigate through our physical environment.
The scientists report in the April 29 issue of the journal Science that neurons called "grid cells" that create maps of the external environment in one portion of our brain require precisely timed electrical oscillations in order to function properly from another part of the brain that ...
LAST 30 PRESS RELEASES:
Scientists unlock secrets behind flowering of the king of fruits
Texas A&M researchers illuminate the mysteries of icy ocean worlds
Prosthetic material could help reduce infections from intravenous catheters
Can the heart heal itself? New study says it can
Microscopic discovery in cancer cells could have a big impact
Rice researchers take ‘significant leap forward’ with quantum simulation of molecular electron transfer
Breakthrough new material brings affordable, sustainable future within grasp
How everyday activities inside your home can generate energy
Inequality weakens local governance and public satisfaction, study finds
Uncovering key molecular factors behind malaria’s deadliest strain
UC Davis researchers help decode the cause of aggressive breast cancer in women of color
Researchers discovered replication hubs for human norovirus
SNU researchers develop the world’s most sensitive flexible strain sensor
Tiny, wireless antennas use light to monitor cellular communication
Neutrality has played a pivotal, but under-examined, role in international relations, new research shows
Study reveals right whales live 130 years — or more
Researchers reveal how human eyelashes promote water drainage
Pollinators most vulnerable to rising global temperatures are flies, study shows
DFG to fund eight new research units
Modern AI systems have achieved Turing's vision, but not exactly how he hoped
Quantum walk computing unlocks new potential in quantum science and technology
Construction materials and household items are a part of a long-term carbon sink called the “technosphere”
First demonstration of quantum teleportation over busy Internet cables
Disparities and gaps in breast cancer screening for women ages 40 to 49
US tobacco 21 policies and potential mortality reductions by state
AI-driven approach reveals hidden hazards of chemical mixtures in rivers
Older age linked to increased complications after breast reconstruction
ESA and NASA satellites deliver first joint picture of Greenland Ice Sheet melting
Early detection model for pancreatic necrosis improves patient outcomes
Poor vascular health accelerates brain ageing
[Press-News.org] Jump in communication skills led to species explosion in electric fishesA novel way to ramp up biodiversity