EAST LANSING, Mich. - On appearance alone, one wonders how the eel-like sea lamprey could ever get a date. Now scientists at Michigan State University have made ground-breaking discoveries of how male lampreys attract mates.
According to a paper published in the April 5 edition of Science Magazine, Weiming Li, MSU assistant professor of fisheries and wildlife, and his research team have devised revolutionary new methods to isolate and understand the chemicals that the fish release to lure females.
Their discoveries have the potential to lead to new ways to control sea lamprey populations in areas where they are destroying sport fish populations. The research also could help boost populations in places where lampreys are considered a delicacy.
"The identification has taken a long time," Li said. "It was a difficult task, but we have finally found a way to isolate and identify this pheromone that has been suspected, but never documented. It has given us a new way to look at pheromone communication."
Sea lampreys are aquatic vertebrates native to the Atlantic Ocean that likely found their way into the Great Lakes via shipping channels. Sea lampreys latch on to popular fish, such as salmon and trout, with a sucking disk and sharp teeth. They suck on body fluids, often scarring and killing host fish.
A sea lamprey, in its parasitic life, can kill 40 or more pounds of fish. They are so destructive that under some conditions, only one of seven fish attacked by a sea lamprey will survive.
Li's team members were: Michael Siefkes, doctoral student; Honggao Yan and Douglas Gage, associate professors of biochemistry and molecular biology; Qin Liu and Sangseon Yun, research associates; and Alexander Scott, senior scientist, Center for Environment, Fisheries and Aquatic Sciences, United Kingdom.
The work's significance:
It creates a new strategy to hunt down and identify chemical compounds that aquatic animals release as pheromones, even though they are diluted in thousands of gallons of water. Until now, it was not known how fish communicate through chemicals over long distances. Pheromones are well documented in insects, but less so in fish. Moreover, it was presumed that females were often the chemical temptresses.
It identifies the potency of the sea lamprey pheromone and how far one fish can cast its chemical net to lure a female. Sea lampreys migrate into streams to spawn in spring. The males arrive earlier than the females and build nests. Then they release pheromones to lure the ripe females. To find the chemical, Li's team spent two years condensing a ton of water to about 30 milligrams of pure compound.
Their painstaking methods included creating bioassays to trace the key chemicals and sorting compounds by washing these compounds through a lamprey's nose and tracking its neurological - called electro-olfactogram - and behavioral responses. High performance liquid chromatography, fast atom bombardment mass spectrometry, nuclear magnetic resonance and thin-layer chromatography were used to examine the structure of the compounds released by spermiating males.
The result: a purified vial of the equivalent of super-powered sea lamprey cologne guaranteed to draw the lady lampreys.
Li said it usually is assumed that females are using the chemical wiles. Discovering that males are releasing a chemical that is manufactured in their liver and delivered through the gills puts a whole new spin on fish courtship.
"People have often thought that it was the sexually mature male that goes after a female," Li said. "But now we know that in the sea lamprey it is the male that is sending the active signal, instead of just being spied by the female. This is important."
Li said evidence suggests that females are putting out chemical come-ons of their own to signal fertility, as well as chemicals to keep the males close to home.
While the purified compound is odorless to humans, the MSU research has shown that one fish can send his invitation far downstream. Further research is ongoing to pinpoint potency and effective distance.
Li said the work on sea lampreys is likely applicable to other fish and that synthesizing pheromones both to control and boost fish populations holds promise.
The Great Lakes Fishery Commission funded the research. For more about the commission, visit http://www.glfc.org
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