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Romancing the Sea Lamprey (Love Potion Number 3KPZS)

A powerful force she couldn't name and couldn't deny drew her to this stream. With less than two weeks to live, every fiber of her sleek body responded urgently to the heady aroma carried on the current. Her graceful movements grew wilder and more certain with every inch she gained on the stream. Her small weak eyes were of little use in this, one of the last major episodes of her life, but the female sea lamprey had a very big nose and she liked the way he smelled. It wasn't luck that brought her slithering to the male lamprey's side just days before the end of her life, it was Love Potion Number 3KPZS.

Weiming Li in front of frozen waterfall

Weiming Li

3KPZS (3-Keto Petromyzonol Sulfate) is a potent sex-pheromone released through the gills of male sea lamprey; it drives female lamprey to frenzied wantonness. Weiming Li, assistant professor of Fisheries and Wildlife at Michigan State University, and his research team who spearheaded the discovery of 3KPZS, believes it is the root of the romantic language of these pesky primitive fish and possibly key to their management in the Great Lakes.

With nose organs about the size of their brains and brains largely dedicated to processing olfactory information, Li made a compelling point when he said, "Sea lamprey are very nosy animals," during two well-received talks hosted by Minnesota Sea Grant in Duluth and Grand Marais, MN.

Listeners learned that adult sea lamprey in love don't follow their hearts, they follow their noses. These aquatic vampires rely on their super-sized snoots and keen senses of smell to find mates and food. And when it comes to eating, it’s their mouths that cause us the most problems. Li stated that lamprey have big mouths and "good taste, eating the medium to large lake trout and salmon that people want. One sea lamprey can kill about 45 to 50 pounds of fish within 20 months," Li said.

Li was inspired to study the sex pheromones of lamprey because, among other reasons, he thought they could be used to effectively control these Great Lakes pests and reduce the need for lampricide applications in Great Lakes streams. He specifically chose male pheromones because they elicited a more robust response; in early trials he found that ovulated females searched for spermeating males about 80 percent of the time but that spermeating males didn't actively seek females. This notable deviation from mammalian norms can be explained; males arrive in streams first, build nests, and launch a passive aromatic pursuit.

"Adult lamprey in large waterbodies are unavailable for us to control," said Li. "It’s the time they are in streams that they become available."

This happens twice in a lamprey's lifetime: while they are growing in the stream bed for three to 17 years, (which is really not a fun life according to Li); and when they return to spawn. After about a year and a half of "fun" cruising around the lake "having buffets when they want to," they have approximately one month in which to find a suitable stream, find each other, and reproduce.

Li believes the sex pheromones function to bring the lamprey together, and is thus a weakness that can be exploited. "If you stop them here, you stop the whole life cycle…and we might be able to manage lampreys more efficiently," said Li.

Earlier studies led by Sea Grant researcher Peter Sorensen at the University of Minnesota, produced evidence that larval lamprey release a pheromone that attracts adult lamprey to spawning streams. Male lampreys arrive in these streams about a week before the females and complete their sexual maturity. When they are ready to spawn, they release the seductive "come-hither" pheromone.

Li's investigations involved controlled "outdoor maze" experiments, stream trials, countless hours of laboratory work, and extensive teamwork. In the outdoor maze, Li and his collaborators found that mature females were ambivalent towards non-spermeating males but most eager to meet spermeating males. Wanting to be certain that it wasn't good looks that drove females to distraction, they pumped the water from a hidden tank containing a spermeating male through the maze and recorded an equally frisky response.

Sea Lamprey in clear plastic tank which is separated into two compartments

A lamprey awaits odor tests in a special tank designed to determine which end of the lamprey releases sex pheromones. Image courtesy of Weiming Li.

Once it was clear that there was some water-borne pheromone released by spermeating males that female lamprey responded to, the questions became where did the chemical originate and what did it look like. After making a combination lamprey belt/clamp (which is tricky on an animal with no waist) and subduing a slippery victim, the researchers found that the sex-pheromone emanated from the head region of a male lamprey's body. Further inquiry lead to a discovery so unusual that it warranted space in the prestigious journal, Science* —the pheromone was produced in the lamprey's liver.

Three years of fastidious and tedious laboratory work revealed that the compound, 3-Keto Petromyzonol Sulfate (3KPZS) is the major component of the male lamprey's sex pheromone.

Then the researchers took their questions to the stream. In this more natural setting, they found that 70 percent of the radio-tagged females purposefully traveled 70 meters upstream to find spermeating males. The average time it took the females to close in on the smell was 20-25 minutes, but one particularly lusty gal lamprey traversed the distance in less than five.

The next piece of Li's puzzle is how 3KPZS can be applied to the population management of lamprey and how his research can serve as an animal model for studies of humans' ability to smell.

"There are several directions that our results could go," said Li. "One is to make sterile males more attractive. If we could produce a 'macho male' that releases more pheromones, he might be able to attract more females and disable their reproductive capacity. A second option would be to drip the synthetic hormone into streams to catch females, which would require approval from the EPA."

If you are interested in seeing a video of Li's presentation, "Romancing the Sea Lamprey," visit the speaker series web page. His talks were part of the "Superior Science for You!" speaker series made possible with a grant funded under the Coastal Zone Management Act by NOAA's Office of Ocean and Coastal Resource Management in conjunction with Minnesota's Lake Superior Coastal Program.

The speaker series runs through June 2003. See the schedule at the speaker series web page.

* Weiming Li, Alexander P. Scott, Michael J. Siefkes, Honggao Yan, Qin Liu, Sang-Seon Yun, and Douglas A. Gage, 2002. Bile Acid Secreted by Male Sea Lamprey That Acts as a Sex Pheromone, Science 296: 138-141.

By Sharon Moen
March 2003

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