Sea lamprey sperm acts as a sex pheromone

July 10 (UPI) -- Before male sea lampreys use their semen to fertilize the eggs of a female, the animals must find mates. To do that, the lampreys use their semen -- it's a multidimensional tool.

Like human semen, lamprey semen contains spermine. Thankfully, humans don't rely on spermine to attract mates. The same can't be said for lampreys.

For lampreys, spermine works like cologne -- a cologne designed to attract only sexually mature females.

"We found the male ejaculate contains spermine, a highly specific and potent pheromone, which attracts only mature females," Weiming Li, fisheries and wildlife professor at Michigan State University, said in a news release. "Mature females likely use spermine to identify males actively releasing sperm in the spawning aggregation."

As previous studies have shown, male lampreys use different pheromones to lure females upstream to spawning sites on river gravel beds. Once arrived, females don't seek a single mate. Instead, they mate with a several males, one at a time, spawning several times per hour.

According to the new study, published this week in the journal PLOS Biology, spermine helps the females decide which of the males, ready and waiting on their gravel nests, to mate with. It's the first time scientists have identified the manner in which females select the best mating partners.

"We also were able to document a specific receptor in the noses of females that picks up spermine, and it can be smelled at trace-level concentrations," said Richard Neubig, pharmacology professor at MSU. "This was a big job requiring nearly 12,000 tests in the MSU high-throughput screening lab to figure out the right pair of chemical and receptor."

During tests, females and their spermine receptor, called TAAR, were able to detect trace amounts of the pheromone, the equivalent of a drop of cologne in a swimming pool.

Sea lampreys are an invasive species in the Great Lakes. They feed by attaching themselves to fish and are a threat to native salmon and trout in the region. Scientists hope the latest research will inspire new control strategies. By blocking females' TAAR receptors, researchers could potentially disrupt the invasive species' reproductive cycles.