Feb. 6 (UPI) -- Is the sex real? At lamprey spawning sites, the answer is often no.

New research suggests much of the sex at lamprey gatherings is simulated. Though males may release sperm during the act, females don't make their eggs available. Scientists call the act "sham mating."


Scientists knew the nonparasitic lamprey, Lethenteron kessleri, like many lamprey species, was promiscuous -- taking on dozens of mates. But they wondered why. Mating uses up significant amounts of energy and exposes the involved parties to the risk of predation.

Experiments suggest females use "sham mating" as a way to maintain control over her eggs. Females can can go through motions until they find the right male.

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When a scientists at Hokkaido University in Japan placed two lampreys, one female and one male, in the same tank, sham mating was infrequent. Most of the sex was real. Females had no choice.

But when a female lamprey was placed in a tank with multiple males, the rate of sham mating -- mating without the release of eggs -- increased. Females faked it more often.

"The study shows there is a possibility that, despite the presence of many males, females recognize individual males and actively control when they release their eggs; and that this depends on the body size, nest-building abilities, and other qualities of the male," researcher Itsuro Koizumi said in a news release. "The discovery of pre-breeding mate selection in highly promiscuous creatures is a new finding and of great interest."

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Researchers detailed their findings in the Journal of Ethology.

"It is highly advantageous for females if they can choose their mate even when a large number of females and males gather at a single spawning site," Koizumi added. "Even though our results are only preliminary, further examination of the lampreys' breeding behavior should give us a deeper understanding of mate selection and the evolution of breeding systems."