Sea lampreys ( Petromyzon marinus ) are those jawless fish that look like huge leeches and live attached, with their sharp teeth and rough tongue, to the body of sharks, salmon, cod and marine mammals to suck blood and body fluids until they is satiated or kills its victim. Their larvae live in rivers for five years; then they become adults and go to the sea.
Well, according to a study carried out, among others, by researchers Anne M. Scott, from Michigan State University (USA), and Zhe Zhang, from Shanghai Ocean University (China), on their semen there is an aphrodisiac pheromone that attracts females ready to mate.
The finding is relevant because, although it was known that in fish and other animals that use external fertilization – the female lays the eggs and the male sprays them with his semen – exposure to semen promotes spawning behaviors in females, so far not Specific compounds had been identified in semen to act as aphrodisiac pheromones.
The study, published on July 9 in the open access journal PLOS Biology , has identified a pheromone from the milk – fish semen – of the sea lamprey, a fish that spawns in aggregations where each male defends a nest and the females in ovulatory phase they move from nest to nest to mate.
A reliable indicator for females
The researchers hypothesized that the compounds in milk may indicate to females that they are ovulating the presence of spawning and of males releasing sperm. They discovered that an odorous compound called spermine, originally identified from human semen, is in fact a pheromone in milk.
At very low concentrations, spermine stimulated the lamprey’s olfactory system and attracted ovulatory females, but did not attract pre-ovulatory males or females. They identified the specific receptor activated by spermine in lamprey olfactory tissue, and a compound that blocks this receptor prevented the attraction of ovulating females to spermine.
“We discovered that sea lamprey semen contains spermine, a highly specific and potent pheromone that attracts female sea lampreys ready to mate,” explains Anne Scott. “This discovery implies a new strategy used by male animals to recruit mates: a through the release of chemical signals in the semen. Females who are ovulating probably perceive the spermine released along with the sperm as a reliable signal of the presence of actively spawning males nearby. “
The results clarify the mechanism by which a pheromone in semen attracts females ready to mate and implies a possible evolutionary preservation, by humans, of the olfactory detection capacity of semen that jawless vertebrates already possessed. According to the authors, the identification of milk pheromones may also have implications for the control or conservation of sea lamprey populations.
Photo credit: Anne M. Scott
