Male Salmon Can Make Sperm Faster To Beat Nearby Rivals: Study

A joint research team from the University of Otago and University of Canterbury, in New Zealand, have revealed that male salmon can change their sperm's swimming speed when competing with other males during mating season.

According to a study published in the journal eLife, the team set out to investigate the link between male social status and the quality of sperm in chinook salmon.

According to Michael Bartlett, a PhD student at the University of Canterbury's School of Biological Sciences, the team found interesting links between the fish’s biology and competition while mating. According to a report by Phys.Org, "Males adjust their sperm swimming speed when their social status/sperm competition risk changes (increasing speed with increased risk) in less than 48 hours," he said.

The study involved researchers setting up vitro fertilization experiments at a hatchery. They raced the sperm between two males, using natural and remixed ejaculates. According to the report, they then genotyped the eggs to see which male fertilized more eggs.

The study showed a definitive link between male social status and the competition for sperm to the quality of their sperm, or how fast it could swim.

The study showed that males changed their sperm velocity via semen or seminal fluid. They altered the number of eggs they fertilized relative to a rival male by changing their seminal fluid. The alteration of seminal fluid changed the speed of the sperm.

"This rapid change in sperm speed is caused by differences in seminal fluid, not the sperm themselves. At present, we still don't know what component of seminal fluid is involved," he said in the report.

"In other words, the adjustment of sperm velocity altered male reproductive success and therefore fitness," Bartlett added.

The study showed that sub-dominant males had faster-swimming sperm compared to dominant ones. The sperm incubated in the seminal fluid of sub-dominant males fathered more eggs than sperm incubated in the seminal fluid of dominant males.

According to the team, the males that are socially dominant have good mating positions near females. They put resources into chasing away the socially sub-dominant males. Therefore, the sub-dominant males have to speed up their semen in order to fertilize more eggs.

"When we did competitive fertilization experiments, we raced sperm from two males to see who fertilized the greatest amount of eggs. Those males with fast sperm fertilized more eggs, and the seminal fluid from males with fast sperm sped up the sperm of other males," said Patrice Rosengrave, a member of the team.

"Taken together, our results provide novel insight into the evolution of male reproductive biology," said Bartlett.