Competitive males can adjust sperm speed

First past the post: New research reveals competitive males can adjust sperm speed

It’s a fish tale of a sexual nature that may impact our understanding of male fertility. A University of Canterbury doctoral researcher has discovered that male salmon can adjust their sperm’s swimming speed if competing with a rival to reproduce.

Michael Bartlett, a PhD student in the University of Canterbury’s School of Biological Sciences, says that males of many species fight to establish social dominance and control over access to females and the opportunity to reproduce.

His PhD research involves investigating the link between male social status (dominance), which reflects sperm competition risk, and sperm quality (sperm swimming speed) in chinook salmon.

“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 says.

Michael’s paper on the discovery, Sperm competition risk drives rapid ejaculate adjustments mediated by seminal fluid, will be published this month in a high impact open access journal, eLife.

His discovery contributes to a better understanding of the reproductive biology of chinook salmon, a species that is valued both commercially and culturally and is of conservation concern.

Improved knowledge of the effects that seminal fluid has on sperm function may also have important consequences for our wider understanding of male fertility, he says.

“We found that when males changed their sperm velocity (via seminal fluid) that this altered the number of eggs that they fertilised relative to a rival male. In other words, the adjustment of sperm velocity altered male reproductive success and therefore fitness.”

“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.”

“Taken together, our results provide novel insight into the evolution of male reproductive biology.”

Michael’s research was undertaken as part of a Marsden grant held by his principal supervisor Dr Patrice Rosengrave, a fellow of the University of Canterbury and a research fellow in the Department of Anatomy, University of Otago. Conservation geneticist Dr Tammy Steeves, UC School of Biological Sciences, and Professor Neil Gemmell, Department of Anatomy, University of Otago, were also involved in the study.

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