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When it comes to paternity success in salmon it's the speed of sperm that counts, according to a collaborative study by researchers from The University of Western Australia and the University of Otago in New Zealand.

Lead researcher, Professor Jon Evans from the UWA Centre for Evolutionary Biology said that although sperm competition is rife among sexually reproducing species, "we know little about the factors that determine which sperm successfully fertilise eggs".

In the study published today in the Proceedings of The Royal Society B , the researchers applied a new experimental framework to an externally fertilising model in order to delineate the roles of males, females and their interactive effects on fertilisation success under competition.

The study focused on the Chinook salmon, Oncorhynchus tshawytscha, a species in which the female's ovarian fluid is thought to influence her choice for genetically compatible mates.

"Here we used competitive IVF experiments to try to explain why sperm from certain males are more successful than others in the competition to fertilise eggs.  In particular, we wanted to determine the relative influence of female effects (ovarian fluid), male-by-female interaction effects (i.e. male-female compatibility, mediated by interactions between sperm and ovarian fluid), and intrinsic differences among males in their sperm competitive abilities," Professor Evans said.

"Our results reveal no evidence for female or compatibility effects but show that sperm competition is primarily determined by male effects, largely attributable to differences in sperm swimming velocity between competing ejaculates."

"Together, these findings provide evidence that variation in paternity success can be attributed to the differences in the sperm's ability to compete against rival males, and reveal that sperm swimming speed is a key target of sexual selection."

The research has been supported under UWA's Research Collaboration Award scheme.

Both UWA and the University of Otago are members of the Matariki network of universities leading international best practice in research and education.

Media references

Professor Jon Evans (Centre for Evolutionary Biology)  (+61 8)  6488 2010
Michael Sinclair-Jones (UWA Public Affairs)  (+61 8)  6488 3229  /  (+61 4) 00 700 783