Chemical cues direct sperm in healthier choice

Chemical signals secreted from unfertilised female mussel eggs have been shown to attract genetically compatible sperm.

Chemoattraction of sperm, where sperm locate unfertilised eggs by following a concentration gradient of egg-derived chemical cues, has been widely documented; but the evolutionary forces underpinning this process are yet to be understood.

Professor Jon Evans and Matthew Oliver from the University of Western Australia studied sperm-egg interactions in mussels (Mytilus galloprovincialis) and found that mussel sperm exhibit consistent but differential ‘preferences’ for chemical cues secreted from eggs from different females.

The work also reveals that these preferences predict the compatibility of sperm and eggs at fertilisation and the chances of the offspring surviving.

“We know that eggs emit chemical cues that attract sperm,” Professor Evans said. “We also know from previous studies that sperm are attracted to eggs from the same species. What this research shows is that there are differences in chemical cues from each egg and somehow the sperm is exhibiting preferences in response to those cues that leads to healthier offspring.”

The study also found that by experimentally separating the chemoattractants from eggs, sperm swimming behaviour was influenced by the particular combination of sperm and chemoattractants, and that these patterns of sperm behaviour predicted fertilisation and survival.

The researchers concluded that sperm are fine-tuned to respond to chemical cues emitted from genetically compatible eggs, thus maximising fertilisation and larval survival.

“So what we found is that there is a survival advantage for offspring of females who send out the right cues to attract the right sperm,” Professor Evans said.

The research team is now working to explore the biochemical and molecular mechanisms underlying these patterns to better understand how sperm and eggs interact in the sea.

The research has been published in the Proceedings of The Royal Society B.