Oral Presentation The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2017

Female-induced remote regulation of sperm physiology enables eggs to ‘choose’ sperm from compatible males (#111)

Jon Evans 1
  1. University of Western Australia, Crawley, WA, Australia

Sperm chemotaxis occurs when sperm cells are guided towards an unfertilized egg by following a concentration gradient of a chemoattractant. Such chemical communication between gametes is a critical factor moderating fertilization in numerous taxa. There are currently two broad adaptive explanations for sperm chemotaxis. First, egg chemoattractants can act as a chemical ‘halo’, thereby increasing an egg’s effective target size and consequently elevating the rate of sperm-egg encounters. Second, sperm chemotaxis may help maintain species barriers (i.e. species-specific sperm attraction), especially in species where pre-mating interactions are absent and where sperm and eggs are released into the environment for external fertilization (e.g. broadcast spawning organisms such as corals and other marine invertebrates). Our recent research on the broadcast spawning mussel Mytilus galloprovincialis leads us to suggest a third, sexually selected, explanation for sperm chemotaxis. Results from a series of recent studies have shown that egg-chemoattractants can differentially regulate sperm attraction, such that sperm from genetically compatible males are consistently favoured when sperm from two or more males compete to fertilize a female’s eggs. In addition to revealing the fitness benefits associated with this form of differential sperm attraction (higher fertilization rates and improved offspring survival), our ongoing studies are beginning to uncover the physiological mechanisms underpinning the process. This work shows that eggs release (yet-to-be-identified) chemical cues that differentially regulate the sperm acrosome reaction, and is beginning to reveal clues about the genetic regulation of differential sperm attraction. Given the widespread prevalence of sperm chemotaxis across taxa with highly divergent reproductive strategies, our findings may have implications that extend beyond broadcast spawning marine invertebrates.