New research from the University of Washington's Friday Harbor Laboratories shows that common assumptions about sea urchin reproduction don't hold true for all species of the invertebrate creature. The work could lead to better understanding of fertilization among mammals, including the potential to solve some baffling human reproductive problems.
"The importance for people is understanding the process. People come to fertility clinics wondering why their eggs don't fertilize," said Christiane Biermann, a research associate at Friday Harbor Labs in Washington state's San Juan Islands and an adjunct biology faculty member at Portland State University in Oregon.
In some places, different sea urchin species breed at different times of the year, or they occupy different ocean depths, so there is little chance of hybrids turning up. But in other places, such as the waters off the West Coast of North America, the species breed at the same time and occupy the same waters, and still hybrids are rare.
The purple sea urchin has been the most closely studied of the urchins and for years has served as the reproduction model for all sea urchins. Like other species, purple sea urchins are free spawners females inject large clouds of eggs into the water and males do the same with sperm. Scientists found that the key to species-specific fertilization is a sperm protein called bindin connecting with the correct receptor in the plasma membrane on the surface of the egg. The sperm have to pass through a jelly-like coating, made up of complex carbohydrates, or sugars, to reach the egg surface. They react to the jelly coating by exposing the bindin protein.