The study looked at how easily sea urchin eggs can be fertilized and how likely they are to be fertilized by multiple sperm. They found that sea urchins with eggs that need fewer sperm to fertilize them are more likely to experience polyspermy, where multiple sperm fertilize one egg. On the other hand, sea urchins with eggs that require more sperm to fertilize them are less likely to experience polyspermy. This suggests that the ease of fertilization and susceptibility to polyspermy are related in sea urchins, which could lead to the evolution of gamete traits and reproductive isolation.