MANY species鈥� sperm make a beeline to fertilise an egg 鈥� but not that of sea urchins, and now we know why.
Sea urchin eggs release an attractant chemical to lure sperm towards them, but currents in the water disperse the signal. Ben Friedrich and Frank J眉licher of the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, used models to show that a helical swim pattern allows the sperm to sample its chemical surroundings in a way that enables it to take the motion of the water into account (New Journal of Physics, ).
Once the chemical is detected, the sperm follow the concentration gradient to the egg. They may have to make more than one turn before reaching the correct trajectory: 鈥淲hat matters in the end is the averaged direction after several circular turns,鈥� Friedrich says.
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