We thank Thomas Horn for generous advice with sperm microscopy and Patrice Del Carmine for assistance with the rat experiments. This research was supported by a European Research Council (ERC) Advanced Grant (No. 321381) and in part by the Swiss National Science Foundation as part of the National Centre of Competence in Research (NCCR) Molecular Systems Engineering. T.K., M.Fo., and M.Fu. designed the study, analyzed the results, and wrote the manuscript. T.K., M.Fo., and M.D.‐E.B. performed the experimental work. The authors declare no competing financial interests.