several structures featuring a variety of hooksFor The Scientist, Natalia Mesa (@natmesanash) explored the mystery of why the sperm of most mouse species have hooks on their heads. The bigger hooks slow down the sperm as they swim — so why are they there? Some scientists point to competition between sperm as a possibility. Others wonder whether the hooks help the sperm travel through the female’s reproductive tract. For now, the function of these odd little microscopic features remains obscure. Image from Immler S, Moore HD, Breed WG, Birkhead TR (2007) By Hook or by Crook? Morphometry, Competition and Cooperation in Rodent Sperm. PLoS ONE 2(1): e170. (open access)