Sperm Guidance in Non-mammalian Species
Sperm guidance in non-mammalian species is performed by chemotaxis. The oocyte secretes a chemoattractant, which, as it diffuses away, forms a concentration gradient: a high concentration close to the egg, and a gradually lower concentration as the distance from the oocyte is longer. Spermatozoa can sense this chemoattractant and orient their swimming direction up the concentration gradient towards the oocyte. Sperm chemotaxis was demonstrated in a large number of non-mammalian species, from marine invertebrates (Cosson, 1990; Miller, 1985) to frogs (Al-Anzi and Chandler, 1998).
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