Xenopus spermatozoon: correlation between shape and motility.

Xenopus spermatozoa have a characteristic corkscrew-shaped head and a flagellum with a conventional "9 + 2" structure (Bernardini et al.: J Ultrastruct Md Struct Res: 94:188-194. They are motile in water and media of low osmolarities, but not in media of osmolarities higher than 200 mosm/liter, regardless of the ionic composition. External calcium and pH are not involved in the inhibition of sperm movement at high osmolarities. The duration of sperm motion was less than 10 min, and both flagellar beat frequencies and sperm velocities declined progressively. However, in demembranated and reactivated tails, flagellar beating was sustained for longer times. Flagella propagated three-dimensional waves that induced a spinning motion of the whole spermatozoon. This pattern of movement is not dependent on the shape of the sperm head, since isolated, reactivated flagella exhibited three-dimensional waves.