Effects of increased viscosity on the movements of some invertebrate spermatozoa.

In the wave pattern of a flagellum generating planar undulatory bending waves, bending and unbending are represented by rather abrupt transitions between bent and unbent states (Brokaw & Wright, 1963; Brokaw, 1965). The magnitude of these transitions is indicated by the radius of curvature of the bent regions of the wave pattern, but their detailed time course cannot be resolved. The propagated bending waves required for propulsion are generated by the progression of these transitions along the flagellum. Bending and unbending require internally generated bending moments sufficient to overcome any internal resistances to bending and the external resistance imposed by viscous drag forces as the flagellum moves through its surrounding medium. The bending moment required to overcome the external viscous drag and the work done by this moment can be calculated in terms of wave parameters and viscous drag coefficients (Brokaw, 1965). The present experiments were undertaken to examine the changes in wave parameters resulting from alterations in the viscous drag coefficients, in an attempt to provide a more detailed characterization of the mechanisms for generating and controlling bending and unbending. Spermatozoa of three species of marine invertebrates were examined under the same conditions previously used to study their normal movements, except that the viscosity of the sperm suspensions was increased by the addition of methyl cellulose. To assist the interpretation of the different results obtained with the spermatozoa of different species, additional experiments were carried out in the presence of thiourea, an inhibitor of motility which reduces the beat frequency, and with glycerinated spermatozoa, where the beat frequency can be controlled by the concentration of adenosine triphosphate used for reactivation of their movements.