TEMKIN, , M.H.: A Comparison of Gymnolaemate Bryozoan Sperm Waveform Dynamics

Sperm waveform dynamics are compared between two gymnolaemate bryozoan species, Membranipora membranacea and Thalamoporella floridana. M. membranacea spawns spermatozeugmata, sperm aggregates of 32 or 64 cells. In contrast, T. floridana releases sperm as individuals into the water column. Spermatozeugmata of M. membranacea generate at least four types of waveforms even though sperm in aggregates are tightly bound to one another long most of their lengths. Three of the four types of waveforms generate enough force to move spermatozeugmata. Type II and type IV waveforms move spermatozeugmata in a forward direction (heads first), whereas type III waveforms move spermatozeugmata in a backward direction (tail first). The underlying waves of type I and type II waveforms propagate from the head to the tail of spermatozeugmata whereas the waves of type III and IV waveforms propagate from the tail to the head of spermatozeugmata. The tail to head waves generated during type IV waveforms cause the anterior portions of spermatozeugmata to undergo movements functionally similar to the effective stroke/recovery stroke of a cilium. Unlike the spermatozeugmata of M. membranacea, the sperm of T. floridana frequently generate a flexing motion that reorients the head end of the sperm in the water column. T. floridana sperm also generate rapid tail to head waves that move the sperm backward through the water column over short distances. The combination of reorientation and bursts of swimming produce a pattern of random movement for sperm within a parcel of water. The ability to modulate the direction of wave propagation is unusual among animal sperm, but may be typical for gymnolaemates as the sperm of M. membranacea and T. floridana both generate head to tail and tail to head waves.