Reference: Biol Bull 206: 35-45. (February 2004) 2004 Marine Biological Laboratory Waveform Dynamics of Spermatozeugmata During the Transfer From Paternal to Maternal Individuals of Membranipora membranacea M. H. TEMKIN' * AND S. B. BORTOLAMI 2 1 Biologv Department, St. Lawrence University, Canton, New York 13617; and 2 Ashton Graybiel Spatial Orientation Laboratorv, Braiuleis Unirerxitv, Wait/lain, Massachusetts 02254 Abstract. Analysis of standard (60 frames/s) and high-speed (200 frames/s) video records revealed that unencap-sulated sperm aggregates (spermatozeugmata) of the gymnolaemate bryozoan Membranipora membranacea spontaneously generate at least three types of waveforms: small amplitude, large amplitude, and reverse. All three waveforms significantly differed from one another in am-plitude. Additionally, small-and large-amplitude wave-forms propagated from the base to the tip of axonemes, whereas the reverse waveform propagated from the tip to the base of axonemes. Small-amplitude waveforms, which were generated most frequently by spermatozeugmata in the paternal perivisceral coelom and in the water column after spawning, produced almost no curvature of the axoneme. Large-amplitude waveforms were produced by spermato-zeugmata in the water column and within lophophores. Re-verse waveforms were produced while spermatozeugmata moved tail-end forward through the paternal tentacles dur-ing spawning and after spermatozeugmata had contacted the intertentacular organ (ITO), a tubular structure that sperma-tozeugmata pass through to enter the maternal coelom and that eggs pass through to enter the seawater. The production of reverse waveforms by spermatozeugmata after reaching the ITO may be evidence for a behavioral response of bryozoan sperm to conspecific maternal individuals. Introduction Fertilization success for many benthic marine inverte-brates is dependent on the transfer of sperm or an aggregate Received 12 September 2003; accepted 3 November 2003. * To whom correspondence should be addressed. E-mail: mtemkinft" stlawu.edu Abbreviation: ITO, intertentacular organ. of sperm from males to females through the water column (see Franzen, 1956, 1998; Ryland and Bishop, 1993). Sperm aggregates may be either encapsulated (spermatophores) or unencapsulated (spermatozeugmata). The transfer of sperm, spermatophores, or spermatozeugmata from male to female conspecific benthic marine invertebrates may be influenced by numerous physical and biological factors. For example, water flow, population density, spawning synchrony, sperm chemoattractants, gamete longevity, and sperm motility are all factors that have been reported to increase or decrease fertilization success by altering the probability that sperm will find maternal individuals (see Ryland and Bishop, 1993; Levitan. 1995). In species that transfer sperm from males to females through the water column, fertilization success may ulti-mately depend on sperm motility and behavior once a conspecific female has been approached or contacted. For example, sperm become attached to external maternal struc-tures where they wait for eggs to be spawned, as in some sabellid polychaetes (e.g., Daly and Golding, 1977; Rouse, 1996) and some bivalves (e.g., 6 Foighil, 1985, 1989). In other species, sperm enter maternal individuals to fuse with eggs internally, as in some hydroids (see Miller, 1983), the sea cucumber Leptosynapta clarki (Sewell and Chia. 1994), the colonial ascidian Diplosoma lixterianuin (Bishop and Ryland, 1991; Burighel and Martinucci, 1994a, b), pho-ronids (see Zimmer, 1991 ), and the gymnolaemate bryozoan Membranipora membranacea (Temkin, 1994). Yet few ob-servations have been made on how sperm attach to or enter conspecific females, or on how sperm locate eggs prior to fertilization. Among gymnolaemate bryozoans, one of the most de-tailed descriptions of sperm transfer has been reported for Membranipora membranacea (Temkin, 1994). Zooids of 35
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