Shiba Kogiku, Shibata Daisuke, Inaba Kazuo
Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka 415-0025, Japan.
J Exp Biol. 2014 Mar 15;217(Pt 6):986-96. doi: 10.1242/jeb.095398. Epub 2013 Dec 5.
The sperm of the gastropod Strombus luhuanus show dimorphism. The eusperm have a nucleus and fertilize the egg, whereas the other type of sperm, parasperm, are anucleate and are thought to assist fertilization. Here we report the autonomous changes in the swimming pattern of S. luhuanus eusperm. In artificial seawater, the eusperm collected from S. luhuanus sperm ducts formed sperm bundles and initially swam backward with asymmetric flagellar waveforms to detach from the bundles. One hour later, the sperm began to swim forward and in a circle. After an additional 1 h incubation, the sperm swam straight, with a change in the flagellar waveforms from asymmetric to symmetric. Spontaneous backward swimming with symmetric waveforms was also observed. The eusperm stored in the female seminal receptacle were motile and showed forward symmetric swimming with spontaneous backward swimming, which appeared necessary for detachment from the wall of receptacle. All of these motility changes were observed in the absence of parasperm, suggesting that these changes autonomously occur in eusperm. Our waveform analysis of these swimming patterns revealed that only the swimming with symmetric waveform showed reverse propagation of the flagellar waveforms. Both types of backward swimming were diminished in Ca(2+)-free seawater and in seawater containing Ni(2+), indicating the regulation of swimming direction by Ca(2+)-dependent signal transduction.
腹足纲动物大砗磲的精子表现出二态性。真精子有细胞核并使卵子受精，而另一种精子，副精子，无细胞核，被认为有助于受精。在此我们报道大砗磲真精子游泳模式的自主变化。在人工海水中，从大砗磲输精管收集的真精子形成精子束，最初以不对称鞭毛波形向后游动以从束中分离。一小时后，精子开始向前游动并呈圆周运动。再孵育1小时后，精子直线游动，鞭毛波形从不对称变为对称。还观察到具有对称波形的自发向后游动。储存在雌性交配囊中的真精子具有活力，表现出向前对称游动并伴有自发向后游动，这似乎是从交配囊壁分离所必需的。所有这些运动变化在没有副精子的情况下都能观察到，表明这些变化在真精子中自主发生。我们对这些游泳模式的波形分析表明，只有对称波形的游动显示鞭毛波形的反向传播。两种类型的向后游动在无钙海水和含镍（2+）的海水中都减弱，表明游泳方向受钙依赖性信号转导的调节。
