Werner Michael, Simmons Leigh W
Centre for Evolutionary Biology, School of Animal Biology (M092), The University of Western Australia, Crawley, WA 6009, Australia.
Naturwissenschaften. 2011 Mar;98(3):213-23. doi: 10.1007/s00114-011-0763-6. Epub 2011 Jan 29.
Sperm competition is thought to be an important selective pressure shaping sperm form and function. However, few studies have moved beyond gross examinations of sperm morphology. Sperm length is subject to sexual selection via sperm competition in the scarab beetle Onthophagus taurus. Here, the structure and ultrastructure of spermatozoa in this species were investigated using light and electron microscopy. Spermatozoa were found to be filiform, measuring about 1,200 mm in length. The sperm head consists of a three-layered acrosome and a nuclear region bearing the anterior extension of the centriole adjunct. Acrosome and nuclear regions are bilaterally symmetric, with their axes of symmetry being orthogonal to each other. Head and flagellar structures are connected by a well-developed centriole adjunct. The sperm heads are asymmetrically surrounded by accessory material and embedded into the cytoplasm of the spermatocyst cell. The accessory material is produced inside the spermatids and then transferred to the outside due to a new membrane formed around the sperm's organelles. The old spermatid membrane separates the accessory material from the cyst cell. The flagellum contains a 9+9+2 axoneme, two accessory bodies, and two mitochondrial derivatives of unequal size. The major mitochondrial derivative is significantly larger than the minor one. The axoneme is arranged in a sinusoidal manner parallel along the major mitochondrial derivative. The spermatozoa show no progressive motility when released in buffer solution which is likely to be the result of the flagellar arrangement and the structure of the major mitochondrial derivative. The cross-sectional area of the minor and the major mitochondrial derivatives show different patterns of genetic variation. The data provide the first estimates of genetic variation in sperm ultrastructure for any species, and give evidence for the persistence of genetic variation in ultrastructure required for the rapid and divergent evolution that characterizes spermatozoa generally.
精子竞争被认为是塑造精子形态和功能的一种重要选择压力。然而，很少有研究超越对精子形态的粗略检查。在粪金龟子金牛座中，精子长度通过精子竞争受到性选择的影响。在此，利用光学显微镜和电子显微镜研究了该物种精子的结构和超微结构。发现精子呈丝状，长度约为1200毫米。精子头部由三层顶体和一个带有中心粒附属物前部延伸的核区域组成。顶体和核区域是双侧对称的，它们的对称轴相互正交。头部和鞭毛结构通过发育良好的中心粒附属物相连。精子头部不对称地被附属物质包围，并嵌入精囊细胞的细胞质中。附属物质在精子细胞内产生，然后由于在精子细胞器周围形成新膜而转移到外部。旧的精子细胞膜将附属物质与囊细胞分开。鞭毛包含一个9+9+2轴丝、两个附属体和两个大小不等的线粒体衍生物。主要的线粒体衍生物明显大于次要的。轴丝以正弦方式沿着主要的线粒体衍生物平行排列。当精子在缓冲溶液中释放时，它们没有表现出渐进运动，这可能是鞭毛排列和主要线粒体衍生物结构的结果。次要和主要线粒体衍生物的横截面积显示出不同的遗传变异模式。这些数据首次估计了任何物种精子超微结构的遗传变异，并为精子一般特征的快速和多样化进化所需的超微结构遗传变异的持续性提供了证据。
