Soley J T
Department of Anatomy, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.
Onderstepoort J Vet Res. 1993 Jun;60(2):119-30.
The origin and relationships of the tinamous (Order Tinamiformes), ratites (Order Struthioniformes, Rheiformes, Casuariiformes, Apterygiformes) and birds of the order Galliformes and Anseriformes is the subject of much debate and it has been suggested that the ultrastructural analysis of a wide variety of avian sperm may provide information relevant to this problem. This paper describes the fine structure of ostrich sperm and compares the results with published information for other non-passerine birds. Ostrich sperm display a short, conical acrosome which covers the tapered tip of the long, cylindrical nucleus. A nuclear invagination housing an acrosomal rod extends deep within the karyoplasm. A centriolar complex is situated beneath the head and consists of a short proximal centriole and a long (3.0 microns) distal centriole which extends the complete length of the midpiece. The central cavity of the distal centriole contains a pair of microtubules embedded in a rod of electron-dense material. The midpiece is surrounded by a mitochondrial sheath. Concentrations of fine granular material are present between the mitochondria. The principal-piece of the tail is demarcated from the midpiece by a distinct annulus and characterized by a ribbed fibrous sheath enclosing a typical axoneme. Rudimentary coarse fibres are observed between the fibrous sheath and the doublet microtubules of the axoneme in the proximal region of the principal-piece. The end-piece contains a disorganized collection of axonemal microtubules. Ostrich sperm differ in a number of respects from that of other non-passerine birds (the absence of a typical perforatorium; the presence of a ribbed fibrous sheath; a deep nuclear invagination; the structure and length of the distal centriole) but show a close similarity to sperm of the rhea and crested tinamou, both representatives of primitive avian families. These observations add further support to the theory that the ratites and tinamous constitute a monophyletic group. The evidence presented also reinforces the hypothesis that the ratites were the first group to branch off from the main avian stem, to be followed by the Galliformes & Anseriformes. Although it was impossible to determine whether the sperm of the tinamou are more "primitive" than those of the ostrich or rhea, it is clear that ostrich and rhea sperm are closely allied and distinct from tinamou sperm.
䳍形目（䳍科）、平胸总目（鸵鸟目、美洲鸵鸟目、鹤鸵目、几维鸟目）以及鸡形目和雁形目的起源与亲缘关系一直是备受争议的话题，有人提出对多种鸟类精子进行超微结构分析可能会为解决这一问题提供相关信息。本文描述了鸵鸟精子的精细结构，并将结果与已发表的其他非雀形目鸟类的信息进行了比较。鸵鸟精子的顶体短而呈锥形，覆盖着长圆柱形细胞核的锥形尖端。一个容纳顶体杆的核内陷深入核质内部。一个中心粒复合体位于头部下方，由一个短的近端中心粒和一个长（3.0微米）的远端中心粒组成，远端中心粒延伸至中段的全长。远端中心粒的中央腔包含一对嵌入电子致密物质杆中的微管。中段被线粒体鞘包围。线粒体之间存在细颗粒物质的聚集。尾部的主段通过一个明显的环与中段区分开来，其特征是有一个带肋的纤维鞘包围着一个典型的轴丝。在主段近端区域的纤维鞘和轴丝的双联体微管之间观察到残留的粗纤维。末段包含一团杂乱无章的轴丝微管。鸵鸟精子在许多方面与其他非雀形目鸟类不同（没有典型的穿孔器；存在带肋的纤维鞘；核内陷深；远端中心粒的结构和长度），但与美洲鸵鸟和凤头䳍的精子非常相似，它们都是原始鸟类家族的代表。这些观察结果进一步支持了平胸总目和䳍形目构成一个单系类群的理论。所提供的证据也强化了这样一种假设，即平胸总目是第一个从主要鸟类谱系中分支出来的类群，随后是鸡形目和雁形目。尽管无法确定䳍的精子是否比鸵鸟或美洲鸵鸟的精子更“原始”，但很明显鸵鸟和美洲鸵鸟的精子关系密切，且与䳍的精子不同。
