Ultrastructure of the spermatozoon of Apus apus (Linnaeus 1758), the common swift (Aves; Apodiformes; Apodidae), with phylogenetic implications

The spermatozoon of Apus apus is typical of non‐passerines in many respects. Features shared with palaeognaths and the Galloanserae are the conical acrosome, shorter than the nucleus; the presence of a proximal as well as distal centriole; the elongate midpiece with mitochondria grouped around an elongate distal centriole; and the presence of a fibrous or amorphous sheath around the principal piece of the axoneme. The perforatorium and endonuclear canal are lost in A. apus as in some other non‐passerines. All non‐passerines differ from palaeognaths in that the latter have a transversely ribbed fibrous sheath whereas in non‐passerines it is amorphous, as in Apus, or absent. The absence of an annulus is an apomorphic but homoplastic feature of swift, psittaciform, gruiform and passerine spermatozoa. The long distal centriole, penetrating the entire midpiece, is a remarkably plesiomorphic feature of the swift spermatozoa, known elsewhere only in palaeognaths. The long centriole of Apus, if not a reversal, would be inconsistent with the former placement of the Apodiformes above the Psittaciformes from DNA–DNA hybridization. In contrast to passerines, in A. apus the microtubules in the spermatid are restricted to a transient single row encircling the cell. The form of the spermatozoon fully justifies the exclusion of swifts from the passerine family Hirundinidae.     

Spermatozoon structure and motility in the anuran Lepidobatrachus laevis

Synthetic human gonadotropin releasing hormone (GnRH) injections were used for induction of spermatozoon release followed by cloacal lavage or mechanical stimulation of sperm release in Lepidobatrachus laevis . Light microscopic observations of Lepidobatrachus laevis spermatozoa indicated an acrosomal segment with a length of 4.1 μm delineated by an indentation, a nuclear region of 12.6 μm in length and a midpiece of 0.87 μm in length. The tail was 54.9 μm long by 1.35 μm wide with two lateral axial fibers and a central undulating membrane. At the electron microscopic level, the unusual tail had two complete axonemes that emanated from the distal centriole. The tail also contained two axial fibers 77 nm in diameter medial to the axonemes and was connected by an undulating membrane. An unusual accessory cell adherent to the head of the spermatozoon was noted in freshly obtained suspensions of spermatozoa. Spermatozoa with the accessory cell were motile and a subsequent loss of motility was correlated with the shedding of the accessory cell.     

Spermatogenesis of a marine snail,Littorina sitkana

Summary The fine structure of the spermatogonium, spermatocyte and spermatid of a marine snail, Littorina sitkana is described. The ring centriole (annulus) is formed from the distal centriole and it migrates to the base of the mitochondrial region where it lies in a joint-like structure which is formed by an area of invaginated plasma membrane. The distal and proximal centrioles are at first perpendicular to each other but the proximal centriole rotates to a position coaxial with the distal centriole and fuses with it. The peripheral doublet fibers are continuous between the two centrioles but the central fibers originate only in the distal centriole. The acrosome differentiates from the proacrosomal granule which is derived from a Golgi body. Microtubules, present at this stage, may assist acrosomal formation. Chromatin condensation begins with the formation of fibrous strands, then to lamellar plates which become folded and later twisted around the flagellar shaft. In the final stages the lamellae appear in cross section as concentric rings which eventually fuse to form a homogeneously dense nuclear tube.     

The ultrastructure of the spermatozoa of Epipedobates flavopictus (Amphibia,Anura, Dendrobatidae), with comments on its evolutionary significance

We describe, for the first time, the spermatozoon ultrastructure of a dendrobatid frog, Epipedobates flavopictus. Mature spermatozoa of E. flavopictus are filiform, with a moderately curved head and a proportionally short tail. The acrosomal vesicle is a conical structure that covers the nucleus for a considerable distance. A homogeneous subacrosomal cone lies between the acrosome vesicle and the nucleus. The nucleus contains a nuclear space at its anterior end, and electron-lucent spaces and inclusions. No perforatorium is present. In the midpiece, the proximal centriole is housed inside a deep nuclear fossa. Mitochondria are scattered around the posterior end of the nucleus and inside the undulating membrane in the anterior portion of the tail. In transverse section the tail is formed by an U-shaped axial fiber connected to the axoneme through an axial sheath, which supports the undulating membrane. The juxta-axonemal fiber is absent. The spermatozoon of E. flavopictus has several characteristics not observed before in any anurans, such as a curved axial fiber, absence of a juxta-axonemal fiber, and presence of mitochondria in the typical undulating membrane. Our results endorse the view that, in anurans, the conical perforatorium and subacrosomal cone are homologous and that Dendrobatidae should be grouped within Bufonoidea rather than Ranoidea.     

Sperm ultrastructure in the marine bivalve families Carditidae and Crassatellidae and its bearing on unification of the Crassatelloidea with the Carditoidea

An investigation of sperm ultrastructure in representatives of the marine bivalve families Carditidae (Carditoidea) and Crassatellidae (Crassatelloidea) reveals features o f taxonomic significance. Spermatozoa of Cardita muricata (Carditidae) and Eucrassatella cumingii, E. kingicola, Talabrica aurora (Crassatellidae) differ from the classic aquasperm type in having an elongate acrosomal vesicle and elongate nucleus. In addition, the midpiece region in these species is composed of a distinctive, and here considered t o be apomorphic. arrangement of 8 (rarely 7 or 9), tightly abutted mitochondria grouped around ii dense rod which is continuous with the distal centriole (basal body). A recognizable (i.e. triplet-substructure) proximal centriole is therefore absent in mature spermatozoa of crassatellids and carditids. This situation contrasts with the presence of an unmodified proximal centriole in the spermatozoa o f all other investigated bivalves. Observations on crassatellid and carditid spermatids indicate that the dense r o d is derived through metamorphosis of the proximal centriole. The shared and highly characteristic midpiece features of spermatozoa of the Crassatellidae and Carditidae clearly indicate ii close relationship between these families and support the unification of the Crassatelloidea and Carditoidea into a single superfamily Carditoidea Fleming. 1820 (date priority over Crassatelloidea Férussac. 1822).     

Sperm ultrastructure in the inseminating Macropsobrycon uruguayanae (Teleostei: Characidae: Cheirodontinae)

Macropsobrycon uruguayanae is a small, inseminating characid (tetra) of the tribe Compsurini. Although spermatozoa can be found within the ovarian cavity close to oocytes, the exact moment of fertilization has not yet been determined. Spermatozoa have moderately elongate nuclei with electron-dense chromatin. During spermiogenesis, nuclear rotation takes place. Elongate mitochondria with lamellar cristae are found posterior to the nucleus. Centrioles are parallel to one another with the proximal centriole slightly anterior to the longer distal one. The anterior tip of the proximal centriole is located within a shallow nuclear fossa. Electron-dense spurs are associated within the anterior and posterior ends of the distal centriole. Striated centriolar rootlets radiate both anteriorly and posteriorly from the distal centriole. Nine longitudinal accessory microtubules surround the axoneme in the proximal flagellum. The flagellum has a typical 9 + 2 axoneme with no intratubular differentiation. Atypical spermatozoa are also found in the testicular lumen. These cells resemble spermatozoa in most aspects, except that their nuclei are variable in shape, with the granular chromatin less electron-dense than that seen in spermatozoa. The origin and function of these cells could not be determined. The specializations seen in the spermatozoa are discussed as possible adaptations related to the habit of insemination.     

峨眉髭蟾精子形态结构及分类学意义

应用透射电镜、扫描电镜和光学显微镜对峨眉髭蟾(Vibrissaphoraboringii)精子的形态和超微结构研究的结果表明:峨眉髭蟾的精子具角蟾科物种精子基本的形态和结构特征,即精子头部呈螺旋状,尾部呈弯曲状;精子具锥形的顶体、纤维束构成的穿孔器、平行排列的中心粒和双轴丝;线粒体位于尾部;精子核窝不明显、无轴纤维和波动膜等特征。此外,对已有报道的角蟾科和无尾类物种精子的特征进行分析比较表明:(1)角蟾科精子细胞核呈螺旋状,中心粒平行排列,尾部具双轴丝等结构不同于无尾类其他科精子的结构,具有明显的科间差别;(2)角蟾科精子各部的量度,尾部线粒体的分布和数量,以及轴丝的排列等特征在属间和种间表现出明显的差异;(3)峨眉髭蟾和东南亚拟髭蟾指名亚种精子的形态和超微结构存在明显的差异。     

蓝尾石龙子精子的超微结构

蓝尾石龙子(Eumeces elegans)附睾以2．5％戊二醛和1％锇酸双重固定,按常规制作超薄切片,用H-600透射电镜研究观察精子的超微结构。精子由头部和尾组成,头部由顶体复合体和核组成,尾由颈段、中段、主段和末段组成。头部的顶体囊前部扁平,分为皮质和髓质,顶体下锥由类结晶状的顶体下物质组成,穿孔器顶端尖,、穿孔器基板塞子状,细胞核延长,核内小管缺,核伸展部前端具一电子透明区,核肩圆,核陷窝锥形。颈段具片层结构,近端中心粒和远端中心粒的长轴呈直角,9束外周致密纤维与远端中心粒相应的9束三联微管相联,向后与轴丝相应的9束双联微管相联,中央纤维与2个中央单微管相联。中段短,含有线状嵴的柱状线粒体,由连续的规则小卵状或小梯形致密体组成线粒体间的环状结构,纤维鞘伸入中段,终环紧贴于细胞膜的内表面。线粒体与环状结构的模式为：rs1／mi1,rs2／mi2,rs3／mi3,rs4／mi4,横切面上每圈线粒体数目为10个。主段前面部分具薄的细胞质颗粒区。纤维3和8至主段前端消失。轴丝复合体呈“9 2”型。蓝尾石龙子精子超微结构与已描述的石龙子科种类比较发现,与蜓蜥群和胎生群的石龙子相似;但没有发现石龙子科精子的独征。     

Spermatogenesis in the earthwormMicrochaetus pentheri (Oligochaeta,Microchaetidae)

Summary Spermatogenesis inMicrochaetus pentheri (Microchaetidae) follows the familiar pattern known for other oligochaetes. Spermatogenic stages develop around an anucleate cytophore from which they separate as mature spermatozoa. During spermiogenesis the nucleus elongates and becomes surmounted by a complex, elongate acrosome; the flagellar axoneme develops from the distal centriole. The centriole is positioned posterior to the mid-piece, which consists of six mitochondria radially adpressed to form a cylinder about 2 m long.Microchaetus shows many plesiomorphic features in the structure of its acrosome, which are also seen in two other taxa of the Diplotesticulata,Haplotaxis (Haplotaxidae) andSparganophilus (Sparganophilidae, Aquamegadrili), each of which has the greatest number of plesiomorphies in spermatozoal characters in its group. The Aquamegadrili constitute the sister-group of the Terrimegadrili which contain the earthworm families including the Microchaetidae. The numerous symplesiomorphies in spermatozoal characters do not, however, establish monophyly of microchaetids with haplotaxids and sparganophilids. An apomorphy in the acrosome ofMicrochaetus is its greater length (3.8 m vs less than 1 m inHaplotaxis and 1.5 m inSparganophilus), in this respect resembling other investigated terrimegadriles, the lumbricids, hormogastrids and megascolecids. The axial rod of the acrosome ofMicrochaetus appears apomorphic relative to that ofHaplotaxis, Sparganophilus, lumbricids and megascolecids in lacking an anterior expansion, the capitulum. It ends posteriorly in a cylindrical body, somewhat resembling the node diagnostic of the axial rod of megascolecid earthworms.     

The Ultrastructure of the Spermatozoa of Three Species of Myobatrachid Frogs (Anura,Amphibia) with Phylogenetic Considerations

Comparison of the spermatozoa of three genera of limnodynastines (Myobatrachidae: Anura) with those of 42 other species of frogs (in 11 families) previously examined allows the following phylogenetic inferences. The bufonoid neobatrachians (corresponding with the Arcifera of some classifications) form a monophyletic assemblage which is characterized by the possession, unique for the Anura, of a conical perforatorium; the rod-like perforatorium, which is plesiomorphic for tetrapods, is absent. Of the taxa investigated, the myobatrachids appear to be the sister-group of the remaining bufonoids, here termed eubufonoids (leptodactylids, rhinodermatids, hylids, and bufonids). The spermatozoa of the myobatrachids Limnodynastes, Neobatrachus, and Mixophyes are very similar to each other despite extremely varied fertilization biology. Symplesiomorphies for the Anura which they exhibit include the conical acrosome with subacrosomal material, the elongate, cylindrical nucleus, single flagellum and, paralleling this, an undulating membrane which is supported by a longitudinal element, the axial (major) fibre, the latter being accompanied in the midpiece by mitochondria. A myobatrachid synapomorphy appears to be the presence of a periaxial sheath enclosing the axial fibre of the flagellum. Forward extension of the axial fibre into the centriolar fossa in myobatrachids is seen elsewhere only exceptionally (in the bufonid Nectophrynoides). Bufonids, and most other eubufonoids including leptodactylids, differ apomorphically from Limnodynastes, and Neobatrachus in location of the mitochondria at the axonemal end (and in a collar) rather than the axial fibre end of the undulating membrane. In Mixophyes, mitochondria surround the nuclear-axonemal junction in a cytoplasmic droplet and are probably shed with this at maturity.     

中国石龙子成熟精子的超微结构

利用透射电镜观察中国石龙子附睾成熟精子的超微结构。顶体囊前部扁平、由皮质和髓质组成 ,穿孔器中度倾斜、顶端尖 ,穿孔器基板塞子状 ,细胞核长形 ,核内小管缺 ,核前电子透亮区小 ,核肩圆 ,核陷窝锥形。颈段具片层结构 ,近端中心粒和远端中心粒的长轴呈直角 ,9束外周致密纤维与远端中心粒相应的 9束三联微管相联 ,向后与轴丝相应的 9束双联微管相联 ,中央纤维与 2个中央单微管相联。中段短 ,多层膜结构缺 ,含有线状嵴的柱状线粒体 ,不规则卵状致密体组成不连续的环状结构 ,纤维鞘伸入中段 ,具终环。线粒体与环状结构的模式为 :rs1 /mi1 ,rs2 /mi2 ,rs3/mi3,rs4 /mi4。主段前面部分具薄的细胞质颗粒区。纤维 3和 8至主段前端消失。轴丝呈“9 2”型。中国石龙子精子超微结构具有塞子状的穿孔器基板、致密体形成不连续的环状结构和纤维鞘始于ms2等特征与巨石龙子群和蜓蜥 -胎生群不同。没有发现石龙子科精子的独征     

Sperm ultrastructure and spermiogenesis in two Exogone species (Polychaeta, Syllidae, Exogoninae)

Abstract. The spermatozoa of Exogone naidina and E. dispar are characterized by a prominent bell-shaped acrosome, a spheroidal nucleus, and a conventional flagellum. During spermiogenesis, the acrosomal vesicle undergoes conspicuous modifications leading to its final bell shape with a posterior opening. The subacrosomal material initially shows radiating filaments but in mature sperms it appears as a meshwork of electron-opaque material. The acrosomal axis is oblique with respect to the main longitudinal sperm axis. The chromatin is arranged in electron-opaque strands in the early spermatids, then becomes amorphous, and is finally organized in filaments in mature sperms. Centrioles are orthogonally arranged beneath the nucleus and fibers radiate from the distal centriole to contact the plasma membrane and the single mitochondrion. The latter is located eccentrically on the side of the nucleus opposite the acrosome. A disk-shaped structure is evident beneath the distal centriole. The flagellar axoneme has a 9+2 microtubule pattern. A conspicuous glycocalyx surrounds the flagellar plasma membrane, and an electron-lucent space is present between these two structures at the distal tip of the flagellum. We compare the sperm morphology of these two species of Exogone with that described in other members of the subfamily Exogoninae. The fine structure of these two species supports the occurrence of an ent-aquasperm type within Exogoninae, in accordance with the brood strategy present within this subfamily. The mode of reproduction is of taxonomic importance for defining subfamilies within Syllidae, and is likely also of phylogenetic significance. Because epitoky is probably plesiomorphic, the ent-aquasperm type found in Exogoninae can be considered a derived feature within Syllidae.     

Ultrastructure of the spermatid of Caprimulgus europaeus Linnaeus 1758, the European nightjar (Aves; Caprimulgidae), with phylogenetic implications

The sperm of Caprimulgus europaeus is typical of other nonpasserines in many respects. Features shared with Paleognathae and Galloanserae are the conical acrosome, shorter than the nucleus; the presence of a perforatorium and endonuclear canal; the presence of a proximal as well as distal centriole; the elongate midpiece with mitochondria grouped around a central axis (here maximally six mitochondria in approximately 10 tiers); and the presence of a fibrous or amorphous sheath around the principal piece of the axoneme. A major (apomorphic) difference from paleognaths and galloanserans is the short distal centriole, the midpiece being penetrated for most of its length by the axoneme and for only a very short proximal portion by the centriole. Nonpasserines differ from paleognaths in that the latter have a transversely ribbed fibrous sheath, whereas in nonpasserines it is amorphous, as in Caprimulgus, or absent. The absence of an annulus is an apomorphic feature of Caprimulgus, apodiform, psittaciform, gruiform, and passerine sperm, homoplastic in at least some of these. In contrast to passerines, in Caprimulgus the cytoplasmic microtubules in the spermatid are restricted to a transient longitudinal manchette. The structure of the spermatid and spermatozoon is consistent with placement of the Caprimulgidae near the Psittacidae, but is less supportive of close proximity to the Apodidae, from DNA-DNA hybridization and some other analyses.     

Structure and formation of the unusual sperm of Patelloida latistrigata (Mollusca : Patellogastropoda): implications for fertilization biology

The structure of the spermatozoa and spermatogenesis of the lottiid limpet Patelloida latistrigata is described by transmission electron microscopy. Although the lengths of the spermatozoa (about 60 μm) and their head region (about 12 μm) are similar to those of other patellogastropods, the structure of the sperm head and midpiece are very different. The head consists of an unusually large acrosome (about 11-μm long) with a broad posterior invagination that houses the relatively small nucleus. The midpiece mitochondria, which are rather elongate with large folded tubular cristae, are housed in a cytoplasmic sheath posterior to the nucleus. The proximal centriole is unusually elongate (about 2-μm long). The axoneme that emerges from the distal centriole is surrounded anteriorly by the cytoplasmic sheath in which the cytoplasmic side of the plasma membrane has electron-dense material. The flagellum is enlarged at its terminal end. Spermatogenesis is similar to that described for other patellogastropods. Patelloida latistrigata, therefore, has spermatozoa that seem to meet the morphological criteria of ent-aquasperm, which raises the question of whether fertilization is truly external in this limpet. However, it is also possible that the modifications to the sperm are linked to unknown specializations of the egg or egg envelope.     

THE STRUCTURE AND FUNCTION OF CENTRIOLES AND THEIR SATELLITES IN THE JELLYFISH PHIALIDIUM GREGARIUM

Testes of jellyfish Phialidium gregarium were fixed in 2 per cent OsO₄ in Veronal-acetate buffer at pH 7.4. Thin sections showed that in young spermatids the spindle fibers of the last maturation division are attached to satellites of the filament-forming centriole. In more mature spermatids this attachment is not observed. During the developmental phase, nine satellites can be observed emanating from the interspaces between the nine tubular triplets of this centriole. A circular region on each of the enlarged distal ends of the satellites attaches them to the cell membrane. The satellites apparently provide a firm anchor for the axial filament. Each of the epithelial cells covering the testis produces a single long flagellum. On the filament-forming centriole often a satellite can be observed to which tubules are attached. These tubules are 180 A in diameter and probably represent remnants of spindle fibers. It is suggested that the distal centriole has the ability to form several satellites or appendages at appropriate times during the cell cycle. These satellites are distinct from the daughter centrioles in that they are supportive structures: in certain phases of cell life, spindle fibers may attach to them, while in other instances the distal centriole and the flagellum it is forming are anchored by them.     

Neck region of gerbil spermatozoa

In the course of the reorganization and degeneration of the proximal centriole in the mature acentriolate spermatozoon of the Mongolian gerbil, both the proximal and distal centrioles appear in the early cap phase of spermatid development. During the acrosome phase, both distal and proximal centrioles become highly active in the formation of a segmented column. The proximal centriole becomes actively involved in the formation of the capitulum, while the distal centriole forms the axonemal complex and dense fibers. During the maturation phase of spermatid development, the “pinwheel” arrangement of the proximal centriole becomes an “S”-shaped structure, turned 90° on its vertical axis. The few “doublet” microtubules that can be detected later in that stage completely disappear during spermiation. The distal centriolar area develops a single central pair of microtubules and membranous elements. Another prominent feature in the neck region of the gerbil spermatozoa is the presence of two dense rudimentary columns in association with the mitochondria. Although their density is similar to that of the other columns, these two columns have no connection with the dense fibers; in fact, they are closely associated with the mitochondria.     

北方山溪鲵精子发生不同阶段的显微与超微结构

用光镜和电镜观察了北方山溪鲵(Batrachuperus tibetanus)精子发生过程中各种类型生精细胞的显微与超微结构变化。结果显示,北方山溪鲵在4~8月时处于精子发生期,精子形成在7~8月。成熟精子的结构具有小鲵科精子的一些共同特征,如顶体前端呈三叶草状,尾部由轴纤维、波动膜、轴丝及轴丝旁纤维构成,轴纤维粗大呈圆柱形,尾部无线粒体等。比较分析认为,在两栖类的系统发育中,轴纤维、波动膜和轴丝旁纤维的消失为近裔性状。