Ultrastructure of the spermatozoon of Myrmecocichla formicivora (Vieillot, 1881) and Philetairus socius (Latham, 1790) (Aves; Passeriformes), with a new interpretation of the passeridan acrosome

Passerine spermatozoa exhibit apomorphies that distinguish them from non‐passerine neognaths and palaeognaths. The acrosome is longer than the nucleus (excepting the suboscines, most Corvida, and a few Passerida). A perforatorium and endonuclear canals are absent. The proximal centriole is absent (except in the suboscines). The distal centriole is secondarily short, contrasting with its elongate condition in palaeognaths and Galloanserae. In the Passerida a single mitochondrial strand winds extensively along the axoneme (restricted to the anterior axoneme in suboscines and Corvida). A fibrous, or amorphous, periaxonemal sheath, seen in palaeognaths and many non‐passerines, respectively, is absent. The acrosome in Myrmecocichla formicivora and Philetairus socius is bipartite: an acrosome core is surmounted by an acrosome crest; the core is ensheathed by a layer which is a posterior extension of the crest. The acrosome helix is a lateral extension of the crest and the crest layer with (Myrmecocichla) or without (Philetairus) protrusion of material of the acrosome core into it. In M. formicivora, as in other muscicapoids, a fibrous helix is intertwined with at least the more proximal region of the mitochondrial helix. The fibrous helix is absent at maturity in Philetairus and other described passeroid spermatozoa with the possible exception of Passer italiae. In Philetairus a granular helix precedes the mitochondrial helix.     

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.     

Ultrastructure of the spermatozoon of the American Alligator,Alligator mississippiensis (Reptilia: Alligatoridae)

This study details the ultrastructure of the spermatozoa of the American Alligator, Alligator mississippiensis. American Alligator spermatozoa are filiform and slightly curved. The acrosome is tapered at its anterior end and surrounded by the acrosome vesicle and an underlying subacrosomal cone, which rests just cephalic to the nuclear rostrum. One endonuclear canal extends from the subacrosomal cone through the rostral nucleus and deep into the nuclear body. The neck region separates the nucleus and midpiece and houses the proximal centriole and pericentriolar material. The distal centriole extends through the midpiece and has 9 × 3 sets of peripheral microtubules with a central doublet pair within the axoneme that is surrounded by a dense sheath. The midpiece is composed of seven to nine rings of mitochondria, which have combinations of concentrically and septate cristae. The principal piece has a dense fibrous sheath that surrounds an axoneme with a 9 + 2 microtubule arrangement. The sheath becomes significantly reduced in size caudally within the principal piece and is completely missing from the endpiece. Dense peripheral fibers, especially those associated with microtubule doublets 3 and 8, penetrate into the anterior portion of the principal piece axoneme. The data reported here hypothesize that sperm morphology is highly conserved in Crocodylia; however, specific morphological differences can exist between species. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Ultrastructure of the unusual spermatozoon of the Eurasian bullfinch (Pyrrhula pyrrhula)

The Eurasian bullfinch spermatozoon differs from typical passeridan spermatozoa in several major respects. The mature acrosome consists of a concavo‐convex vesicle differing from the typical passeridan acrosome, which is a helical structure, is usually longer than the nucleus and has a prominent helical keel. The nucleus differs from that of other oscines in not showing a twisted cylindrical form, in being shorter, and in tending to be an elongate ellipsoid in shape. The chromatin often appears in an uncondensed form reminiscent of a spermatid and consists of discrete fascicles. A small proportion of the mature sperm population however, is characterized by marked chromatin condensation. The midpiece comprises a small group of mitochondria clustered around the nuclear–axonemal junction in contrast to the single, long mitochondrion wound helically around the axoneme that is found in typical Passerida. The presence of a proximal centriole (in addition to the distal one) is a notable difference from all other oscine passerines. We suggest that the unusual morphology of the Eurasian bullfinch spermatozoon, resembling that of a spermatid, is the result of the progressive suppression of the final stages of spermiogenesis and is associated with the likelihood that sperm competition is infrequent in this species.     

An ultrastructural comparative study of the sperm of<Emphasis Type="Italic"> Hyla pseudopseudis</Emphasis>,<Emphasis Type="Italic"> Scinax rostratus</Emphasis>, and<Emphasis Type="Italic"> S. squalirostris</Emphasis> (Amphibia: Anura: Hylidae)

We make detailed comparisons of the ultrastructure of the spermatozoon among three species of the family Hylidae, Hyla pseudopseudis, Scinax rostratus, and S. squalirostris. The acrosome complex consists of two conical structures covering the nuclear rostrum, the acrosome vesicle, and the subacrosomal cone. The nucleus has a moderately condensed chromatin with a conical shape in longitudinal sections and a circular shape in cross-sections. In H. pseudopseudis, mitochondria are numerous and circular, and in S. rostratus and S. squalirostris there are fewer mitochondria that are more elongate in longitudinal and transverse sections. In H. pseudopseudis, the mitochondrial collar starts adjacent to the distal centriole, occupying the whole midpiece, whereas in both Scinax species the mitochondrial collar starts only at the posterior one-third of the midpiece. In both Scinax species, the presence of juxta-axonemal fiber, axial sheath, and axial fiber in the tail are seemingly plesiomorphic characters, widespread among bufonoid frogs. In H. pseudopseudis, however, the absence of axial fiber and axial sheath seems to be derived from the typical bufonoid condition. The differences between Hyla and Scinax sperm endorse the separation of the two genera and suggest that sperm ultrastructure can be a useful tool to investigate relationships at the intrafamily level.     

The ultrastructure of the spermatozoon of Haplotaxis ornamentus (Annelida,Oligochaeta, Haplotaxidae) and its phylogenetic significance

Summary The spermatozoon of Haplotaxis ornamentus has characteristics common to all oligochaete sperm: filiform; primary acrosome vesicle carried on an acrosome tube and containing an axial rod (perforatorium) in an invagination (subvesicular space or secondary acrosomal invagination); an elongate, highly condensed cylindrical nucleus followed by a cylindrical midpiece of radially adpressed mitochondria not penetrated by the axoneme; a single (distal) centriole persistent, though modified, at maturity; axoneme with 9 doublets, each with two outer glycogen granules, and centrally two singlets accompanied by two solid fibres. A peculiar haplotaxid combination of characters (none unique) is slight withdrawal of the primary vesicle into the acrosome tube with a strongly emergent capitulate axial rod and moderately short midpiece. This ultrastructure is consistent with location of the Haplotaxidae at the base of the Haplotaxida (Haplotaxina — Alluroidina — Moniligastrina — Lumbricina). Tubificida sperm, although also plesiomorph for the Oligochaeta, have the autapomorphy elongate periaxial sheath (secondary tube), excepting the Phreodrilidae whose sperm show convergent resemblances to the Lumbricina. The term annuloid has been introduced for annulus-like structures of varied origins.     

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.     

Components and development of the centriolar complex during and beyond spermiogenesis in a passeridan bird, the Masked weaver (Ploceus velatus)

The fate of the proximal centriole in passeridan birds is an area of controversy and relative lack of knowledge in avian spermatogenesis and spermatology. This study examines, for the first time, spatiotemporal changes in the centriolar complex in various phases of spermiogenesis in a passerine bird, the Masked weaver (Ploceus velatus). It also describes the configuration of the centriolar complex and the relationship between it and the granular body in both intra- and extra-testicular spermatozoa. It is shown that the proximal centriole is retained and attaches, at its free end, to the granular body of spermatids in every step of spermiogenesis, as well as in mature intra-testicular and post-testicular spermatozoa, including those in the lumen of the seminal glomus. As the centriolar complex, along with its attached granular body, approaches the nucleus in the early spermatid, the proximal centriole articulates with the distal centriole at an acute angle of about 45°, and thereafter, both centrioles, still maintaining this conformation, implant, by means of their articulating proximal ends, at the implantation fossa of the nucleus. In the mature spermatid and spermatozoon, the granular body winds itself helically around the centriolar complex in the neck/midpiece region of the cell, and, thus, becomes the granular helix. The significance of this observation must await future studies, including possible phylogenetic re-evaluation and classification of birds.     

The Ultrastructure of the Spermatozoa of Squamata—I. Scincidae,Gekkonidae and Pygopodidae (Reptilia)

Abstract Squamate autapomorphies seen in sperm of the Scincidae (e.g. Ctenotus robustus, Carlia pectoralis, Cryptoblepharus virgatus, and Lampropholis delicata) are penetration of the fibrous sheath of the axoneme into the midpiece, and the paracrystalline subacrosomal cone. Sphenomorphus group spermatozoa (e.g. Ctenotus) and the Egernia group (Tiliqua) differ from the more derived Eugongylus group (C. virgatus, L. delicata and C. pectoralis) in that the acrosome is elongate and apically depressed; the perforatorium is strongly oblique; the midpiece is relatively short, with four dense ring structures in longitudinal succession; mitochondria are columnar; and enlarged peripheral fibres 3 and 8 do not show the gross anterior enlargement seen in Carlia and Lampropholis. Heteronotia binoei (Gekkonidae) sperm have no epinuclear electron-lucent region; nuclear shoulders are smooth, as in sphenomorph but not Eugongylus group skinks; mitochondria are columnar; unlike skinks, the median surfaces of the mitochondria are indented by triangular, sometimes longitudinally, interconnected dense bodies. In Lialis burtonis (Pygopodidae) sperm, the perforatorium extends virtually to the tip of the fore-shortened apically domed acrosome; nuclear shoulders are absent; the mitochondria alternate singly or in groups with one or more dense bodies which also form an interrupted collar around the distal centriole. Spermatozoal ultrastructure suggests that a common ancestry of snakes and pygopods deserves consideration.     

Complex spermatozoon of the live-bearing half-beak,Hemirhamphodon pogonognathus (Bleeker): Ultrastructural description (Euteleostei,Atherinomorpha, Beloniformes)

The spermatozoon of Hemirhamphodon pogonognalhus shows modifications that are frequent though not obligate in internally fertilizing sperm, notably elongation of the nucleus and extension of the mitochondria of the midpiece as an elongate sheath around the proximal region of the axoneme. These similarities to poecilid and jenynsid sperm are considered homoplasic. As in the mature sperm of all but one investigated teleost, an acrosome is absent. The elongate, blade-shaped, electron-dense nucleus has a mean length of 3.2 μm; its basal implantation fossa, less than one-tenth of the length of the nucleus, houses the anterior half of the distal and only centriole (of triplet construction with satellite rays), a centriolar plug, and a mass connecting the centriole to the wall of the fossa. A unilateral putative centriole adjunct is present. The anterior region of the axoneme is surrounded by a mitochondrial sleeve, and internal to this, separated by a cisterna, by a submitochondrial sleeve. The mitochondrial sleeve unites posteriorly with the submitochondrial sleeve. Between the submitochondrial sleeve and the axoneme is a space, the cytoplasmic canal, that is open to the exterior posteriorly. The discrete, cristate mitochondria, in their sleeve, are unique in investigated atherinomorph sperm in being bilateral, grouped on only two opposing sides of the axoneme, with an arc-shaped ‘intermitochondrial link’ between. The 9 + 2 flagellum is unique for the Animalia in having 23 radial subplasmalemmal rods, repeated longitudinally (periodicity 0.025 pm) in a quasicrystalline array. Internal fertilization is deduced to have arisen in the Exocoetoidei independently of that in the Cyprinidcntiformes.     

Structural features of the spermatozoon of a passeridan bird,the Carib grackle,Quiscalus lugubris

The spermatozoon of the Carib grackle, Quiscalus lugubris, a member of the family Icteridae, is generally similar in organization to the passerine-type of spermatozoon, in being highly elongated and displaying a helical structure of the acrosome, nucleus and principal piece of the tail. There are subtle variations in acrosomal structural features between this organelle in the grackle and that in some of the very few passerine species of birds in which the spermatozoon has been studied. The proximal centriole is present, and, thus, the Carib grackle is the third passeridan bird in which this organelle, hitherto regarded as absent in passerine birds, has been described in the spermatozoon. The spermatozoon of this bird also possesses a granular helix, which feature has been found variably even in the scanty available reports on passerine spermatozoa. It is advocated that the spermatozoon be studied in many more species of this large clade of birds. This report provides a basis for the study of spermiogenesis in the Carib grackle, with the aim of exposing, inter alia, a number of developmental features and processes of certain organelles that have received attention, recently, in the spermatozoa of passerine birds.     

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).     

Ultrastructural study of spermiogenesis and the testicular and spermathecal spermatozoon of the Gonochoristic Tardigrade Xerobiotus pseudohufelandi (Eutardigrada,Macrobiotidae)

This paper investigates by scanning and transmission electron microscopy spermiogenesis and spermatozoon morphology of the gonochoristic eutardigrade Xerobiotus pseudohufelandi (Macrobiotidae). During spermiogenesis clusters of spermatids are connected by cytoplasmic bridges that persist up to an advanced stage of maturation. Spermiogenesis is characterized by distinctive modifications of the nucleus and by the differentiation of an acrosome, tail and substantial midpiece. Testicular spermatozoa are folded with the hinge located between the head and midpiece, thus resembling a nut-cracker. The head includes a rod-shaped, bilayered acrosome and an elongated, helicoidal nucleus with condensed chromatin. The large kidney-shaped midpiece has hemispherical swellings/ovoid elements surrounding the centriole and an incomplete mitochondrial sleeve. The flagellum contains a ‘9+2’ axoneme and terminates in a tuft of microtubules. Spermathecal spermatozoa always have linear profiles. The acrosome and nucleus have the same morphological pattern as in testicular spermatozoa, whereas the midpiece is thin and lacks the hemispherical swellings, and the tail is reduced to a short stub. Functional considerations are presented, based upon this different morphology. Moreover, phyletic comparisons are made on the basis of sperm morphology, both for the family Macrobiotidae and the class Eutardigrada. J. Morphol. 234:11–24, 1997. © 1997 Wiley-Liss, Inc.     

An Ultrastructural Study of the Spermatozoa from Prionospio cf. queenslandica and Tripolydora sp.: Two Spionid Polychaetes with Different Reproductive Methods

The fine structure of the spermatozoa of two spionids is described. The spermatozoon of Prionospio cf. queenslandica is typical of an animal utilizing external fertilization, in having a subspheroidal nucleus, a midpiece composed of unmodified rounded mitochondria surrounding two centrioles and a free flagellum. The acrosome is unusual in showing bilateral symmetry. The spermatozoon of Tripolydora sp. resembles that of spionids utilizing spermatophores, in possessing an extremely elongate nucleus and midpiece. The nucleus is penetrated by the 9+2 axoneme for its entire length, linking with a single centriole at the anterior end. Platelets surround the nucleus and intermingle with the mitochondria of the midpiece, which terminates with an annulus. The acrosome shows some internal vesiculation and substructuring. Sperm structure in relation to reproductive methods is discussed and the view of external fertilization as primitive is questioned.     

Fine structure of the spermatozoon of the viviparous teleost, Cymatogaster aggregata

The approximately 50 μm long sperm of Cymatoguster aggregata is composed of an elongate head (4 μm), an elongate mitochondria1 midpiece (3.5 μm) and a tail flagellum (roughly 40 μm). The sperm lacks an acrosome. Contained within depressions on one surface of the compressed head are a proximal centriole and a distal centriole separated by an electron dense, intercentriolar body. The anterior portion of the tail flagellum originates at the basal body (distal centriole) and is contained within an extracellular, flagellar tunnel within the mitochondria1 midpiece. The morphological similarity of C. uggregutu sperm to sperm of other internally fertilizing fishes supports the hypothesis that spermatozoan morphology is related to the mode of fertilization and that an elongate head and midpiece are specializations for internal fertilization.     

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     

Ultrastructure of spermatogenic cells and spermatozoa in Hoplias malabaricus (Teleostei, Characiformes, Erythrinidae)

The differentiation of spermatids in Hoplias malabaricus is characterized by chromatin compaction, flagellum development, nuclear rotation, nuclear fossa formation, and excess cytoplasm elimination. In the resulting spermatozoon, the head is round and the nucleus contains chromatin compacted in thick filaments, peripherically arranged, to a central electron-lucent area. The acrosome is absent. The nuclear fossa is eccentric but not pronounced. The proximal centriole penetrates it and is oblique to the flagellum. The long midpiece has several converging elongate vesicles, forming membranous hoops in the initial segment of the flagellum, but has no cytoplasmic channel. The mitochondria are elongate and branched or C-shaped and located around the initial segment of the axoneme. The lateral flagellum does not show lateral projections. The ultrastructural characteristics of H.malabaricus spermatozoa are similar to the Cypriniformes.     

Spermatozoa morphology and ultrastructure in Nile perch,Lates niloticus (Linnaeus, 1758)

Lates niloticus is a valuable commercial fish species with good potential for aquaculture. However, there is limited information on the type and structure of the Nile perch spermatozoon, which could potentially aid in culture of this species. Here, we describe the spermatozoon ultrastructure in L. niloticus using transmission and scanning electron microscopy. The spermatozoon had a round head-shape, medio-laterally flat, no acrosome, a short midpiece located laterally to the nucleus, uniflagella with one wing. The head of the spermatozoon contained the nucleus, centriolar system, proximal part of the flagellum, and cytoplasmic channel. Centrioles were arranged at an angle of 90° to each other, forming a T-shape, parallel to the nucleus. The midpiece was cylindrical, loaded with cytoplasm, five to seven spherical mitochondria; and the flagellum’s plasma membrane extended to form one lateral wing. The spermatozoa were classified as type II spermatozoa. L. niloticus spermatozoon differed from that of its Australian congener L. calcarifer, especially in the centriole arrangement and nuclear shape, length of the midpiece and the number of mitochondria and lateral wings.