Functional anatomy of the sperm storage organs in Pulmonata: the simple spermatheca of Bradybaena fruticum (Gastropoda, Stylommatophora)

Data on sperm storage and paternity analyses in the pulmonate land snail Arianta arbustorum suggest that the complex, multitubular sperm storage organ, the spermatheca, may influence paternity after multiple matings. Ultrastructural investigations show that the spermatheca is provided with the morphological correlates to exert cryptic female choice. However, in order to understand the function of a multitubular spermatheca it is necessary to understand how a single spermathecal tubule functions. In order to explore the potential to serve as a model for such a simple system in future experiments, the fine structure of the unitubular spermatheca and its interaction with spermatozoa were investigated in Bradybaena fruticum, another member of the Helicoidea. The spermatheca of B. fruticum is only about one-half as long as the fertilization chamber. Its epithelium is densely ciliated throughout its length. Vacuole, Golgi complex, rough endoplasmic reticulum, various vesicles, wide intercellular spaces, and an extensive basal labyrinth indicate strong secretory activity, providing the environment for sperm storage and capacitation. Prior to transfer, sperm are characterized by a perinuclear sheath and an acrosome tilted at about 50°. In the spermatheca, the perinuclear sheath is dissolved and, probably as a consequence, the acrosome folds up in line with the nuclear longitudinal axis. The spermatheca is surrounded by a network of differently oriented smooth muscle cells, which are extensively connected with each other through dense plaques. The fine structure of the muscle cells suggests that they are neither very strong nor enduring. The main function of the spermathecal musculature is certainly expulsion of sperm prior to fertilization. The musculature around the spermathecal tubule of B. fruticum appears to be a highly integrated system not allowing for much functional flexibility compared to A. arbustorum, where the muscle cells are more individualized, permitting finely tuned operations. This restricted flexibility needs to be taken into consideration in future experiments using B. fruticum as a model for the simple, unitubular sperm storage system.     

Sperm structure and spermiogenesis in Atelura formicaria Heyden (Zygentoma, Insecta)

The spermatozoon of Atelura formicaria (Zygentoma) shows several features that are typical of insects: an apical acrosome, an elongated dense nucleus, a centriole with expanded centriolar adjunct material, two large mitochondrial derivatives, and two thin accessory bodies located beneath the nucleus. The axoneme exhibits a 9 + 9 + 2 pattern with accessory tubules formed by 16 protofilaments and intertubular material. However, spermatozoa of A. formicaria show some remarkable features. The sperm cell is short for an insect, being only 50 µm in length. The nucleus is characterized by the presence of two lateral grooves which are filled with numerous infoldings of the nuclear envelope. In a cross-section the chromatin has the configuration of the Leonardo da Vinci's 'Vitruvian man'. Each mitochondrial derivative has a peculiar structure with peripheral cristae and four crystalline bodies in its matrix; two of these crystalline bodies are large and have differently orientated cristal planes. At the end of spermiogenesis, sperm bundles are stored in the proximal part of the testes. Secretions from the epithelial wall of this region give rise to large globular structures. These include sperm bundles intermingled with dense granules, forming the so called 'spermatolophids'. These formations descend along the deferent duct and are stored in the expanded seminal vesicle. Atelura spermatozoa do not pair as in some Lepismatidae, nor do they fuse as in Tricholepidion (Lepidotrichidae). Thus, sperm aggregation in Zygentoma is realized according to different modalities and can hardly be considered as a synapomorphic trait of its subtaxa.     

Ultrastructure of the biflagellate spermatozoon of tomopteris helgolandica greef, 1879 (annelida,polychaeta)

The spermatozoon of the polychaete Tomopteris helgolandica is of an aberrant type with two flagella, each measuring about 40μm. The nucleus is roughly conical and weakly bent. At the anterior end it is rounded and covered only by the nuclear and plasma membranes. Membraneous, electron-dense structures are applied laterally to the nucleus. These structures may have a helical arrangement. The middle piece contains about ten mitochondria, two centrioles, and two centriolar satellite complexes. The centriolar regions are connected with the posterior part of the nucleus. The axonemes of the two tail flagella lack the usual central complex with central tubules, radial spokes, or related structures. No arms seem to be present on the A tubules of the doublets. In the middle piece the tail flagella are surrounded by invaginations of the plasma membrane forming flagellar canals. The sperm has a bilateral symmetry whereas the primitive sperm has a radial symmetry. The occurrence of two tail flagella in this spermatozoon has no phylogenetical connection with biflagellate spermatozoa in other animal groups. A series of mutations has resulted in the development of two flagella emerging from the two centrioles, the lack of a central complex in the axoneme, and the lack of a typical acrosome. In the Polychaeta, sperm structure is generally more related to function that to phylogenetics. During swimming the spermatozoon of Tomopteris rotates around its longitudinal axis.     

Giant sperm cells with accessory macrotubules in a neuropteran insect

The flagellar axoneme of the atypical spermatozoa (paraspermatozoa) of Mantispa perla (Neuroptera, Planipennia) contains accessory microtubules or rather macrotubules that are 55 nm in diameter and that has a wall consisting of about 40 protofilaments. The sperm tail further contains two giant mitochondrial derivatives, which during spermiogenesis store an electron dense material. The mature spermatozoon has a flattened acrosome and a elliptical nucleus. These giant spermatozoa may furnish nutrients to the functional spermatozoa (euspermatozoa) when they reach the female genital tracts or/and they function in sperm competition filling the spermatheca.     

Structure, cytoskeleton, and development of the acrosome of Platycleis albopunctata (Orthoptera: Tettigoniidae).

The acrosome of Platycleis albopunctata (Orthoptera: Tettigoniidae) is relatively large and complex, consisting of an apical vesicle and two large wing-like extensions that give the spermatozoon the shape of an arrow. The wings have actin microfilaments and microtubules and are covered with a noticeable extracellular material. Actin filaments are present in the acrosome when it first appears in spermatid stages. The acrosome and the acrosomal attachment to the nucleus are more resistant than other structures to the reducing agents DTT and SDS. At the end of spermiogenesis, groups of spermatozoa juxtapose their sperm heads and become joined to form a spermatodesm encircled by an amorphous material. Treatment with the ionophore A23187 rapidly disrupted acrosomes of the free gametes, but acrosomes from spermatozoa contained in the spermatodesm were not disassembled. Packaging of sperm in a spermatodesm appears to protect the acrosome.     

Excurrent duct system of the male turtle Chrysemys picta

The epididymis and efferent duct system of the turtle Chrysemys picta were examined. Seminiferous tubules are drained by a series of ducts that form a rete exterior to the tunica albuginea. The rete is located lateral to the testis and consists of anastamosing tubules of varying diameters, lined by a simple epithelium consisting of squamous to cuboidal cells. The rete is highly vascularized. A series of tubules (efferent ductules) connect the rete to the epididymis proper. The efferent ductules are highly convoluted, running between the epididymal tubules and are of varying diameters. The simple columnar epithelium lining these tubules possesses tight junctions, with every third or fourth cell possessing long cilia that protrude into the lumen. The cytoplasm of these epithelial cells contains abundant mitochondria. In the central portion of the efferent ductule, epithelial cells possess granules that appear to be secreted into the lumen by an apocrine process. The epididymis proper is a single, long, highly convoluted tubule that receives efferent ductules along its entire length. It is lined by a pseudostratified epithelium containing several cell types. The most abundant cell (vesicular cell) lacks cilia, but has a darkly staining apical border due to numerous small vesicles immediately beneath the luminal membrane. The small vesicles appear to fuse with each other basally to form larger vesicles. These cells appear to have an absorptive function, and occasionally sperm are embedded in their cytoplasm. The second-most abundant cell is a basal cell found along the basement membrane. The number of these cells fluctuates throughout the year, being most abundant in late summer and early fall. A small narrow cell with an oval nucleus and darkly staining cytoplasm, extending from the basement membrane to the apical surface, is present in small numbers, particularly in the caudal regions of the epididymis. This cell is frequently found in association with another narrow cell having a rounded nucleus and abundant mitochondria in its cytoplasm.     

Aflagellate sperm in three species of leptophlebiidae (Ephemeroptera)

Immotile spermatozoa of 3 species of Ephemeroptera, Habroleptoides umbratilis, Habrophlebia eldae and Choroterpes picteti (Leptophlebiidae) are described. In all 3 species, sperm present a coccoidal shape and lack flagella or microtubule systems. Habrophlebia eldae shows very atypical sperm with a roundish nucleus and scarce cytoplasm, including an apical acrosome. By contrast, a fibrillar perforatorium and a mitochondrion are present in the sperm of H. umbratilis and C. picteti. This latter species also shows electron-dense bodies located in the space between the nucleus and the cell membrane. Our findings suggest that sperm/egg interaction should depend in leptophlebiids on the contraction of the genital duct muscles.     

TELEOGRYLUS EMMA精子体外顶体反应的超微结构比较研究

采用相同种类卵水诱导的方法对直翅目,蟋蟀科,黄脸油葫芦的受精囊精子的顶体反应过程进行系统观察.发现黄脸油葫芦精子顶体反应可划分为3个阶段,第1阶段,精子质膜膨胀、断裂或丢失;第2阶段,顶体复合体的顶体外层与顶体本体外膜发生融合,囊泡化;第3阶段,顶体复合体大部分脱落,只留有短锥状的顶体位于核前端.据观察,蟋蟀精子质膜不参与囊泡形成,此结果与家蝇及哺乳类的猪、牛、绵羊、猕猴精子的顶体反应结果很相似.经过比较发现卵水对受精囊内精子的诱导率明显高于精巢内,据分析,可能与精子的生理成熟有关,即便受精囊内精子比精巢内精子更趋于成熟.与其他学者的实验结果相比,蟋蟀精子顶体反应率与家蝇的相似,但明显低于其他动物.这可能与动物的授精方式有关.     

Ultrastructure of the Spermatozoa and Spermatophores of the Zuwai Crab,Chionoecetes opilio (Majidae,Brachyura)

The fine structure of the spermatozoa and spermatophores of the zuwai crab, Chionoecetes opilio, was examined electron microscopically. The spermatophores embedded in the secretory droplets within the vasa deferentia showed a spherical structure with an extremely wrinkled envelope and contained numerous spermatozoa. The mature spermatozoa of this crab, similar to those of other brachyurans, were stellate in shape and had a globular acrosome surrounded by a cup-like nucleus with several radiating processes. The acrosome was ultrastructurally complex and its apical part was characterized by an electron-dense discoid structure, whereas its innermost part was occupied by an electron-lucent cylindrical structure containing assemblies of thin tubules and a reticular formation of electron-dense material. The cytoplasm interposed between the nucleus and acrosome was remarkably reduced in volume and displayed a membranous lamellar complex, few mitochondria, and a centriole. The nuclear chromatin was not condensed but represented by finely flocculent material. The morphological aspects of the zuwai crab spermatozoa are discussed in comparison with those of other decapod crustaceans.     

The ultrastructure of the spermatheca of Biomphalaria glabrata (gastropoda,pulmonata)

A study of the ultrastructure of the spermatheca of virgin freshwater snails Biomphalaria glabrata, kept in isolation since hatching, and in freely mating individuals maintained in colonies, shows that the spermatheca, an accessory organ of the female genital tract of pulmonate snails, is a pear-shaped blind pocket, lined with a single-layered columnar epithelium, surrounded by a thin muscle and pigmented connective. The apex of each epithelial cell may be ciliated, whereas the basis lies on a thick basement membrane. In virgin snails the spermatheca is smaller, its lumen contains a gelatinous, amorphous material; the apex of the epithelial cells contains many mitochondria but few granules. The nucleus appears in the basal third of the cell, topped by the Golgi complex and endoplasmic reticulum elements. In snails which have mated, the spermatheca is swollen, with a somewhat distended lower epithelium; its lumen contains numerous spermatozoa, in various degrees of degradation, which increases with the passage of time after copulation. The apex of the epithelial cells becomes very rich in granules with varied content, including multivesicular bodies. The latter are apparently exocytosed. Pinocytosis occurs at the base of microvilli. Glycogen can be seen accumulating in some cells. Tubular structures, ca. 60 nm in diameter, arranged regularly within the endoplasmic reticulum elements, could occasionally be seen at the basal part of the epithelial cells. It is suggested that the multivesicular bodies may contain enzymes which are secreted to the lumen. The partially digested sperm material would then be absorbed by micropinocytosis, and further digested in the secondary phagosomes at the apical portion of the epithelium.     

The spermatogenesis and sperm structure of Acerentomon microrhinus (Protura, Hexapoda) with considerations on the phylogenetic position of the taxon

The spermatogenesis of the proturan Acerentomon microrhinus Berlese, (Redia 6:1–182, 1909) is described for the first time with the aim of comparing the ultrastructure of the flagellated sperm of members of this taxon with that of the supposedly related group, Collembola. The apical region of testes consists of a series of large cells with giant polymorphic nuclei and several centrosomes with 14 microtubule doublets, whose origin is likely a template of a conventional 9-doublet centriole. Beneath this region, there are spermatogonial cells, whose centrosome has two centrioles, both with 14 microtubule doublets; the daughter centriole of the pair has an axial cylinder. Slender parietal cells in the testes have centrioles with nine doublet microtubules. Spermatocytes produce short primary cilia with 14 microtubule doublets. Spermatids have a single basal body with 14 microtubule doublets. Anteriorly, a conical dense material is present, surrounded by a microtubular basket, which can be seen by using an α-anti-tubulin antibody. Behind this region, the basal body expresses a long axoneme of 14 microtubule doublets with only inner arms. An acrosome is lacking. The nucleus is twisted around the apical conical dense structure and the axoneme; this coiling seems to be due to the rotation of the axoneme on its longitudinal axis. The posterior part of the axoneme forms three turns within the spermatid cytoplasm. Few unchanged mitochondria are scattered in the cytoplasm. Sperm consist of encysted, globular cells that descend along the deferent duct lumen. Some of them are engulfed by the epithelial cells, which thus have a spermiophagic activity. Sperm placed in a proper medium extend their flagellar axonemes and start beating. Protura sperm structure is quite different from that of Collembola sperm; and on the basis of sperm characters, a close relationship between the two taxa is not supported.     

Queen-worker differences in spermatheca reservoir of phylogenetically basal ants

Ant queens mate when young and store sperm in their spermatheca to fertilize eggs for several years until their death. In contrast, workers in most species never mate. We have compared the histological organization of spermathecae in 25 poneromorph species exhibiting various degrees of queen-worker dimorphism. The spermathecae of both castes in all species are similar in having a reservoir connected by a sperm duct to the ovary, and a paired gland opening into this duct. The reservoir of queens typically has a columnar epithelium in the hilar region (near the opening of the sperm duct), whereas the epithelium in the distal region is cuboidal. Abundant mitochondria together with apical microvilli and basal invaginations indicate an osmoregulatory function. In contrast, the reservoir epithelium of workers is flattened throughout and lacks these transport characteristics. This single difference shows the importance of a columnar epithelium in the reservoir for sperm storage. However, our data have not revealed inter-specific variations in the development of the hilar region linked with higher fecundity. We have found no consistent differences in associated structures, such as the spermatheca gland or sperm ducts, or in the musculature between queens and workers.This work was funded by IWT, FWO, KULeuven OT and JSPS.     

Microfilaments and the mechanism of light-triggered sperm release in ascidians

In nature, the ascidian Ciona intestinalis sheds spermatozoa at dawn; however, gravid individuals can be induced to spawn at any time by a 1-hr dark-adaptation period followed by 25-min exposure to 415–430 nm irradiation. Spawning can be induced similarly from a preparation of the isolated sperm duct. A combined light and electron microscopic study was initiated to define morphological aspects of the sperm duct complex and, if possible, elucidate the receptor and effector systems. Results of this investigation indicate that the duct is composed of a tubelike epithelium with a distal closure apparatus consisting of approximately 12 tubules encased by, but not in contact with, subepithelial pigmented cells. There are no nerve or muscle elements associated with the complex. A microfilament system oriented circumferentially about the major cell axis and closely allied with numerous small vesicles is present within epithelial cells along the main portion of the duct. A similar system, oriented along the major cell axis, occurs in epithelial cells of the distal tubules. The potential roles of these epithelial cells as both receptors and effectors of the spawning response is discussed, and an hypothesis is presented to account for the mechanism of light-triggered sperm release.     

Morphological changes in eupyrene and apyrene spermatozoa in the reproductive tract of the male butterfly Atrophaneura alcinous Klug

Summary

Eupyrene and apyrene spermatozoa are contained in separate cysts in the testis of the butterfly Atrophaneura alcinous. Spermatozoa of both types from various parts of the male reproductive tract were examined with particular reference to their morphological characteristics. All spermatozoa collected from the vas deferens and the vesicula seminalis were found to be immotile under a dissecting microscope. No spermatozoa of either type were recognized in any part of the ejaculatory duct. Within the testis, eupyrene spermatozoa are present in bundles and each spermatozoon has a slender nucleus with an acrosome and a long flagellum containing mitochondrial derivatives. Two kinds of appendages, lacinate and reticular, are present on the surface of the sperm membrane. They are replaced with an extracellular sheath during passage through the vas deferens. In contrast, apyrene spermatozoa have neither nucleus nor acrosome, whereas a cup-shaped structure was found at the sperm tip instead of the acrosome. Unlike eupyrene spermatozoa, they are surrounded by a concentric sheath outside the sperm membrane in the vas deferens. Individual apyrene spermatozoa and coiled bundles of eupyrene spermatozoa were both found to accumulate in the vesicula seminalis before mating. These morphological changes during passage through the male reproductive tract suggests the occurrence of a kind of maturation and capacitation process reminiscent of mammalian spermatozoa.     

Ultrastructure of spermiogenesis, sperm, and the spermatheca in Terebrasabella heterouncinata (Polychaeta: Sabellidae: Sabellinae)

Abstract. The sabellid polychaete, Terebrasabella heterouncinata, forms burrows in gastropod shells. It is a small, intratubular brooder that breeds semi‐continuously. It has been shown to self‐fertilize, but its reproductive biology suggests that some form of sperm transfer must occur between individuals. To gain an understanding of its fertilization biology, the ultrastructure of spermiogenesis and the sperm in T. heterouncinata was described, and the animal examined for sperm storage structures. Spermiogenesis occurs in clusters of eight spermatids. The mature sperm has an elongate nucleus and a bilaterally symmetrical acrosome with twisted subacrosomal spaces. The midpiece is short, with three crescent‐shaped mitochondria, and forms a tight sheath around the axoneme. A single spermatheca, which opens on the inner ventral part of the crown near the buccal region, is present. It is a simple blind‐ending duct that runs below the ventral nerve cord and is longer than 100 μm. This is the first record of a single spermatheca in Sabellidae. The shape of the sperm and the presence of a spermatheca confirm that individuals of T. heterouncinata produce ent‐aquasperm and would normally cross‐fertilize.     

The ultrastructure of the spermatozoon ofParadynomene tuberculata Sakai, 1963 (Crustacea,Brachyura, Dynomenidae): Synapomorphies with dromiid sperm

The dynomenid spermatozoon, exemplified here byParadynomene tuberculata, resembles the spermatozoa of the Dromiidae, Homolidae and lyreidine raninoids and differs markedly from those of other crabs (the heterotreme, thoracotremes, raninines and raninoidines) in the depressed, discoidal form of the acrosome and the capitate form of the perforatorium. Four or five apparent dynomenid—dromiid sperm synapomorphies are recognizable. (1) Dynomenids (P. tuberculata) and dromiids differ from homolids and lyreidines in the greater depression of the acrosome (ratio of length to width=0.3); (2) the capitate head of the perforatorium is bilaterally prolonged inP. tuberculata as in dromiids though symmetrical in homolids; (3) dynomenid and dromiid sperm lack the—albeit variably developed—posterior median process of the nucleus seen in homolids, anomurans, raninoids and lower heterotremes; (4)P. tuberculata, like dromiids and less distinctly homolids, has an apical protuberance of subopercular material through the opercular perforation, unknown in other crabs, being distinct from the apical button of thoracotreme sperm; (5) a less certain synapomorphy is the anterolateral electron-pale peripheral zone of the acrosome. These synapomorphies endorse a sister-group relationship of dynomenids and dromiids,P. tuberculata sperm differs notably from the sperm of dromiids in the more complex zonation of the acrosome. The perforatorium lacks the radial rays (“spiked wheel”) of homolid sperm and does not show the “amoeboid” form seen in lyreidines. Absence of internal corrugations of the perforatorial chamber is a major difference from all examined raninids. Centrioles are only very tentatively identifiable. Nuclear arms are absent in glutaraldehyde fixed spermatozoa ofP. tuberculata and have not been observed in the dromiidPetalomera lateralis but are present as three small radial vertices in the dromiidDromidiopsis edwardsi and in homolids.P. tuberculata resemblesPetalomera lateralis in the large size of the sperm nucleus relative to the acrosome compared withD. edwardsi and homolids.     

Umsatz von Lymphozyten in Blut und Lymphknoten der Ratte

Summary Mature spermatozoa from the seminal vesicles of adult Agriolimax reticulatus have been studied by means of phase contrast and electron microscopy; sperm were either live, or sectioned or mounted whole and shadowed with gold. The cell is of the typical pulmonate sperm type with a simple acrosome and a spiral nucleus comprising the head, and a tail which is ensheathed along its entire length by mitochondrion. The 9 peripheral fibrils of the axial complex show no indication of a double nature. Within the spermatheca or gametolytic gland breakdown of sperm occurs; the nucleus and axial fibre bundle of the flagellum survive the longest. The complexity of the flagellum and the relative simplicity of the acrosome are discussed in light of the ecology of the spermatozoa. Many problems concerning the functional physiology of the sperm organelles remain to be investigated.     

Ultrastructural characterization of the gonads of Triops cancriformis (Crustacea, Notostraca) from populations containing both females and males: no evidence for hermaphroditic reproduction

 The gonads of female and male Triops cancriformis specimens from populations of the northern part of the species distribution area were examined by conventional transmission electron microscopy in order to gain insight into the complicated reproductive mode of the species. Ovarian follicles consisted of an oocyte and three nurse cells and were surrounded by a thin layer of follicular cells. Oocytes are initially smaller than nurse cells and contained mitochondria of the cristae type as well as many free ribosomes. The prominent nucleus contained a nucleolus. The cytoplasm of oocytes was filled with yolk globules that were surrounded by membranes of the endoplasmic reticulum. Nurse cells also contained yolk globules. The follicle duct walls consisted of closely packed elongated cells covered by a lamellar basal lamina. No distinct Golgi apparatus was found in the follicle duct cells. The passage of oocytes through the duct was accompanied by a marked flattening of the follicle duct cells. Simultaneously, the oocytes were wrapped in eggshell material before entering the longitudinal oviduct. Testicular lobes were not found in any of the investigated female specimens. In male animals, the epithelial wall of the testicular tubules consisted of both germinal and vegetative cells. Maturing spermatids formed multicellular nests located in clearly delimited cysts in the intercellular space of the testicular epithelium. The lumen of the testicular tubules contained, exclusively, free mature spermatozoa. These characteristics point to the cystic type of spermiogenesis. Mature spermatozoa were non-flagellate, had a regular ovoid shape of 4–5 μm diameter, and an acrosome was not found. Only a negligible amount of spermatozoa (< 5%) showed signs of degeneration. In conclusion, the results provide evidence for a parthenogenetic and/or bisexual reproduction mode rather than a hermaphroditic one in the populations examined. Accepted: 4 August 1997     

Fine structure of the germinating cells during the spermiogenesis of Arion rufus (Mollusca,Pulmonate Gastropoda)

Changes in spermatozoan ultrastructure have been studied during spermiogenesis of the slug Arion rufus (Gastropoda, Pulmonata, Stylommatophora). The ovotestis was investigated during the male stage, definite by the presence of spermatozoa. Some peculiar characteristics are shown by early spermatids: Around the nucleus, the nuclear envelope presents two thick layers located on opposite sides, the apical and basal plates, that will determine the antero-posterior axis of the spermatid. The chromatin, first dispersed throughout the nucleoplasm gives later on thick filaments which become attached over the inner surface of these plates. The chromatin filaments are then arranged parallel to the antero-posterior axis as the nucleus elongates. The position of the plates determines the antero-posterior axis of the spermatid. In the mature spermatozoa, the chromatin is more condensed and the nucleus presents an helical organization. The acrosome and flagellum are respectively attached externally to the center of the apical and basal plates. The acrosome consists of a membrane-bound vesicle and forms a column of homogeneous material. In the middle piece, the mitochondria have been transformed into a mitochondrial derivate by the way of a complicated metamorphosis. The axoneme is surrounded by three mitochondrial helices but only one of them contains glycogene granules. © 1996 Wiley-Liss, Inc.