Accessory Tubules Research Articles

New findings on sperm ultrastructure of Xenos vesparum (Rossi) (Strepsiptera, Insecta)

The systematic position of insect order Strepsiptera is still under debate. It was, therefore, thought of interest to examine the ultrastructure of a strepsipteran in a search for synapomorphies shared with Coleoptera, Diptera, or any other insect order. The fine structure of spermatozoa and the spermatid from Xenos vesparum (Rossi) was re-examined using scanning and transmission electron microscopy and a fixation technique that permits the visualization of the macromolecular organization of the organelles. The spermatozoon was shown to possess several traits that are characteristics of insects in general, such as a 9+9+2 axoneme, two mitochondrial derivatives containing a crystalline material and two ‘zipper lines’ present along the sperm tail. Seventeen protofilaments occurred along most of the accessory tubules, which reduced to 16 posteriorly. An acrosome is absent. The neck region contains a prominent centriolar adjunct, which gives rise to two accessory bodies which adhere to the mitochondrial derivatives, and to slender strands of the so-called intertubular material found between the accessory tubules. Of interest is the finding that the glycocalyx consists of prominent filamentous strands, similar to those found in siphonapterans, mecopterans and basal dipterans.

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

AbstractThe 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.

Sperm ultrastructure and spermiogenesis in the relic species Tricholepidion gertschi Wygodzinsky (Insecta, Zygentoma)

The silverfish Tricholepidion gertschi is of interest in that it is the most basal representative of Zygentoma. An ultrastructural study of its spermiogenesis was performed to find out whether there are traits which resemble those of other, more advanced insects. This was found to be the case; spermiogenesis can be considered to be of a common insectan type, leading to the formation of elongated sperm cells with acrosome, nucleus, neck region and a tail with axoneme and two mitochondrial derivatives. Total cell length, 50μm, is short for an insect. There are some specializations, which probably represent autapomorphies. The acrosome has a posterior canal or cleft that makes a U-turn. The centriole adjunct forms a prominent post-nuclear ring surrounding the centriole and have a posterior extension, and further originates nine intertubular fibers with a longitudinal periodicity and two accessory bodies. The mitochondrial derivatives have five rows of regularly spaced cristae within a crystalline matrix. The axoneme has accessory tubules consisting of 16 protofilaments, formed at the B-tubules of the doublets and placed at some distance from them in the posterior part of the sperm tail.

The developmental morphology of the spermatophore of Gryllus bimaculatus

Summary Examination of the early stages of spermatophore development revealed a fluid, almost invisible material, forming an apparently amorphous mass when removed from the ejaculatory duct. Innovative techniques were devised to preserve the material, as far as could be determined in its original state of organization. A clear sequence of events was then identified. Immediately following the reference point, which itself had proved difficult to identify, secretions from the accessory reproductive gland tubules produce the material which becomes the primary capsule (the earliest identifiable stage of the ampulla) and the beginnings of the attachment plate. At this very early stage, the forerunner of the sperm tube also appears. Following this, the pressure bodies form and the sperm mass can be seen occupying a posterior position in the developing spermatophore, prior to moving into its final position within the sperm sac itself. More attachment plate material is added and assimilated into the existing attachment plate material. The newly forming spermatophore is protruded onto the subgenital plate, and the attachment plate material and sperm tube are pushed into the dorsal cavity. The sperm tube extends and hardens, as does the attachment plate, which itself takes the shape of its mould. As the ampulla hardens, it is moulded by the ventral lobes. The spermatophore is now ready for transfer to the female.

An ultrastructural investigation of Hrabeiella Pizl & Chalupský, 1984 (Annelida). II. The spermatozoon

The mature spermatozoa of the terrestrial non-clitellate annelid Hrabeiella periglandulata Pizl & Chalupský, 1984 s.l. were examined using light and electron microscopy. They are about 150 μm long, filiform and extremely slender (maximum diameter, 450–475 nm). The acrosome is very elongate (about 25 μm), tapering and conical. Its transverse section is circular apically but shows an evident six-rayed symmetry in its basal region. The nucleus appears convex at both ends; apically, it extends laterally into the acrosome, and basally, it plugs into the centriolar region. The nucleus is about 23 μm long and has a rounded, tri- to pentalobed, slightly helical profile. The midpiece contains one elongate, free (paraxonemal) mitochondrion, 27 accessory tubules, which are slightly larger and more opaque than the axonemal microtubules; and seven electron-dense, non-membrane-bounded rods distributed around the axoneme. The flagellum tapers rapidly posteriorly. None of the observed similarities to the sperm (introsperm) of questids, protodrilids or other polychaetes seems to represent an immediate synapomorphy. None of the spermatozoal autapomorphies of the Euclitellata is shared by Hrabeiella.

Characteristics of sperm ultrastructure in the gall midges Porricondylinae (Insecta, Diptera, Cecidomyiidae), with phylogenetic considerations on the subfamily

Sperm ultrastructure was studied in ten genera of the Porricondylinae (Cecidomyiidae). Sperm structure is remarkably simplified by the absence of the acrosome and the accessory tubules, as happens in all the cecidomyiid flies. All genera of the Porricondylinae show a peculiar 9+3 axonemal model exceptDiallactes, which retains the plesiomorphic condition of a 9+2 axoneme, andWinnertzia, which appears to have secondarily acquired a 9+0 model. A cladistic analysis of relevant sperm characters (based on the axonemal model, the number of mitochondrial derivatives and the size and structure of the centriolar adjunct) was performed to infer phylogenetic relationships among six tribes of the Porricondylinae. In this cladogram, the Porricondylini are the sister group to the Asynaptini, Heteropezini and Winnertzini and these four taxa form the sister group to the Dicerurini. The tribe Diallactini are regarded as the group with the most plesiomorphic characters within the family.

Spermatozoa from the supertribes Lasiopteridi and Stomatosematidi (Insecta, Diptera, Cecidomyiidae): ultrastructure data and phylogeny of the subfamily Cecidomyiinae

Spermatozoa from seven gall‐midge species, representing the supertribes Lasiopteridi and Stomatosematidi, have been examined by electron microscopy and compared to the spermatozoa of 30 previously examined gall‐midge species of the subfamily Cecidomyiinae. Derived characteristics of all examined representatives of this subfamily are the lack of acrosome and the absence of accessory tubules in their axoneme. The sperm axoneme of Didactylomyia has a unique ‘9 + 5 pattern’, i.e. with 9 outer doublets and 5 inner singlet microtubules. Unlike other members of Cecidomyiinae, Didactylomyia has retained some plesiomorphic traits, namely crystal containing mitochondria and a homogeneously condensed nucleus. Stomatosema has a 10 + 0 axoneme and an irregular nuclear condensation. Thus, Didactylomyia may serve as an useful outgroup for phylogenetic analysis within the subfamily Cecidomyiinae. The supertribe Stomatosematidi is a paraphyletic assemblage. Nearly all members of Lasiopteridi, Ozirhincus, Arnoldiola, Brachineura and Ledomyia, have a synapomorphic character in the great number of microtubules in parallel to the axoneme. A notable exception is Rhizomyia, which shares certain apomorphic traits with several genera that have previously been classified within the Cecidomyiidi, i.e. Contarinia, Allocontarinia, Lestodiplosis and Myricomyia. Moreover, these genera have a flat sperm tail and microtubular doublets located close to the cell membrane, both characteristics that differ markedly from the very peculiar sperm tail found in other members of Cecidomyiidi.Cladistic analysis of sperm characters suggests that the supertribe Cecidomyiidi is a polyphyletic taxon and supports the existence of a sister‐group relationship between the supertribe Lasiopteridi and the genera Rhizomyia, Contarinia, Allocontarinia, Lestodiplosis and Myricomyia.

Characteristics of the sperm flagellum in fungus gnats (Insecta, Diptera, Mycetophiloidea)

Spermatozoa from several members of the closely related Mycetophilidae and Keroplatidae were examined by electron microscopy using a fixative that contains glutaraldehyde and tannic acid, followed by a post-fixative that consists of uranyl acetate rather than osmium tetroxide. With this fixative, the detailed architecture of the flagellar axoneme and its various microtubules could be resolved. The so-called accessory tubules, which surround the central 9+2 unit of the sperm axoneme, were found to have 16 protofilaments in several examined Mycetophiloidea, but in no other Diptera. As 16 is the common number in holometabolic insects, it is presumably the plesiomorphic condition in Diptera. Other fungus gnats have accessory tubules with 15 or 14 protofilaments. The intertubular material situated between the accessory tubules is smaller in the examined members of the Mycetophilidae than in the Keroplatidae. The acrosome consists of an apical vesicle, which in one species, Macrorhyncha ancae, has three microtubular doublets in its anterior part and two large and three small extensions which extend posteriorly along the sperm axoneme.

The Basal Bodies in Spermatids of a Caddisfly, Potamophylax rotundipennis (Limnephilidae, Trichoptera), Possess a Central Pair of Microtubules

The restructuring of basal bodies was analyzed in spermatogenesis of a caddisfly, Potamophylax rotundipennis (Limnephilidae), using electron microscopy of ultrathin serial sections. Flagellar outgrowth was characterized by the belated formation of the central pair of microtubules. Flagellar stubs of metaphase I spermatocytes were devoid of central microtubules. The proximal portion of the basal bodies contained a cartwheel structure. Spermatids showed long flagella with the usual 9 + 2 arrangement of microtubules. Surprisingly, the central pair of flagellar microtubules extended deeply into the lumen of the basal body. This may be rendered possible by the attachment of the basal bodies to the outer face of the nuclear envelope in spermatids. The outer nuclear membrane may nucleate the assembly of the central pair of microtubules in spermatogenesis of the caddisfly. Another unusual feature of basal bodies in the caddisfly was the presence of a cylinder of electron-dense material within their lumen. Its function may lie in linking the microtubular blades of the basal bodies with one another. Finally, an observation within the spermatid tail is remarkable: the accessory tubules consistently possessed a central filament throughout their length.

Sperm structure of Trichoptera. IV. Rhyacophilidae and Glossosomatidae

The families Rhyacophilidae and Glossosomatidae (Trichoptera) are considered to be the most primitive ones within the order. We examined the spermatozoa of members of these families to see whether their ultrastructure is consistent with an ancestral position. Axonemal structures, after fixation with a tannic acid-containing fixative, have been shown to be particularly useful as taxonomical indicators. It was found that 4 members of Rhyacophilidae, representing 3 subgenera ( Rhyacophila, Pararhyacophila, and Hyporhyacophila) all have motile spermatozoa, with a 9 + 9 + 2 axoneme in which inner (but no outer) dynein arms are present. The accessory tubules have a wall consisting of 17 protofilaments, decreasing to 16 near the distal end, whereas the examined member of Glossosomatidae, Catagapetus nigrans, has accessory tubules with 18 protofilaments and a 9 + 9 + 2 axoneme with inner dynein arms and with motility similar to the Rhyacophilidae. Sperm motility is consistent with the inclusion of these 2 families within the suborder Integripalpia, and the axonemal pattern 9 + 9 + 2 indicates that the families indeed occupy a primitive position within Trichoptera.

Three-Dimensional Reconstructions of Accessory Tubules Observed in the Sperm Axonemes of Two Insect Species

The sperm-tail axonemes of several insect species are known to have accessory microtubules with a diameter greater than that of ordinary cytoplasmatic microtubules. This provides an opportunity to investigate the three-dimensional organization of naturally occurring tubules with more than 13 protofilaments. For this purpose electron micrographs of negatively stained axonemes of a dipteran species, Exechia seriata, and a trichopteran, Limnephilus bipunctatus , were taken for computer analysis. The original micrographs contained long stretches of somewhat curved microtubules that, in a first step, were straightened by an appropriate algorithm. The results were used to determine helical models from spectral analysis, to obtain filtered images of the front and back tubule sides, and to compute three-dimensional reconstructions by Fourier methods. The tubule segments used in the present study were about 500 nm long. All accessory microtubules analyzed consisted of a double-stranded helix of clearly distinguishable heterodimers with a pitch of 16 nm and skewing protofilaments. Most segments of the dipteran accessory tubules consisted of 16 protofilaments, although 15 were found in some images portraying the distal region of the flagellum. The accessory tubules of the trichopteran had 19 protofilaments. The repeat periods that describe the skewness of protofilaments (128 nm for 16 and 320 nm for 19 protofilaments) are in any case considerably thicker than an electron microscopical section which encompasses about 50 nm. It is hence valid to count the number of protofilaments in cross-sectioned axonemes.

Sperm structure of Trichoptera. I. Integripalpia : Limnephiloidea

Spermal ultrastructure in 16 caddisflies (Trichoptera) belonging to the suborder Integripalpia, superfamily Limnephiloidea, was examined in a search for apomorphic and plesiomorphic features. In all species examined, the sperm tail axoneme was of the 9 + 9 + 2 + type, the axonemal doublets lacked outer dynein arms but had inner ones, and the cell membrane was scalloped with a prominent glycocalyx. The number of protofilaments in the accessory tubules depended on the phylogenetic position: 18 in the family Leptoceridae, 19 in Limnephilidae, Goeridae and Odontoceridae (with a reduction in the number distally), and 20 in Sericostomatidae. Spermatozoa in Leptoccridae are further characterized by the 2 central microtubules being flattened and eccentric and not being surrounded by a central sheath. Spermatozoa of Sericostomatidae have an accessory body and a helicoidal array of the sperm tail.

Characteristics of the flagellar axoneme in Neuroptera, Coleoptera, and Strepsiptera.

Spermatozoa from representatives of the five insect orders in superorder Neuropteroidea were examined by electron microscopy following a new fixation method that includes tannic acid in the primary fixative but has uranyl acetate rather than osmium tetroxide as the secondary fixative. The sperm axoneme was found to be similar in the four orders Megaloptera, Raphidioptera, Neuroptera, and Coleoptera, and is characterized above all by its so-called intertubular material being divided into two portions, one located outside, but in contact with the doublet, and the other projecting from the accessory tubule and having a beak-like shape. These features have not been seen in insects from other orders and may be a synapomorphy for these neuropteroid orders. The accessory tubules in these four orders have 16 protofilaments. The shape of the accessory bodies adjacent to the mitochondrial derivatives is nearly the same in insects from the more primitive neuropteroid orders and in Coleoptera. The sperm tail of the examined strepsipteran deviates in several respects from that of other neuropteroids: the particle row in the wall of accessory tubules is incomplete, an intertubular material is missing, and the mitochondria contain no crystal. © 1994 Wiley-Liss, Inc.

The dipteran sperm tail: ultrastructural characteristics and phylogenetic considerations

The sperm tail from representatives of several families of Diptera has been examined by high resolution electron microscopy and a computer analysis that improved the visualization of recorded patterns. A considerable variability in sperm tail structure is found within Diptera, and is actually greater than that of any other insect order. The ‘generalized insect sperm axoneme’. which is characterized as a 9+9+2 axoneme and by the accessory microtubules having 16 protofilaments, was found only in some dipterans; these are members of Mycetophilidae. From this fact we conclude that Mycetophilidae is likely to be the most primitive extant dipteran group. Another mycetophilid, Boletina, was seen to have accessory tubules with 15 protofilaments as have members of families Dixidae, Chironomidae, Culicidae, and Bibionidae. The last two families have spermatozoa of a type designated as 9+9+‘1’ there is a central rod rather than two microtubules. We regard this 9+9+‘1’pattern with 15 protofilaments to represent a synapomorphic feature. Representatives of the neatoceran families Tipulidae and Trichoceridae have accessory tubules with 13 protofilaments as do examined members of several brachyceran families. Brachycera is hence likely to be derived from the vicinity of the tipulid family. The intertubular material is small in Mycetophilidae and most nematoceran groups, whereas in Tipulidae and Brachycera it is enlarged; here it bridges the space between the accessory tubules and contains various inclusions.

Substructure of the axoneme of pterygote insect spermatozoa: Phylogenetic considerations

Spermatozoa from a great number of insect species were fixed in a tannic acid-containing fixative and the ultrastructure of the flagellar axoneme was examined in a search for apomorphies. Most of the examined species, representing a majority of insect orders. have accessory tubules outside the axoneme (hence a 9 + 9 + 2 pattern), and these consist of 16 protofilaments. Some important apomorphies concern the number of protofilaments in the accessory tubules: 13 (plus 7 inner elements) in Ephemeroptera, 13 in the (elliptic) tubules of Psocoptera + Anoplura + Mallophaga (thus a synapomorphy), 13 in Tipulidae + Brachycera, 15 in the dipteran families Dixidae + Chironomidae (with a 9 + 9 + 2 axoneme) and Culicidae + Bibionidae (with a 9 + 9 + “1” axoneme), 17 in Phasmatodea, and 17–20 in Trichoptera. Other apomorphies concern the appearance of the so-called intertubular material outside the microtubular doublets, the appearance of the interior of the various microtubules, and the loss, in some taxa, of outer or inner dynein arms of both dynein arms. In some cases, the flagellum is completely abnormal; the sperm tail of Thysanoptera, for example, consists of 27 elements of 3 different kinds. The different taxa within orders Diptera and Trichoptera have sperm tail axonemes of different appearances, where those from other orders have a rather uniform appearance. The conclusions that can be drawn from this spermatological study, generally agree with data from classical studies, except with some variations, in some cases.

Native microtubules with a variable number of protofilaments

AbstractInsect spermatozoa are characterized by having a set of accessory tubules that surrounds the microtubular doublets of the axoneme and that are formed from the B‐subtubules of the doublets. In trichopteran species, the accessory tubules have an unusually large diameter. Those of one species, Odontocerum albicorne, were seen to have a number of protofilaments that is 19 in the main part of the axoneme, but gradually decreasing to 18, 17, and 16 near the distal tip. The accessory tubule of the trichopteran axoneme has an asymmetrical shape and a skewed orientation, which makes it easy to distinguish a tubule that is viewed from its plus‐end from one viewed from the minus‐end. The shape of a cross‐sectioned protofilament in the trichopteran accessory tubules differs from that of microtubules in general, including accessory tubules of other insects, by being polygonal with the most acute angle pointing centripetally. © 1993 Wiley‐Liss, Inc.

The sperm tail axoneme studied at high magnification

Abstract The axoneme of the insect sperm tail is usually described with the 9 + 9 + 2 formula which refers to 9 accessory tubules surrounding the classical 9 + 2 organelle. When studied with traditional methods the 9 + 9 + 2 pattern is seen as a more or less uniform entity. We describe here some techniques, which show that the axoneme actually is far from uniform and has a structure that in most cases is specific for the insect order. These techniques include fixation with a glutaraldehyde‐tannic acid mixture and computer‐aided image analysis. Several findings are reviewed here, for instance a non‐equidistant distribution of the 13 protofilaments in the wall of axonemal A‐tubules, the elliptical shape of the A‐tubules and of the accessory tubules of the three related insect orders Psocoptera, Anoplura and Mallophaga, and the existence of singlet microtubules with the same characteristics as A‐subtubules in insect order Thysanoptera.

Axonemal structure and insect phylogeny

Abstract It is now widely accepted that sperm structure can be used to resolve problems of phylogenetic relationship. In the present study we consider one component of the spermatozoon only, namely the flagellar axoneme, and we restrict the study to insects, in particular to Diptera and Trichoptera. In material fixed with glutaraldehyde plus tannic acid and followed by uranyl acetate rather than osmium tetroxide, it was possible to see the individual protofilaments in microtubular doublets and singlets and in the so called accessory tubules. The latter have 16 protofilaments in most insect orders, but this number was found in one dipteran family only, namely Mycetophilidae. Other members of this family lack accessory tubules as do the primitive members of some other insect orders. For either of these reasons Mycetophylidae is regarded as the most primitive family within Diptera. The higher dipteran suborder, Brachycera, shares with Tipulidae a 13 protofilament pattern. Just as there is a much greater axon...

Sperm flagellum of insects belonging to orders Psocoptera, Mallophaga and Anoplura. Ultrastructural and phylogenetic aspects

Abstract Spermatozoa from seven insect species belonging to the three orders Psocoptera, Mallophaga and Anoplura were examined by electron microscopy. Primary fixation was in a glutaraldehyde‐tannic acid mixture and post‐fixation in 1 % uranyl acetate rather than in an osmium tetroxide solution. With this fixation method the individual protofilaments of the axonemal microtubules are well resoved. The accessory tubules of the axoneme were found to have a wall consisting of 13 rather than 16 protofilaments, to have an elliptic cross‐section, and to have a lumen that appears electron‐dense except for a less dense centra! axis. The centriole was seen to consist of nine micrdtubular doublets, rather than triplets, and nine accessory tubules located at some distance from the doublets. The centriolar doubles are immersed in an electron‐dense material termed centriolar adjunct. These listed features of accessory tubules seem to be synapomorphic traits; they have not been seen in any other insect species. All exam...

Sperm flagellum of Dacus oleae (Gmelin) (Tephritidae) and Drosophila melanogaster Meigen (Drosophilidae) (Diptera)

The spermatozoa of the 2 fruit fly species, Dacus oleae (Gmel.) and Drosophila melanogaster Meig. (Diptera), have been fixed in a glutaraldehyde-tannic acid mixture, followed by uranyl acetate postfixation, and the sperm tail studied by high resolution electron microscopy. Spermatozoa of both species were seen to possess a centriole containing 9 microtubular triplets. The centriolar A-, B- and C-subtubules have 13, 10 and 9 protofilaments, respectively. The outer subtubules (the C-subtubules) seem to be continuous with the accessory tubules of the main part of the tail. The accessory tubules and their intertubular material have a complex fine structure similar to that described in some other brachyceran flies. In the end piece of the sperm tail, the A-subtubules undergo degeneration, characterized by swelling and a loss of dynein arms and spokes. The tail region appears to be immotile, possibly to enable it better to stick to receptors on the egg micropyle.