The ultrastructure of the spermatozoa of Boa constrictor occidentalis, with considerations on its mating system and sperm competition theories

Sperm ultrastructure has been described for several families of Squamata in which it has been considered a valuable character source for phylogenetic studies. However, sperm competition and mating systems have been demonstrated to influence variations in the sperm morphology and dynamics. The mating system of Boa constrictor occidentalis is likely to have a high degree of sperm competition. We investigated, for the first time, the ultrastructure of the spermatozoa of B. c. occidentalis and, thus, of the family Boidae. Active mating groups were captured from the field, and the spermatozoa of the males was collected by ejaculation and processed to obtain transmission electron micrographs and fluorescence micrographs. The spermatozoa are filiform and their morphology fits the general model described for snakes, and several synapomorphies belonging to the squamates can be identified in these cells. Nevertheless, the head is 25% longer and the midpiece presents a lower frequency of mitochondrial transformations than that of other snakes. We propose that this last trait, along with the extraordinary elongation of the midpiece and the system of multilaminar membranes covering this section (both synapomorphies of the snake spermatozoa), are adaptive responses to processes of sperm competition and sperm storage.     

Silhouettella loricatula (Arachnida, Araneae, Oonopidae): a Haplogyne spider with complex female genitalia

The female genital system of the oonopid Silhouettella loricatula is astonishingly complex. The genital opening is situated medially and leads into an oval receptaculum that is heavily sclerotized except for the ventral half of the posterior wall that appears chitinized only. A large striking sclerite lying in the posterior wall of the uterus externus is attached anteriorly to the receptaculum and continues dorsally into a globular appendix that bears a furrow. The uterus externus shows a peculiar modification in its anterior wall: a paddle-like sclerite with a nail-like posterior process. This sclerite lies opposite to the furrow proceeding in the globular appendix and may serve females to lock the uterus externus by muscle contractions. Massive muscles connect the sclerite with the anterior scutum of the opisthosoma and with two other sclerites that are attached to the receptaculum and serve as attachments for further muscles. Gland cells extend around a pore field of the receptaculum. They produce secretion that encloses spermatozoa in a discrete package (secretory sac) inside the receptaculum. In this way, the mixing of sperm from different males and thus sperm competition may be severely limited or completely prevented. During a copulation in the laboratory the ejection of a secretory sac that most probably contained spermatozoa was observed, indicating sperm dumping in S. loricatula. The ejection of the secretory sac may be caused by female muscle contractions or by male pedipalp movements. The majority of the investigated females have microorganisms in the receptacula that could represent symbionts or infectious agents. The microorganisms can be identified partly as bacteria. They are enclosed in secretion and are always found in the same position inside the receptaculum.     

The ultrastructure of the book lungs of the Italian trap-door spider Cteniza sp. (Araneae,Mygalomorphae, Ctenizidae)

The fine structure of book lungs is not homogeneous across Arachnids and is considered phylogenetically informative, however few reports on the ultrastructural features of this organ have been published. In this study, we examined the general morphology and ultrastructure of adult spiders of the genus Cteniza. The respiratory system of Cteniza sp. consists of two pairs of well-developed book lungs, which is considered indicative of primitive spiders. The general organization of the book lungs is similar to that described for other arachnids and consists of leaves of alternating air and hemolymph channels. The air channels are lined with cuticle and open to an atrium that leads to a slit-like spiracle. The air channels are held open by cuticular trabeculae. The space holders in the hemolymph channels are pillar trabeculae formed by two cells from the opposed walls. The pillar cells have a complex ultrastructure that includes an interdigitating connection, gap junctions, microtubules and hemidesmosomes. These features apparently help strengthen the pillar cells and their interconnections with each other and the underlying cuticle. The cytoskeleton resembles that of arthropod tendon cells where substantial structural support is needed.     

The chromosome-scale assembly of the Canary Islands endemic spider Dysdera silvatica (Arachnida,Araneae) sheds light on the origin and genome structure of chemoreceptor gene families in chelicerates

Here, we present the chromosome-level genome assembly of Dysdera silvatica Schmidt, 1981, a nocturnal ground-dwelling spider endemic from the Canary Islands. The genus Dysdera has undergone a remarkable diversification in this archipelago mostly associated with shifts in the level of trophic specialization, becoming an excellent model to study the genomic drivers of adaptive radiations. The new assembly (1.37 Gb; scaffold N50 of 174.2 Mb), was performed using the chromosome conformation capture scaffolding technique, represents a continuity improvement of more than 4500 times with respect to the previous version. The seven largest scaffolds or pseudochromosomes, which cover 87% of the total assembly size, probably correspond with the seven chromosomes of the karyotype of this species, including a characteristic large X chromosome. To illustrate the value of this new resource we performed a comprehensive analysis of the two major arthropod chemoreceptor gene families (i.e., gustatory and ionotropic receptors). We identified 545 chemoreceptor sequences distributed across all pseudochromosomes, with a notable underrepresentation in the X chromosome. At least 54% of them localize in 83 genomic clusters with a significantly lower evolutionary distances between them than the average of the family, suggesting a recent origin of many of them. This chromosome-level assembly is the first high-quality genome representative of the Synspermiata clade, and just the third among spiders, representing a new valuable resource to gain insights into the structure and organization of chelicerate genomes, including the role that structural variants, repetitive elements and large gene families played in the extraordinary biology of spiders.     

Ultrastructural observations of spermatozoa and spermiogenesis in Wandella orana Gray, 1994 (Araneae: Filistatidae) with notes on their phylogenetic implications

Spermatozoa and spermiogenesis of the prithine filistatid spider Wandella orana are described. The spider produces coenospermia, i.e. sperm aggregations that include several single sperm cells commonly surrounded by a secretion sheath. One sectioned coenospermium in W. orana contains at least five spermatozoa. During copulation many coenospermia are transferred into the female. Coenospermia are regarded as a peculiar transfer form of sperm which occurs in early derivative spiders such as Liphistiomorphae and Mygalomorphae. The only exception which was found in Araneomorphae until now was the filistatine spider Filistata insidiatrix. Our observation is the second case and supports the view that Filistatidae represent an early derivative taxon. Furthermore, the individual sperm cells show characteristics which also may be regarded as being plesiomorphic. There is a cone-shaped acrosomal vacuole, a very long acrosomal filament, a rather stout nucleus and a small implantation fossa. The axoneme shows the 9x2+3 pattern of microtubules which is synapomorphic in Megoperculata (Uropygi, Amblypygi and Araneae). The finding of coenospermia in two distant taxa of Filistatidae may have consequences for phylogenetic and systematic considerations.     

Comparative analysis of the sperm ultrastructure of three species of Phyllomedusa (Anura, Hylidae)

We describe the sperm ultrastructure of three species of frogs in the genus Phyllomedusa . According to micrographs, total size of the spermatozoon of Phyllomedusa hypochondrialis is significantly smaller than those of Phyllomedusa bicolor and Phyllomedusa tarsius . The acrosome complex consists of two conical structures covering the nucleus, the acrosome vesicle and the subacrosomal cone. The subacrosomal cone of P. bicolor and P. tarsius is less electron-dense and appears more granular in transverse section than in P. hypochondrialis . In P. bicolor and P. tarsius , the nuclear space is reduced and the subacrosomal cone fills most of the space between the acrosome vesicle and nucleus. The anterior region of the nucleus in the spermatozoa of P. bicolor and P. tarsius ends abruptly, while in P . hypochondrialis it is sharp-ended. In P. bicolor and P. tarsius , the axial fibre is much larger than in P . hypochondrialis . The sperm ultrastructure of Phyllomedusa appears conservative at the intrageneric level. Future studies on the sperm ultrastructure of hylids can provide new insights on the systematics of the group and a larger database for a cladistic analysis.     

Mechanism of signal production in the vibratory communication of the wandering spider Cupiennius getazi (Arachnida,Araneae)

The communication with substrate vibrations produced by vibrations of the body or its appendages is widespread among arthropods, especially among spiders. Its biomechanics, however, is poorly understood. Males of the wandering spider Cupiennius getazi produce such substrate vibrations during courtship by means of dorsoventral movements of their opisthosoma without hitting their dwelling plant.Simultaneous recordings of the plant vibrations (accelerometry), of the opisthosoma movements (laser Doppler vibrometry) and of the electromyograms of the opisthosomal depressor muscle, revealed that the main frequency of the vibratory signal of about 80 Hz originates from the activity of the opisthosomal depressor muscle. The transfer functions of the spider's body show resonances which could amplify the main frequency before it is transmitted into the plant.A low frequency component of the opisthosomal movement (duration c. 0.3 s, displacement c. 6 mm (peak-peak) 30° deflection angle, frequency 10–20 Hz) can be distinguished from a main frequency component (duration c. 0.1 s, displacement c. 0.5 mm 2.5° deflection angle, frequency c. 80 Hz). The main frequency component is superimposed on an upward movement of the low frequency component.     

Male gonads morphology,spermatogenesis and sperm ultrastructure of the seahorse Hippocampus guttulatus (Syngnathidae)

Testes morphology, spermatogenetic process and mature sperm ultrastructure were analysed in Hippocampus guttulatus, using both light and transmission electron microscopy. Both testes were organized in a single large germinal compartment, with a central lumen. Spermatocysts only contained spermatogonia and primary spermatocytes. Inside the testis lumen, together with mature sperm, two types of large mono‐nucleate cells, flagellate and aflagellate, were present. Both types of cells were interpreted as developing germ cells precociously released inside the testis lumen, where their maturation was completed. According to the different morphological features of the nuclei, such as chromatin condensation degree, aspect of the nuclear fossa and others, the flagellate cells were unquestionably developing spermatids. On the contrary, the developmental stage of the aflagellate was more difficult to interpreted. They could be secondary spermatocytes or young spermatids. No dimorphic sperm were recognizable, the only sperm type observed have features typical of the intro‐sperm reports in other syngnathids species. They had a cylindrical head, a short midpiece, characterized by two mitochondrial rings housed inside a cytoplasmic collar, and a long flagellum. These and previous data about the same topic reported on other syngnathids species were compared and discussed.     

The sperm ultrastructure of Merluccius merluccius (Teleostei,Gadiformes): phylogenetic considerations

The anacrosomal aquasperm of the gadiform Merluccius merluccius is ultrastructurally similar to the advanced type II spermatozoa (perciform‐type sperm) typically found in most Perciformes. The perciform‐type spermatozoon is characterized by the lateral insertion of the flagellum and the location of the centrioles outside the nuclear fossa. Apart from these characteristics, the spermatozoon of M. merluccius is remarkable because of the mutually parallel arrangement of the centrioles, a rare feature among fishes, which is considered an apomorphic condition for animal sperm cells. Within the superorder Paracanthopterygii, which contains a large diversity of sperm patterns resulting from a high number of apomorphies, a perciform‐type sperm is present only in the order Gadiformes. The significance of the presence of perciform‐type spermatozoa in the three investigated gadiform families is discussed in a phylogenetic context.     

The ultrastructure of the ascus apical apparatus of some Dermateaceae (Helotiales)

The ascus apical apparatus ultrastructure of 12 species of the Dermateaceae (Helotiales, Ascomycota) was studied. Its development and details are described on the basis of transmission electron microscopy micrographs for all studied species. A majority of them, 8 species belonging to the genera Belonopsis, Mollisia, and Pyrenopeziza, show considerable similarity in the structure of their ascus apical apparatus. Two species, Mollisia melaleuca and Mollisia ramealis, show some deviations from this type, suggesting that the genus Mollisia is not fully homogeneous. Two other species, Podophacidium xanthomelum and Pezicula cinnamomea represent two ascus apical apparatus structure types of their own, which are remarkably different from the Mollisia type. The possible taxonomic implications arising from ascus apical apparatus diversity in the Dermateaceae are discussed.     

Sperm ultrastructure and spermiogenesis of Coniopterygidae (Neuroptera, Insecta)

The spermiogenesis and the sperm ultrastructure of several species of Coniopterygidae have been examined. The spermatozoa consist of a three-layered acrosome, an elongated elliptical nucleus, a long flagellum provided with a 9+9+3 axoneme and two mitochondrial derivatives. No accessory bodies were observed. The axoneme exhibits accessory microtubules provided with 13, rather than 16, protofilaments in their tubular wall; the intertubular material is reduced and distributed differently from that observed in other Neuropterida. Sperm axoneme organization supports the isolated position of the family previously proposed on the basis of morphological data.     

Anatomy and ultrastructure of the male reproductive system in Pleioplana atomata (Platyhelminthes: Polycladida)

Abstract. The ultrastructure of the male reproductive system in the polyclad flatworm Pleioplana atomata is described. Numerous testes are scattered throughout the entire body but are heavily concentrated on the ventral side. All stages of differentiating sperm cells are present in all testes follicles. Intercellular bridges connect spermatocytes and spermatids derived from a single spermatogonium. In the distal part of spermatids, a zone of differentiation develops with a row of microtubules beneath the plasmalemma. Adjacent to these microtubules, an intercentriolar body is flanked by two basal bodies that give rise to two axonemes (each with a 9+“1” microtubular pattern) that face in opposite directions. The Golgi complex appears in the central portion of the spermatid and produces numerous small and large electron-dense bodies. The small bodies surround the nucleus, whereas the large bodies cluster along with the mitochondria in the central part of the spermatid. Development of the spermatid leads to cell elongation and formation of a filiform, biflagellate mature spermatozoon with cortical microtubules all along the sperm shaft. The male canal system consists of paired vasa deferentia that separately enter a single seminal vesicle. A single prostatic canal connects the seminal vesicle to the prostatic vesicle. Ultrastructurally, the seminal vesicle and prostatic canal are very similar, and along with the prostatic vesicle and stylet pocket, are lined by a ciliated epithelium. The ultrastructure of the prostatic vesicle indicates that it probably produces a large volume of seminal fluid that, along with spermatozoa, is transferred to the mating partner through a stylet. Some of the findings, particularly on sperm ultrastructure, may provide characters useful for phylogenetic analysis.     

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.     

Genital morphology of female goblin spiders (Arachnida: Araneae: Oonopidae) with functional implications

Spider genital morphology usually provides the best characters for taxonomy. Furthermore, functional genital morphology helps to understand the evolution of complex genitalia and their role in the context of sexual selection. The genital systems of most haplogyne spider families are poorly investigated with respect to their morphology. The present study investigates the female genitalia of the oonopids Oonops pulcher, Oonopinus kilikus, and Pseudotriaeris sp. by means of light microscopy and SEM. The male palps are briefly described. Females of O. pulcher store spermatozoa in an anterior and a posterior receptaculum (PRe). The genitalia resemble the primitive dysderoid genitalia supporting the hypothesis that the subfamily Oonopinae contains more basal oonopids. In O. kilikus, the anterior receptaculum is reduced to a sclerite. Spermatozoa are stored in a PRe. The receptacula of Pseudotriaeris sp. are reduced to sclerites. Spermatozoa in the uterus internus indicate that fertilization happens there or in the ovary. The anterior sclerite might serve females to lock the uterus during copulation as suggested for other gamasomorphines. The male palp of O. kilikus is simple, whereas the palps of O. pulcher and Pseudotriaeris sp. appear more complex. Complicated structures on the palp of Pseudotriaeris sp. indicate that males exert copulatory courtship.     

Ultrastructure of spermiogenesis and spermatozoa in Marchalina hellenica (Gennadius) (Hemiptera: Sternorrhyncha,Marchalinidae)

The spermiogenesis, the sperm structure and the sperm motility of Marchalina hellenica (Gennadius) were examined. In the early spermiogenesis a centriolar apparatus was identified, but this structure is not involved in the production of the sperm flagellum. As in other Coccoidea, the flagellar axoneme originates by the activity of the thickened tip of the numerous microtubules surrounding the nuclear anterior region close to the periphery of the cell. This region pushes against a narrow cytoplasmic layer, giving rise to a papilla. In this region a novel structure, consisting of a regular network of thin filaments, arranged orthogonally to the bundle of microtubules, is visible. The sperm flagellum consists of a series of about 260 microtubules, regularly arranged in rings around the axial nucleus. This latter extends in the middle part of the sperm length. As usual in scale insects, sperm form a bundle, which in M. hellenica is composed of 64 sperm cells, surrounded by somatic cyst cells. The sperm bundle has an helicoidal array, with a cap of dense material at its apex, lending the anterior and the posterior region of the sperm bundle with a different structural organization. This difference is responsible of the different speed gradient observed in the helical wave propagating along the sperm bundle.