The sperm of Matsucoccus feytaudi (Insecta, Coccoidea): Can the microtubular bundle be considered as a true flagellum?

Ultrastructure of the Spermiogenesis in Halyomorpha halys (Hemiptera: Pentatomidae): X-Irradiation and New Insights on the Centriolar Region Organization

Halyomorpha halys (Heteroptera: Pentatomidae) is an insect pest native to Asia that has spread over the last two decades to most of the North America, parts of South America, Europe and North Africa. Its impact is significant as it can feed on more than 300 host plants, rendering affected fruits and vegetable crops unsellable or of lower quality. Various chemical and biological methods have been used to control this pest, with varying degrees of success. The sterile insect technique (SIT) is a pest control method involving the sterilization of insects via ionizing radiation and their subsequent mass release into the field. In the present contribution, the spermiogenesis of H. halys was studied from an ultrastructural point of view in both irradiated and non-irradiated adult males. In both cases, we observed ultrastructural characteristics typical of hemipteran sperm cells: bridges connecting the mitochondrial derivatives and the axonemal microtubules, the absence of accessory bodies, and the presence of two or three crystalline inclusions within the mitochondrial derivatives, an acrosome composed of tightly packed tubules, and an atypical, plaque-shaped microtubular organizing center (MTOC) in the centriolar region. Moreover, in the same region, we seldom observed the presence of two centrioles in the spermatids, one of which disappeared at a later stage of maturation. This feature is a novelty for insect spermiogenesis. The cysts of irradiated adults were not all uniformly affected by the radiation. However, irradiated cysts sometimes exhibited a general disorganization of sperm arrangement, incomplete divisions of sperm cells resulting in multiple copies of the same organelle within the same cell, failure to reabsorb the cytoplasm, and the lack of axonemes. Finally, rod-shaped viruses or virus-like particles were observed in vasa deferentia independently of irradiation.

Sperm ultrastructure and spermatogenesis in the Japanese beetle Popillia japonica (Coleoptera, Scarabaeidae)

Popillia japonica is an invasive scarab beetle native to Japan that in 1916 invaded New Jersey in USA. From that moment onwards, the insect has spread invading several US states, Canada, the Azores, Italy and, recently, Switzerland. It is a severe agricultural pest included in the EU priority pest list being able to feed on more than 300 plant species and having an important biotic potential. The general morphology of the reproductive apparatus shows paired testes, each of them having six testicular lobes grouped in threes. From the ventral part of each testicular lobe, each containing about 20 follicles, an efferent vessel originates that fuses with the other efferent vessels to form the deferent duct. A pair of long tubular accessory glands is present. The deferent ducts and accessory glands fuse together into an ejaculatory duct before entering the aedeagus. The sperm is a typical pterygote sperm, 110 μm long, composed of a head and a tail. In the head a three-layered acrosome of about 6 μm in length and a nucleus of about 18 μm long are present. During sperm maturation two C-shaped structures appear in the cytoplasm from the opposite sides of the nucleus that then disappear in late spermatids. In the tail a typical 9 + 9 + 2 flagellar axoneme and two mitochondrial derivatives are present. Moreover, in the head-tail transition region the centriolar adjunct forms a sheath from which three elongated accessory bodies originate. Two of these accessory bodies are placed alongside the axoneme, whilst the third one is placed beneath the mitochondrial derivatives. Mature sperm are grouped in cysts containing about 256 sperm cells. A morphological comparison with related species is provided.

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.

Sperm morphology of the leafhopper Diaphorina citri Kuwayama (Hemiptera: Sternorrhyncha: Psylloidea: Liviidae)

In this study, by using light and electron microscopy, we describe the sperm morphology of the leafhopper Diaphorina citri, a serious pest of citrus throughout the world. In this species the sperm measures 538.49±8.75μm in length, and as observed in psylloids, the sperm, when manipulated, opens into two filaments, one of which is attached to the nuclear base and the other becomes free. Along the flagellum, and only of it, there are lateral projections, about 2μm in length. Furthermore, at the end of the flagellum three appendages, with approximately 7μm in length, are observed. The head region is formed by the nucleus with compact chromatin, and, parallel to it, a structure of median electron density that extends about 25μm in length ahead of the nuclear tip. The flagellum consists of an axoneme with a 9+9+2 microtubule arrangement, two mitochondrial derivatives, and two accessory bodies each with two regions of different electron density. The presence of lateral projections is a characteristic observed in other Sternorrhyncha. As seen previously, the sperm opening in two filaments, when manipulated, was observed only in Psylloidea, and the presence of the three appendices at the end of the flagellum distinguishes D. citri from the other Psylloidea species studied.

A microtubule organizing centre (MTOC) is responsible for the production of the sperm flagellum in Matsucoccus feytaudi (Hemiptera: Coccoidea)

A microtubule organizing centre (MTOC) has been described in the spermatid of the hemipteran Matsucoccus feytaudi (Coccoidea). This structure, revealed as a fluorescent ring by treatment with γ-tubulin antibody, gives rise to a bundle of microtubules which surrounds the elongated cylindrical nucleus. This microtubule bundle has been considered an atypical sperm flagellum provided with sperm motility. A comparison of the M. feytaudi MTOC with the material associated with the centriole of Drosophila melanogaster spermatids confirms the great similarity between the two structures, both involved in the nucleation of microtubules. Like the D. melanogaster material associated with the centriole, the M. feytaudi MTOC is a transient structure which disappears or degenerates at the end of spermiogenesis and is no longer visible in the mature sperm.

Evolutionary problems in centrosome and centriole biology

Centrosomes have been an enigma to evolutionary biologists. Either they have been the subject of ill-founded speculation or they have been ignored. Here, we highlight evolutionary paradoxes and problems of centrosome and centriole evolution and seek to understand them in the light of recent advances in centrosome biology. Most evolutionary accounts of centrosome evolution have been based on the hypothesis that centrosomes are replicators, independent of the nucleus and cytoplasm. It is now clear, however, that this hypothesis is not tenable. Instead, centrosomes are formed de novo each cell division, with the presence of an old centrosome regulating, but not essential for, the assembly of a new one. Centrosomes are the microtubule-organizing centres of cells. They can potentially affect sensory and motor characters (as the basal body of cilia), as well as the movements of chromosomes during cell division. This latter role does not seem essential, however, except in male meiosis, and the reasons for this remain unclear. Although the centrosome is absent in some taxa, when it is present, its structure is extraordinarily conserved: in most taxa across eukaryotes, it does not appear to evolve at all. And yet a few insect groups display spectacular hypertrophy of the centrioles. We discuss how this might relate to the unusual reproductive system found in these insects. Finally, we discuss why the fate of centrosomes in sperm and early embryos might differ between different groups of animals.