The sperm structure of Embioptera (Insecta) and phylogenetic considerations

The sperm structure of two species of Embioptera, Embia savignyi Westwood 1837 and Aposthonia japonica (Okajima 1926), was studied. Spermatozoa of both species exhibit a monolayered acrosome and a layer of material surrounding the sperm cells for most of their length. The presence of a 9+9+2 axoneme provided with accessory microtubules with 16 protofilaments, two accessory bodies and two crystallized mitochondrial derivatives are characters shared with other polyneopteran taxa. The supposed close relationship between Embioptera and Phasmatodea is not supported by characters of the sperm ultrastructure.     

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.     

Estimates of nuclear DNA content in bryophyte sperm cells: phylogenetic considerations

Nuclear DNA contents of developing sperm were estimated for 17 species of bryophytes by cytophotometry in squash preparations of antheridia after Feulgen staining. Genome sizes are in the lower end of the range for land plants. Two homwort C-values have the lowest recorded for bryophytes at 0.17 and 0.26 pg DNA per nucleus. In liverworts, C-values range from 0.49 pg in Blasia pusilla to 4.05 pg in Pellia epiphylla, while moss genome sizes are less variable, ranging from 0.38 pg in Takakia ceratophylla to 0.92 pg in Atrichum oerstedianum. DNA content is not correlated with chromosome number in these bryophytes, but sperm cell size and cellular complexity are directly related to C-value. Structural variations in the locomotory apparatus are viewed as evolutionary modifications associated with changes in genomic complexity, with a generalized increase in complexity of the motile assemblage accompanying increases in DNA content. Nuclear DNA values are not as variable in bryophytes as they are in pteridophytes and seed plants. We suggest that in plants producing biflagellated gametes, lower DNA contents afford a selective advantage. Comparisons with plants that produce multiflagellated or pollen-dispersed sperm indicate operation of a nucleotypic effect in archegoniates with biflagellated sperm. This effect may be on sperm cell functioning, which in turn influences reproductive success.     

Comparisons of dipteran, hymenopteran and coleopteran parasitoids: provisional phylogenetic explanations

We consider differences between dipteran, hymenopteran and coleopteran parasitoids in the following categories: taxonomic range and developmental stage of hosts attacked; habitats they are attacked in; developmental stage of the parasitoid contacting the host; occurrence of phoresy, and attacking hosts during flight. Using existing phylogenetic classifications we reconstruct possible ancestral conditions to the parasitoid clades in the three orders. By considering these as phylogenetic constraints and potentialities we attempt to account for the observed differences between the parasitoids within the orders.     

Taxonomic considerations of Bartonella bacilliformis based on phylogenetic and phenotypic characteristics

The 16S-rRNA gene of Bartonella bacilliformis was amplified using the polymerase-chain reaction (PCR). The amplification product was sequenced using a linear-PCR procedure and compared with other published 16S-rRNA sequences. The results of this analysis placed B. bacilliformis in the alpha subgroup of the proteobacteria, and more specifically demonstrated its close phylogenetic relationship to Rochalimaea quintana. This relationship is supported by similarities in the size and mean base composition of the genomes of the two species, and by shared phenotypic characteristics.     

The sperm, a neuron with a tail: 'neuronal' receptors in mammalian sperm

A number of plasma membrane receptor types originally thought to be specific to neurons have been found in other somatic cells. More surprisingly, the mammalian sperm and neuron appear to share many of these 'neuronal' receptors. The morphology, chromosome number, genomic activity, and functions of those two cell types are as unlike as any two cells in the body, but they both achieve their highly disparate goals with the aid of a number of the same receptors. Exocytosis in neurons and sperm is essential to the functions of these cells and is strongly influenced by similar receptors. 'Neuronal' receptor types in sperm may also play a role in the control of sperm motility (a function of course not shared by neurons). This review will consider the evidence for the presence of sperm plasma membrane 'neuronal' receptors and for their significance to mammalian sperm function. The persuasiveness of the evidence varies depending on the receptor being considered, but there is strong experimental support for the presence and importance of a number of 'neuronal' receptors in sperm.     

How the sperm lost its tail: the evolution of aflagellate sperm

The typical sperm is comprised of a head, midpiece and flagellum. Around this theme there is an enormous diversity of form--giant sperm, multi-flagellate sperm and also sperm that lack flagella entirely. Explaining this diversity in sperm morphology is a challenging question that evolutionary biologists have only recently engaged in. Nonetheless, one of the selective forces identified as being an important factor in the evolution of sperm form is sperm competition, which occurs when the sperm of two or more males compete to fertilize a female's ova. In species with a truly monandrous mating system, the absence of sperm competition means that the selection pressure on males to produce motile sperm may be relaxed. Potentially aflagellate sperm are less costly to produce, both in terms of energy and time. Thus, selection may therefore favour the loss of the sperm flagellum and any other motile mechanisms in monandrous taxa. A review of the literature revealed that 36 taxonomic groups, from red algae to fish, were found independently to have evolved aflagellate sperm. I review what is known about the mating systems of each of these taxa and their nearest sister taxa. A sister-group analysis using this information provided weak evidence suggesting that the evolution of aflagellate sperm could be linked to the removal of selective pressures generated by sperm competition.     

A specific oligoteratozoospermia in a bull: The sperm tail stump defect

The first known case in the United States of a bull with the sterilizing oligoteratozoospermia known as “sperm tail stump defect” is reported. Ejaculates of semen were characterized by a watery appearance, extremely low sperm concentrations, sperm akinesia, and 100% abnormal spermatozoa. Different degrees of partial tail development were observed. The most common abnormalities were a short midpiece remnant or a cytoplasmic droplet-like rounded body replacing the midpiece and tail. Also, a high percentage of sperm head abnormalities were found. Testicular histology revealed seminiferous tubules with a low rate of spermatogenesis. Elongation of the spermatids did not proceed normally and no normal tail development was observed.     

The phylogenetic significance of sperm morphology in the Platyhelminthes

The phylogenetic significance of flatworm sperm morphology is discussed against the background of general spermatology. The modified type of spermatozoon of the Nemertodermatida, a group of primitive flatworms, indicates that the Platyhelminthes evolved from forms characterized by the primitive type of metazoan sperm and by the primitive mode of fertilization, implying the release of sperm freely into sea water.The occurrence of aberrant types of spermatozoa in most platyhelminths is obviously a consequence of early evolution of the internal mode of fertilization, which characterizes all true members of this group. It can be concluded, from the ultrastructure of these aberrant spermatozoa that higher metazoans cannot have evolved from seriated flatworms related to the recent Seriata (Proseriata and Tricladida). Even the seemingly primitive Acoela have such aberrant spermatozoa that evolution of higher metazoans from acoels related to the recent Acoela seems highly improbable.The ultrastructure of the spermatozoa of the parasitic groups of flatworms (Monogenea, Digenea, Cestoda) is very similar to that found in the Kalyptorhynchia, a further indication that the parasitic groups are related to the rhabdocoel turbellarians.     

Lateralisation in birds of prey: adaptive and phylogenetic considerations

Lateralisation, the different use of one or other side or appendix of the body, is basically determined by brain asymmetry which, in turn, is likely to be due to adaptive reasons. Several studies have been carried out on birds in general. However, birds of prey in particular, although they are very good candidates, have not been investigated from the sensory lateralisation point of view. In fact, many species scan for prey while perched and capture terrestrial prey with the feet, having at the same time the obvious necessity to keep their balance. This paper, therefore, investigates the existence of some sort of lateralisation in several species of both Falconiformes and Strigiformes temporarily in captivity. Attention is given to: (a) the direction of body rotation when perceiving a sound stimulus from behind the body and (b) the use of the feet when grasping a terrestrial prey. Lateralisation was found to be clearly present in both types of tests, although with some difference in its expression. In fact, almost every species tested rotated its body anti-clockwise, i.e. to the left, both in the first test and in repeated tests, with no noticeable difference between Falconiformes and Strigiformes. Also prey grasping showed a preferential use of one foot. Falconiformes preferred clearly to grasp the prey with one foot only in both the first test and in subsequent ones. Strigiformes, on the other hand, preferred using both feet, although a not insignificant proportion of individuals used one foot. Only the little owl seemed to have the tendency to prefer to use the right foot only, in a similar manner to Falconiformes. In fact, this bird is the most "diurnal" owl species among those tested, suggesting that lateralisation in footedness might be affected by adaptive constraints more than by phylogenetic similarities. Lateralisation, therefore, seems to be very widespread among birds of prey. Preferential use of the right foot also appears to be a general habit, and this is probably connected to the use of left hemisphere when manipulating food items.     

Cardiac metabolism in the Myxinidae: physiological and phylogenetic considerations

Cardiac muscle hearts of Atlantic hagfish continuously function under hypoxic conditions that would lead to cardiac failure in most other vertebrates. Contractile performance of hagfish systemic hearts is resistant to anoxia and respiratory poisons but shows a significant decrement when carbohydrate catabolism is blocked by 0.5 mM iodoacetic acid. Enzyme activity profiles of hagfish ventricle reveal a robust capacity for glycolysis of carbohydrate in comparison to that for general aerobic metabolism and catabolism of alternate metabolic fuels. Isolated working hagfish ventricles preferentially oxidize radiolabeled glucose even when fatty acid fuels are present in the incubation medium. Work output of the isolated ventricular preparation is maintained only in the presence of exogenous glucose. The results indicate that energy metabolism of the hagfish myocardium is predominantly carbohydrate-based and that energy demand of the tissue can be sustained by anaerobic glycolysis during extended periods of extreme hypoxia. Cardiac metabolism of this primitive species is compared with that of hearts from higher vertebrates and an evolutionary hypothesis relating cardiac workload to preferred metabolic fuel is discussed.     

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.     

KLC3 is involved in sperm tail midpiece formation and sperm function

Kinesin light chain 3 (KLC3) is the only known kinesin light chain expressed in post-meiotic male germ cells. We have reported that in rat spermatids KLC3 associates with outer dense fibers and mitochondrial sheath. KLC3 is able to bind to mitochondria in vitro and in vivo employing the conserved tetratrico-peptide repeat kinesin light chain motif. The temporal expression and association of KLC3 with mitochondria coincides with the stage in spermatogenesis when mitochondria move from the spermatid cell periphery to the developing midpiece suggesting a role in midpiece formation. In fibroblasts, expression of KLC3 results in formation of large KLC3 aggregates close to the nucleus that contain mitochondria. However, the molecular basis of the aggregation of mitochondria by KLC3 and its role in sperm tail midpiece formation are not clear. Here we show that KLC3 expression from an inducible system causes mitochondrial aggregation within 6h in a microtubule dependent manner. We identified the mitochondrial outer membrane porin protein VDAC2 as a KLC3 binding partner. To analyze a role for KLC3 in spermatids we developed a transgenic mouse model in which a KLC3ΔHR mutant protein is specifically expressed in spermatids: this KLC3 mutant protein binds mitochondria and causes aggregate formation, but cannot bind outer dense fibers. Male transgenic mice display significantly reduced reproductive efficiency siring small sized litters. We observed defects in the mitochondrial sheath structure in a number of transgenic spermatids. Transgenic males have a significantly reduced sperm count and produce spermatozoa that exhibit abnormal motility parameters. Our results indicate that KLC3 plays a role during spermiogenesis in the development of the midpiece and in the normal function of spermatozoa.     

The spermatozoon of Mengenilla moldrzyki (Strepsiptera,Mengenillidae): Ultrastructure and phylogenetic considerations

Even though the spermatozoa of several strepsipteran species were described earlier, no data were available for the basal family Mengenillidae. Well-fixed material of the recently described Tunisian species Mengenilla moldrzyki was used for a detailed examination of the sperm ultrastructure. The total length is c. 30 μm. The head region contains a conical acrosome vesicle (0.3-0.35 μm) and an elongated nucleus (7.3 μm) with dense chromatin. Some granular material along with a uniformely dense centriole adjunct and two mitochondrial derivatives are visible at the posterior end of the nucleus. The material of the centriole adjunct does not extend along the flagellum and accessory bodies are absent. The mitochondrial derivatives are elongated structures crossed by a longitudinal crista but lacking parallel transverse cristae and paracrystalline material in the dense matrix. The mitochondrial derivatives gradually reduce their size and end at the most posterior tail region. The flagellar axoneme has a 9 + 9 + 2 pattern and originates beneath the nucleus. In the terminal tail region the axoneme gradually disintegrates. Despite the extreme specialization of the endoparasitc group, strepsipteran spermatozoa are mostly characterized by plesiomorphies. The pattern within the order is largely uniform, but Mengenilla displays several apomorphic features compared to the presumptive strepsipteran groundplan (e.g., absence of crystallizations and cristae in the mitochondrial derivatives). The subdivision of the intertubular material into two compartments with a dense beak-like structure adhering to the tubular wall supports a clade Coleopterida (=Strepsiptera + Coleoptera) + Neuropterida.     

Pig sperm tail tubulin. Its extraction and characterization

Axonemal tubulin extracted from pig sperm tails has been characterized by one- and two-dimensional electrophoresis and by one-dimensional peptide mapping. The electrophoretic mobilities of its subunits after reduction and carboxymethylation were similar to those of the major subunits of pig brain tubulin. Sperm tail tubulin subunits also had roughly the same isoelectric points as pig brain tubulin subunits, except that they appeared to have a relatively larger tailing effect. The proteolytic cleavage pattern of the pig sperm tail beta-tubulin closely resembled those of both the tunicate (Ciona intestinalis) sperm beta-tubulin and pig brain beta-tubulin. The peptide pattern of pig sperm tail alpha-tubulin, however, was more similar to that of tunicate sperm tail alpha-tubulin than to that of pig brain alpha-tubulin. This supports the hypothesis put forward in a previous investigation [1] that functionally similar tubulins from taxonomically distant species can be more related than functionally dissimilar tubulins from the same species.     

Spermatid manchette: plugging proteins to zero into the sperm tail

Spermiogenesis pursues three major objectives: (1) The safeguard of the male genome within the confines of a compact nucleus. (2) The accumulation of enzymes in the acrosome of be released at fertilization. (3) The development of a sperm propelling tail consisting of an axoneme surrounded by a scaffold of keratin-containing outer dense fibers and a fibrous sheath. Recent experimental data indicate that three keratins-Sak57, 0df1 and 0df2-and other proteins (the 26S proteasome and the 0df1-binding protein Spag4) are temporarily stored in the manchette before being sorted to the developing sperm tail. These findings support a general model for the manchette as an ephemeral structure timely developed and strategically positioned to provide a transient storage to both structural and signaling proteins. Some of the proteins are later sorted to the developing tail; others may participate in the reciprocal nuclear-cytoplasmic signaling pathways as the gene activity of the male genome gradually becomes silent. Mol. Reprod. Dev. 59: 347-349, 2001.     

Ultrastructural characteristics of the spermatozoa of Scelionidae (Hymenoptera, Platygastroidea) with phylogenetic considerations

The Scelionidae sperm are distinguished from those of all hymenopterans already studied at least by the presence of a single mitochondrial derivative and the absence of a centriolar adjunct. The absence of an acrosome, in Telenomus podisi , is also unique. The helical nucleus and mitochondrial derivative spiralling around a twisted axoneme can be considered as synapomorphies shared with the Chalcidoidea, and the mitochondrial derivative running together with the nucleus for a long distance can be considered as a synapomorphy shared with the Diapriidae. Therefore, from a consideration of these features, it is possible to suppose that the Scelionidae, Chalcidoidea and Diapriidae are more closely related between themselves than are any of them to the Cynipoidea, since the latter does not share any of the above-mentioned features. This supposition agrees with phylogenetic analyses that supported the inclusion of Platygastroidea (Scelionidae and Platygastridae) and Chalcidoidea within the Proctotrupomorpha lineage, as well as the close relationship of these to the Diapriidae, and the exclusion of the Cynipoidea from this lineage.