Sperm morphology in the Malagasy rodents (Muroidea: Nesomyinae)

The morphology of the spermatozoon of representative species of the subfamily Nesomyinae (Muroidea: Nesomyidae), a monophyletic group of rodents endemic to Madagascar, was examined by light and electron microscopy to determine the sperm head shape and tail length across the species. Marked interspecific differences were found to occur in both the form of the sperm head and length of the tail. The species that possess a sperm head with an apical hook, which largely contains acrosomal material, generally displayed longer sperm tails, and a species with a spatulate sperm head had the shortest tail. The association between sperm head shape and tail length mirrors that previously found in Eurasian and Australasian murine rodents. Thus, the repeated association between sperm head shape and tail length across these groups of muroid rodents clearly indicates a functional relationship between these two features. A comparison of sperm morphology of the nesomyines to that of related muroid rodents on the mainland of Africa suggests that the possession of an apical hook is the ancestral condition. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Structure and ultrastructure of the spermatozoa of Trichogramma pretiosum Riley and Trichogramma atopovirilia Oatman and Platner (Hymenoptera: Trichogrammatidae)

Lino‐Neto, J., Báo, S. N. and Dolder, H. 2000. Structure and Ultrastructure of the Spermatozoa of Trichogramma pretiosum Riley and Trichogramma atopovirilia Oatman and Platner (Hymenoptera: Trichogrammatidae). —Acta Zoologica (Stockholm) 81 : 205–211 Spermatozoa of the Trichogramma pretiosum and T. atopovirilia are very slender and long, about 0.35 µm in diameter and 283 µm and 106 µm in length, respectively. Under light microscopy, they appear wavy along their entire length. The head contains a small acrosome which, together with the initial nuclear region is surrounded by an ‘extracellular sheath’, from which innumerable filaments irradiate. The nucleus is filled with homogeneous, compact chromatin and is attached to the flagellum by an electron dense centriolar adjunct, which extends anteriorly from the nuclear base. The flagellum consists of an axoneme with the 9 + 9 + 2 microtubule arrangement pitched in a long helix, as well as a pair of spiralling mitochondrial derivatives which coil around the axoneme. Based on these characteristics, the sperm of these Trichogramma are very similar to the chalcidoids studied to date and differ from non‐chalcidoid Hymenoptera. They differ widely from the sperm of T. dendrolimi and T. ostriniae studied, where no helically twisted structure is shown. However, based on these results we argue that the spiralling of the flagellar structures is a synapomorphy for Trichogrammatidae as well as for Eulophidae + Eurytomidae + Pteromalidae.     

Co‐evolution of gametes of the Greater Bandicoot Rat,Bandicota indica – a murine rodent from South‐East Asia

Most Old World mice and rats, subfamily Murinae, have a spermatozoon with an apical hook, a long tail and, as seen typically in eutherian mammals, a bilaterally flattened head. Dramatically different from this are the sperm of the Greater Bandicoot Rat, Bandicota indica. Here, we ask the question has the structure of the sperm head co‐evolved with that of the egg coat, the zona pellucida? For this, we first summarise the morphological features of the spermatozoon of B. indica that may relate to zona pellucida penetration at the time of fertilisation, and we confirm that the sperm head is generally round, not bilaterally flattened, in profile and has a huge acrosome. We then show that the zona pellucida around oocytes in tertiary follicles also differs from that of the other murine rodents in being only about 4 μm thick and, as demonstrated by lectin staining, has an unusual abundance of alpha‐L‐fucose. These findings indicate that both the male and female gametes of this South‐East Asian murine rodent are highly divergent in their structural organisation. One of the functional implications of this probably relates to sperm–zona interactions and the release of acrosomal enzymes that probably facilitate penetration by digestion of the zona matrix at the time of fertilisation.     

Evolution of the spermatozoon in muroid rodents

In the rodent superfamily Muroidea, a model for the evolution of sperm form has been proposed in which it is suggested that a hook-shaped sperm head and long tail evolved from a more simple, nonhooked head and short tail in several different subfamilies. To test this model the shape of the sperm head, with particular emphasis on its apical region, and length of sperm tail were matched to a recent phylogeny based on the nucleotide sequence of several protein-coding nuclear genes from 3 families and 10 subfamilies of muroid rodents. Data from the two other myomorph superfamilies, the Dipodoidea and kangaroo rats in the Geomyoidea, were used for an outgroup comparison. In most species in all 10 muroid subfamilies, apart from in the Murinae, the sperm head has a long rostral hook largely composed of acrosomal material, although its length and cross-sectional shape vary across the various subfamilies. Nevertheless, in a few species of various lineages a very different sperm morphology occurs in which an apical hook is lacking. In the outgroups the three species of dipodid rodents have a sperm head that lacks a hook, whereas in the heteromyids an acrosome-containing apical hook is present. It is concluded that, as the hook-shaped sperm head and long sperm tail occur across the muroid subfamilies, as well as in the heteromyid rodents, it is likely to be the ancestral condition within each of the subfamilies with the various forms of nonhooked sperm heads, that are sometimes associated with short tails, being highly derived states. These findings thus argue against a repeated evolution in various muroid lineages of a complex, hook-shaped sperm head and long sperm tail from a more simple, nonhooked sperm head and short tail. An alternative proposal for the evolution of sperm form within the Muroidea is presented in the light of these data.     

Sperm morphology and its influence on swimming speed in Atlantic cod

A protocol for staining fish spermatozoa using Hemacolor-stain was developed for light microscopy and successfully applied to Atlantic cod ( Gadus morhua ). Sperm head morphology was characterized by size (length, width, area and perimeter) and shape (ellipticity, rugosity, elongation and regularity) (n   =   6500 spermatozoa), and tail length (n   =   260 spermatozoa) of 12 individual cod. Two spermatozoa heads sperm were clearly identified: round and elongated, being this last one more abundant (86.3%). No evidence was detected in tail length for both head types. Tails were 96.4% length of sperm and no difference in tail length was detected between head types. A positive correlation existed between head and tail length, with variability existing among males. Sperm swimming speeds varied among males with a maximum curvilinear velocity between 151.5 and 201.5  μ m s⁻¹. Mean swimming speed declined by 8.2% from 30 to 70 s post-activation. Spermatocrit was negatively correlated with curvilinear velocity at 30 s post-activation. Males with short sperm heads maintained their swimming velocity for longer periods that those with long heads. Fulton's condition factor was negatively correlated with straightness of path.     

The spermatozoon of the Old Endemic Australo‐Papuan and Philippine rodents – its morphological diversity and evolution

Breed, W.G. and Leigh, C.M. 2010. The spermatozoon of the Old Endemic Australo‐Papuan and Philippine rodents – its morphological diversity and evolution.—Acta Zoologica (Stockholm) 91 : 279–294 The spermatozoon of most murine rodents contains a head in which there is a characteristic apical hook, whereas most old endemic Australian murines, which are part of a broader group of species that also occur in New Guinea and the Philippines, have a far more complex sperm form with two additional ventral processes. Here we ask the question: what is the sperm morphology of the New Guinea and Philippines species and what are the trends in evolutionary changes of sperm form within this group? The results show that, within New Guinea, most species have a highly complex sperm morphology like the Australian rodents, but within the Pogonomys Division some species have a simpler sperm morphology with no ventral processes. Amongst the Philippines species, many have a sperm head with a single apical hook, but in three Apomys species the sperm head contains two additional small ventral processes, with two others having cockle‐shaped sperm heads. When these findings are plotted on a molecular phylogeny, the results suggest that independent and convergent evolution of highly complex sperm heads containing two ventral processes has evolved in several separate lineages. These accessory structures may support the sperm head apical hook during egg coat penetration.     

Spermatozoa of murid rodents from Africa: morphological diversity and evolutionary trends

The diversity of the structural organization of the spermatozoa of African murid rodents is described at the light and transmission electron microscopical level of resolution. In most species the sperm head is falciform in shape but it varies somewhat in overall breadth, width, and length. A typical perforatorium is present and the acrosome splits into a large head cap over the convex surface and a smaller ventral segment similar to the sperm head of most Asian and Australasian murids. In a few species, however, the morphology is very different. In Acomys and Uranomys spermatozoa, the apical hook is more bilaterally flattened, has a large apical acrosomal region, and no separate ventral segment. Two species of Aethomys have, in addition to an apical hook, a 4μ long extension of the cytoskeletal material that projects from the concave surface of the sperm head, whereas in Dasymys two large ventral processes extend from the upper concave region which contain nuclear material basally and a huge extension of cytoskeleton apically. In Aethomys chrysophilus type B, the sperm nucleus is unique in form and often has a central region in which threads of chromatin can be seen; it is capped by a massive acrosome whose apical segment is complex and convoluted in structure. Stochomys longicaudatus appears to have a conical sperm head, and in all three Lophuromys species the sperm head is spatulate in shape with the flat, plate-like nucleus capped by a thin acrosome. The evolutionary trends in changes of sperm head shape and design of these rodents are discussed. It is suggested that some of the differences in morphology may relate to the variation in structural organization of the coats around the egg through which the spermatozoon has to pass in order for fertilization to occur.     

The Gerbil Spermatozoon – interspecific variation in morphology does not invariably follow murine rodent evolutionary trends in response to predicted intermale sperm competition

In various groups of mammals, the intensity of intermale sperm competition relates to relative testes mass (RTM) with some evidence suggesting that this may also be the case for some aspects of sperm form. In murid rodents, a large RTM generally correlates with a streamlined sperm head, long apical hook and long tail with most data coming from species in the subfamily Murinae. In this study, RTM and sperm form are compared across 15 species of gerbils, seven from the Tribe Taterillini and eight from the Tribe Gerbillini. Marked interspecific differences in RTM and sperm morphology were observed. However, the Gerbilliscus species with the largest RTM do not have a sperm head with an apical hook nor a longer sperm tail than other species with smaller RTM whereas, by contrast, in the Tribe Gerbillini, species where the sperm head lacks a hook have a relatively small testes mass. We thus suggest that in gerbils, unlike in murine rodents, high levels of postcopulatory sexual selection have not invariably resulted in the evolution of a spermatozoon with a long apical hook and long sperm tail. The possible reasons for this are briefly discussed.     

Giant,accordioned sperm acrosomes of the greater bulldog bat,Noctilio leporinus

Sperm of the greater bulldog bat Noctilio leporinus display an architecture that is totally unique among mammalian spermatozoa. The sperm head of Noctilio is extraordinarily large and flat and lies eccentrically with respect to the sperm tail. The major portion of the atypically large acrosome lies anterior to the nucleus and is shaped into a dozen accordionlike folds that run parallel to the long axis of the sperm. The ridge of each fold is shaped into ∼60 minute, evenly spaced rises that extend along the entire length of the fold. We speculate that acrosome ridges may serve to strengthen the sperm head during transport. Mol. Reprod. Dev. 48:90–94, 1997 © 1997 Wiley-Liss, Inc.     

Sperm ultrastructure in Kellia suborbicularis (Bivalvia: Galeommatoidea: Kellidae)

The sperm cells of Kellia suborbicularis are narrow with a short bullet‐shaped acrosome, a 5.0–5.5 µm long and 0.4–0.6 µm broad nucleus, and a short midpiece with a ring of five mitochondria. The disposition of the subacrosomal substance into a coronet‐like formation is unique, and the sperm structure offers no clue to the relationship between Kellia and other galeommatoidean genera. The possible significance of narrow elongate sperm for their entry into the brood pouch is discussed.     

Morphology of gametes in sea urchins from Peter The Great Bay,Sea of Japan

The fine structure of the gametes in six sea urchin species of the Sea of Japan was studied. The sperm in Strongylocentrotus nudus, S. intermedius, Echinocardium cordatum, Scaphechinus mirabilis, Sc. griseus and Echinarachnius parma are species-specific. The conical head and symmetrically disposed ring-shape mitochondrion are common to regular sea urchin sperm cells. S. nudus is characterized by the bulb-shaped head of the sperm; S. intermedius, by a bullet-shaped one. The sperm spearhead and small amount of post-acrosome material are common to irregular sea urchins; the sperm width: length ratio varies for different species, with the highest for Sc. mirabilis. The sperm of Sc. griseus is characterized by two lipid drops in the middle part of sperm. Asymmetrical mitochondrion disposal is usual for E. parma. Actin filaments are found in the postacrosome material in the sperm of heart-shaped sea urchins. The differences in the fine structure of sperm in cosmopolitan species Ech. cordatum inhabiting the Sea of Japan and coastal areas of the Northeast Atlantic may bear record to the complex existence of species Ech. cordatum. The fine structure of sperm is unique for each of the studied families, Strongylocentrotidae, Scutellidae, and Loveniidae. The eggs of all the species are characterized by vitelline and jelly-like membranes. The vitelline membrane is formed by cytoplasm protrusions; the area between them is filled with fibrillar material. The jelly-like membrane is formed by fibrillar material associated with apical parts of microvilli of the vitelline membrane. The irregular sea urchins Sc. griseus, Sc. mirabilis and E. parma are characterized by chromatophores situated in the jelly-like membrane, with the highest abundance in Sc. mirabilis.     

Ultrastructure of spermiogenesis in <Emphasis Type="Italic">Cristatella mucedo</Emphasis> Cuvier (Bryozoa: Phylactolaemata: Cristatellidae)

In Cristatella mucedo spermiogenesis occurs in a morula consisting of a large number of spermatids connected with a central cytophore. The mature sperm cell is filiform and consists of a head, a midpiece and a tail region, the latter two separated by a deep circular constriction. The comparatively short head contains a drop-shaped, bilaterally symmetrical and pointed nucleus capped by a minute acrosome. The single centriole is placed in a deep posterior invagination of the nucleus followed by the axoneme with the typical 9 + 2 pattern. The elongated midpiece is 0.9–1.1 μm thick and contains several helices of mitochondria surrounding the axoneme. The tail is thicker (1.3 μm) and richer in cytoplasm with many compact accumulations of an electron-dense substance lying peripherally and another less dense material wrapped around the axoneme. The course of the spermiogenesis and the fine structure of the sperm are very similar to that of Plumatella fungosa. Comparison with other species shows that the same sperm type is recognizable in four of the five families of Phylactolaemata and, provided it occurs also in the fifth family, the Stephanellidae, is a synapomorphy of the entire class.     

Growth and cellular organization of Arabidopsis pollen tubes in vitro

Tricellular pollen tubes of Arabidopsis thaliana were cultured in vitro on solid media and studied with respect to growth, cellular organization and ultrastructure, cytoskeletal organization, organelle movement, deposition and structure of the wall and the occurrence of coated pits, all elements assumed to be relevant for tip growth. For our ultrastructural studies we used freeze fixation and freeze substitution. Although Arabidopsis pollen tubes are broadly similar to those of bicellular species such as Nicotiana tabacum and Lilium spec. and in vivo grown pollen tubes of Arabidopsis, some differences occurred. The density of the equally distributed, relatively small (85 nm) secretory vesicles (SV) in the tip is low (five/µm ²). In between the SV of the tip, membranous material, possibly smooth endoplasmic reticulum, fragments of rough endoplasmic reticulum and loose ribosomes are present. The wall in the tip is not amorphous but layered and a secondary wall is formed already in the flanks of the tip. The general pattern of organelle motion is reverse fountain-like, but individual organelles move in distinct lanes at speeds of up to 2 µm/s, and about half of the organelle population shows a moderate velocity or Brownian movement. These properties are discussed in relation to the low growth rate (10 µm/h) of Arabidopsis pollen grown in vitro. The two similar sperm cells are closely attached and are always found near the vegetative nucleus. No surrounding wall and no cytoskeletal elements were obvious in the sperm cells. The preferential location of the mitochondria at the wall and the large (up to 400 nm) coated pits are unique for angiosperm pollen tubes. The size of the coated pits may allow not only membrane retrieval but also pinocytosis.     

Sperm head structure of a murid rodent from Southern Africa: The red veld rat Aethomys chrysophilus

The morphology of spermatozoa from the red veld rat, Aethomys chrysophilus, of Southern Africa is described; two very different types were found, which came from animals from two separate, as-yet-undescribed, species. In individuals from South Africa the sperm head had a somewhat disc-shaped nucleus and a large acrosome with a huge apical segment that, during epididymal transit, changed in form from initially projecting anteriorly to a highly complex structure that was flexed caudad and lay alongside part of the rest of the sperm head. In addition, the chromatin generally appeared to be not fully condensed. Spermatozoa from animals collected in Malawi were very different in morphology and had a head with a typical apical hook, a perforatorium, fully condensed chromatin, and a 4-μm-long ventral spur. Its sperm tail was also significantly longer. The time of divergence of these two groups of animals from a common ancestor is not known, but the present results show that a considerable morphological change in the sperm nucleus, acrosome, and subacrosomal space can evolve even between two, presumably closely related, species.     

Abundance and size change of Hannaea baicalensis in Lake Baikal

Hannaea baicalensis is a benthic pennate diatom that predominantly grows at depths of less than a metre attached to rocks and filamentous algae in Lake Baikal, Russia. This narrow zone at the edge of the lake is subject to frequent wave action and lake level fluctuations, which combine with other factors to affect seasonal abundance. During ice cover from January to May in 2008, when lake levels decreased from 42 to 14 cm above datum, H. baicalensis cell abundance remained low (0.39 × 10⁶ cells cm^–2). The main period of net cell increase occurred in autumn, when there was a period of stable lake level (±10 cm changes in water depth) that coincided with the return of nutrients during autumn overturn. Cell abundance reached 1.52 × 10⁶ cells cm^–2 on 31 October. Alongside the changes in abundance, cyclic size changes in cell apical lengths were found (40 to 144 µm), which were associated with timing of the length of the life cycle. Size decline occurred in both spring and autumn, with an average decrease in apical length of 36 µm per year. It took two years for the mean apical length of a single cohort to decrease from 128 µm to 56 µm, which was then below the threshold (< 65 µm) for initiation of size regeneration.     

Ultrastructure of the sperm and spermatogenesis and spermiogenesis of Dina lineata (hirudinea,erpobdellidae)

The mature sperm of Dina lineata is of the modified type. The sperm are 48 μm long and 0.3 μm wide. The sperm are filiform and helicoidal cells with a distinct head, a midpiece, and a tail. There are two distinct regions in the head: the acrosome and the posterior acrosome, each with its own characteristic morphology. The midpiece is the mitochondrial region and has a single mitochondrion. Two distinct portions can be observed in the tail: the axonematic region and the terminal piece. In the process of spermatogenesis the early spermatogonia divide to form a poliplast of 512 spermatic cells. In the spermiogenesis the following sequential stages can be distinguished: elongation of the flagellum; reciprocal migration of mitochondria and Golgi complex; condensation of chromatin and formation of the posterior acrosome; spiralization of nuclear and mitochondrial regions; and, finally, formation of the anterior acrosome. The extreme morphological complexity of the Dina spermatozoon is related to the peculiar hypodermal fertilization which characterizes the erpobdellid family. Correlation between sperm morphology and fertilization biology in the Annelida is revised.     

Spermiogenesis and ultrastructure of spermatozoa in Saxipendium coronatum (Hemichordata,Enteropneusta), with consideration of their relation to reproduction and dispersal

Summary Sperm ultrastructure and spermiogenesis of the enteropneust hemichordate Saxipendium coronatum conforms to the general pattern of the prototype spermatozoon found in many phyla. The sperm is about 29 m long, including head, middle piece, and tail. The Saxipendium spermatozoon has some unique features. The head is pyramidal in shape and the nucleus has four frontal ridges radiating from the base of the acrosomal region. The acrosome is composed of a large acrosomal vesicle surrounded by periacrosomal material. The acrosomal region projects about 1 m in front of the nucleus and has a width at the base of 1.5 m. The middle piece is dish-shaped and contains a large mitochondrial mass surrounding the centriolar region. The centriolar region is partially located in a centriolar fossa at the basal part of the nucleus. In spermatids, an anchoring fiber apparatus is observed surrounding the centriolar region. The distal ends of the fibers are attached to the plasmalemma by electron-dense thickenings. The tail is a simple flagellum. The sperm of Saxipendium and the small eggs found in the female suggest non-specialized external fertilization and embryogeny leading to a planktotrophic larva. The main results of the fine structure of the spermatozoon in Saxipendium are summarized in Fig. 12.Abbreviations used in the figures an antrum - av acrosomal vesicle - ax axoneme - d distal centriole - ep epidermis - f flagellum - gp gonopore - m mitochondrion - mp middle piece - n nucleus - p proximal centriole - per periacrosomal material - sp sperm - te testis - vac vacuolated cells     

Structure of the zona pellucida and cumulus oophorus in three species of native Australian rodents

The sperm head of many Australian hydromyine rodents has three curved hooks projecting from its anterior margin; the structure of the hooks has been characterized, but their function is unknown. In this study, we have investigated whether the hooks might have evolved to assist sperm penetration through more formidable egg vestments, particularly the zona pellucida. Cumulus-oocyte complexes were obtained from two species that possess a three-hooked sperm head (Pseudomys australis and P. nanus) and one species that does not (Notomys alexis) and examined by light and electron microscopy. After fixation in the presence of ruthenium red, the zona pellucida was found to consist of a fibrillar meshwork, but there were no interspecific structural differences. A corona radiata was absent, and the cumulus extracellular matrix was composed of filaments and electron-dense granules in each species. Measurements of the zona thickness in freshly ovulated, unfixed oocytes revealed that it was thinnest (7.8 μm) in P. australis. Which has a three-hooked sperm head, and thickest (11.4 μm) in N. alexis, the species in which the ventral hooks are absent. Hence, no correlation was found between the thickness of the zona pellucida or the structure of the cumulus-oocyte complex, and the presence of three hooks on the sperm head. We conclude, therefore, that it is unlikely that the evolution of the three-hooked sperm head is an adaptation for penetration of increased barriers around the oocyte.     

Variation in Apical Hook Length Reflects the Intensity of Sperm Competition in Murine Rodents

Background

Post-copulatory sexual selection has been shown to shape morphology of male gametes. Both directional and stabilizing selection on sperm phenotype have been documented in vertebrates in response to sexual promiscuity.

Methodology

Here we investigated the degree of variance in apical hook length and tail length in six taxa of murine rodents.

Conclusions

Tail sperm length and apical hook length were positively associated with relative testis mass, our proxy for levels of sperm competition, thus indicating directional post-copulatory selection on sperm phenotypes. Moreover, our study shows that increased levels of sperm competition lead to the reduction of variance in the hook length, indicating stabilizing selection. Hence, the higher risk of sperm competition affects increasing hook length together with decreasing variance in the hook length. Species-specific post-copulatory sexual selection likely optimizes sperm morphology.     

The Fluorescent Dye 3, 3′ Dihexyloxacarbocyanine Iodide Selectively Stains the Midpiece and Apical Region of the Heads of Murid Rodent Spermatozoa

Fluorescence microscopy of caudal epididymal spermatozoa stained with 3, 3′ dihexyloxacarbocyanine iodide (DiOC₆(3)) showed intense fluorescence along the concave surface of the apical hook of spermatozoa of Rattus species and along the upper concave margin of the sperm head in Mus musculus In the spermatozoa of Hydromys chrysogaster, Melomys cervinipes, and Pseudomys australis, the two ventral processes also fluoresced brightly. In P. australis, fluorescence in the apical hook of sperm heads was largely localized to its upper and lower surfaces. The sperm of N. alexis did not show consistent positive fluorescence. The localization of fluorescence in these spermatozoa after staining with DiOC₆(3) was mainly restricted to regions where a large accumulation of perinuclear theca material lies beneath the plasmalemma. The reason for this remains to be determined, but DiOC₆(3) may be useful for quickly demonstrating areas of abundant perinuclear thecal material in sperm heads of eutherian mammals by light microscopy.