Ovary of the seahorse,Hippocampus erectus

The ovary of the seahorse, Hippocampus erectus, is a cylindrical tube bounded by an outer layer consisting of a mesothelium and muscular wall and by an inner luminal epithelium, with a single row of developing follicles sandwiched between the two layers. Follicles are produced by a germinal ridge, which contains oogonia, early oocytes, and prefollicle cells, and which runs along the length of the ovary. The germinal ridge is an outpocketing of the luminal epithelium, as indicated by a continuous underlying basal lamina. Prefollicle cells invest diplotene oocytes and the complex eventually pinches off the germinal ridge as a primordial follicle surrounded by a basal lamina derived from the germinal ridge. Subsequent investment of the primordial follicle by elements of the theca complete the process of folliculogenesis. H. erectus has two ovaries and each ovary has two dorsally located germinal ridges. Thus, in each ovary the derived follicular lamina is bilaterally symmetrical: two temporally and spatially arranged sequences of developing follicles are produced, with the largest follicles found along the ventral midline of the ovary. The advantages of developmental, kinetic, and systemic analyses of these unusual ovaries are indicated.     

A monogamous pipefish has the same type of ovary as observed in monogamous seahorses

Syngnathid fish (pipefish and seahorses) are unique among teleost fish in that their ovary consists of a rolled sheet with germinal ridge(s) on the dorsal side running along the entire length of the sheet. A distinct difference is seen in the ovarian structure between polygamous Syngnathus pipefish and monogamous seahorses (Hippocampus spp.), the former having one germinal ridge and the latter with two ridges. This study examined the ovarian structure and the mode of egg production in a monogamous pipefish Corythoichthys haematopterus. The ovary of C. haematopterus had two germinal ridges like that observed in monogamous seahorses. There were two distinct groups of follicles in the ovary, one being a cohort of extremely small follicles and the other a cohort of follicles developing and increasing in size with the passage of time. We suggest that the ovarian structure and the mode of egg production in this pipefish are adaptations to monogamy.     

Basic reproductive biology of the barbed pipefish <Emphasis Type="Italic">Urocampus nanus</Emphasis> (Syngnathidae) under laboratory conditions

The mating behaviour, fecundity characteristics and egg production process were investigated in the barbed pipefish Urocampus nanus under aquarium conditions. The mating behaviour consisted of five motor patterns, some of which have been generally reported in other syngnathids. Neither the number nor size of newborns related to the size of parents, although there was a negative correlation between the number and size of newborns. The ovary consisted of two germinal ridges, and mature eggs were produced synchronously with multiple ovulations. This type of egg production has thus far been reported only in a polyandrous and sex-role-reversed pipefish.     

The ovarian structure and mode of egg production in two polygamous pipefishes: a link to mating pattern

In this study, the ovarian structure and mode of egg production were examined in two pipefishes, the broad-nosed pipefish Syngnathus typhle and the straight-nosed pipefish Nerophis ophidion, which show different types of polygamous mating patterns. Syngnathus typhle showed an ovary with one germinal ridge and asynchronous egg production, corresponding to previous findings in other polygamous Syngnathus pipefishes. In contrast, the ovary of N. ophidion had two germinal ridges and eggs were produced synchronously in groups, similar to what has been observed in monogamous syngnathids. The egg production of N. ophidion, however, is clearly distinguished from that of monogamous syngnathids by the additional egg production after an ovulation. It is suggested that the differences in female mating strategies result from the difference in egg production process and that this is related to the difference in mating pattern between these two polygamous species.     

Reproduction and sexual development in a freshwater gastrotrich

Summary Six small cells are present in each of the bilateral gonads of parthenogenically reproductive Lepidodermella squammata. Early in the extended postparthenogenic phase of the life history, these cells undergo limited proliferation followed by differentiation. Primary oocytes of three types are present 0.3 days after deposition of the final parthenogenic egg: small oocytes with presynaptic nuclei; intermediate oocytes with nuclei containing synaptonemal complexes; and larger oocytes with a germinal vesicle. Oocytes persist without further development at least until day four of the postparthenogenic phase. Older isolated animals may contain and even deposit an enlarged egg, but successful progeny does not result. Oocytes are located at the anterior pole of each of the bilateral gonads, adjacent to developing male tissues producing sperm. More posterior cells in the gonad are initially undifferentated in the postparthenogenic phase. Dorsal and central cells first show specialization for secretory activity, and by day four contain peripheral layers of RER and central accumulations of polymorphic secretion droplets. The posterior and ventral cells produce secretion droplets that aggregate into an enlarging bilobed structure called the X-body. Two or three cells in each gonad contribute secretions to the X-body, which is intracellular in a secondary syncytium formed by the contributing cells. Functions for the postparthenogenic gametes and for the X-body are not yet demonstrated.     

Generational shape shifting: changes in egg shape and size between sexual and asexual generations of a cyclically parthenogenic gall former

Successive generations of multivoltine species experience selection specific to the spatiotemporal environments encountered that may lead to adaptive divergence in reproductive traits among generations. To compare reproductive effort within and between generations, appropriate volumetric models, selected on the basis of the analysis of egg shape, are required to estimate the sizes (volumes) of individual eggs. We assessed the shape and estimated the volume of individual eggs produced by the temporally and spatially segregated sexual and asexual generations of the gall former, Belonocnema treatae Mayr (Hymenoptera: Cynipini: Cynipidae). Egg shape, indexed as the difference between the polar and equatorial axes of the ellipsoidal eggs, was independent of egg size, but differed between generations. The relationship of egg shape and female body size within and between generations confirmed that egg shape is an intrinsic property of each generation. Generational differences in egg shape then informed the selection of volumetric models to estimate egg size. We modeled asexual generation eggs as both spheres and prolate spheroids, and sexual generation eggs as both cylinders and prolate spheroids. Choice of volumetric model changed estimates of egg size within the asexual generation by 23% and within the sexual generation by 50%. Comparisons between generations based on the above models produced estimated differences in egg volume that ranged from 16 to 114%. In both generations, a prolate spheroid was the most parsimonious model of egg volume. Based on this model, sexual generation eggs averaged 43% larger than asexual generation eggs. The increased size of sexual eggs was achieved via conservation of the egg’s equatorial axis and elongation of the polar axis. The shift in egg shape between sexual and asexual B. treatae is the first documented dimorphism in an egg characteristic expressed between generations of a cyclically parthenogenic organism.     

Reproductive allocation and reproductive ecology of seven species of Diptera

1. Variation in resource allocation to egg size and number was investigated in seven sympatric species of Piophilidae that oviposit on carcasses or discarded cervid antlers: Liopiophila varipes (Meigen), Prochyliza xanthostoma Walker, Protopiophila latipes (Meigen), Protopiophila litigata Bonduriansky, Stearibia nigriceps (Meigen), and two unidentified species of Parapiophila McAlpine. 2. Following optimal reproductive allocation theory, relatively larger, fewer eggs were expected in (1) species that oviposit on antlers, where larvae probably experience lower risk of predation and greater competition than larvae in carcasses, and (2) species with aggressive males and male-biased sex ratios on the oviposition substrate, where risk of injury during oviposition may have favoured females laying fewer eggs. 3. Variation in reproductive allocation strategies could not be explained by known differences in larval or adult environment, but congeneric species clustered by reproductive allocation patterns. The Parapiophila species produced larger, fewer eggs than the other species, and egg number increased slowly with body size. The Protopiophila species did not deviate from expected egg sizes and numbers, and egg number increased steeply with body size. 4. An interspecific egg size–egg number trade-off resulted in a tight linear scaling of ovary volume to body size, suggesting common physiological constraints on relative ovary mass. 5. Within each species, egg size was nearly constant whereas egg number increased with female body size, suggesting species-specific stabilising selection on egg size.     

Ovarian structure and mode of egg production in the seaweed pipefish Syngnathus schlegeli (Syngnathidae)

This study investigated ovarian structure and mode of egg production in the seaweed pipefish, Syngnathus schlegeli. The ovary had a rolled sheet-like structure where developing follicles were arranged serially in sequence according to their development, with a single germinal ridge running along the edge of the sheet. Oocytes of various developmental stages were concomitantly present in the ovary, and the number of mature eggs increased continuously over time, indicating that egg production is asynchronous. This would be a physiological basis for multiple spawning within a short time span associated with polygamy in this fish.     

Ovary cord structure and oogenesis in Hirudo medicinalis and Haemopis sanguisuga (Clitellata, Annelida): remarks on different ovaries organization in Hirudinea

In Hirudo medicinalis and Haemopis sanguisuga, two convoluted ovary cords are found within each ovary. Each ovary cord is a polarized structure composed of germ cells (oogonia, developing oocytes, nurse cells) and somatic cells (apical cell, follicular cells). One end of the ovary cord is club-shaped and comprises one huge apical cell, numerous oogonia, and small cysts (clusters) of interconnected germ cells. The main part of the cord contains fully developed cysts composed of numerous nurse cells connected via intercellular bridges with the cytophore, which in turn is connected by a cytoplasmic bridge with the growing oocyte. The opposite end of the cord degenerates. Cord integrity is ensured by flattened follicular cells enveloping the cord; moreover, inside the cord, some follicular cells (internal follicular cells) are distributed among germ cells. As oogenesis progresses, the growing oocytes gradually protrude into the ovary lumen; as a result, fully developed oocytes arrested in meiotic metaphase I float freely in the ovary lumen. This paper describes the successive stages of oogenesis of H. medicinalis in detail. Ovary organization in Hirudinea was classified within four different types: non-polarized ovary cords were found in glossiphoniids, egg follicles were described in piscicolids, ovarian bodies were found characteristic for erpobdellids, and polarized ovary cords in hirudiniforms. Ovaries with polarized structures equipped with apical cell (i.e. polarized ovary cords and ovarian bodies) (as found in arhynchobdellids) are considered as primary for Hirudinea while non-polarized ovary cords and the occurrence of egg follicles (rhynchobdellids) represent derived condition.     

Structure and function of the spermathecal complex in the phlebotomine sandflyPhlebotomus papatasi Scopoli (Diptera: Psychodidae): II. Post-copulatory histophysiological changes during the gonotrophic cycle

The spermathecal complex ofPhlebotomus papatasi Scopoli (Diptera: Psychodidae) undergoes histological and physiological changes during its gonotropic cycle. The present histochemical study revealed a mucopolysaccharide secretory mass in the spermathecae of the newly emerged sandfly. Sperm competition occurs when two or more males compete to fertilize an ovum in the female reproductive tract. In this study, spermatophores of two or more competing males were deposited at the base of the spermathecal ducts, which originate from the female bursa copulatrix. This suggests that females play a role in sperm displacement, which is defined as any situation in which the last male to mate with a female fertilizes maximum number her eggs. A blood meal ingested by the female for ovary development and egg laying stimulates the release of sperm from the spermatophore. The spermatozoa then migrate to the lumen of the spermatheca. The ultrastructure of spermatozoa comprises a head with double-layered acrosomal perforatorium, an elongate nucleus, and the axoneme with a 9 + 9 + 0 flagellar pattern. This axomene differs from the aflagellate axoneme of other Psychodinae. Morphological changes, such as the casting off of the acrosomal membrane, and histological changes in the spermatophore are also described. Mating plugs that have been described previously in sandflies appear to be artefacts. Females ofP. papatasi may be inseminated more than once during each gonotrophic cycle, and additional inseminations may be necessary for each cycle. The relationships between the volumes of the sperm and the spermatheca were calculated to determine sperm utilization and fecundity ofP. papatasi. As the females ofP. papatasi mate polyandrously, the anatomical and physiological complexity of the spermathecal complex may be related to post-copulatory sexual selection.     

Ovary of the pipefish,Syngnathus scovelli

Gross dissection, light microscopy, and transmission electron microscopy were used to generate a detailed understanding of the ovarian anatomy of the pipefish, Syngnathus scovelli. The ovary is a cylindrical tube bounded by an outer layer consisting of a smooth muscle wall and an inner layer of luminal epithelium, with follicles sandwiched between the two layers. A remarkable feature of this ovary is a sequential pattern of follicle development. This pattern begins at the germinal ridge with a gradient of follicles of increasing developmental age extending to the mature edge. The germinal ridge is an outpocketed region of the luminal epithelium containing early germinal cells and somatic prefollicular cells. Therefore, the germinal ridge and luminal epithelium share the same ovarian compartment and follicle formation occurs within this compartment. The mature edge is defined as the site of oocyte maturation and ovulation. The outer ovarian wall contains unmyelinated nerve fibers throughout. Longitudinally oriented unmyelinated nerves are also observed near the smooth muscle bundles associated with the mature edge. Oocytes near the mature edge are polarized such that the germinal vesicle (nucleus) is generally oriented toward the luminal epithelium. The sandwichlike organization of the ovary results in follicles that have a shared theca. An extensive lymphatic network is also interspersed among the follicles. Thus, the exceptional features of the pipefish ovary make it particularly well suited for the examination of early events in oogenesis. Specifically, we characterize pipefish folliculogenesis in detail.     

蕨受精作用的细胞学观察

为了阐明进化蕨类受精作用的特点和细胞学机制,该文采用透射电镜观察了蕨(Pteridium aquilinum var.latiusculum)受精作用的主要过程,观察结果显示:(1)蕨精子通过受精孔进入卵细胞,多数情况下,该精子的螺旋运动先在受精孔的下方产生一个受精腔,然后精子再与卵细胞质融合。(2)第一个精子的这种延迟的螺旋运动和因精子的钻入而引起的卵细胞固缩反应可能是阻止多精受精的重要因素。(3)卵发育时期产生的核外突在受精后仍能持续12 h,然后与核本体分离,逐渐在细胞质中消解。(4)合子通过其后方细胞质的液泡化而建立了水平极性,此后再进行细胞分裂。该研究观察到了进化蕨类受精作用过程中的一些新现象,包括产生受精腔、卵细胞固缩反应、核外突的命运以及合子极性建立等,这有助于理解蕨类植物的受精作用机制及有性生殖的演化。     

Ovulation and egg segregation in the tunic of a colonial ascidian,Diplosoma listerianum (Tunicata,Ascidiacea)

Summary The process of egg segregation in the tunic of the ovoviviparous ascidian Diplosoma listerianum was studied by light and electron microscopy. One egg at a time was seen to mature in each zooid. The eggs had large yolk and grew on the ovary wall enveloped in four layers: (1) outer follicle cells (OFC), long and rich in RER (rough endoplasmic reticulum) and with dense granules in the Golgi region; (2) flat inner follicle cells (IFC); (3) a loosely fibrillar vitelline coat (VC); (4) test cells encased on the egg surface. The growing egg protrudes from the ovary wall and presses on the contiguous epidermis. Granulocytes enter the space between the epidermis and the egg and insinuate cytoplasmic protrusions, disrupting the continuity of the OFC layer. At ovulation, OFC and IFC are discharged and form a post-ovulatory follicle (corpus luteum). The epidermis shrinks and closes, possibly by activation of microfilaments, causing the egg to be completely surrounded by the tunic. In the zooid, the wound caused by the passage of the egg is repaired both by contraction of the epidermis and by phagocytic activity. Altered spermatozoans are found in phagocytosing cells in the lumen of the ovary. These are presumably remnants of those which entered to fertilize the egg before segregation.     

Gonad history of the Antarctic krill Euphausia superba dana during its breeding season

Summary Krill were collected in January–February 1986, north of Prydz Bay, Antarctica. Their gonad history was reconstructed from observations of live krill maintained on board ship, and subsequently fixed for histology. Size, molt-stage and external stage of sexual maturity were recorded for each individual. Males appeared to be continually producing sperm. Among mature females, the ovaries had various compositional zones: germinal zones and 1 to 3 batches of maturing oocytes (in primary or secondary vitellogenesis) were simultaneously present. Therefore a female can successively lay at least three batches of eggs, at short intervals corresponding to the duration of one cycle of secondary vitellogenesis. Most post-spawn females had reverted to juvenile status (ovary reduced to germinal zones). Large females were found with an already reorganized ovary with numerous secondary oogonia and very young oocytes. It is concluded that oogenesis occurs before the winter rest and that only the vitellogenetic cycles are postponned until the next reproductive season.     

Ultrastructure of the ovary and oogenesis in the polychaete Capitella jonesi (Hartman, 1959)

Ultrastructural features of the ovary and oogenesis in the polychaete Capitella jonesi (Hartman, '59) have been described. The ovaries are paired, sac-like follicles suspended by mesenteries in the ventral coelom throughout the midbody region of the mature worm. Oogenesis is unsynchronized and occurs entirely within the ovary, where developing gametogenic stages are segregated spatially within a germinal and a growth zone. Multiplication of oogonia and differentiation of oocytes into the late stages of vitellogenesis occur in the germinal region of the ovary, whereas late-stage vitellogenic oocytes and mature eggs are located in a growth zone. Follicle cells envelop the oocytes in the germinal zone of the ovary and undergo hypertrophy and ultrastructural changes that correlate with the onset of vitellogenesis. These changes include the development of extensive arrays of rough ER and numerous Golgi complexes, formation of microvilli along the surface of the ovary, and the initiation of extensive endocytotic activity. Oocytes undergo similar, concomitant changes such as the differentiation of surface microvilli, the formation of abundant endocytotic pits and vesicles along the oolemma, and the appearance of numerous Golgi complexes, cisternae of rough ER, and yolk bodies. Yolk synthesis appears to occur by both autosynthetic and heterosynthetic processes involving the conjoined efforts of the Golgi complex and rough ER of the oocyte and the probable addition of extraovarian (heterosynthetic) yolk precursors. Evidence is presented that implicates the follicle cells in the synthesis of yolk precursors for transport to the oocytes. At ovulation, mature oocytes are released from the overy after the overlying follicle cells apparently withdraw. Bundles of microfilaments within the follicle cells may play a role in this withdrawal process.     

Antispectrin antibodies stain the oocyte nucleus and the site of fertilization channels in the egg of Discoglossus pictus (Anura).

In Discoglossus pictus eggs, only the dimple contains ionic channels active at fertilization; in particular, chloride channels are found in the central portion of the dimple, which is also the site of sperm penetration. Moreover the dimple hosts an imposing cytoskeleton, consisting of a cortical network and bundles of microfilaments extending from the microvilli. Since spectrin cross links actin and is connected through ankyrin to anion transporters in the plasma membrane of erythrocytes as well as to anion channels in other cells, we studied, in D. pictus egg, the relationship between the localization of spectrin and the high polarization of ionic channels and cytoskeletal organization. By means of immunocytochemistry, we localized spectrin exclusively in the egg dimple. In an attempt to trace back the source of spectrin localization, we immunostained sections of D. pictus ovary and localized spectrin in the nuclei of previtellogenic oocytes, where actin is also present. Antispectrin staining remained until germinal vesicle breakdown. By contrast, a cortical localization was found only when the oocytes divided into two hemispheres and into the germinative area (GA), which, after germinal vesicle breakdown, gives rise to the dimple. At this stage the antispectrin signal was particularly strong in the GA. Using Rho-pialloidin, we also established that spectrin is generally present where F-actin is found. However, spectrin and F-actin do not have the same pattern of fluorescence. In conclusion, our data suggest that spectrin may play a role in oocyte and egg polarity. In eggs, it could be instrumental in anchoring to the cytoskeleton membrane proteins such as receptors and ionic channels, including chloride-permeable channels.     

Some observations on the development and cyclic changes of the oöcytes in a brooding starfish, Leptasterias hexactis

There are two ovaries in each arm and each ovary bears a single oviduct which opens orally at the interradial angle. The ovarian wall consists of three layers: mesothelium, muscular-connective tissue layer and germinal epithelium. The haemal space between the germinal epithelium and muscular-connective tissue layer is filled with a PAS positive fluid. It is suggested that this space may provide storage and transportation of nutrient to the germ cells.
The oögonium, situated along the germinal epithelium, is distinguished from the surrounding follicle cells by its clear cytoplasm and large nucleus with a single nucleolus. It measures 10 to 15 μ in diameter.
The development of primary oöcytes is divided into premeiotic, growth and germinal vesicle migration stages. The distribution of mitochondria seems to indicate the existence of a definite polarity in the young oöcytes; but this soon disappears at the beginning of vitellogenesis. Morphological evidence seems to suggest that some of the yolk granules may be synthesized first in follicle cells and then transferred into the oöcyte. Histochemical tests indicate that the yolk platelet is a carbohydrate-protein-lipid complex.
The first meiotic division occurs six hours after sperm penetration and the second meiotic division follows two hours later.
Monthly measurement of the oöcyte throughout a year indicates a well-defined annual spawning cycle; however, the growth of an oöcyte from an oögonium to a mature oöcyte requires about two years.     

Process of Egg Formation in the Female Body Cavity and Fertilization in Male Eggs of Phytoseiulus Persimilis (Acari: Phytoseiidae)

The process of egg formation in the body cavity of a phytoseiid mite, Phytoseiulus persimilis, was observed to examine fertilization of male eggs. After insemination, one of the ova at the periphery of the ovary began to expand, taking up yolk. Two pronuclei appeared in the expanded egg, located dorsally in the ovary, and yolk granules were formed gradually. After the egg became filled with yolk granules the two pronuclei fused. The egg moved via the narrow entrance at the ventral region into the oviduct, where the eggshell was formed. When the eggshell was complete, and while embryogenesis proceeded, the egg was deposited. In the meantime some ova began to expand sequentially and two joining pronuclei appeared in expanding eggs. The joining pronuclei in the first egg proved male diploidy. This is additional evidence of pseudo-arrhenotoky in this phytoseiid mite species, since the first eggs developed into males.     

Reproductive biology of the slender smoothhound,Gollum attenuatus,collected from New Zealand waters

Synopsis The reproductive biology of 385 male and 373 female slender smoothhounds,Gollum attenuatus, collected from New Zealand waters was examined. Size at maturity for both sexes was about 700 mm TL. Litter size was usually two. The sex ratio of embryos was 1:1. The right ovary ovulated 50–100 ova, 4–8 mm in diameter, and 30–80 ova were enclosed in each egg capsule. Only one embryo developed from the many ova in each egg capsule, the other undeveloped ova were ingested and passed to an external yolk sac which formed the yolk supply for the developing embryo.