A scanning electron microscopical study of sperm development and activation in Arenicola marina L. (Annelida: Polychaeta)

Abstract

The lugworm, Arenicola marina L. has an annual cycle of reproduction with epidemic spawning and external fertilisation. The spermatozoa of Arenicola are unusual in that they are held immotile (as plates of several hundred cells known as morulae) in the coelomic fluid until activated just prior to spawning. Activation of Arenicola sperm is brought about by a sperm maturation factor (SMF) from the prostomium and can be carried out in vitro using an assay technique developed by Bentley (1985). Scanning electron microscopy is used here to examine the changes which occur during in vitro activation. This revealed that the bundles of flagella of inactive sperm become disorganised as flagella beating commences but the flagella at this stage are still bound together at their tips. The sperm heads then become separated from the cytophore and finally the distal binding of the flagella is broken to give free-swimming spermatozoa. Coelomocytes present in the coelomic fluid resorb unspawned gametes prior to the initiation of the next gametogenic phase.     

Fertilization,post-fertilization development and larval biology of the South African polychaete,Arenicola loveni loveni (Kinberg 1866)

Summary

Larval development in the South African polychaete Arenicola loveni loveni is described, and the effects of seawater temperature on fertilization success, post-fertilization development and early post-settlement survivorship are experimentally determined. Fertilization success was significantly effected by seawater temperature, with maximum fertilization success measured in the range 15–18°C, which is close to the ambient temperature range at the time of natural spawning. Poor fertilization success and abnormal cleavage were observed at the low temperature treatment of 7°C and the high temperature treatment of 23°C. A. loveni loveni exhibits spiral cleavage typical of polychaetes and has a short lecithotrophic swimming trochophore larval stage of 4–5 days. High mortality was noted during the transitional periods from gastrula-trochophore and during the settlement process. Settlement occurs just 4–5 days post-fertilization and the postsettlement stage begins feeding 1 week post-fertilization. Temperatures in the range 16.5–23°C were found to have a significant effect on larval and post-larval survivorship and growth rate increased with temperature within this range. The effects of manipulating spawning date on subsequent offspring survival and development rates were also investigated. Advancing or delaying spawning time caused reduced development rates, and delaying spawning for 3 months was found to significantly reduce offspring survivorship.     

Evidence for a coelomic maturation factor controlling oocyte maturation in the polychaete Arenicola marina (L.)

Summary

Previous studies on Arenicola marina suggested that oocyte maturation was induced by a single maturation hormone from the prostomium. This maturation hormone was thought to act directly on the oocyte (Meijer and Durchon, 1977), A recently described species, Arenicola defodiens (Cadman and Nelson-Smith, 1993), morphologically very similar to A. marina, has been found at the sampling sites described by Meijer and Durchon (1977). Results presented here from studies on British populations of Arenicola marina show that in this species, oocyte maturation is controlled by two hormonal steps. The first step involves the prostomial maturation hormone. The second step depends on a maturation inducing substance in the coelomic fluid. We will refer to this as the coelomic maturation factor (CMF). A reliable in vitro assay for oocyte maturation in the lugworm Arenicola marina has been adopted. It utilizes fluorescence staining of the chromosome material with DNA labelling dyes (Hoechst 33342 and 33258). Maturation of oocytes in A. marina involves germinal vesicle breakdown (GVBD). This is accompanied by the movement of chromosomes from late prophase to metaphase of meiosis I and chromosome condensation. The chromosomes are stained brightly by the dyes and their relative positions can be easily identified so that mature and immature eggs can be distinguished by the differences in chromosome position and form. The development of the in vitro fluorescence assay has enabled us to demonstrate that there are two endocrine steps involved in the induction of oocyte maturation. We have begun the characterization of CMF, and data show this to be a thermolabile molecule with a molecular mass greater than 10 kd.     

Reproductive cycle and gonadal development of the Atlantic sea urchin Arbacia punctulata in the Gulf of Mexico: changes in nutritive phagocytes in relation to gametogenesis

ABSTRACT

The annual reproductive cycle comprises steady gametogenic activities that synchronize gonadal maturation and spawning rhythms, which are important for aquatic organisms including marine echinoderms (Echinodermata, Echinoidea). In this study, we report the annual reproductive cycle, gonadal development, and changes in nutritive phagocytes (NPs, which accumulate nutrients in germ cells) in relation to gametogenesis of the Atlantic sea urchin (Arbacia punctulata, an edible echinoid) in the Gulf of Mexico. Monthly changes in gonadal development and maturation were observed morphologically and histologically. We calculated gonadosomatic index (GSI) and compared the stages of gonadal development in order to determine the NPs index, and characteristics of germ cells (eggs and sperm) during the annual reproductive cycle. According to GSI and histological analyses, gametogenic activities were classified into four stages of both sexes: mature (June–August), spent (September–November), recovery (December–March), and growing (April–May). The GSI values in both sexes were high during summer months. In males, testicular lobules were densely packed with sperm from June to August. In females, however, mature eggs first appeared in some ovaries in May, numerically increased from June to July, and decreased in August. During gametogenesis, on the other hand, NPs in both testes and ovaries were depleted from June to August. Collectively, our results suggest that the Atlantic sea urchin spawns during summer months in the Gulf of Mexico. This is the first report, to the best of our knowledge, on gonadal development and changes in NPs during the annual reproductive cycle of any Arbacia species in the Gulf of Mexico.     

Changes of major carotenoids in gonads of sea urchins (Strongylocentrotus intermedius and S. nudus) at maturation

Changes in the carotenoid content in gonads of two sea urchins species were investigated during maturation. The content of echinenones and carotenes, the two major carotenoid fractions in gonads, is highest for Strongylocentrotus intermedius at the spawning gametogenic stage of gonad maturation for both sexes. For S. nudus, the content of these pigments is highest at stages of active gametogenesis and spawning for males and at the growth stage for females. A comparison of the carotenoid content dynamics during maturation of gonads for males, females and animals at the resting (sexual inactivity) stage was also carried out.     

Constraints on the rate of parthenogenetic reproduction and pest status of aphids

Summary

Reproduction in the lugworm Arenicola marina is annual and, for most populations, occurs in the late autumn or early winter. Oocyte maturation in females and sperm activation of males and spawning are under hormonal control. In males the polyunsaturated fatty acid, 8, 11, 14-eicosatrienoic acid, causes both activation of the spermatozoa (Bentley et al., 1990) and spawning (Pacey and Bentley, 1992). Dissociation of syncitial sperm masses occurs in response to the fatty acid. Active swimming of spermatozoa then follows on dilution in seawater (as a consequence of elevation of internal pH, pHi), and fertilization of the eggs takes place in the burrow of the female. Sperm activation can also be induced by arachidonic and 5, 8, 11-eicosatrienoic acids but not by the 11, 14, 17-isomer. This suggests a possible role for cyclooxygenases or lipoxygenases. Sperm activation by the PUFAs is inhibited by nordihydroguaiaretic acid (50 μM) and eicosatriynoic acid (13 μM) suggesting that 12-lipoxygenase acts during activation. Possible involvement of the fatty acid in coordination of reproduction between individuals is also discussed.     

Annual gametogenic cycle of the freshwater pearl mussel,Lamellidens marginalis (Lamarck, 1819) collected from a perennial lentic habitat of Bangladesh

ABSTRACT

We investigated the annual gametogenic phenology of the freshwater pearl mussel, Lamellidens marginalis (Lamarck, 1819), collected from a lentic habitat at Mymensingh, Bangladesh, using biometry and histology through monthly sampling from August 2015 to July 2016. After biometric measurements, thin slices of dorso-ventral sections were cut from the middle of the mussels for histology to determine sex and level of gonadal maturation. The condition index (CI) ranged from 0.64 (March) to 0.99 (January) over the study period. The CI peaked three times (January, April and July) indicating that the mussels were ripe during these months and subsequent decreases in CI indicated spawning, which was consistent with histology. Both males and females exhibited similar patterns in terms of gonadal development, maturation and spawning activity. It was confirmed that natural populations of L. marginalis spawn throughout the year with remarkable temporal variations, except during December when the surface water temperature reaches annual minima (16.5°C). Highest spawning activity of L. marginalis was noted during February–March, May and July–November. The data obtained in the present study could be useful for the conservation managers of this commercial species by allowing harvesting of better quality mussels to be timed without interrupting major spawning activity.     

Reproduction in the piranha Serrasalmus spilopleura, a neotropical fish with an unusual pattern of sexual maturity

Synopsis Reproduction in female Serrasalmus spilopleura (Characiformes, Characidae) from the Itumbiara reservoir (18°28 S, 48°36 W), Paranaíba River, Brazil, was examined with emphasis on the relationship between condition factors and coelomic fat, the annual reproductive cycle and the unusual dynamics of its sexual maturity. The condition factor and coelomic fat index follow a similar pattern along the stages of reproductive cycle. Variations in the condition factor along the reproductive cycle were assigned to variations in the fat contents of the carcass. Serrasalmus spilopleura exhibits characteristics of partial spawning fish and reproduces throughout the year. Sexual maturity occurs at 17.8 cm standard length. Resting and totally spent females were not captured. Females cycle from partially spent to intermediate/advanced maturation without going into the totally spent or resting stages. The initial maturation stage is restricted to fish of intermediate size. Once the initial maturation stage has started the fish remains there for a considerable period of its lifetime before entering in the intermediate maturation stage, an uncommon sexual maturity pattern. The long duration of the initial maturation stage was responsible for the females not returning to the resting stage after spawning.     

Reproductive cycle of gilt sardine,Sardinella aurita,Valenciennes 1847, in the eastern middle Adriatic Sea

The annual reproduction cycle of gilt sardine, Sardinella aurita, based on gonad maturity stages, gonad weight and gonadosomatic index was the subject of this study. A total of 2033 gilt sardines (983 males, 1021 females and 29 undetermined) were analysed. Fish were collected monthly from commercial purse seiners between November 2007 and January 2009 in the eastern middle Adriatic Sea (mesh size 8 mm/bar length/; sampling: five boats per month). Based on the monthly evolution of gonad maturation stages, gonad weights and gonadosomatic index, the peak spawning season was determined to be from June to August. Variations in sea surface temperature (SST) coincided with monthly variations of the gonadosomatic index. Highest monthly average values for both analysed parameters were recorded in July (GSI = 3.38; T = 26.5°C). Fifty per cent (L₅₀) of males and females reached sexual maturity at TL 15.8 cm and at 16.6 cm, respectively. Absolute fecundity ranged from 8458 to 48 032 (mean 34 565 ± 10 310), whereas relative fecundity was from 171 to 722 (mean 385 ± 104.35). Mean value of the oocyte size was 0.53 ± 0.10 mm.     

Spatial variation in the annual reproductive cycle of Turbo (Batillus) cornutus (Gastropoda: Trochidae) at Jeju Island,Korea

The annual reproductive cycle of the top shell Turbo cornutus from Jeju Island was investigated in two populations using histology. In the northern population, gametogenesis commenced in January as the surface water temperature reached 14?°C, while in the southern population gametogenesis began a month earlier, as the water temperature remained at 17?°C. Ripe top shells first appeared in June and spawning continued from June to October when water temperatures were between 20 and 24?°C. Histology indicated that the spawning period of the southern population was a month earlier and lasted longer (June–October) than in the northern population (July–September). The percentage gonad area of animals in the southern population in March and April was significantly higher than in the northern population (p?相似文献   

Control of Gonadal Maturation and Regression by Experimental Variation of Environmental Factors in the Mormyrid Fish, Mormyrus rume proboscirostris

We used spawning, external appearance of the females and in part histology of gonads of the African mormyrid fish Mormyrus rume proboscirostris to evaluate the reaction of the fish to experimental variation of environmental factors. Conductivity changes are sufficient to induce gonadal maturation (decrease of conductivity) and regression (increase of conductivity), respectively. Increase of water level and simulation of rain at constant conductivity values did not induce gonadal maturation and spawning. Neither males nor females of M. rume proboscirostris showed postbreeding refractoriness. Social stress apparently prevented complete gonadal maturation and successful spawning. The females laid on average 364 eggs per fractional spawning; the spawning intervals were 21 days. Hatching rate amounted to about 40% in all experiments taken together.     

The effects of prostomium and proventriculus removal on sex determination and gametogenesis inTyposyllis pulchra (Polychaeta: Syllidae)

Summary The prostomium alone or the prostomium and proventriculus of reproductiveTyposyllis pulchra were periodically removed at known stages of oogenesis and the gametes were examined by transmission electron microscopy. If the proventriculus and prostomium were simultaneously removed prior to day 3 of the stolonization sequence, before gonial differentiation, the time reruired for stolon formation and concomitant gametogenesis was shortened; the animals, all of which had previously reproduced as females, produced only ultrastructurally normal sperm. Spermatogenesis in these induced males began earlier in the stolonization period than in normal males. However, the cytological events of spermatogenesis were not accelerated. When the same operation was performed after differentiated oocytes were present, gamete cytodifferentiation and development time did not appear to be affected and the animals remained female. Removal of the prostomium alone, formerly thought to have no effect, caused high mortality and if removed prior to day 3 appeared to prevent both stolonization and gametogenesis. Ultrastructural investigation of these animals shows that gonads are maintained, but that gonial cells fail to differentiate or produce gametes. The subsequent removal of the proventriculus and regenerating prostomium from these animals allows them to mature as induced males. This suggests a prostomial role in regulating the endocrine activity of the proventriculus during the reproductive cycle.     

Assessment of field fertilization success in the infaunal polychaete Arenicola marina (L.)

Summary

Previous studies on the fertilization rates in externally fertilizing marine invertebrates have been concerned principally with free spawning epifaunal organisms (e.g., Babcock et al., 1992). A technique has been developed to investigate fertilization success in the intertidal infaunal polychaete Arenicola marina. The spawning period at the East Sands, St Andrews, is predictable from previous data, and this facilitates the study of spawning behaviour. Female worms spawn within their burrows, where the eggs may remain for several days. Male worms release sperm puddles on to the surface of the sediment at low water. The sperm is carried on the incoming tide over the surface of the sediment where it is actively drawn into female burrows by pumping. The decrease in sperm concentration as the tide comes in has been measured, and it is estimated that there are typically about 10⁶ sperm.ml^?1 in the water column and available to the female at 1 min after covering by the incoming tide. By placing the worms into artificial plastic burrows with removable stoppers, they can be transplanted into the field prior to spawning, and removed afterwards whilst retaining all the contents of the tube (worms, gametes, sediment and water).Preliminary data on the fertilization success suggests that it is highly variable (between 0% and 90%), with typical values of 40–60% for Arenicola marina. Laboratory assays investigating fertilization rate with varying sperm concentration have shown that there is a marked increase in success at 10⁴ and 10⁵ sperm per ml, with values of 30–70%. The field data therefore appear to be consistent with laboratory studies.     

Gonadal maturation is dependent on body size in the sea urchin,Echinometra tsumajiroi

Summary

This study examined gonadal maturation in the sea urchin, Echinometra tsumajiroi, in relationship to body size. In the breeding season, E. tsumajiroi were collected and divided into six groups based on the length of the major axis (LM) as a measure of body size: Group 1 (6–10 mm in LM), Group 2 (11–15 mm in LM), Group 3 (16–20 mm in LM), Group 4 (21–25 mm in LM), Group 5 (26–30 mm in LM), and Group 6 (> 31 mm in LM). Although gonads were present in individuals larger than 8 mm in LM, the germ cells were undifferentiated in Group 1. Gonadal sex differentiation was first seen in Group 2: a few young oocytes appeared at the periphery of the ovary, and both spermatogonia and spermatocytes were also observed at the periphery of the testis. As size increased from Group 3 to Group 4, more mature germ cells such as ripe ova or spermatozoa were observed in ovaries and testes. In Group 5, the ovaries and testes were filled with a large number of mature eggs and spermatozoa, respectively. Spawning could be induced in this group by the injection of 0.5 M KCl into the coelomic cavity. In contrast, gonads of some of the biggest individuals, belonging to Group 6, appeared to be spent due to spawning, because few eggs were present in the ovary and relict spermatozoa were present in the testis. These results suggest that reproductive activity in the sea urchin, E. tsumajiroi, depends on body size.     

The myth of intercalary segment in insect head

Embryonic development of the head of Oxyrhachis tarandus (Membracidae) has been investigated in detail to settle the controversy of head segmentation and to refute the occurrence of an intercalary segment. The head is formed from six distinct elements: the prostominal lobe, the paired cephalic lobes, the antennal segment and the three noncontroversial gnathal segments. The prostomial lobe, which possesses a neuromere and a pair of coelomic cavities, represents the first body segment, called the prostomial segment. The tritocerebral lobes of the brain and the stomatogastric nervous system, consisting of a frontal ganglion, clypeolabral nerves, and the recurrent nerve etc., develop from the neuromere of the prostomial lobe. The tritocerebrum thus belongs to the prostomial segment rather than to an imaginary intercalary segment and mainly represents the ganglionic center of the stomatogastric nervous system in the brain. Frons, clypeus, and labrum develop from the outer wall of the prostomial lobulate plate, whereas the epipharyngeal wall, including the cibarial pump, develops from its inner wall. The presence of three coelomic cavities and of three distinct neural masses in the cephalic lobes during the initial stages of development shows that they have developed by the fusion of three distinct segments during the long phylogenetic history of insects. The portion of the germ band presently considered as the intercalary segment is actually the sternal part of the antennal segment. The neural cells located in this region give rise to the deutocerebrum by shifting forward, around the stomodaeum, and always leaving a commissure behind. The intercalary segment is thus a complete illusion. The antennal segment is postoral in the beginning and bears a pair of coelomic cavities, but later on it shifts forward and its sternal part invaginates into the stomodaeum.     

Life history characteristics and age validation of southern kingfish (Menticirrhus americanus (Linnaeus, 1758)) in the middle South Atlantic Bight

The purpose of this study was to determine critical components of the life history including otolith age validation, growth estimation, and reproductive characteristics for southern kingfish Menticirrhus americanus. A total of 2233 southern kingfish were collected from March 2009 to December 2010. Ages were estimated and validated using thin‐sectioned otoliths. Marginal increment analysis showed a single annulus was deposited once a year between April and May. Growth was significantly different (P < 0.0001) between sexes L_inf = 418.97 ± 16.58 mm, k = 0.29 ± 0.03, t₀ = ?1.30 ± 0.10 for females and L_inf = 290.74 ± 6.93 mm, k = 0.52 ± 0.05, t₀ = ?1.08 ± 0.11 for males. Southern kingfish spawn from March to August with a peak spawn in April. Based on evidence of multiple oocyte maturation stages and post‐ovulatory follicles (POFs) southern kingfish are multiple spawners exhibiting indeterminate fecundity. Spawning frequency for females ranging from 222 to 351 mm TL (age 1–5) was estimated as one spawning event every 2.0–4.2 days with up to 6 million total ova produced per spawning season per female.     

Husbandry of the Annual Killifish Austrofundulus limnaeus with Special Emphasis on the Collection and Rearing of Embryos

Annual killifish development is unique compared to other teleosts and is characterized by the dispersion and subsequent reaggregation of pre-embryonic blastomeres and the occurrence of embryonic diapause. Austrofundulus limnaeus is an excellent species to use for studies of development and embryonic diapause in annual killifish. A. limnaeus has a high fecundity, reproduces readily in a laboratory environment, and has a relatively long laboratory life span compared to many other species of annual killifish. Methods are presented for rearing A. limnaeus in the laboratory with an emphasis on collecting and incubating large numbers of embryos for biochemical and physiological studies. Females produce an average of 29 eggs during a two to four hour spawning. Egg quality (% fertilization and survival) and egg production (eggs female^-1) are affected by the number of days between spawning events. Percent fertilization of eggs and survival of embryos decreases as the interval between spawning increases from two to eight days. The number of fertile embryos produced per female remains relatively constant as a function of spawning interval. Fertilization rates may be maintained at high levels by replacing aged males (1.5 years old) with younger males. An embryo medium was formulated to mimic the natural waters inhabited by A. limnaeus. The developmental rate and survival of embryos in the embryo medium was essentially equivalent when compared to Yamamoto's fish saline solution.     

MECHANISM OF STARFISH SPAWNING. III. PROPERTIES AND ACTION OF MEIOSIS-INDUCING SUBSTANCE PRODUCED IN GONAD UNDER INFLUENCE OF GONAD-STIMULATING SUBSTANCE

The gonad-stimulating substance (GSS) contained in nerve extract of the starfish, Asterina pectinifera, acts on the ovary to produce an active substance responsible for oocyte maturation, meiosis-inducing substance (MIS). MIS was successfully separated from GSS by gel-filtration on Sephadex. The MIS fraction had also spawning-inducing activity. Starfish testis also produced MIS under the influence of GSS. MIS production was shown in six starfish species. Although some species specificity characterizes GSS, this was not observed in MIS. Production of MIS in the ovary was found to begin immediately after the addition of GSS. The amount of MIS produced increased as the concentration of GSS was raised, and the longer the time of treatment with GSS, the greater was the amount of MIS produced. MIS was rather heatstable, insoluble in ether, benzene and petroleum ether but soluble in 95% ethanol. Its activity was not destroyed by pronase. Injection of MIS into the coelomic cavity induced gamete-shedding in both male and female. However, MIS failed to induce spawning when applied from the outside of the body. Both GSS and MIS were found in the coelomic fluid only when the starfish were undergoing natural spawning. A mechanism of starfish spawning, based on the action of GSS and MIS is discussed.     

The anatomy and histology of the nervous system and excretory system of the maldanid polychaetes Clymenella torquata and Euclymene oerstedi

The nervous system of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparede) (= Caesicirrus neglectus [Arwidsson, '11-'12]) retains its primitive association with the epidermis. It shows only slight metamerism in the presence of larger collections of neurones opposite the parapodia and of larger nerves at the segmental boundaries. Multicellular giant fibers are present in the ventral nerve cord; giant neurones which show a characteristic pattern of distribution in each species are also present. The cerebral ganglia supply nerves to the prostomial wall, nuchal grooves and the wall of the buccal cavity, and a pair of large nerves from the circumpharyngeal connectives also appear to join the buccal system. The organs of special sense are the elongated prostomial nuchal grooves, and prostomial ocelli in Euclymene but not in Clymenella. Statocysts are absent. Four pairs of nephromixia are present. They lie in the aseptate anterior trunk, in chaetigers 5–9 of Clymenella, and 6–10 of Euclymene. The nephridiopores lie at the ventral ends of the neuropodia of chaetigers 6–9 and 7–10, respectively. Each nephromixium consists of coelomostome, tubule and contractile bladder. The wall of the tubule and bladder consists of both excretory and ciliated cells. Most of the cytoplasm of the latter forms a bounding layer at the outer surface. The cytoplasm of the excretory cells contains lipid material and appears to synthesize lipofuscin. The tips of the excretory cells swell, fill with granules, and break off in the form of vesicles which are periodically expelled in clouds from the nephridiopores. Glycogen is present, especially in the ciliated cells of the tubule and coelomostome. Granules of a lipoid nature accumulate in (or between) cells of the nephridia, epidermis, and some regions of the gut, and may be excretory. Lipid granules also appear to be synthesized by coelomocytes which eventually end up in masses in the ventrolateral coelomic cavities of the tail. The nephridia act as gonoducts, but show no seasonal variation in either size or histological structure.