Nutritive Phagocytes Research Articles

Effects of food type and ration on reproductive maturation and growth of the sea urchin Strongylocentrotus droebachiensis

We investigated the effects of food quality and quantity on reproductive maturation and growth of juveniles of Strongylocentrotus droebachiensis (Muller) in a 22 month laboratory experiment in which we fed sea urchins four diets: (1) kelp (Laminaria spp.) for 6 d wk−1 and mussel (Mytilus spp.) flesh for 1 d wk−1 (KM); (2) kelp for 7 d wk−1 (high ration, KH); (3) kelp for 1 d wk−1 (low ration, KL) and (4) no food other than encrusting coralline algae (NF). At their first and second opportunity for reproduction, all sea urchins in the KM and KH treatments, and most in the KL treatment were reproductively mature, whereas all sea urchins in the NF treatment remained immature. Gonad index differed significantly among all fed treatments at first and second reproduction, and was highest in the KM and lowest in the KL treatment. Gonad index was similar in both sexes at first reproduction, but it was higher in females than in males at second reproduction. Diet had little or no effect on the relative abundance of spermatocytes, spermatozoa, or nutritive phagocytes in testes at first and second reproduction. In ovaries, nutritive phagocytes were significantly more abundant in females in the KM and KH treatments than in the KL treatment at first reproduction, and significantly more abundant in unfed (NF) than fed (KM, KH, KL) females at second reproduction. Mean oocyte size was similar in all fed females at first reproduction, but significantly larger in fed than unfed females at second reproduction. Mean ovum size was similar in all fed females in both reproductive periods. Increase in test diameter was greatest in the KM treatment and smallest in the KL treatment; sea urchins in the NF treatment decreased slightly in size. Survival was 95 to 100% in all fed sea urchins but significantly lower in unfed ones. The feeding rate on kelp was significantly greater in the KL than the KM and KH treatments. In the KM treatment, the feeding rate on kelp increased significantly over a 6 d period after mussel flesh was provided. Our results demonstrate that a diet of high food quality and quantity accelerates reproductive maturation and growth rate, and enhances gonad production and survival in juvenile and young adult S. droebachiensis. These findings contribute to our understanding of the reproductive ecology of S. droebachiensis in habitats with differing food supplies (e.g., kelp beds and barrens). Our results also can be used to improve aquacultural practices for sea urchins.

Manipulation of food and photoperiod promotes out-of-season gametogenesis in the green sea urchin, Strongylocentrotus droebachiensis : implications for aquaculture

Green sea urchins, Strongylocentrotus droebachiensis OF Muller, collected off the coast of New Hampshire, USA, in late February 1995, were brought into the laboratory and fed an artificial diet ad libitum, and subjected to a photoperiod advanced by 4 months. During this study, temperatures and salinities for experimental urchins mirrored those recorded at the collection site. We examined the effects of changes in feeding regime and photoperiod on gametogenesis and compared the experimental urchins with those from the source population. During the 7-month period, experimental urchins showed no detectable changes in mean test height or diameter. Experimental urchins had a significantly higher gonad index (GI) in March, April and May (18 ± 6%) compared with field urchins in March (11 ± 3%). Subsequently, experimental urchins had a mean monthly GI of 25 to 30%, while the mean GI for field urchins was 11 to 13%. Gonial cell mitosis and gametogenesis occurred earlier in experimental male and female urchins compared with field urchins. Stereological and histological observations and stage–frequency data showed that the ovaries of experimental urchins were large because of the accelerated development of nutritive phagocytes, the volume fraction (Vv) of which was 89 to 90% of the gonad, while new vitellogenic primary oocytes occupied <1% Vv. In males, stereological and histological observations and stage–frequency data suggested a mobilization of materials from the nutritive phagocytes beginning between June and August, i.e. earlier than in females, and, by September, new gametes occupied a Vv of 49 ± 3% of the testes. Oocyte size–frequency distributions demonstrated that most primary oocytes were <80 μm in diameter between March and September, suggesting that cold temperatures may be needed for completion of vitellogenesis. We describe changes in the two principal cell types in the germinal epithelium of urchin gonads and indicate how knowledge of their population dynamics may be useful in aquaculture applications.

Reproductive cycle of the echinoid Paracentrotus lividus: analysis by means of the maturity index

Summary The gonad and maturity index cycles of the echinoid Paracentrotus lividus and their relations with environmental abiotic parameters are assessed after 2 years of observation in southern Brittany, France. The gonadal cycle is briefly described and eight gonadal stages are characterized. The annual cycle, the time of spawning and the period of gonadal growth are well established, suggesting they are controlled externally. The reproductive cycle has three main phases: the growing phase (late autumn and winter) when gonads accumulate reserve material; the maturation phase (spring and early summer) in which gametogenesis then spawning take place; and the spent/regenerating phase when relict gametes are resorbed by the nutritive phagocytes, the gonads being virtually devoid of sexual cells. The maturity index based on the histological diagnosis of gonads and the use of circular data and polar graphical representation make it possible to reliably determine the spawning period, the rate of gametogenesis and the synchronization of males and females among the echinoid population. From this analysis, we can reasonably say that the gonadal cycle (represented by the gonad index), the rate of gametogenesis, and the end of the spawning period are influenced by temperature whereas the first spawning event appears to be triggered by day length.

Annual reproductive cycle of the green sea urchin, Strongylocentrotus droebachiensis, in differing habitats in Nova Scotia, Canada

We monitored the reproductive cycle of Strongylocentrotus droebachiensis (OF Muller) between April 1993 and August 1995 in kelp beds, barren grounds and grazing fronts at both a wave-exposed and a sheltered site along the Atlantic coast of Nova Scotia. Gonad index and histological analyses showed that S. droebachiensis has an annual reproductive cycle that is synchronous across sites and habitats, and between females and males. Spawning occurs in March/April of each year but a small proportion of sea urchins in the study populations also spawned in fall 1995. During most of the year, sea urchins in kelp beds and grazing fronts have a higher gonad index than those in barren grounds. Gonad indices also tended to be higher at the wave-exposed than the sheltered site. Interannual variability in peak gonad index was significant in the barren grounds at the wave-exposed site and in the grazing front at the sheltered site. The gametogenic cycle is characterized by six stages based on the abundance of nutritive and germinal/gametic cells. Nutritive phagocytes are abundant after spawning and replaced by increasing numbers of germinal and gametic cells as the gametogenic cycle progresses. The temporal patterns of abundance of each cell type were similar among habitats indicating that the gonads were qualitatively similar despite large differences in gonadal mass. The quantity of gut contents (ratio of food volume to body volume) was similar among habitats, but the quality (percentage of organic material) tended to be higher in kelp beds and grazing fronts than in barren grounds suggesting that differences in gonad index of S. droebachiensis in different habitats are related to differences in diet. The high density of sea urchins in grazing fronts combined with their high fecundity suggests that they make the greatest contribution, per unit area, to the overall larval pool.

A Protein Identical to the Yolk Protein Is Stored in the Testis in Male Red Sea Urchin, Pseudocentrotus depressus.

Female sea urchins store the major yolk protein (MYP) in ovarian nutritive phagocytes before vitellogenesis. Using immunological procedures, we detected MYP in the testicular nutritive phagocytes of Pseudocentrotus depressus, the red sea urchin, and then compared the distribution of MYP between sexes during gametogenesis. MYP was purified from unfertilized eggs by ion exchange chromatography (Q Sepharose) and gel filtration (Superdex 200), and an antiserum (anti-MYP) was raised against MYP. Immunoblot analysis demonstrated that immature testes, as well as ovaries, contained a large quantity of MYP. Immunohistochemistry showed that MYP was distributed in the nutritive phagocytes occupying the follicular lumen in both males and females. In both sexes, as gametogenesis proceeded, the nutritive phagocytes degenerated and the gonadal lumen filled with gametes. MYP accumulated in ripe ova as a yolk protein in the mature ovary. In contrast, MYP was not detected in mature testes, because stored spermatozoa did not react with anti-MYP. We conclude that in male P. depressus, MYP is stored in the testicular nutritive phagocytes and utilized as the nutrient source for spermatogenesis.

Effects of food ration and feeding regime on growth and reproduction of the sea urchin Strongylocentrotus droebachiensis

To determine the effects food ration and feeding regime on growth and reproduction of Strongylocentrotus droebachiensis (Muller), sea urchins in laboratory aquaria were fed kelp (Laminaria longicruris) supplied at either a high (H, ad libidum daily) or a low (L, ad libidum 1 d wk−1) ration in two successive 12-wk intervals during the reproductive period. After 24 wk, urchins fed the high ration continuously (HH) or for the last 12 wk only (LH) had a significantly greater mean gonad index [(gonad weight/total body weight) × 100] and body weight than urchins fed the low ration continuously (LL) or for the last 12 wk only (HL). Urchins in the HL treatment had a significantly greater gonad index than those in the LL treatment; there was no significant difference in gonad index between the LH and HH treatments. Females had a greater gonad index than males in the low ration (LL and HL) treatments at the end of the experiment; there was no significant difference between sexes in the high ration (LH, HH) treatments. Gametogenesis proceeded to maturation in all treatments and some individuals spawned at the end of the experiment. Females in the high ration (HH and LH) treatments had a greater proportion of nutritive phagocytes in their ovaries than females in the low ration treatments, but there was no effect of feeding treatment on oocyte or ovum size. Feeding treatment had no effect on the relative abundance of nutritive phagocytes in the testes, although the proportion of spermatocytes was higher (and that of spermatozoa lower) in the high ration than in the low ration treatments. Urchins in the high ration treatments had a lower mean jaw height index [(jaw height/test diameter) × 100] and greater mean test diameter than those in the low ration treatments at the end of the experiment, although these differences were not statistically significant. Feeding rate on kelp at the end of the experiment was significantly greater for urchins in the low ration than in the high ration treatments. Our experimental results show that even relatively low rations of kelp support somatic and gonadal growth in S. droebachiensis. Increasing the supply of kelp, particularly during the period of active gametogenesis, results in maximal rates of growth and reproduction. These results suggest that populations of S. droebachiensis in barrens may derive a substantial proportion of their nutrition from drift kelp, which may contribute to their persistence in these habitats. They also explain the large body size, high reproductive effort and fecundity of urchins grazing on kelp beds. These findings have important implications for understanding the dynamics of natural populations of S. droebachiensis and for development of effective aquacultural practices.

Reproductive seasonality in the comatulid crinoidAntedon bifida(Pennant) from the English Channel

Genital pinnules from the north east Atlantic comatulid crinoid Antedon bifida (Pennant) were sampled monthly over a five-season period , from a site at Berry Head , English Channel, U .K .A. bifidauniquely broods its spawned ova and early larvae, during the period May to July . Nevertheless, a high level of sexual maturity was maintained throughout the annual cycle in both males and females. Three cellular gametogenic features: facets on the mature oocyte cell wall, nutritive phagocytes in the gonad lumen and yolk nuclei in the pre-vitellogenic oocytes, were present at all times of the seasonal cycle. Development of gonads along the length of an arm was not synchronous. All specimens sampled had pinnules, sections of arm or whole arms missing, an damean of 17% of all pinnules from the population were missing or regenerating The commonest small fish in the area, Crenilabrus was observed to nibble oil the genital pinnules. A strategy is suggested involving toleration of such losses, in place of less-expendable parts of the body.

Seasonal changes in testicular structure and localization of a sperm surface glycoprotein during spermatogenesis in sea urchins.

Testes of the sea urchin, Strongylocentrotus purpuratus, undergo morphological changes consistent with a reproductive season that includes the winter months in the northern hemisphere (c. November to March). These changes can be observed in the basal germinal epithelia (BGE) of testicular acini as alterations in the gradients of meiosis and spermatogenesis from the peripheral (basal) to the inner (luminal) regions. Early in the season, large numbers of spermatogonia and primary spermatocytes along with large, spherical nutritive phagocytes (NPs) occupy most of the BGE. Relatively few secondary spermatocytes, spermatids, and spermatozoa are present. In the middle of the season more spermatocytes, spermatids, and spermatozoa are observed within well-defined spermatogenic columns that run between elongated NPs. Late in the season the BGE diminishes as the number of spermatogenic cells within it decreases dramatically and the lumen becomes distended with mature spermatozoa. To trace the origin and location of a 210 KD sperm surface antigen during spermatogenesis, a monoclonal antibody that recognizes this antigen, MAb J18/2, was used to probe testis sections. Indirect immunofluorescence microscopy detected the antigen throughout the BGE. Immunogold electron microscopy further localized it to the intracellular vesicles within spermatogenic cells of all stages. In mature spermatozoa the 210 KD surface antigen was detected not only on the sperm surfaces overlying the acrosomes and tails but also within the acrosome, suggesting the presence of an intracellular store of this antigen. Other than the occasional detection of antigen within the residual bodies of NPs, which contain phagocytosed spermatozoa, no antigen was detected in somatic cells of the testis, indicating that it is generated within the spermatogenic cells themselves.

Reproduction of sympatric populations ofHeliocidaris erythrogramma andH. tuberculata (Echinoidea) in New South Wales

Reproduction ofHeliocidaris erythrogramma (Valenciennes) andH. tuberculata (Lamarck) was compared through examination of oogenesis, spermatogenesis and monthly measurement of the gonad index. These species occur sympatrically in the Sydney region. Their reproduction was examined at two sites near Botany Bay, New South Wales, Australia, from February 1989 through January 1990.H. erythrogramma produces buoyant, 450µm-diam eggs and the sperm have a head region 10µm in length. By contrast,H. tuberculata produces negatively-buoyant, 95µm-diam eggs and the sperm have a head region 4µm in length. Histochemical examination of the gonads revealed that periodic acid Schiff-positive (PAS +) material stored in the nutritive phagocytes appears to support vitellogenesis in both species. InH. tuberculata this material is utilized in the formation of PAS + yolk oligolecithal eggs, whereas inH. erythrogramma the PAS + material appears to be converted to lipid yolk in macrolecithal eggs.H. erythrogramma had a seasonal reproductive pattern with a 3 mo summer spawning period, whereas both populations ofH. tuberculata had a 9 mo breeding period characterized by the continual presence of nutrient reserves and vitellogenic oocytes which rapidly replaced spawned ova. Spawning ceased only for 3 mo over the summer. Due to the 9 mo spawning ofH. tuberculata it is not clear what factors serve to cue reproduction in this species.

Annual reproductive cycles of the commercial sea urchinParacentrotus lividus from an exposed intertidal and a sheltered subtidal habitat on the west coast of Ireland

Reproduction of the commercial sea urchinParacentrotus lividus (Lamarck) from contrasting habitats on the west coast of Ireland was examined from May 1986 through August 1988. Urchins were collected intertidally from an exposed rocky shore and subtidally from a protected bay. Monthly measurements of the gonad index and histological examination of the gonads demonstrated thatP. lividus has an annual reproductive cycle. Although the two populations exhibited similar reproductive patterns over three breeding seasons, there were inter-annual and inter-population differences in the amplitude of gonadal growth and in the time when spawning started. The subtidal urchins had significantly larger gonads and exhibited a longer period of reproductive maturity compared with the intertidal urchins. This difference was also evident in the histology of the ovaries at the beginning of breeding, when most of the subtidal females contained mature ovaries, whereas most of the intertidal females contained premature ovaries. An inter-annual difference in the onset of spawning was observed, with the start of gamete release differing by as much as four weeks between years. It appears that inter-annual differences in sea temperature influence the temporal variation in spawning byP. lividus and that increasing temperature may serve as an exogenous cue for gamete release. The inter-annual variability in the onset of spawning suggests that photoperiod does not cue gamete release. Gonadal growth, on the other hand, occurs during the coldest months of the year and during the period of shortest days, suggesting that temperature and photoperiod may both influence gonadal growth during the winter. Oogenesis and spermatogenesis ofP. lividus were examined histologically. During the post-spawning recovery and growth stages, the gonads gained weight through growth of the nutritive phagocytes and the accumulation of periodic acid Schiff (PAS) + droplets by these cells. The PAS + material appears to play a nutritive role in gametogenesis. For the females, the frequencies of six ovarian maturity stages was assessed at approximately monthly intervals. Small oocytes were present throughout the year and clusters of early oocytes were most apparent during the spent and recovery stages. With the onset of vitellogenesis and subsequent accumulation of ova, the nutritive phagocytes and their PAS + droplets became depleted. The ovarian condition at the onset of breeding was variable, due to differences in the number of vitellogenic oocytes, differences in the number of ova in storage, and differences in the amount of PAS + material. In general, the nutritive phagocyte tissue is reduced by the onset of spawning and is exhausted by the termination of breeding. A similar series of events occurs during spermatogenesis. The relevance of this study for the use ofP. lividus as a brood-stock organism for mariculture is discussed.

Histone gene expression during sea urchin spermatogenesis: an in situ hybridization study.

The expression of testis-specific and adult somatic histone genes in sea urchin testis was investigated by in situ hybridization. The testis-specific histone genes (Sp H2B-1 of Strongylocentrotus purpuratus and Sp H2B-2 of Lytechinus pictus) were expressed exclusively in a subset of male germ line cells. These cells are morphologically identical to replicating cells pulse-labelled with 3H-thymidine. Genes coding for histones expressed in adult somatic and late embryo cells (H2A-beta for S. purpuratus and H3-1 for L. pictus) were expressed in the same germ line cells, as well as in the supportive cells (nutritive phagocytes) of the gonad. All histone mRNAs detected in the male germ lineage declined precipitously by the early spermatid stage, before cytoplasmic reduction. The data suggest that both testis-specific and adult somatic histone genes are expressed in proliferating male germ line cells. Testis-specific gene expression is restricted to spermatogonia and premeiotic spermatids, but somatic histone expression is not. The decline of histone mRNA in nondividing spermatids is not merely a consequence of cytoplasmic shedding, but probably reflects mRNA turnover.

Reproductive periodicity inEvechinus chloroticusin the Hauraki Gulf

Abstract Test diameter and gonad volume were recorded over 1 year for bimonthly samples of Evechinus chloroticus (Valenciennes) from each of 3 subtidal populations 10 km apart in the Hauraki Gulf. Histological analysis was used to relate cellular events during gametogenesis to the annual cycle of change in gonad size. Mean gonad sizes of the different sea urchin populations were compared by analysis of covariance. Gametogenesis began in the spring, and major spawning occurred in mid to late summer. The proportion of the gonads taken up by nutritive phagocyte cells increased from autumn to spring. During proliferation and growth of gametes the nutritive phagocytes declined in abundance and globulation, suggesting that reserves stored in these cells were transferred to developing gametes. Gonad size doubled during gametogenesis, declined after spawning, and remained low in autumn and winter. Differences in gonad size between populations were significant during most of the year, and were most pronounced in m...

Mechanisms of nutritive endocytosis. I. Phagocytic versatility and cellular recognition in Chlorohydra digestive cells, a scanning electron microscope study.

The quantity of surface membrane internalized during phagocytosis by Chlorohydra digestive cells was estimated for a range of particle types. Challenge with 2 of these particles, freshly isolated symbiotic algae (FIS) and latex spheres (LS), resulted in a greater (2.5 X) quantity of surface membrane interiorized than with heat-treated symbiotic algae (HTS) and free living algae (FA), Chlorella vulgaris. This discriminatory process was investigated further by a scanning electron microscope (SEM) and transmission electron microscope (TEM) comparison of the surface events associated with phagocytosis of each of these 4 particles. Those particles that were avidly phagocytized, FIS and LS, were both enveloped by a tightly fitting extension of digestive-cell surface, and obtained a prominent surface coating after their injection into the gut of Chlorohydra. Phagocytic challenge with FIS resulted, furthermore, in the rapid formation of a dense microvillar cover on digestive-cell surfaces. HTS and FA, on the other hand, were enveloped by a less closely fitting extension of digestive-cell surface, did not obtain a prominent surface coating, and did not induce the formation of microvilli. In addition, SEM revealed that at least 3 morphologically distinct phagocytic modes were utilized by the versatile nutritive phagocyte of Chlorohydra: (I) envelopment by the progressive movement of numerous, overlapping tubular protrusions (microvilli) over the particle (FIS) surface, forming first a network of tubular interlocking members, and finally a continuous but rough enclosing surface; (2) envelopment by a single, smooth-surfaced, funnel-like extension of digestive-cell surface (FIS, LS, HTS, FA); and (3) envelopment by multiple, broad folds, often of unequal size, and with overlapping margins (Artemia particles).

Food, reproduction and organic constitution of the common Antarctic echinoid Sterechinus neumayeri (Meissner).

1. The common Antarctic echinoid Sterechinus neumayeri (Meissner) feeds mostly on diatoms, although such things as seal feces are also used for food when available.2. Specimens of S. neumayeri in McMurdo Sound have discrete reproductive periodicities as do most echinoids in other parts of the world. Oocyte growth begins in the summer between November and May, the oocytes take from 18 to 24 months to reach maturity after beginning growth, and spawning occurs sometime in the winter or spring between May and December. The embryos presumably develop slowly into demersal echinopluteus larvae in the summer when plant food is available.3. Nutrients seem to be accumulated in the nutritive phagocytes of the gonads during the summer when phytoproduction occurs, and the gonads increase in size during this period. These nutrients are probably utilized during the winter to maintain a relatively constant rate of gametogenesis.4. The lipid, carbohydrate, protein and total nitrogen levels in the gonads, test, gut and gut contents of S. neumayeri are similar to those of other echinoids, although the carbohydrate content in the gonads is generally higher than in most other echinoid gonads that have been studied.5. Differences among the populations of S. neumayeri in McMurdo Sound support an earlier suggestion that food conditions are better at Cape Evans and farther north than they are south of Cape Evans.

AN AUTORADIOGRAPHIC INVESTIGATION OF THE GONADS OF THE PURPLE SEA URCHIN (STRONGYLOCENTROTUS PURPURATUS)

1. The DNA-synthesizing cells in the gonads of the purple sea urchin were labeled with tritiated thymidine and detected with autoradiography.2. Some fibroblasts in the connective tissue-muscle layer and some cells of the visceral peritoneum covering the gonads synthesize DNA.3. Some of the non-germinal cells (the nutritive phagocytes) of the germinal layer proliferate during the spring and early summer, but proliferation ceases in the late summer as the nutritive phagocytes begin to accumulate cytoplasmic globules of reserve. Nutritive phagocytes labeled with tritiated thymidine in their deglobulated phase in the spring are still labeled up to several months later, after they have acquired cytoplasmic globules.4. In the testes of male urchins at the beginning of the reproductive season, not only relict spermatozoa, but also some newly-formed spermatozoa are ingested by the nutritive phagocytes. The phagocytosis of newly-formed spermatozoa ceases later in the reproductive season, at approximately the same time that spermatozoa begin to accumulate in the lumen.5. In the germinal epithelium of the testis, the germ cells which synthesize DNA are the spermatogonia and primary spermatocytes. Primary spermatocytes labeled with tritiated thymidine differentiate into early spermatids in about six days, while spermiogenesis takes approximately four days.6. Throughout the portion of the annual reproductive cycle when spermatozoa are being produced (August through March), the time course for the later events of spermatogenesis remains constant. Therefore, the events which control the rate of sperm production must occur early in spermatogenesis.7. In the germinal layer of the ovary, the germ cells which synthesize DNA are the oogonia and the pre-leptotene primary oocytes. During the same annual reproductive cycle, long-term experiments failed to demonstrate the differentiation of pre-leptotene primary oocytes into growing primary oocytes, maturing oocytes or ova. Therefore, it is likely that labeled primary oocytes remain small and inconspicuous until the following annual reproductive cycle when they grow and mature into ova.8. The sex of very small, immature urchins may be determined by histological examination of their gonads. The ovaries of immature female urchins contain small primary oocytes which are presumably the source of ova developing during the first annual reproductive cycle.