Invertebrate Eggs Research Articles

Comparative biases from pushnet and pullnet zooplankton samples

Biases in pushnet and pullnet zooplankton samples were investigated by obtaining paired samples sequentially with the 2 types of net, alternating the order of net type to control for the effect of order. There were no significant differences between pushnet and pullnet samples in total numbers of zooplankton, dry weight, or ash-free dry weight. Daytime pullnet samples contained significantly greater numbers of relatively passive drifters (fish eggs, invertebrate eggs, and siphonophores). There were no such differences among samples taken on moonless nights. Copepods (Acartia spp.) were more abundant in pushnet than in pullnet samples in all 32 palrs of daylight samples, but not at night. Therefore, the bias for motde zooplankton probably resulted from avoidance influenced by light. The greater abundance of floating eggs in pullnet samples may have been a result of mixing the surface water w t h water 60cm below by turbulence created by the boat hull and the propeller There were generally no significant interactions in results between net type and date or location, therefore either pushnet or pullnet could be used in studies to test hypotheses because statistical analysis requires a standardized sampling technique withn the program and because w~thout interaction, any bias should be consistent across the sampling program. However, slnce all methods for sampling zooplankton are probably biased, a variety of sampling methods should be used in combination for estimating parameters.

Fine structure of the mammalian egg cortex.

The cortices of a number of mammalian eggs are not structurally homogeneous but are polarized. In mouse ova the plasma membrane is a mosaic; the cytoplasm overlying the meiotic spindle is devoid of cortical granules and consists of a filamentous layer containing actin. Functionally, this cortical polarity may be related to the restriction of sperm-egg interaction and fusion to a specific region of the ovum cortex and to dynamic changes of the egg cortex during fertilization, including cortical granule exocytosis, polar body formation, and fertilization cone development. The origin of cortical polarity in mammalian oocytes and its possible relation to components of the cytoskeletal system and meiotic apparatus are discussed and compared with cortical features of eggs of other vertebrates and invertebrates.

Egg envelopes in vertebrates.

As the material presented in this chapter was being collated, our existing perceptions about the basic similarities of vertebrate (and indeed most, if not all, invertebrate) egg envelopes became increasingly strengthened. Perhaps without exception, all vertebrate and invertebrate eggs acquire a "vitelline" envelope. Interestingly, its filamentous ultrastructure and chemical composition--basically protein and carbohydrate--is similar in all species as is its permeability to large molecules. Furthermore, many (if not all) of its functions are shared among the animal phyla as is its potential to become altered at the time of fertilization and, in its altered state, to provide a new set of modi operandi. It provides sperm receptors that are generally species specific and helps prevent polyspermy; it protects the developing embryo yet yields at the time of hatching. In most vertebrate eggs (including some mammals), a jelly or albumen coat is added to the vitelline envelope. These components may vary immensely in thickness, but again their basic chemical composition is common to all. The functions of these envelopes, while perhaps somewhat less clear than those of the vitelline envelope, are related to species-specific fertilization and to embryonic protection. Albumen serves a nutritional role--most clearly shown in the birds. Finally, the shell membrane and shell present in diverse groups contribute additional adaptations for embryo protection. Vertebrate egg envelopes, then, are basically similar; the modifications, including the addition of shell membranes and shells in some groups, reflect adaptations to differing reproductive strategies and to the environmental exigencies with which the egg must cope. With the growth of our understanding about the structure, chemistry, function, and evolution of egg envelopes new questions will continually be formulated. Many will be the same as those asked years ago but they will be answered with newer techniques and with greater insight.

Predation on zooplankton by the benthic anthozoans Alcyonium siderium (Alcyonacea) and Metridium senile (Actiniaria) in the New England subtidal

The Alcyonacean octocoral Alcyonium siderium Verrill and the sea anemone Metridium senile (L.), the only common perennial zooplanktivores on shallow (≦16-m depth) subtidal rock walls in much of northern New England, USA, are of similar heights and overlap in their habitat and microhabit distributions. The coelenteron contents of both species were sampled at four-hour intervals over a diel cycle and were compared to zooplankton available in the water at 1 to 5 cm from the rock wall, the height at which the cnidarians held their feeding tentacles. Prey in coelenterons of A. siderium were significantly smaller (means of 256 to 345 μm), and those in coelenterons of M. senile were equal to or slightly greater in length (means of 415 to 1006 μm) than the available zooplankton. The diets of A. siderium and M. senile differed significantly from each other and from the available zooplankton. A. siderium showed strong positive electivites for ascidian larvae and for foraminiferans, and strongly negative electivities for most crustaceans. M. senile had strong positive electivities for barnacle cyprids, ascidian larvae, and gammarid amphipods, and strong negative electivities for invertebrate eggs, foraminiferans, calanoid and harpacticoid copepods, and ostracods. Electivities may reflect tentacle avoidance or escape by motile prey as well as predator preference. Substratum-associated organisms (e.g. demersal crustaceans, larvae of benthic invertebrates) were the most common items in the diets of both species, suggesting a tight benthic food web, similar to the situation for coral reef anthrozoans which rely on reef-generated zooplankton. A. siderium ate large numbers of ascidian larvae which, as benthic adults, compete for space with A. siderium and can overgrow small colonies. Predation on the larvae of a competing species may alleviate competition by decreasing the competitor's recruitment.

若狭湾に出現する子魚の食性に関する研究 ＩＩＩ タマガンゾウビラメ・メイタガレイ子魚の鉛直分布と食性

This paper deals with vertical distribution and feeding habits of two larval flatfish Pseudorhombus pentophthalmus GÜNTHER and P! euronichthys cornutus (TEMMINCK et SCHLEGEL), collected in the western wakasa Bay, Japan Sea from May to August 1981. The larvae of two species distributed abundantly in the waters between 25m and 50m depths. The larvae of P. pentophthalmus of 3.0-3.9mm body length began to feed on invertebrate eggs (6.2%, showing the percentage of number of food items) and Chaetoceros spp. (75.0%), the larvae of 4.0-4.9mm fed mainly on copepod nauplii (92.3%), and the larvae of more than 5.0mm fed abundantly on Paracalanus parvus (11.1-17.9%), Penilia avirostris (5.6-40.0%) and Oikopleura longicauda (10.3-83.3%). Most of P. cornutus larvae of 4.5-8.2mm body length ate particularly O. longicauda. From digestive degree of O. longicauda in each larva gut, it is suggested that the larvae feed on the large amount of O. longicauda for a short time nd that the diurnal aggregated distribution of O. longicauda is closely related to the feeding habite of P. cornutus. According to the feeding habits of three flatfish collected together in the western Wakasa Bay, the availability of O. longicauda as food is in the order of P. cornutus, P. pentophthalmus and Paralichthys olivaceus.

Novel surface specialization on a sea anemone egg: "Spires" of actin-filled microvilli.

The ultrastructure of the "spiny" surface of Tealia crassicornis eggs is examined in detail by scanning and transmission electron microscopy in order to understand its function. Long microvilli are clustered together in spiral aggregates of 50-75 microvilli called "spires." There are about 15,000 spires per egg. Dense bundles of microfilaments making up the cores of these microvilli are shown to be composed of actin by staining with the fluorescent dye nitrobenzoxadiazole (NBD)-phallacidin. It is postulated that the bundles of actin and the spires of microvilli are stiff and provide reinforcement to the egg surface. Such postulated properties would provide physical protection for these large eggs which, unlike the eggs of most invertebrates, appear to lack all extracellular investing coats.

Morphologic Changes in the Egg of the Polychaete Worm Mercierella Enigmatica after Fertilization

Comparative ultrastructural studies of changes in the morphologies of invertebrate eggs that occur after fertilization may shed light on the evolution of the fertilization process and the incorporation of mechanisms that may serve to insure monospermy as well as to provide protective envelopes for the developing embryo. This report describes changes that occur in the egg of Mercierella enigmatica as noted 35 minutes after fertilization.Eggs or sperm were shed spontaneously when the worms were pulled from their tubes and placed in individual watch glasses containing sea water. The unfertilized eggs were fixed for 1 hour in 2.5% glutaraldehyde in 0.1M cacody- late buffer at pH 7.5. The eggs were rinsed in sea water and post fixed for 1 hour in 1% osmium tetroxide buffered with 0.1M phosphate buffer at pH 7.5. Other eggs were fertilized by the addition of sea water containing sperm and fixed as above after 35 minutes. Eggs were embedded in Epon and compared by TEM. Embedments of the unfertilized eggs and fertilized eggs were fractured and coated with vacuum evaporated gold for SEM.

Feeding Ecology of Capelin (Mallotus villosus) in the Estuary and Western Gulf of St. Lawrence and its Multispecies Implications

The feeding ecology of juvenile (< 140 mm TL) and adult (> 140 mm TL) capelin (Mallotus villosus) in the St. Lawrence River Estuary and western Gulf of St. Lawrence was studied between October 1974 and October 1975. Both juveniles and adults fed almost exclusively on zooplankton. Three prey totally dominated the diet. Copepods were numerically most abundant but euphausiids were dominant in terms of biomass. Appendicularians ranked third in both number and biomass. This differed from the diet of capelin in the Canadian Atlantic only to the extent that amphipods replace appendicularians in the diet in the Atlantic and large copepods are more abundant in the diet there. A shift in diet occurred during growth. Premetamorphic capelin (< 75 mm TL) consumed small prey exclusively: invertebrate eggs, cyclopoid copepods, and diatoms predominated. The diets of juvenile (75–139 mm TL) and adult (> 140 mm TL) capelin overlapped considerably but a pronounced shift from small copepods to adult euphausiids occurred at ~ 140 mm TL. Early morning and evening feeding peaks occurred between May and August. A single midday feeding peak prevailed in October–November. Feeding of adult capelin was active in the spring prior to spawning but virtually ceased during spawning. Juvenile capelin fed actively throughout spring and summer. The daily ration of zooplankton by capelin was estimated to be 5% of wet body weight in summer May–September and ~ 2.5% in October–November. Year-to-year variations in average daily consumption in excess of 100 000 t have occurred between 1972 and 1978 and average daily consumption has declined by up to 310 000 t during the same interval. This significant year-to-year and long-term release of zooplankton from predation by capelin may be an important regulator of changes in year-class strength in other species of the area, notably arctic cod, Boreogadus saida and short-finned squid, Illex illecebrosus.Key words: capelin, Mallotus villosus; Gulf of St. Lawrence, ecology, food habits, daily ration, estuaries, zooplankton, multispecies interactions, arctic cod, Boreogadus saida; squid, Illex illecebrosus

Bongo Net Retention Rates as Effected by Towing Speed and Mesh Size

A comparison of 0.253- and 0.333-mm mesh bongo net retention rates at towing speeds of 1.5 and 3.5 knots showed no significant mesh size related variation in filtration efficiency or in abundance of larval herring at either towing speed. For 1.5-knot tows there was no significant mesh size difference in larval herring length frequency distribution. For 3.5-knot tows, the distributions of lengths were significantly different for the two mesh sizes. The condition of herring larvae was noticeably better in the 1.5-knot tow samples (3%, of yolk-sac larvae caught in 3.5-knot tows had their yolk sac intact compared to 50% from 1.5-knot tows). Feeding incidence was higher for larvae caught in 1.5-knot tows (71%) than for larvae caught in 3.5-knot tows (50%).At a towing speed of 3.5 knots the 0.253-mm mesh zooplankton displacement volumes were significantly greater than the 0.333-mm mesh displacement volumes. At a towing speed of 1.5 knots the difference in displacement volumes was not significant. Adult Oithona spp. and Pseudo-Paracalanus spp., unidentified copepodites, and adult and juvenile Hyperia spp. were caught in significantly greater numbers by the 0.253-mm mesh net at both towing speeds. The 0.253-mm/0.333-mm abundance ratios were greatest for the smaller and more abundant invertebrate taxa. The variation in zooplankton retention rates resulted in large part from differences in mesh size, although catching efficiency was also influenced by tow speed. A substantial proportion of the food items in the guts of all size groups of larval herring consisted of taxa which were not retained by either mesh net (invertebrate eggs, copepod nauplii, Oithona spp., and Pseudo-Paracalanrrs spp. copepodites). Size was the most important factor in prey selection and the average size of food items increased with increased length of herring larvae. On the basis of this analysis, sampling strategies are suggested for future surveys. Key words: bongo nets, retention rates, ichthyoplankton, larval herring, zooplankton, feeding incidence

A method for the demonstration of pores in calcified eggs of vertebrates and invertebrates.

Determination of pore number, pore size as well as pore canal distribution is important in understanding the biology of calcified eggs among vertebrates as well as invertebrates. Various techniques have been applied to elucidate pore structure of avian egg shells, including fracturing coupled with scanning electron microscopy and differential histochemical staining of the matrix. The best results reported have thus far been from plastic impregnated, etched specimens (Board & Tullett, 1974). The present report is a modification of this latter technique, utilizing the very low viscosity, highly penetrating electron microscopic embedding medium developed by Spurr (1969). This modification is used in this report of the previously undescribed pores from the egg shells of the giant South American land snail, Strophocheilus oblongus. These eggs, which can be up to 50 mm in length, have recently been investigated with respect to the calcium carbonate mineralogy (Tompa, 1976) as well as with respect to the matrix biochemistry Tompa et al., 1977). (Similar resin has been used successfully for the plastic impregnation and ultrathin sectioning of that region of the snail shell where the body muscles insert into the shell comumella (Tompa & Watabe, 1976).) This technique, which can be utilized on avian eggs or on any other calcified material in probing for pores, relies on the high penetrating ability of the resin as well as on its easy commercial availability around the world.

Involvement of an acrosin-like enzyme in the acrosome reaction of sea urchin sperm

Extracts of the jelly coat of eggs of several marine invertebrates are known to induce in homologous sperm morphological changes known as the acrosome reaction. When sperm of the sea urchin Strongylocentrotus purpuratus are treated with low concentrations (0.2 μg fucose/ml) of egg jelly coat or 30 m M CaCl 2 in artificial seawater the acrosome reaction does not occur. However, either of these treatments causes the exposure of an acrosin-like enzyme to exogenous substrate and inhibitors. Subsequent addition of jelly coat to 3.7 μg fucose/ml to sperm in this “initial stage” induces the acrosome reaction (as judged by the appearance of an acrosomal filament). This concentration is also effective for untreated sperm. If inhibitors of the enzyme (diisopropylphosphofluoridate or phenylmethanesulfonyl fluoride) are added to sperm in the initial stage, no acrosomal filaments are observed when the high concentration of jelly coat is added. Whether other morphological changes occur in these sperm has not been examined. If phenylmethanesulfonyl fluoride is added 4 sec after the jelly coat, the acrosomal filaments are observed, but the sperm still fail to fertilize eggs. These results suggest a dual role for the acrosin-like enzyme(s), first in the mechanism of the acrosomal filament formation and then in a subsequent event in the fertilization process.

The program of fertilization.

The eggs of marine invertebrates particularly the echinoderms as sea urchins sand dollars and starfish are used for the study of fertilization. The specific recognition of the egg by the sperm is thought to occur when the sperm makes contact with the jelly coat that surrounds the egg. Substances in the jelly coat interact with the outer membranes of the sperm cell to release digestive enzymes that enable the sperm to dissolve a hole in the layers surrounding the egg so that the sperm can reach the surface of the egg. A single fertilizing sperm enters the egg. Once the sperm has entered the egg its nucleus rotates 180 degrees and migrates toward the nucleus of the egg. About 20 minutes later paternal and maternal nuclei fuse. With the condensation of the chromosomes and the 1st cleavage of the egg fertilization is completed. The fusion of a sperm and an egg triggers a series of transient changes in the concentration of ions that prevent the fusion of additional sperm and initiate development of the embryo. It seems likely that regulation through the transient or permanent modulations of ionic content is widespread in the living world and that mechanisms for regulating cellular acivity at fertilization are utilized throughout the life span of the organism.

Size and organic content of eggs of echinoderms and other invertebrates as related to developmental strategies and egg eating

In 7 species of echinoderms, 2 species of polychaetes, and 1 species of oyster with feeding larvae, larger eggs were found to contain more organic matter. Although organic matter per egg increases with egg diameter or volume, it is not proportionate to egg volume, because small eggs have more concentrated organic matter than larger eggs. There appear to be differences among higher taxa in the minimum size of freely spawned eggs. These differences could result from different relationships between mortality and reduced egg size arising from differences between larval feeding mechanisms or differences in size at metamorphosis. An egg has more than five times the organic matter of a diatom of the same size and is thus a bigger meal for suspension feeders.

Feeding of laboratory-reared larvae of the sea bream Archosargus rhomboidalis (Sparidae)

Feeding by larvae of the sea bream Archosargus rhomboidalis (Linnaeus) was investigated from late September, 1972 to early May, 1973 using laboratory-reared larvae. Fertilized eggs were collected from plankton tows in Biscayne Bay, and the larvae were reared on zooplankton also collected in plankton nets. Techniques were developed to estimate feeding rate, food selection, gross growth efficiency, and daily ration. Daily estimates of these were obtained through 16 days after hatching at rearing temperatures of 23°, 26°, and 29°C. Feeding rate increased exponentially as the larvae grew, and increased as temperature was raised. At 23°C larvae began feeding on Day 3, at 26° and 29°C larvae began feeding on Day 2. Feeding rates at initiation of feeding and on Day 16 were, respectively: 23°C, 7.16 food organisms per larva per hour (flh) and 53.78 flh; 26°C, 7.90 flh and 168.80 flh; 29°C, 17.62 flh and 142.07 flh. Sea bream larvae selected food organisms by size. At initiation of feeding they selected organisms less than 100 μm in width. As larvae grew they selected larger organisms and rejected smaller ones. The major food (more than85% of the organisms ingested) was copepod nauplii, copepodites, and copepod adults. Minor food items were barnacle nauplii, tintinnids, invertebrate eggs, and polychaete larvae. Mean values for gross growth efficiency of sea bream larvae ranged from 30.6% at 23°C to 23.9% at 29°C. Mean values for daily ration, expressed as a percentage of larval weight, ranged from 84% at 23°C to 151% at 29°C and tended to decline as the larvae grew.

Chemical estimates of the RNA and DNA contents of the early mouse embryo.

AbstractDNA and RNA were extracted from mouse embryos at several stages prior to implantation. RNA was measured by extinction at 200 nm, and DNA by a fluorometric assay. The mean values of RNA in the ovulated oocyte, 1‐cell, 2‐cell, and blastocyst‐stage embryo were 0.554, 0.545, 0.396, 0.458, and 1.37 ng, respectively. The mean values of DNA in embryos at these same stages were 23.8, 29.3, 41.1, 155, and 439 pg. There was no significant rise in total RNA per embryo until after the 8‐cell stage. The amount of DNA in mouse spermatozoa was also measured, and found to be 3.8 pg per spermato‐zoan. From this study it is clear that the mouse oocyte and early embryo do not contain the large quantities of DNA, in excess of the diploid value, found in some amphibian and invertebrate eggs.

Trophic Analysis of Juvenile Pink and Chum Salmon (Oncorhynchus gorbuscha and O. keta) in Puget Sound

Pink and chum salmon (Oncorhynchus gorbuscha and O. keta) fry and Clarke–Bumpus plankton tows were collected from three beach areas in Puget Sound in spring 1970. Chum fry and benthic pump samples were taken in 1971. The diets of the young of the two species were similar. Epibenthic harpacticoid copepods were the chief prey of the chum and pink salmon (57 and 36%, respectively, in 1970). Distinct differences were apparent, the more notable being the preference for invertebrate eggs exhibited by the pinks and the higher preferences for small gammarid amphipods and harpacticoids exhibited by the chums. The stomach contents showed no resemblance to the plankton hauls taken in the same area. The onshore stage of development appears to be a distinct ecological stage in the life cycles of these species.

Loss of cortical granules in rabbit eggs exposed to spermatozoa in vitro.

Cortical granules are found in the unfertilized eggs of many invertebrates and vertebrates, including mammals, but are essentially absent in fertilized eggs (Austin, 1968). The extruded contents of the granules are thought to play a rôle in the prevention of polyspermy (Austin, 1961). In the sea urchin, the cortical granule breakdown occurs after sperm penetration has begun and appears to be a propagated reaction over the egg surface (Austin, 1961). Szollosi (1967), studying cortical granules in the hamster and rat, found that the granule breakdown in these species is generally activated by the attachment of a spermatozoon to an egg. Pikó (1969) reported that the reaction is triggered when membrane fusion and breakdown of the postnuclear cap region of the spermatozoon has begun. Thus, the presence

Filaments in the division furrow of mouse mammary cells.

Of the various theories that have been advanced to account for the mechanism of furrow formation and cytokinesis in animal cells (9, 21), the notion of active constriction in the equatorial cortex has recently received support from physical measurements such as those reported by Wolpert (22) and Rappaport (13) . A probable structural manifestation of the ring has been found through ultrastructural studies of cleaving invertebrate eggs, in which equatorially oriented filaments in the cleavage furrow suggest a region specialized for contraction (3, 7, 15, 17, 18) . These bundles of presumably contractile filaments have not been described in dividing cells of vertebrates or in dividing tissue cells of any organism . The present study reports the presence of a well organized filamentous component in the division furrows of mouse mammary epithelial cells .

Division of isolated furrows and furrow fragments in invertebrate eggs

This investigation was designed to determine whether the established cleavage furrow requires the presence of the polar and subpolar cell regions for normal function. Furrows and furrow fragments were surgically isolated from flattened, cleaving eggs of Echinarachnius parma, Hydractinia echinata and Aurelia aurita. The isolated furrows completed division despite the trauma of the operation and drastic shifting of the internal cytoplasm. Evidently the presence of the polar regions of the cell is unnecessary for furrowing at the equator.

Augmentation and dispersion of the in vivo mitotic apparatus of living marine eggs.

The effects of a number of organic reagents on the structure of the mitotic apparatus (MA) of several invertebrate eggs were investigated. In general, the agents induced either a large increase in the volume and retardation of the MA (hexylene glycol, dimethylsulfoxide, etc.) or caused it to partially or completely disappear (formamide, dithiodiglycol, dimethylacetamide, etc.). The immediate effects of the agents on the MA were reversible, but reversibility of embryonic development was only obtained if the eggs did not remain in the reagent for too long a time. The analysis of the specific effects of these agents suggests that the eggs utilized possess a pool of unoriented (or unpolymerized) MA material which may be reversibly affected by the agents studied. In the case of augmenting agents, the material is oriented into the MA or into aster-like bodies, in the case of dispersing agents, the material returns to the pool. Although no decision could be made as to whether the agents act directly or indirectly on the MA, the totality of the observations support the latter possibility.