Invertebrate Eggs Research Articles

Experimental mineralization of invertebrate eggs and the preservation of Neoproterozoic embryos

Understanding the processes that led to the mineralization of Precambrian metazoan eggs and embryos is essential to informed interpretations of such fossils and their significance in early metazoan evolution. Here we show that rapid mineralization of invertebrate eggs is possible under laboratory conditions. Under anaerobic conditions, eggs become coated in mainly calcium carbonate within three weeks. Preservation of the external morphology is comparable to that of fossil material, but no internal mineralization was observed in the laboratory. This is the first report of the laboratory mineralization of metazoan eggs in the absence of a decaying carcass, and demonstrates that eggs, and probably small embryos, can be preserved in the absence of larger organisms as a source of phosphorus or calcium. Thus, it is possible for organisms of this size to have been fossilized prior to the evolution of large metazoans.

How frequent is external transport of seeds and invertebrate eggs by waterbirds? A study in Doñana, SW Spain

Dispersal of aquatic organisms by birds has long been assumed to be an important process, but quantitative studies of its frequency are scarce. We determined the presence of plant and invertebrate propagules adhering to the plumage or feet of 47 waterbirds of 6 species (2 ducks, 2 waders and 2 rallids) trapped during the spring migration period in two localities in Donana, south-west Spain. The percentage of waterbirds transporting propagules was high, with large differences between sites in the proportion of individuals carrying propagules (35 % and 100 %, respectively) and the numbers and types of propagules carried. Seeds of at least 15 plant species, eggs of at least 6 invertebrate species and at least one alga were encountered, with each bird carrying up to 12 different types. Seeds tended to be attached to the plumage, and invertebrate eggs to the feet. The efficiency of protocols for removing propagules from birds varied between bird and propagule species. External transport of propagules by waterbirds seems a frequent process at least at a local scale and is likely to facilitate the rapid colonisation of new or temporary wetlands, and maintain gene flow between populations.

From Cdc2 to Cdk1: when did the cell cycle kinase join its cyclin partner?

The idea that Cdc2 and cyclins play a key role in the control of the G2/M transition of the cell cycle came largely from genetic analysis of fission yeast and physiological studies of clam, frog, sea urchin and starfish eggs and oocytes. However, it took a long time to realise that Cdc2 and cyclins form a stoichiometric complex and that a cyclin subunit is necessary for the Cdc2 subunit to gain its protein kinase activity. Cyclins were first recognized as proteins whose abundance oscillates during the early cell cycles of marine invertebrate eggs and their connection with MPF (maturation-promoting factor), the entity defined in frog and starfish oocytes whose activity controls entry into M phase, was far from clear at first. Indeed, it was a long time before MPF was shown to be a protein kinase, and direct proof that MPF is a heterodimer comprising one molecule of cyclin and one molecule of Cdc2 was finally obtained only when the Cdc2-associated component of purified starfish MPF was sequenced and found to be cyclin B. When this fundamental discovery was confirmed in vertebrates and mammalian members of the Cdc2 family were also shown to bind cyclins, Cdc2 became Cdk1, the first cyclin-dependent protein kinase.

THE IMPORTANCE OF MEIOFAUNA IN FOOD WEBS: EVIDENCE FROM AN ACID STREAM

Seasonal food webs were constructed for the whole invertebrate assemblage (meio- and macrofauna) inhabiting Broadstone Stream (southeast England). High and uniform taxonomic resolution was applied in a dietary analysis, by resolving the complete benthic community to species, including the meiofauna, protozoa, and algae. Meiofauna accounted for 70% of all species in the summary web and for 73% and 63% of those in the summer/autumn and spring webs, respectively. The web structure changed between summer/autumn and winter/spring, due to differences in species composition. Many stream invertebrates fed on meiofauna and organic matter. Addition of meiofauna to the Broadstone web increased the percentage of intermediate species. Seasonal webs contained between 54 (spring 1997) and 86 (autumn 1996) interactive taxa and 229–378 trophic links. Marked differences in web complexity were found between the summer/autumn and winter/spring periods. Meiofauna accounted for most of the links in the web with a high proportion of intermediate–intermediate links in summer and autumn (0.421–0.440) and also of intermediate–basal links during winter and spring (0.509–0.628). In general, the summary web showed that intermediate species and basal resources were numerically dominant components in this stream. Web connectance rose slightly between summer (0.052) and winter (0.061) and increased further in spring (0.079), coinciding with a reduction in species number. A high fraction of detritivores was combined with omnivorous predators, many of which supplemented their diets with organic matter and, depending on season, with algae and invertebrate eggs. In addition, a wide range of feeding modes was found among meiofaunal species. The diversity of the Broadstone community suggests that the impact of top predators tends to dissipate. A low proportion of top predators in the web was combined with a low mean number of prey items, other than detritus, in their guts (large predators, 1.08–1.26 prey/individual gut; small-sized tanypods, 2.15–2.32 prey/individual gut). Dietary similarity was highest in autumn and winter 1996, and observed feeding links of the most common predatory species showed low overlap in their diets. The web architecture of this stream is reticulate and complex, and the patterns observed in these seasonal webs differed from previous stream webs, resulting in low connectance, high linkage density, long food chains, and a high proportion of intermediate species and of intermediate–intermediate links. The food web derived from Broadstone Stream clearly demonstrates that the meiofauna increases web complexity and thus, taking into account their functional diversity, may be crucial to the understanding of food web properties and ecosystems processes in streams.

The Importance of Meiofauna in Food Webs: Evidence from an Acid Stream

Seasonal food webs were constructed for the whole invertebrate assemblage (meio- and macrofauna) inhabiting Broadstone Stream (southeast England). High and uniform taxonomic resolution was applied in a dietary analysis, by resolving the complete benthic community to species, including the meiofauna, protozoa, and algae. Meiofauna accounted for 70% of all species in the summary web and for 73% and 63% of those in the summer/autumn and spring webs, respectively. The web structure changed between summer/autumn and winter/spring, due to differences in species composition. Many stream invertebrates fed on meiofauna and organic matter. Addition of meiofauna to the Broadstone web increased the percentage of intermediate species. Seasonal webs contained between 54 (spring 1997) and 86 (autumn 1996) interactive taxa and 229–378 trophic links. Marked differences in web complexity were found between the summer/autumn and winter/spring periods. Meiofauna accounted for most of the links in the web with a high proportion of intermediate–intermediate links in summer and autumn (0.421–0.440) and also of intermediate–basal links during winter and spring (0.509–0.628). In general, the summary web showed that intermediate species and basal resources were numerically dominant components in this stream. Web connectance rose slightly between summer (0.052) and winter (0.061) and increased further in spring (0.079), coinciding with a reduction in species number. A high fraction of detritivores was combined with omnivorous predators, many of which supplemented their diets with organic matter and, depending on season, with algae and invertebrate eggs. In addition, a wide range of feeding modes was found among meiofaunal species. The diversity of the Broadstone community suggests that the impact of top predators tends to dissipate. A low proportion of top predators in the web was combined with a low mean number of prey items, other than detritus, in their guts (large predators, 1.08–1.26 prey/individual gut; small-sized tanypods, 2.15–2.32 prey/individual gut). Dietary similarity was highest in autumn and winter 1996, and observed feeding links of the most common predatory species showed low overlap in their diets. The web architecture of this stream is reticulate and complex, and the patterns observed in these seasonal webs differed from previous stream webs, resulting in low connectance, high linkage density, long food chains, and a high proportion of intermediate species and of intermediate–intermediate links. The food web derived from Broadstone Stream clearly demonstrates that the meiofauna increases web complexity and thus, taking into account their functional diversity, may be crucial to the understanding of food web properties and ecosystems processes in streams.

Consequences of a superabundance of larval walleye pollock Theragra chalcogramma in the Gulf of Alaska in 1981

Abundances of larval walleye pollock in Shelikof Strait, Gulf of Alaska, in 1981 were far greater than any recorded estimates before that time or since (some patch estimates exceeded 100000 larvae per 10 m 2 ). In spite of this extraordinary input, the ensuing 1981 year class was relatively poor. An examination of the feeding habits of larvae collected from inside and outside dense larval patches revealed that in 1981, larval walleye pollock consumed significantly more invertebrate eggs (x = 66.7% of the total diet) and fewer copepod nauplii (x = 13.6%) inside of larval patches relative to outside (x = 11.4 and 63.2%, respectively). These observations suggest that density dependent com- petition inside patches may have locally depleted the primary food source, copepod nauplii, prompting a diet switch to a lower quality but more abundant prey resource, invertebrate eggs. Results from a bioenergetics simulation support this theory, indicating that dense patches of walleye pollock larvae in 1981 were capable of exhausting naupliiar prey resources in Shelikof Strait in a relatively short period of time (14 to 40 d). Our observations contrast with other studies that suggest that ichthyoplankton exert little or no influence on microzooplankton standing stocks. Rather, we present evidence that, in certain unusual circumstances, particularly dense aggregations of larvae are capable of locally de- pleting the prey community. Such events may weaken larval condition and exacerbate natural death rates, which may have contributed to the poor recruitment success of the 1981 year class.

The Role of Jelly Coats in Sperm‐Egg Encounters, Fertilization Success, and Selection on Egg Size in Broadcast Spawners

Sperm limitation may be an important selective force influencing gamete traits such as egg size. The relatively inexpensive extracellular structures surrounding many marine invertebrate eggs might serve to enhance collision rates without the added cost of increasing the egg cell. However, despite decades of research, the effects of extracellular structures on fertilization have not been conclusively documented. Here, using the sea urchin Lytechinus variegatus, we remove jelly coats from eggs, and we quantify sperm collisions to eggs with jelly coats, eggs without jelly coats, and inert plastic beads. We also quantify fertilization success in both egg treatment groups. We find that sperm-egg collision rates increase as a function of sperm concentration and target size and that sperm are not chemotactically attracted to eggs nor to jelly coats in this species. In fertilization assays, the presence of the jelly coat is correlated with a significant but smaller-than-expected improvement in fertilization success. A pair of optimality models predict that, despite the large difference in the energetic value of egg contents and jelly material, the presence of the jelly coat does not diminish selection for larger egg cell size when sperm are limiting.

The Role of Jelly Coats in Sperm-Egg Encounters, Fertilization Success, and Selection on Egg Size in Broadcast Spawners

Sperm limitation may be an important selective force influencing gamete traits such as egg size. The relatively inexpensive extracellular structures surrounding many marine invertebrate eggs might serve to enhance collision rates without the added cost of increasing the egg cell. However, despite decades of research, the effects of extracellular structures on fertilization have not been conclusively documented. Here, using the sea urchin Lytechinus variegatus, we remove jelly coats from eggs, and we quantify sperm collisions to eggs with jelly coats, eggs without jelly coats, and inert plastic beads. We also quantify fertilization success in both egg treatment groups. We find that sperm‐egg collision rates increase as a function of sperm concentration and target size and that sperm are not chemotactically attracted to eggs nor to jelly coats in this species. In fertilization assays, the presence of the jelly coat is correlated with a significant but smaller‐than‐expected improvement in fertilization success. A pair of optimality models predict that, despite the large difference in the energetic value of egg contents and jelly material, the presence of the jelly coat does not diminish selection for larger egg cell size when sperm are limiting.

Nicotinic acid adenine dinucleotide phosphate: a new Ca2+ releasing agent in kidney.

Nicotinic acid adenine dinucleotide phosphate (NAADP), a molecule derived from beta-NADP, has been shown to trigger Ca2+ release from intracellular stores of invertebrate eggs and mammalian cell microsomes. NAADP-induced Ca2+ release occurs through a mechanism distinct from that of inositol-1,4,5-trisphosphate- or cyclic ADP-ribose-elicited Ca2+ release. This study investigated whether NAADP can be synthesized in rat kidney. Extracts from glomeruli, mesangial cells, and papilla have high NAADP synthetic capacities. Conversely, synthesis of NAADP in kidney cortex was almost undetectable. Furthermore, 9-cis-retinoic acid significantly up-regulated NAADP synthesis in mesangial cells. Authenticity of NAADP biosynthesis in glomeruli was affirmed by HPLC analysis. NAADP stimulated Ca2+ release from mesangial cell microsomes through a pathway distinct from that of inositol-1,4,5-trisphosphate or cyclic ADP-ribose. NAADP-triggered Ca2+ release may play an important role in regulation of renal function.

Predatory impact of an epiphytic hydrozoan in an upwelling area in the Bay of Coliumo (Dichato, Chile)

The natural diet of the epiphytic hydrozoan Obelia geniculata has been studied in an upwelling area in the Bay of Coliumo (Dichato, Chile) during two 24-h cycles. Number of prey per predator and predatory density have been measured. In both cycles more than 78% of the diet consisted of eggs of invertebrates and faecal pellets. Compared with other species of hydrozoans studied in a similar way, O. geniculata had a heterogeneous diet and a capture rate which was scarcely related to the peaks of abundance of its prey. This catch rate was between 632×10 3 and 10 393×10 3 prey m −2 day −1, which corresponds to a mean ingestion rate of 113% of the hydranth biomass per day. These results indicate the importance of small-sized benthic suspension feeders in upwelling systems.

Effect of nicotinic acid adenine dinucleotide phosphate on ryanodine calcium release channel in heart.

Nicotinic acid adenine dinucleotide phosphate (NAADP), a molecule derived from nicotinamide adenine dinucleotide phosphate (NADP+), is a recently identified nucleotide that activates Ca2+ release from intracellular stores in invertebrate eggs and in mammalian cells. NAADP could function as an intracellular messenger for mobilizing internal Ca2+ stores, however the targets and nature of NAADP-induced Ca2+ release are unknown. We report here that NAADP (3-10 microM) induces Ca2+ release from rat heart microsomes and that NAADP (1-10 microM) activates single ryanodine receptor/calcium release channels (RyR2) from dog heart incorporated into bilayer lipid membranes. The results indicate that NAADP may play a role in cardiac excitation-contraction coupling by acting on RyR2 channels.

Widespread Distribution of Binding Sites for the Novel Ca2+-mobilizing Messenger, Nicotinic Acid Adenine Dinucleotide Phosphate, in the Brain

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca(2+)-mobilizing agent in invertebrate eggs that has recently been shown to be active in certain mammalian and plant systems. Little, however, is known concerning the properties of putative NAADP receptors. Here, for the first time, we report binding sites for NAADP in brain. In contrast to sea urchin egg homogenates, [(32)P]NAADP bound reversibly to multiple sites in brain membranes. The rank order of potency of NAADP, 2',3'-cyclic NAADP and 3'-NAADP in displacing [(32)P]NAADP was, however, the same in the two systems and in agreement with their ability to mobilize Ca(2+) from homogenates. These data indicate that [(32)P]NAADP likely binds to receptors mediating Ca(2+) mobilization. Autoradiography revealed striking heterogeneity in the distribution of [(32)P]NAADP binding sites throughout the brain. Our data strongly support a role for NAADP-induced Ca(2+) signaling in the brain.

Intraspecific co-variation between egg and body size affects fertilisation kinetics of free-spawning marine invertebrates

Fertilisation of eggs of free-spawning marine invertebrates depends on factors affecting sperm concentration in the field and also on gamete characteristics such as egg size. In the free-spawning intertidal ascidian Pyura stolonifera mean egg size increased with maternal size in 2 separate populations. The largest ascidian produced eggs that were, on average, 50% greater in volume than the eggs produced by the smallest individual studied. There was no evidence to suggest that egg density varied with adult size and egg dry organic weight increased with maternal size. The fertilisation kinetics of this species were strongly affected by the variation in egg size, with the eggs of large individuals requiring much less concentrated sperm to achieve maximal levels of fertilisation success than the eggs of small individuals. We suggest that variation in egg size between individuals of different sizes and ages may be an important factor in determining fertilisation success for ascidians of this species.

Mechanical Resistance to Shear Stress: The Role of Echinoderm Egg Extracellular Layers.

Extracellular layers (jelly coats) on echinoderm eggs are composed of a fibrous network imbedded in a gelatinous material. This type of fibrous network has the potential to protect eggs from mechanical stress. To determine the effects of shear stress and the role of jelly coats in protecting eggs from these stresses, eggs of the sea urchin Lytechinus variegatus, both with and without intact jelly coats, were exposed to shear stresses ranging from 0.3 to 2 Pa in a cone and plate viscometer. The percentage of eggs remaining intact after exposure to the shear stress was assessed. The results indicate that shear stress can damage eggs and that jelly coats may play a role in decreasing the effects of these stresses. Eggs with jelly coats remained intact and fertilizable at greater shear stresses than those with the coats removed. This is the first evidence that extracellular layers on invertebrate eggs can provide protection from mechanical forces.

Nicotinic acid adenine dinucleotide phosphate triggers Ca2+ release from brain microsomes

Mobilization of Ca2+ from intracellular stores is an important mechanism for generating cytoplasmic Ca2+ signals [1]. Two families of intracellular Ca2+-release channels – the inositol-1,4,5-trisphosphate (IP3) receptors and the ryanodine receptors (RyRs) – have been described in mammalian tissues [2]. Recently, nicotinic acid adenine dinucleotide phosphate (NAADP), a molecule derived from NADP+ , has been shown to trigger Ca2+ release from intracellular stores in invertebrate eggs [3–6] and pancreatic acinar cells [7]. The nature of NAADP-induced Ca2+ release is unknown but it is clearly distinct from the IP3- and cyclic ADP ribose (cADPR)-sensitive mechanisms in eggs (reviewed in [8,9]). Furthermore, mammalian cells can synthesize and degrade NAADP, suggesting that NAADP-induced Ca2+ release may be widespread and thus contribute to the complexity of Ca2+ signalling [10,11]. Here, we show for the first time that NAADP evokes Ca2+ release from rat brain microsomes by a mechanism that is distinct from those sensitive to IP3 or cADPR, and has a remarkably similar pharmacology to the action of NAADP in sea urchin eggs [12]. Membranes prepared from the same rat brain tissues are able to support the synthesis and degradation of NAADP. We therefore suggest that NAADP-mediated Ca2+ signalling could play an important role in neuronal Ca2+ signalling.

Fossilized metazoan embryos—The historical testimony of the Cambrian explosion

IN zoology, the developmental stage of individual from zygote to hatching was called embryo. The modem embryology is a branch of study on the organism’ s embryos. The palaeoembryology is a new field in palaeontology, and it has not been considered an important field before, because the invertebrate’s eggs or embryos are minute size and without mineralized envelope. Until now, fossilized eggs of invertebrates in Cambrian have been rarely reported and most of them are small globular structures without recognizable features. Other reported fossilized embryos found from Middle Cambrian are spherical with a smooth

Redox Changes during Fertilization and Maturation of Marine Invertebrate Eggs

Previous studies on sea urchin eggs indicate that activation of NAD kinase is one of the earliest Ca2+-mediated events of fertilization. The subsequently produced NADP is converted to NADPH by the pentose shunt pathway, and some of this NADPH is used by an NADPH oxidase for generation of H2O2. To examine whether these changes apply generally, we have analyzed changes in pyridine nucleotide content during meiotic maturation and fertilization in eggs from four phyla. Surprisingly, fertilization-associated increases in NAD kinase were found only in echinoid eggs. The ratio of NADPH/NADP (redox ratio) increased from 1–1.6 to 2.5–6 following fertilization of echinoid and also clam eggs. However, the ratio is already >2 for unfertilized asteroid, tunicate and echiuroid eggs, and this ratio is unaffected by fertilization. We conclude that activation of NAD kinase and shifts in pyridine nucleotide metabolism and thereby cellular redox status may have roles that vary between species. In echinoids, a major role is in providing NADPH for H2O2production, but there may be other yet unappreciated signaling functions for this change.

Expression and Immunolocalization of p59c-fynTyrosine Kinase in Rat Eggs

Fertilization overcomes meiotic arrest by triggering a series of biochemical events, resulting in activation of the egg. A small group of protein tyrosine kinases (PTKs) have been identified in eggs of invertebrates and lower vertebrates and inhibitor studies have suggested that they play a role in late events of egg activation. A recent study using the sea urchin system demonstrated that Fyn kinase was expressed in eggs and was activated within minutes of fertilization. In the present study, Western blot analysis as well as immune complex kinase assay demonstrated that p59c-fynkinase was expressed in both unfertilized and fertilized rat eggs. Immunofluorescence confocal microscopy demonstrated that Fyn kinase was localized to the egg cortex but also to the polar body and the fertilizing cone which are elevated from the cortical cytoplasm of the activated egg. Surprisingly, Fyn was also found to be highly concentrated over the meiotic and mitotic spindles. To date, Fyn is the first PTK demonstrated to be present in the mammalian egg. Localization of Fyn to the egg cortex as well as the spindle microtubules indicates that this protein kinase may have multiple functions within the egg.

Feeding of Sciaenid (Pisces: Sciaenidae) Larvae in Two Coastal Lagoons of the Gulf of Mexico

Stomach contents analyses showed that Leiostomus xanthurus (8.50-12.90 mm SL) had a wide trophic spectrum (15 food categories) with copepods and eggs of invertebrates as main components. In contrast, Micropogonias undulutus (6.65-12.20 mm SL) ingested only six food categories (copepods, eggs of invertebrates, crustacean nauplii, bamacle nauplii, amphipods and other crustaceans). There is an overlap of 73.2 to 83.0% in the diet of these two species. Bairdiella chrysoura (1.17-1.92 mm SL) fed primarily on juvenile pelecypods, crustacean nauplii, eggs of invertebrates, including gasteropods and copepods. Cynoscion nebulosus (1.50-2.42 mm SL) ingested juvenile pelecypods, copepods, crustacean nauplii, eggs of invertebrates and tintinnids, variability in overlap (47.4 to 79.5%) between these species was affected by size of the larvae.

Are Echinoderm Egg Size Distributions Bimodal?

Marine invertebrates can be categorized into species that reproduce by producing either large numbers of small, energetically inexpensive eggs that become planktotrophic larvae, or fewer, larger eggs with more yolk and lecithotrophic development (1). The selective advantages of these alternative strategies were considered in a series of simple mathematical models by Vance (2, 3). These models predicted that intermediate egg sizes should have lower reproductive efficiency, and that only extreme egg sizes should be evolutionarily stable (2, 3). Specifytally, Vance's models (2, 3) and later modifications (4-7), predict that eggs of marine invertebrates should have bimodal size distributions, rejecting the contrast between small egg/feeding and large egg/nonfeeding modes of development and the selection against intermediate egg sizes. Evidence for bimodality in egg size distributions is, however, equivocal, with unimodal distributions seen in the majority of comparative studies that are appropriate tests of the hypothesis (8-13). Bimodal distributions have been described only in a few groups of molluscs (4) and asteroid and echinoid echinoderms (14). Here we test the prediction of bimodality in the holothuroid and ophiuroid echinoderms and show that although the natural log-transformed egg size distributions are visually unimodal, the holothurian egg size distribution is statistically composed of two discrete modes. Moreover, reexamination of the asteroid and echinoid egg size distributions (14) with the addition of data from more recent literature confirms that there are two statistical modes in the egg size distributions of these classes. Thus, in the phylum Echinodermata, there is a bimodal egg size distribution three of the four classes in which this prediction can tested.