Buoyancy variations in eggs of Atlantic cod (Gadus morhua L.) in relation to chorion thickness and egg size: theory and observations

Egg specific gravity is a function of egg volume, chorion volume, perivitelline space (PVS) and the specific gravity of chorion and ovoplasm. Experimental studies on cod ( Gadus morhua L.), a marine multiple batch spawner, showed that approx. forty per cent of the chorion volume is incorporated between batches and that the chorionic material has a mean specific gravity of 1·20 (range: 1·14–1·35). The chorion volume and specific gravity are low at the end of the spawning period in extremely fecund fish. Specific gravity of ovoplasm was observed to be 1·017 in marine eggs and calculated to be about 1·008 in brackish water eggs. Inherent variation in PVS is found to have little influence on egg specific gravity. With the other variables constant, egg specific gravity is inversely related to egg volume supported by studies on single batches of eggs. Measurements on every batch of eggs reveal that the production of large eggs (>1·3 mm) gives low density eggs initially and high density eggs towards the end of spawning, while the production of small eggs (<1·3mm) gives moderate specific gravity. These observations are discussed in relation to vertical distribution of the eggs and reproductive success of recruit and repeat spawners. There are indications that repeat spawners produce larger eggs.     

Effects of egg quality on normal fertilization and early development of the cod, Gadus morhua L

Normal cod eggs respond to insemination by a rapid cortical reaction followed by an increase in total osmolarity and a small increase in egg diameter. The chorion becomes harder, but this is a slower process reaching its maximum strength after c . 24 h. Bad eggs are characterized by a slower or incomplete cortical reaction, resulting in a slower rise in osmolarity and a softer chorion. Bad eggs rapidly lose their capacity for fertilization. In unfertilized eggs in sea water, no cortical reaction is observed. There is, however, a rise in total osmolarity and a hardening of the chorion.     

Nondormanz-Entwicklung prospektiver Diapause-Eier vonBombyx mori mit oder ohne Chorion unter Paraffinöl

Summary Prospective diapause eggs ofBombyx mori become permeable to water in or after contact with paraffin, and they die before reaching diapause. If the eggs are hindered from drying up, their germ anlagen develop to diapausing germ bands. Prospective diapause eggs opened in paraffin, always develop without egg diapause, but their degree of organogenesis depends on the chorion: When eggs are completely dechorionized most of them develop to hatching or nearly hatching larvae; when eggs are completely dechorionized, but their chorion remains in the paraffin, the degree of organogenes is issignificantly lower; and when the opened eggs keep 1/2–3/4 of the chorion, their organogenesis is significantly lower than in the two previous experiments.It is discussed that nondormancy development ofprospective diapause eggs in vitro is not a specific effect of culture media containing water but is possible in paraffin oil too. It is not only possible to stop but also to prevent egg diapause. Nothing, as yet, can be said about the prospective significance of the chorion's reducing factor in organogenesis.     

Sperm Penetration and in vitro Fertilization of the Egg of the House Cricket Acheta domesticus

Summary

A study of sperm penetration of the egg of the house cricket, Acheta domesticus, using a fluorescent microscope technique, showed that sperm penetration of the chorion, prior to fertilization, is not restricted to a specialised area of the egg surface, such as the micropyle. An acrosomal filament is seen on penetrating sperm. Polyspermy (multiple sperm attachment) is seen under normal conditions.

Eggs fertilized in vitro developed to the 4 day (pre-katatrepsis) stage, but did not undergo katatrepsis. Development was confirmed by cytogenetic studies. The percentage of eggs showing cleavage nuclei (i.e. initial development) was 59% after in vitro fertilization and 5% in ovarian eggs incubated in a hypotonic medium.     

The swelling egg of the long rough dab, Hippoglossoides platessoides limandoides (Bloch)

The egg of Hippoglossoides platessoides limandoides swells when released into sea water. The swelling takes place entirely outside the ovoplasm and creates a large perivitelline space which can make up 85% of the total egg volume. Swelling occurs in both unfertilized and fertilized eggs although a small proportion of unfertilized eggs, believed not to have been activated, do not swell. Swelling is dependent upon the breakdown of cortical alveoli, together with an unusually soft and elastic chorion. The cortical alveoli, present in greater numbers than is usual in teleost eggs, release colloidal material when they break down on egg activation; adsorption of water by this material is responsible for the egg volume increase.     

Experimental Parameterisation of Principal Physics in Buoyancy Variations of Marine Teleost Eggs

It is generally accepted that the high buoyancy of pelagic marine eggs is due to substantial influx of water across the cell membrane just before ovulation. Here we further develop the theoretical basis by applying laboratory observations of the various components of the fertilized egg in first-principle equations for egg specific gravity (ρ_egg) followed by statistical validation. We selected Atlantic cod as a model animal due to the affluent amount of literature on this species, but also undertook additional dedicated experimental works. We found that specific gravity of yolk plus embryo is central in influencing ρ_egg and thereby the buoyancy. However, our established framework documents the effect on ρ_egg of the initial deposition of the heavy chorion material in the gonad prior to spawning. Thereafter, we describe the temporal changes in ρ_egg during incubation: Generally, the eggs showed a slight rise in ρ_egg from fertilization to mid-gastrulation followed by a gradual decrease until full development of main embryonic organs just before hatching. Ontogenetic changes in ρ_egg were significantly associated with volume and mass changes of yolk plus embryo. The initial ρ_egg at fertilization appeared significantly influenced by the chorion volume fraction which is determined by the combination of the final chorion volume of the oocyte and of the degree of swelling (hydrolyzation) prior to spawning. The outlined principles and algorithms are universal in nature and should therefore be applicable to fish eggs in general.     

Egg shells in mites: vitelline envelope and chorion in Acaridida (Acari)

This study deals with the formation of vitelline envelope (VE) and chorion compartments in several free living and parasitic acaridid mites.In all investigated mites, the VE is of primary origin (produced by oocyte itself), whereas exochorion material is of tertiary origin (oviduct or chorion gland secretion).In acarid mites Acarus siro and Tyrophagus perniciosus, VE formation starts with the oviductal oocytes in which vitellogenesis already proceeds. It is characterized by stratification (Acarus) or coarse fibrillar texture (Tyrophagus). Oocyte microvilli penetrating VE material were not observed. When the vitellogenesis terminates, VE becomes homogeneous and is transformed into chorion. This is the only layer protecting the deposited egg in A. siro, whereas in T. perniciosus the chorion-coated eggs passing through the distal portion of the oviduct are additionally covered by exochorion material deposited in three distinct forms: dense patches, granules, and most conspicuous locular chambers. In Tyrophagus longior, the egg surface closely resembles that of T. perniciosus, but the locular chambers are smaller. In Aleuroglyphus ovatus the exochorion material forms tiny spherical patches instead of locular chambers.In Sarcoptes scabiei, Notoedres cati and Falculifer rostratus, flocculent VE appears on vitellogenic oocytes in the oviduct. VE development is characterized by formation of numerous lenticular perivitelline spaces, which initially grow to disappear later. Then VE material transforms into fully homogeneous chorion. Chorion glands in Sarcoptes and Notoedres produce multivesicular secretory bodies; their content is released onto the egg surface to form a vesicular monolayer (exochorion) during the egg passage. The chorion gland in Falculifer is composed of two secretory cell types. Its secretion possibly glues the eggs to the host feather barb during highly ordered deposition, and forms the appendage ending with a ribbed plate, here considered to be a print of female undulate lamina acting as an ovipositor. The hatching suture is present. Neither distinct micropyle nor aeropyles have been found in eggs of species under study.The exochorion is proposed to be an adhesive layer which fixes the eggs to the substratum. The same role plays the chorion gland secretion in F. rostratus. It can be argued, however, that locular chambers of Tyrophagus exochorion may participate in reduction of water loss rather than in egg adherence or plastron respiration, as previously suggested in the literature.     

Self and non-self recognition between gametes of the ascidian,Halocynthia roretzi

Summary The self-sterility ofHalocynthia roretzi from Mutsu Bay, Japan, was examined. This sterility is strict and not a single egg can be fertilized in self-sterile animals. Less than 2% of the animals were self-fertile (with 100% cross-fertility). All heterologous sperm can fertilize all eggs, although there are pairs of individuals in which the coelomocytes recognize each other as self. Eggs deprived of follicle cells cannot be fertilized by either autologous or heterologous spermatozoa. Detached autologous or heterologous follicle cells can reattach to the chorion in calcium-enriched sea water and the reconstituted eggs recover their ability to be fertilized. A mosaic egg can therefore be obtained, which consists of oocyte, test cells and chorion originating from one individual and follicle cells from another. The mosaic egg was used to determine the site of recognition of self and non-self. The results indicate that the recognition resides in the chorion and/or test cells, probably the chorion. The relationship between somatic alloreactivity, previously found in coelomocytes ofH. roretzi, and gamete reactivity is discussed.     

Respiratory morphology of the Abedus herberti Hidalgo egg chorion (Hemiptera: Belostomatidae)

Although giant water bugs (Hemiptera: Belostomatidae) are large, aquatic insects known for their obligate paternal egg brooding behaviors, little research has focused on the structure of their eggs. The respiratory requirements of developing embryos likely created selection for brooding, so a thorough understanding of the respiratory morphology of belostomatid eggs could help explain how brooding behaviors facilitate embryonic gas exchange. This study used scanning electron microscopy to document the respiratory microstructure of the eggs of Abedus herberti, a back brooding giant water bug. The exochorion is similar to that of other belostomatids in texture and organization except that the respiratory region is confined to the uppermost quarter of the egg. This is the area exposed to the atmosphere by encumbered males. A plastron network made up of densely packed vertical projections demarcates the boundary between the respiratory and nonrespiratory regions of the chorion. The internal chorion is composed of alternate air‐filled and denser layers that likely facilitate the movement of oxygen from the aeropyles at the top of the eggs to the developing embryonic tissues. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Ultrastructure of the eggshell and its formation in Planipapillus mundus (Onychophora: Peripatopsidae)

Although the majority of onychophorans are viviparous or ovoviviparous, oviparity has been described in a number of species found exclusively in Australia and New Zealand. Light microscopy and scanning and transmission electron microscopy were used to examine developing eggs and the reproductive tract of the oviparous Planipapillus mundus. Deposited eggs and fully developed eggs dissected from the terminal end of the uteri have an outer thick, slightly opaque chorion, and an inner thin, transparent vitelline membrane. The chorion comprises an outermost extrachorion, sculptured with domes equally spaced over the surface; a middle exochorion, with pores occurring in a pattern of distribution equivalent to that of the domes of the extrachorion above; and an innermost, thick endochorion consisting of a spongelike reticulum of cavities comparable to the respiratory network found in insect eggs. The vitelline membrane lies beneath the chorion, from which it is separated by a fluid‐filled space. The vitelline membrane tightly invests the developing egg. Examination of oocytes in the ovary and developing eggs at various stages of passage through the uterus indicate that the majority of chorion deposition occurs in the midregion of the uterus, where vast networks of endoplasmic reticulum are present in the columnar epithelium. The vitelline membrane, however, is believed to begin its development as a primary egg membrane, surrounding the developing oocytes in the ovary. The vitelline membrane is transformed after fertilization, presumably by secretions from the anterior region of the uterus; hence, it should be more accurately referred to as a fertilization membrane. Aspects of the reproductive biology of P. mundus are also included. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Fertilization and normal development inAscidiella aspersa (Tunicata) studied with Nomarski-optics

Normal development ofAscidiella aspersa was studied over a period of approx. 24 h at 20°C from egg insemination through metamorphosis of the tadpole larva using Nomarski-optics. Records were made of spermatozoa attaching to and passing through the cellular envelopes and the chorion of the egg. Egg shape alterations upon entry of the fertilizing sperm, which reflect the early phase of ooplasmic segregation, were monitored in intact and dechorionated eggs. The time course of normal development was recorded, and prominent stages were photographed within or deprived of the egg envelopes. The present observations are compared with recent accounts on early development in other solitary ascidian species.     

EGG MORPHOLOGY AND OVIPOSITION PATTERNS OF THE STRO-BILOMYIA SPP. (DIPTERA: ANTHOMYIIDAE) FLIES DAMAGING SIBERIAN LARCH CONES IN NORTHEASTERN CHINA1)

Abstract The oviposition patterns of 6 larch cone flies, Strobilomyia spp., were surveyed in 1993 in Da Hinggan Mountains, northeastern China. The colonization of distinct phases of cone development and the selection of different sites to lay eggs allowed to distinguish 5 patterns of oviposition. Observations of the egg morphology and of the chorion architecture using scanning electron microscope lead to classify the examined cone fly eggs into 6 different types. Each type of egg was related to a given oviposition pattern. Among the 6 egg types, eggs of S. laricicola, S. melaniola and S. infrequens were identified with certainty. Although hypotheses were given, further experiments under controlled conditions are required to identify which of the 3 other egg types is associated to S. baicalensis, S. svenssoni and S. sanyangi, respectively.     

Effects of 45 insecticides,acaricides and molluscicides on the rove beetleAleochara bilineata (Col.: Staphylinidae) in the laboratory

Effects of 45 insecticides, acaricides and molluscicides on adult females of the rove beetleAleochara bilineata were investigated in the laboratory. The pesticides were tested in concentrations equivalent to the highest recommended dosages for practical use. Mortality, egg production and hatch of the eggs were measured. The reproducibility of the test and the suitability of the strain ofA. bilineata used are discussed. The toxicity of the cholinesterase inhibitors tested was varying, but in general high. Only pirimicarb and acephate showed low toxicity. The pyrethroids tested were highly toxic, even though fluvalinate allowed a few eggs to be laid. The test did not give conclusive results for insect growth regulators. The ecological relevance of laboratory results is discussed, and it is concluded that only for pesticides with no or low toxicity can the results be used for prediction of effects in the field.     

Egg envelopes of Baetis rhodani and Cloeon dipterum (Ephemeroptera, Baetidae): a comparative analysis between an oviparous and an ovoviviparous species

A comparative ultrastructural investigation on the eggshell (vitelline and chorionic envelopes) has been carried out in the nymphs of two mayfly species encompassed into the Baetidae, namely Baetis rhodani and Cloeon dipterum. During oocyte differentiation in the meroistic telotrophic ovarioles, gametes are connected to discrete nurse cells by trophic cords. In B. rhodani, each ovariole contains several eggs arranged in sequence, whereas in C. dipterum each contains a single egg. Follicle cells are competent for vitelline and chorionic envelope synthesis. Baetis rhodani is an oviparous species and the chorion is fairly thick, formed by an alveolate endochorion and a fibrillar exochorion delimited by a honey‐comb roof. Cloeon dipterum stands out among Ephemeroptera for being ovoviviparous. In B. rhodani, ovulation starts in the older nymphs with dark wing‐pads, whereas in C. dipterum choriogenesis ends in the imaginal stage. Here the chorion is very thin and laid eggs hatch almost immediately, allowing the larvulae to move out. The maturation of a single egg per ovariole is synchronized with the achievement of the adult stage. The acquisition of ovoviviparity has led to remarkable changes in the ovariole organization along with a simplification of the eggshell structure.     

Egg cannibalism in Ascia monuste in the field; opportunistic, preferential and very frequent

Newly hatched caterpillars of the specialist herbivorous species Ascia monuste (Lepidoptera, Pieridae) feed on egg chorion before ingesting plant material. They also ingest their exoskeletons and perform egg cannibalism in both the field and the laboratory. Females lay eggs on plants which already have conspecifics (eggs and/or caterpillars) leading to the observation of cannibalism in the field. Two favorable conditions are required for such an occurrence: (1) eggs laid close together on the same leaf, and (2) the finding by older caterpillars of eggs on the same plant. Oviposition preference experiments in cages showed that females do not avoid laying on plants with eggs. However, they do avoid laying eggs on plants predated by caterpillars. All instars perform cannibalism in the field and, in addition to this, the ingested eggs are healthy and cannibalism occurs in the presence of abundant food. The ingestion of eggs from their own clutch was more intense when the clutch was large. Contact with eggs is also important for cannibalism. Caterpillars ingested healthy eggs during three successive days. According to the results, it is possible to state that egg cannibalism in A. monuste is opportunistic, preferential and highly frequent and that there is a tolerance to a diet based on animal protein in this species. Since A. monuste obtains nutrients from both animal and vegetable resources, it is probably better to consider it as opportunistic omnivorous.     

Adhesion mechanisms in European whitefish Coregonus lavaretus eggs: is this a survival mechanism for high‐energy spawning grounds?

This study examined the potential biochemical and mechanical structures that may contribute to egg adhesion in European whitefish Coregonus lavaretus. Experiments showed that eggs from a population of C. lavaretus from Loch Eck remained non‐adhesive in a solution chemically similar to ovarian fluid but became adhesive seconds after contact with water. Examination of the ultrastructure of the chorion showed that the morphology changed significantly after contact with water, with nodule‐like protuberances attached to connective filaments on the surface present in water‐hardened but not non‐water hardened eggs. Biochemical analysis showed the presence of Chain A, RNase ZF‐3e proteins in the chorion of water‐hardened but not non‐water hardened eggs. Histochemical staining of the chorion of C. lavaretus eggs showed that the externa, but not the interna, stained positively for the presence of glycoproteins. From these results, it was concluded that C. lavaretus from Loch Eck possess both anatomical and biochemical adhesive mechanisms that have been undocumented in this species so far.     

Egg structure of Zorotypus caudelli Karny (Insecta, Zoraptera, Zorotypidae)

The structural features of eggs of Zorotypus caudelli Karny are described in detail. The egg is elliptic with long and short diameters of 0.6 and 0.3 mm respectively, and creamy white. The egg shows a honeycomb pattern on its surface, without any specialized structures for hatching such as an operculum or a hatching line. The fringe formed by a fibrillar substance secreted after the completion of the chorion encircles the lateral surface. The egg layer is composed of an exochorion, an endochorion, and a vitelline envelope. The exochorion and endochorion are electron-dense and homogeneous in structure. The exochorion shows a perforation of numerous branching aeropyles. The exo- and endochorion are connected by numerous small columnar structures derived from the latter. The vitelline envelope is very thin and more electron-dense than the chorion. A pair of micropyles is present at the equator on the dorsal side of the egg. Originating at the micropyle, the micropylar canal runs through the chorion obliquely. The structural features of the eggs of Zoraptera were compared with those of other polyneopteran and paraneopteran orders.     

Surface morphology of eggs of Euproctis chrysorrhoea (Linnaeus, 1758)

Candan, S., Suludere, Z. and Bayrakdar, F. 2007. Surface morphology of eggs of Euproctis chrysorrhoea (Linnaeus, 1758). —Acta Zoologica (Stockholm) 88 : 000–000. Filaments covering the egg batches and chorion structure were studied both by light and scanning electron microscopy in the brown‐tailed moth Euproctis chrysorrhoea (Linnaeus, 1758). Females lay eggs in masses on the underside of apple leaves. The egg batches are covered with brown hairs derived from the bodies of the female. Each female lays about 200–400 eggs. The spherical eggs are about 0.84 mm long and 0.47 mm wide. Newly deposited eggs are golden‐yellow and darken after the onset of embryonic development. The micropylar area appears somewhat depressed and has a circular outline. The region is surrounded by a rosette of 10–12 petal‐shaped primary cells, which are completely surrounded by a series of secondary and tertiary cells. The remainder of the egg is largely smooth, but shows aeropyles. These are located in the corners of ill‐defined polygons.     

Laboratory method for testing side-effects of pesticides on the rove beetleAleochara bilineata — Adults

Tests were conducted in glass cells containing moistened sand sprayed with the concentration recommended for the pesticide or with demineralised water (controls). Adult females (1–2 weeks old) ofA. bilineata were placed on the fresh residue in the cells and provided daily with fresh fly eggs as food. The duration of the test was 5 days, mortality being recorded every day. The side effects of the pesticide were expressed as reduction in egg production ofA. bilineata during the whole test period. Results permitted classification of the pesticides according to the 4 categories of harmfulness used by the IOBC working group. 23 pesticides were tested, and the reproducibility of the test appeared to be satisfactory. Generally, insecticides/acaricides had a pronounced effect on the beetles whereas fungicides and herbicides were less detrimental. Exceptions were the insecticides Tedion V 18 and Kilval, classified as harmless, and the fungicides Morestan, Pomarsol forte and Afugan rated as moderately harmful. Among growth regulators Prosevor 85 was highly detrimental while Cycocel Extra and Rhodofix had no effects. Excepting Morestan, Pomarsol forte and Ustinex PA the pesticides did not affect the hatching of eggs. The work was financed by the Danish Environmental Protection Agency.     

Influence of chorion ingestion on the performance of Ascia monuste and its association with cannibalism

1. In some lepidopterans, the newly hatched caterpillars feed on chorion (animal protein) as their first food. This is also a frequent behaviour of newly hatched caterpillars of Ascia monuste. 2. According to some parameters tested (time for pupation, number of adults, male imago weight, and fifth‐instar ingestion), chorion ingestion by first‐instar larvae affects adult performance positively. The ingestion of ultraviolet‐sterilised chorion provided the same positive effect on performance. It is thus suggested that young caterpillars may be benefiting from chorion nutritionally, and that chorion ingestion is a chain of events that leads to positive effects on insect performance. 3. Cannibalism in A. monuste was observed in newly hatched caterpillars and is related to the chorion ingestion behaviour. A condition for this to occur was the interval of time of hatching, which means that, if a group of caterpillars hatches very much before another group, once the caterpillars have ingested the chorion of their own eggs, there is a tendency for them to ingest the chorion of other eggs (including unhatched eggs) and, consequently, practice cannibalism. 4. Ascia monuste immatures are considered to be herbivorous, however it is important to know that they eat animal tissue (chorion and conspecific eggs).