Structure,formation, mechanical properties,and disposal of the embryo attachment system of an estuarine crab,Sesarma haematocheir

In most decapod crustaceans, fertilized eggs extruded from the gonopore attach to ovigerous hairs within the incubation chamber of the female. The attachment is effected by an "embryo attachment system." The three continuous components of this system are the egg envelope, the funiculus, and the investment coat, which wraps around an ovigerous hair. Transmission electron microscopy (TEM) revealed that the embryo of Sesarma haematocheir is enfolded by three distinct envelopes (E1, E2, and E3), whereas the embryo attachment system is composed of only the outermost, single envelope (E1) with two sublayers (E1a and E1b). This envelope (E1) originates from the outer layer of the vitelline membrane (envelope of the ovum) with two sublayers (E1a' and E1b'). The sequence and timing of events in the formation of the embryo attachment system was determined on the basis of observations of female behavior, ultrastructure, and mechanical properties of the membranes. The egg envelope (E1a' + E1b') is not adhesive immediately after extrusion from the gonopore; but 5 min after egg-laying, it becomes adhesive-a change associated with "fusion" of the two sublayers (E1)-and attaches the eggs to the ovigerous hairs from 5 to 30 min after egg-laying. The layer E1a' always binds to an ovigerous hair at specific, electron-dense attachment sites that are distributed longitudinally on the surface of each hair. Plasticity of the egg envelope changes, and the female kneads her eggs by the movement of ovigerous setae; this movement forms the investment coat on the ovigerous hair (10-40 min after egg-laying). Thirty minutes after egg-laying, the egg envelope again divides into two sublayers (E1a and E1b), and the adhesiveness rapidly decreases. The plasticity of the envelope remains, and the funiculus is formed, accompanied by kneading of the eggs (40-90 min after egg-laying). The embryos hatch one month after incubation, and the attachment systems all slip off their ovigerous hairs by the actions of the ovigerous-hair slipping substance (OHSS). This substance appears to act specifically at the attachment sites on the hair, lysing the bond with layer E1a, and thereby disposing of the embryonic attachment system and preparing the hairs for the next clutch of embryos.     

Hatching of an estuarine crab, Sesarma haematocheir: from disappearance of the inner (E3) layer to rupture of the egg case

Hatching of decapod crustaceans is characterized by the sudden rupture of the egg case. This study focused on the following two issues regarding the hatching mechanism of the estuarine terrestrial crab Sesarma haematocheir: (1) dissolution of the egg case, and (2) the site where the egg case breaks. The egg case comprises three layers: the outer two (E1 and E2) layers and the inner (E3) thin layer (0.2 microm in thickness). The outer layers showed no morphological changes upon hatching, but the inner layer (E3) was markedly digested. The digestion of this layer would enable the embryo to absorb ambient water via reverse peristalsis of the intestine, resulting in an increase of the volume. The egg case always ruptured perpendicular to the longitudinal axis of the embryo. In addition, breakage of the egg case occurred at the dorsal thorax of the embryo. The three major organs positioned at this area were (1) a sharp projection (dorsal spine), (2) an assemblage of muscles, and (3) a pair of secretory glands, each of which was about 30 microm in diameter. The dorsal projection is soft before hatching, and it is clear that the egg case does not break with the posterior expansion of this projection. The rupture instead appears to be caused by the expansion of the muscles arranged perpendicular to the body axis. In addition, some (unknown) factor might weaken the egg case just before hatching. The secretory glands may be a kind of rosette gland, but the role that this gland plays at hatching is not known. As a duct comes out from the center and enters the dorsal projection, some active substance may be released at the tip of this projection. However, immunochemical studies are not consistent with this substance being an ovigerous hair stripping substance (OHSS).     

Entrainment of a semilunar rhythm by a simulated moonlight cycle in the terrestrial crab,Sesarma haematocheir

Summary Sesarma haematocheir is a species of terrestrial crabs inhabiting hillsides and paddy fields near the sea. Females show a semilunar rhythm of zoea-release coinciding with days of spring tides and in addition with the time of high water occurring at the nearby seacoast about dusk. Nature of environmental stimuli or zeitgebers that induce the semilunar rhythm of zoea-release was examined experimentally. In case that a population of males and females was kept under the condition of a 24-h light-dark cycle (LD 14:10) only, females showed a free-running semilunar rhythm of egg-laying and zoea-release synchronized from field conditions. On the other hand, a semilunar rhythm of egg-laying and zoea-release was entrained by the combination of the 24-h LD and a simulated 24.8-hr moonlight cycle of which the phase was shifted in relation to the natural lunar cycle. This result suggests that the 24.8-h moonlight cycle acts as a zeitgeber of a semilunar rhythm. The 12.4-h tidal cycle parallels with the 24.8-h moonlight cycle in the field. On the basis of the perception of a distinct phase relationship between the 24-h LD and the 24.8-h moonlight cycle, it is considered that crabs substitute the 24.8-h moonlight cycle for the 12.4-h cycle of tides as a zeitgeber to synchronize the phase of the semilunar rhythm with a tidal situation.     

A pair of rosette glands in the embryo and zoeal larva of an estuarine crab Sesarma haematocheir, and classification of the tegumental glands in the embryos of other crabs

A pair of rosette glands (one of the tegumental glands in crustaceans) is present at the root of the dorsal spine of the thorax in mature embryos of the estuarine crab Sesarma haematocheir. Each rosette gland is spherical, 45-50 microm in diameter. This gland consists of three types of cells: 18-20 secretory cells, one central cell, and one canal cell. The secretory cells are further classified into two types on the basis of the morphology of secretory granules. There are 17-19 a cells, and only one b cell per rosette gland. An a cell contains spherical secretory granules of 2-3 microm in diameter. The granules are filled with highly electron-dense materials near the nucleus but have lower electron-density near the central cell. The secretory granules contained in the b cell have an irregular shape and are 1-1.5 microm in diameter. The density of the materials in the granules is uniform throughout the cytoplasm. The secretory granules contained in both the a and b cells are produced by the rough endoplasmic reticulum. Materials in the granules are exocytotically discharged into the secretory apparatus inside the secretory cell, sent to the extracellular channels in the central cell, and secreted through the canal cell. The rosette gland can be distinguished from the epidermal cells 2 weeks after egg-laying and the gland matures just before hatching. Materials produced by this gland are secreted after hatching and secretion continues through five stages of zoeal larvae. These rosette glands were never found in the megalopal larva. Rosette glands are found in the embryos of Sesarma spp. and Uca spp. In other crabs, tegumental glands are also found at the same position as in the embryo of S. haematocheir, but the fine structure of their glands is largely different from that of the rosette gland. On the basis of the morphology of secretory cells (a-g cell types), the tegumental glands of a variety of crab embryos can be classified into four types, including rosette glands (type I-IV). The function of these tegumental glands is not yet known, but different types of the gland seem to reflect the phylogeny of the crabs rather than differences of habitat.     

The mandibular organ of the female spider crab,Libinia emarginata,in immature,mature, and ovigerous crabs

The cells of mandibular organs of female Libinia emarginata exhibit changes in substructure during molting and vitellogenesis. The cytoplasm is that of a steroid-hormone producing cell. The cells do not appear to produce ecdysones.     

Induction of vitellogenesis by 17-hydroxyprogesterone and methyl farnesoate during post-reproductive period,in the estuarine crab Neohelice granulata

Adult female crabs (Neohelice granulata) were treated during the post-reproductive period with both 17-hydroxyprogesterone (17PG) and methyl farnesoate (MF). During the 4-week in vivo assay, animals were fed hormone-enriched (17PG or MF) pellets twice a week, at a dose of 2 nmol/g of body weight. Additionally, at the middle of the in vivo experiment, ovarian explants were incubated in vitro with each hormone at a concentration of 15 μM for 24 h. At the end of the in vivo assay, both the gonadosomatic index and the vitellogenic protein content (Vg) of crabs treated with either 17PG or MF were significantly higher (p < 0.05) than the values of the concurrent controls. In addition, the hemolymphatic vitellogenin level of both hormonally treated groups was higher. At the end of the in vitro assay, ovary explants incubated with 17PG had a significantly higher (p < 0.05) protein synthesis and content of Vg proteins than controls. Ovary explants incubated with MF had similar levels to controls (p > 0.05). The involvement of these hormones in the regulation of ovarian growth during the reproductive cycle of N. granulata is discussed.     

Larval release in the crab Rhithropanopeus harrisii (Gould): chemical cues from hatching eggs

Decapod crustaceans have rhythmic larval release patterns. Inthe case of Rhithropanopeus harrisii substances associated withhatching eggs induce ovigerous crabs to exhibit stereotypiclarval release behavior involving vigorous abdomen pumping.In this study, the pumping response of ovigerous crabs was usedto investigate the chemistry of the substances (pumping factor)that evoke larval release behavior. Pumping was induced by polarsubstances released into sea water upon egg hatching. Pumpingfactor was concentrated and desalted by adsorption chromatographywith Amberlite XAD-7 resin. Size fractionation by cascade pressuredialysis indicated that most of the active material had a mol.wt. <500 daltons. Biological activity was destroyed by incubationof pumping factor with a non-specific protease. Amino acid analysisof hydrolyzed factor indicated that arginine comprised –50%of the amino acids. Pumping responses were elicited experimentallyby abnormally high concentrations of mixtures of the two majoramino acids (arginine and glycine) in the hydrolysate. Theseresults suggest that pumping factor is a heterogeneous groupof small peptides each containing arginine.     

Detection of female mating status using chemical signals and cues

Males of many species choose their mate according to the female's reproductive status, and there is now increasing evidence that male fitness can depend on this discrimination. However, females will also aim to regulate their mating activity so as to maximize their own fitness. As such, both sexes may attempt to dictate the frequency and timing of female mating, reflecting the potentially different costs of female signaling to both sexes. Here, I review evidence that chemical cues and signals are used widely by males to discriminate between mated and unmated females, and explore the mechanisms by which female odour changes post‐mating. There is substantial empirical evidence that mated and unmated females differ in their chemical profile, and that this variation provides males with information on a female's mating status. Although there appears to be large variation among species regarding the mechanisms by which female odour is altered post‐mating, the transfer of male substances to females during or subsequent to copulation appear to play a major role. This transfer of substances by males may be part of their strategy to suppress reproduction by competing males, particularly in species where females mate more than once.     

Some changes in biochemical composition with sex and size of the crab,Sesarma boulengeri calman

Variations in the biochemical composition (protein and cholesterol) have been studied in the hepatopancreas and thoracic muscle of the crab, Sesarma boulengeri as a function of sex and size. Second degree polynomial regression equations are used in predictive fashion to quantify the biochemical constituents in relation to sex and size. The effect of size is expressed as a power function of body weight. A good agreement is found between the experimental data and the theoretical values based on the polynomial.There is a negative correlation between the mass of crab and the reduced mass of cholesterol and protein of the tissues in both sexes, signifying higher metabolic and growth rates in younger crabs. The cholesterol and protein contents are higher in the male indicating more growth than in the female. However, there is tendency of the muscle protein to increase in large sized female crabs suggesting that bigger sized female are structurally better suited than males.     

Induction of egg hatching by high humidity in the cicada Cryptotympana facialis

The timing of egg hatching in Cryptotympana facialis was examined in relation to short-term weather conditions. The brief underwater submergence, once a week, of dead twigs bearing cicada egg nests resulted in high hatching rates both at 25 degrees C and under outdoor conditions protected from rainfall. Under outdoor conditions with natural rainfall, most eggs hatched on rainy days. There was a significant positive correlation between the number of hatching eggs and daily relative humidity (RH). When eggs picked from twigs were exposed to various humidity levels, many eggs hatched quickly at higher humidity without direct contact with liquid water. Newly hatched nymphs showed a low tolerance to desiccation; at 81% RH at 25 degrees C, most of them died within 6 h. Under outdoor conditions, most nymphs died within 2 h on sunny days, whereas nymphs survived longer on rainy days. When newly hatched nymphs were released on dry ground, only 24% of them succeeded in burrowing into the soil, and many were killed by ants or desiccation. However, 92% of nymphs released onto wet ground successfully burrowed into it. The direct induction of hatching by high humidity ensures the survival and establishment in the soil of newly hatched nymphs in this species.     

Foraging behavior of an estuarine predator, the blue crab Callinectes sapidus in a patchy environment

To define general principles of predator‐prey dynamics in an estuarine subtidal environment, we manipulated predator density (the blue crab, Callinectes sapidus) and prey (the clam, Macoma balthica) patch distribution in large field enclosures in the Rhode River subestuary of the central Chesapeake Bay. The primary objectives were to determine whether predators forage in a way that maximizes prey consumption and to assess how their foraging success is affected by density of conspecifics. We developed a novel ultrasonic telemetry system to observe behavior of individual predators with unprecedented detail. Behavior of predators was more indicative of optimal than of opportunistic foraging. Predators appeared responsive to the overall quality of prey in their habitat. Rather than remaining on a prey patch until depletion, predators appeared to vary their patch use with quality of the surrounding environment. When multiple (two) prey patches were available, residence time of predators on a prey patch was shorter than when only a single prey patch was available. Predators seemed to move among the prey patches fairly regularly, dividing their foraging time between the patches and consuming prey from each of them at a similar rate. That predators more than doubled their consumption of prey when we doubled the number of prey (by adding the second patch) is consistent with optimizing behaviors ‐ rather than with an opportunistic increase in prey consumption brought about simply by the addition of more prey. Predators at high density, however, appeared to interfere with each other's foraging success, reflected by their lower rates of prey consumption. Blue crabs appear to forage more successfully (and their prey to experience higher mortality) in prey patches located within 15–20 meters of neighboring patch, than in isolated patches. Our results are likely to apply, at least qualitatively, to other crustacean‐bivalve interactions, including those of commercial interest; their quantitative applicability will depend on the mobility of other predators and the scale of patchiness they perceive.     

Chemosensory exploration of male scent by female rock lizards result from multiple chemical signals of males

Multiple sexual signals may convey information on males' quality. However, most research focused on visual signals, ignoring chemical signals. In vertebrates, chemical signals are probably often a multicomponent mixture of several active compounds, but they are not well known. We examined the potential additive and interactive effects of 2 compounds (oleic acid and ergosterol) naturally found in femoral gland secretions of male rock lizards on chemosensory exploration behavior of females. Tongue-flick (TF) rates of females to male secretions may result from the combination of responses to multiple compounds. There may be an additive or synergetic effect because male secretions with the highest proportions of both compounds received the highest TF rates, suggesting that their scents were more intriguing. However, there might be an interactive effect too; female TF rates were higher to males' scent with high proportions of ergosterol alone, even if proportions of oleic acid were low, than to high proportions of oleic acid but with low proportions of ergosterol. Further bioassays testing TF behavior of females to standard compounds, presented alone or combined in different concentrations confirmed these findings. Variations in female TF behavior might be explained because different compounds signal different male traits of different importance for females. Our study suggested that femoral secretion of male rock lizards may act as a multicomponent chemical signal.     

Behavioral responses of peripubertal female mice towards puberty-accelerating and puberty-delaying chemical signals

We examined the behavioral responses of peripubertal femalemice to puberty-accelerating urine from male mice and to puberty-delayingurine from females living in groups. Marked attraction was showntowards both chemical signals when they were tested individually.These attraction levels were of comparable size for both urinesources and were little influenced by the age of the subjectsand their hormonal or nutritional status. When both chemicalsignals were presented, grouped-female urine was preferred tomale urine by prepubertal, food-deprived postpubertal and ovanectorruzedfemales. Free-feeding, postpubertal and ovariectomizcd femalesreceiving estrogen replacement failed to show significant preferencesbut did spend more time investigating male chemical signalson average. The effect of prior housing condition (with motherand littermates or isolated) on the subjects' attraction toand preference for these accelerating and delaying chemicalsignals was not pronounced. The magnitude of attraction to maleurine was significantly larger in isolated females comparedto females remaining with their litters. However, the attractionto groupedfemale urine and the preference for it over male urinewere not significantly influenced by housing condition. Whendirect contact with male and grouped-female chemical signalswas prevented, significant attraction and preference were nolonger evident, suggesting that urinary components with lowvolatility may mediate ‘attraction’. These resultsare discussed in terms of the ecology and physiology of thepheromone cueing system of the mouse.     

DNA damage and cell necrosis induced by naphthalene due to the modulation of biotransformation enzymes in an estuarine crab Scylla serrata

The sublethal effect of naphthalene (2.5, 5, and 10 mg L(-1)) was studied in an estuarine crab Scylla serrata with reference to macromolecular changes. Biotransformation enzymes such as cytochrome P450, cytochrome b(5), NADPH cytochrome P450 reductase, aryl hydrocarbon hydroxylase, glutathione-S-transferase, and UDP-glucuronyl transferase were elevated in the hepatopancreas of naphthalene-exposed crabs in comparison with control. Remarkable amount of DNA damage and cell necrosis was observed in hepatopancreas, hemolymph, and ovary of the crabs exposed to naphthalene, when compared with control. For all the parameters studied, a concentration-dependent gradient of the changes was observed. The expression of DNA damage and cell necrosis suggests an increased production of oxidants during naphthalene metabolism.     

Demineralization of crab shells by chemical and biological treatments

To achieve demineralization of crab shell waste by chemical and biological treatments, lactic acid and lactic acid bacterium were applied. In 5.0 and 10% lactic acid, pH rapidly decreased from 6.8 to 4.2 and from 4.5 to 2.4 at day 3, respectively, and thereafter the pH remained at an almost constant level. In a 10% lactic acid bacterium inoculum, pH lowered to 4.6 at day 5. Relative residual ash content rapidly decreased to 49.1 and 16.4% in 5 and 10% lactic acid treatments, respectively, for the initial 12 h. In 2.5, 5 and 10% lactic acid bacterium inoculums, relative residual ash content rapidly decreased to 55.2, 40.9 and 44.7%, respectively, on the first day. Residual dry masses were 76.4, 67.8 and 46.6% in 2.5, 5 and 10% lactic acid treatments, respectively, for the initial 12 h. After a one-time exchange of the lactic acid solution, in the 5.0% lactic acid treatment, residual dry mass rapidly decreased from 66.0 to 41.4%. In 2.5, 5 and 10% lactic acid bacterium inoculums, residual dry masses decreased to 67.6, 57.4 and 59.6% respectively, on the first day. Protein contents after demineralization ranged from 51.3–54.7% in the chemical treatments and decreased to 32.3% in the lactic acid fermentation process. A negative relationship was shown between pH and demineralization rate in lactic acid and lactic acid bacterium treatments. These results suggest that lactic acid fermentation can be an alternative for demineralization of crab shells, even though the rate and efficiency of the demineralization is lower than the chemical treatment.     

Larval hatching in the horseshoe crab, Limulus polyphemus: facilitation by environmental cues

Female horseshoe crabs, Limulus polyphemus (Linnaeus), lay their eggs in nests on sandy beaches near the high water line. Embryos develop within the sand, hatch into trilobite larvae, and enter the water column when the nest is inundated. Given the diversity of tidal and shoreline inundation patterns that populations of L. polyphemus experience throughout their range (semidiurnal and diurnal tides, microtidal, and nontidal), hatching may also be facilitated by environmental triggers that serve to synchronize hatching and larval emergence with periods of high water. The objective of this study was to determine if larval hatching in L. polyphemus is triggered or facilitated by environmental cues. Stage 21 embryos were subjected to one of seven different treatments that simulated conditions experienced during inundation: (1) hydration, (2) agitation, (3) hydration and agitation, (4) hydration and agitation with sand, (5) osmotic shock, (6) terrestrial hypoxia, and (7) aquatic hypoxia. Hatching rates increased significantly under all simulated tidal conditions compared to controls and were highest (96%) for eggs simultaneously exposed to both hydration and agitation with sand. Measurements of the osmolarity of the perivitelline fluid of developing eggs collected from the field indicated that it is hyperosmotic to the ambient seawater and porewater. Thus, when inundated, eggs also experience a hypoosmotic shock, which would likely facilitate hatching by causing the eggs to swell, rupturing the egg membrane and thereby increasing the likelihood that larvae would hatch and enter the water column during periods of high water.     

Seasonal variation in the energy metabolism in an estuarine crab,Chasmagnathus granulata (Dana, 1851)

• 1.1. The effects of seasonal variation on the carbohydrate and lipid metabolism of the Chasmagnathus granulata were investigated.
• 2.2. Glycemia is high in winter and summer and low in spring and fall.
• 3.3. The glycogen content in the hepatopancreas and muscle is higher in fall and winter, and decreases during spring and summer.
• 4.4. The muscle lipids are higher in summer, and decrease during fall and winter whereas hepatopancreas lipids are higher except in the fall.
• 5.5. The crabs show change in the metabolic pattern of lipids and carbohydrates during the seasons of the year.