Hormonal Control of Molting and Reproduction in Ticks

SYNOPSIS. Among ticks there are two developmental and threereproductive patterns that correlate with taxonomic groupings(Argasidae, prostriate and metastriate Ixodidae). Feeding isa prerequisite for molting; feeding and mating are necessaryfor reproduction in all except a few parthenogenetic species.Growth and development in ticks and other chelicerates appearto be controlled by molting hormones (ecdysteroids), as theyare in insects and crustaceans. Ecdysone and 20-hydroxyecdysoneappear to be present in most or all of the major cheliceratetaxa. Epidermis is the site of ecdysone production and fat bodythe site of 20-hydroxylation in the argasid Ornithodoros parkeri,as is probably the case in all ticks. Ecdysteroids influenceearly stages of spermatogenesis by stimulation of DNA synthesisin spermatocytes, but controls for later stages of meiosis areunknown. A polypeptide (12,000 daltons) from male genital accessoryglands stimulates capacitation (maturation) of spermatids intosperm at the time of spermatid transfer to females. Knowledgeof control of egg development and oviposition is incomplete.Stimuli from the synganglion are necessary for completion ofoogenesis and two synganglial factors have been proposed. AnEgg Development Stimulation Factor (EDSF) in O. parkeri is synthesizedand/or released three to six days after feeding. VitellogenesisInducing Factor (VIF) in O. moubata is synthesized and/ or releasedwithin one hour after feeding. The VIF is hypothesized to impactan unidentified tissue which in turn produces a Fat Body StimulationFactor (FSF) that stimulates fat body to synthesize vitellogenin(Vg). Roles of ecdysteroids and juvenile hormones during eggdevelopment and oviposition are unclear.     

Neuroendocrinology of Osmoregulation in Decapod Crustacea

Experimental evidences for neuroendocrine control of osmoreregulationin decapod crustaceans are mounting. The eyestalk system, brainand thoracic ganglionic centers, and the pericardial organ appearto be involved in this control. Evidences based on experimentationwith eyestalk removal and the injection of extracts of neuroendocrinecenters are presented. Neuroendocrine extracts affect the movementsof salts and water in the gills, stomach, intestine and antennalglands. The pericardial organ material may affect osmoregulationby increasing rate of circulation and influencing salt movement. Three factors have been partially separated from CNS tissues.A factor of the freshwater crayfish, and other freshwater decapods,increases the influx of salt. Two factors from an estuarinecrab influence the movement of water, an acetone-soluble factorincreasing its influx and a water-soluble factor decreasinginflux and increasing efflux. The factors may be involved inthe adaptation of the animals to their osmotic environments. None of the factors have yet been identified in circulationnor in effector tissues. Future research must place specialemphasis on the identification of the CNS factors in circulationas well as in secretory cells and effector tissues to establishtheir true hormonal nature.     

Interactions Between Limb Regeneration and Molting in Decapod Crustaceans

Molting and regeneration of lost appendages are tightly-coupled,hormonally-regulated processes in decapod crustaceans. Precociousmolts are induced by eyestalk ablation, which reduces circulatingmolt-inhibiting hormone (MIH) and results in an immediate risein hemolymph ecdysteroids. Precocious molts are also inducedby autotomy of 5–8 walking legs; adult land crabs (Gecarcinuslateralis) molt 6–8 wk after multiple leg autotomy (MLA).Autotomy of one or more of the 1° limb buds (LBs) that formafter MLA before a critical period interrupts proecdysis until2° LBs re-regenerate and grow to the approximate size ofthose lost. Based on these observations, Skinner proposed thatlimb buds produce two factors that control proecdysial events.Limb Autotomy Factor–Anecdysis (LAF_an), produced by 1°LBs when at least five legs are autotomized, stimulates anecdysialanimals to enter proecdysis. Limb Autotomy Factor–Proecdysis(LAF_pro), produced by 2° LBs in premolt animals when atleast one 1° LB is autotomized, inhibits proecdysial processes.Initial characterizations suggest that LAF_pro is a MIH-likepolypeptide that inhibits the synthesis and secretion of ecdysteroidby the Y-organs.     

Hormonal Control of Sexual Differentiation and Reproduction in Crustacea

SYNOPSIS. Sexual differentiation in malacostracan Crustaceais controlled by the androgenic gland hormone (AGH). In males,the primordial androgenic glands (AG) develop and AGH inducesmale morphogenesis. In females, the primordial AG does not developand the ovaries differentiate spontaneously. Implantation ofthe AG into females yields various results, showing that thesensitivity to AGH differs with the species and the receptiveorgans. Purified AGH of the isopod Armadillidium vulgare consistsof at least two molecular forms, which exist as monomeric proteinswith molecular weights of 17,000 ± 800 and 18,300 ±1,000 Da and with isoelectric points of about 4.5 and 4.3, respectively.The antiserum raised against purified AGH makes it possibleto measure AGH activity by immunoassay. Neurohormones control male and female reproduction. In males,they are involved in the maintenance of the male germinativezone and the control of AG activity. In females, the secondaryvitellogenesis is controlled by the vitellogenesis-inhibitinghormone (VIH) and the vitellogenesis- stimulating hormone (VSH).VIH isolated from the lobster Homarus americanus is a peptidewith a molecular weight of 9,135 Da and shows homology to thecrustacean hyperglycemic hormone and moltinhibiting hormone.Involvement of the molting hormone and the juvenile hormone-likecompound in the secondary vitellogenesis have also been suggested.In the amphipod Orchestia gammarella, the vitellogenesis- stimulatingovarian hormone (VSOH) seems to control vitellogenin synthesis     

Effects of Pollutants on Molting and Regeneration in Crustacea

Many environmental pollutants have toxic effects that can alternormal limb regeneration and molting in Crustacea. The mostcommon effect of heavy metals is that of retardation of regenerationof limbs accompanied by a delay in ecdysis; in some cases regenerationis affected without altering the molt cycle. Chlorophenols anddithiocarbamates caused inhibition of regeneration without affectingmolting in shrimp. Organic toxicants such as aromatic hydrocarbonsanddioxins also result in a decrease in the growth increment permolt, while DDT was found to accelerate regeneration and molting.A number of toxicants also produce morphological alterationsin the regenerated limbs of crabs. These may be relatively minor,such as reduced number of pigment cells, setae, or tuberclesin the regenerated limbs (mercury and cadmium), or may be moremajor deformities, such as abnormal bending in the limb or claw(tributyltin), or defects inchitin formation in the exoskeleton(diflubenzuron).     

Pressure Effects on the Respiration of Vertically Migrating Decapod Crustacea

SYNOPSIS. The respiration of five species of North Atlanticdecapods was measured under conditions of pressure and temperaturewhich allow calculation of the metabolism of these animals inthe oceans. The species were: Systellaspis debilis, Acanthephyrapurpurea, Oplophorus spinosus, Parapandalus richardi, and Sergestescrassus. Results indicate a tendency for metabolism to remainrelatively constant with depth, the decrease due to lower temperatureoffset by an increase due to rising pressure. This contrastswith previous work with epipelagic euphausids which tended tohave greatly reduced metabolism with increasing depth. Perhapsthe metabolic rate of the decapods must remain high enough forthem to remain effective predators throughout their depth range,by day as well as night.     

Studies on the Nervous Regulation of the Heart Beat in Decapod Crustacea

The effect of electrical stimulation of cardioaccelerator and cardioinhibitor nerves on the mechanically recorded heart beat of crayfish was studied. Similar experiments were performed with the lobster, Homarus americanus. Quantitative relationships between uni- and bilateral accelerator and/or inhibitor nerve stimulation and the resulting change in frequency and amplitude of the heart beat were established. With increasing frequency of stimulation the accelerator nerves show a relative decrease in their action, while that of the inhibitor nerves increases. It appears that left and right regulator nerves have synaptic contacts at the same areas of the postsynaptic cells within the heart ganglion. Similar results are obtained whether all impulses arrive over one, or over the other, or over both accelerator (or inhibitor) nerves; the resulting acceleration or inhibition depends strictly on the number of accelerator, or inhibitor impulses arriving at the ganglion. The ganglion cells can adapt to the inhibitor action. This is shown to be a postsynaptic phenomenon. Adaptation to accelerator stimulation is virtually absent. Characteristic after-effects of the accelerator and inhibitor action were observed and quantitatively evaluated. The interpretation of the results is based on the assumption of chemical transmitter substances. It is concluded that the accelerating transmitter decays slowly while the inhibitory transmitter is inactivated relatively rapidly.     

Physiological Control of Molting in Insects

SYNOPSIS. The initiation of a molting cycle in insects is neithera random nor a strictly periodic event. Insofar as molting canaccomplish different things under different circumstances, suchas a change in size or a change in form, it is reasonable toasume that the timing of a molt must be adapted to these functions.The onset of a metamorphic molt, in particular, must be preciselycontrolled because the onset of metamorphosis terminates thegrowth phase of a larva and establishes the body size of theadult insect. This aspect of the control of molting has receivedrelatively little attention and our knowledge of specific physiologicalmechanisms for the control of molt initiation is restrictedto three species: the blood-sucking bug, Rhodnius prolixus,the greater milkweed bug, Oncopeltus fasciatus, and the tobaccohornworm, Manduca sexta. The present review discusses the stateof our knowledge about the factors that render these insectscompetent to molt and about the stimuli that serve as a directtrigger for molting.     

Hormonal Effects on Calcium Metabolism in Crustacea

Cyclic shifts of calcium in the exoskeleton and soft tissues,as they are related to the intermolt cycle in crayfish, arereviewed. Regulatory factors, derived from the eyestalk, influencelevels of exoskeletal calcium; eyestalk extracts prepared fromanimals in premolt decrease shell calcium, while reciprocallyextracts from animals in intermolt increase it when these hormonalsources are injected into animals in the premolt stage (D₀-D₄). In addition, premolt eyestalk extract results in an increasein gastrolith calcium. In the exchange of calcium between theanimal and its environment there is evidence for differentialdepositionof recently available calcium in the exoskeleton. Further, intermoltand early premolt animals maintained in Ca⁴⁵-labelled waterfor 15 days concentrate it 4 and 3—fold in the exoskeletonand stomach, respectively. However, removal of a molt-inhibitingfactor through ablation of eyestalks results in a 20 and 40—foldincrease in incorporation inthese same sites relative to environmentalconcentrations. Treatment with mammalian parathyroid extract mobilizes bothexoskeletal and gastric calciumand leads to a rise in bloodcalcium. However, there is little or no effect on levels ofexoskeletal citric acid. Further, citric acid is higher in thecrayfish carapace during stage C, the period of mineralization,than in stage D, the period of demineralization. There are both similarities and differences between the effectsof crustacean and mammalianregulating factors with respect tothe direction and extent of mineralization. Biochemical studiesshould elucidate the mechanisms regulated by these hormones.     

虾蟹精子发育的营养及代谢研究概况

对雄性虾蟹的生殖营养及精子代谢作了综述。大量研究证实,在人工养殖条件下,雄性虾蟹的生殖力会出现明显下降,其原因与人工饲养条件下营养缺乏有关。精子储存在贮精囊和纳精囊中时,不断进行旺盛的代谢活动,其代谢类型主要是无氧代谢,而代谢的能量物质大部分种类为碳水化合物,这些物质主要由精子以外的物质提供。     

An Annotated List of Protozoan Parasites,Hyperparasites, and Commensals of Decapod Crustacea*

SYNOPSIS. An approximately complete list of the known protozoan associates (exclusive of a few aberrant forms like Amallocystis) of decapods is presented. A few taxonomic changes are suggested. Host, site of infection and geographic location are mentioned. Some comments on pathogenicity are made.     

Molting and cuticle deposition in the subterranean trichoniscid Titanethes albus (Crustacea, Isopoda)

Terrestrial isopods are a suitable group for the study of cuticle synthesis and calcium dynamics because they molt frequently and have evolved means to store calcium during molt. Little data is currently available on molting in Synocheta and subterranean isopods. We studied the molting dynamics in the subterranean trichoniscid Titanethes albus under laboratory conditions and performed a microscopic investigation of sternal CaCO(3) deposits and the tergal epithelium during molt in this species. In accordance with its lower metabolic rate, molting in the laboratory is roughly 2-3 times less frequent in Titanethes albus than would be expected for an epigean isopod under similar conditions. Animals assumed characteristic postures following the molt of each body half and did not consume the posterior exuviae after posterior molt. The structure of sternal calcium deposits and the ultrastructural characteristics of the epidermis during cuticle formation in Titanethes albus are similar to those described in representatives of Ligiidae. During the deposition of the exocuticle, the apical plasma membrane of epidermal cells forms finger-like extensions and numerous invaginations. In the ecdysial space of individuals in late premolt we observed cellular extensions surrounded by bundles of tubules.     

The Cytoskeletal Proteins Actin and Tubulin in the Spermatozoa of Four Decapod Crabs (Crustacea,Decapoda)

The mature spermatozoa of four species of European decapod crabs (Clibanarius erythropus, Maja squinado, Cancer pagurusand Potamon fluviatile)have been investigated using indirect immuno-fluorescence techniques for the presence of the cytoskeletal proteins actin and tubulin. Indirect immunofluorescence labelling with monoclonal anti-actin antibody and three different monoclonal anti-tubulin antibodies indicate that actin is present in the spermatozoa of all four species, but tubulins are restricted to the two species with microtubular arms, Clibanariusand Maja.The pattern of actin fluorescence varies between the spermatozoa of the four species, with Majaand Cancershowing intense fluorescence in the acrosome vesicle and in elements of the sperm cell involved in the acrosome reaction. The spermatozoon of each species is described ultrastructurally using transmission electron microscopy and correlations made between observed patterns of fluorescence and the cellular components described. No obvious filamentous actin (F-actin) is visible in the electron micrographs of the spermatozoa of any of the species. In most cases the fluorescence is sufficiently specific to indicate in which region of the mature sperm cell the actin and tubulin occurs. Actin is acrosomal in Maja, Cancerand Potamonbut appears to be cytoplasmic in Clibanarius, while the tubulins appear only to be present in the cytoplasm of Clibanarius, Majaand Cancer.     

Decapod Crustacea from the International Indian Ocean Expedition: the larval development of Heterocarpus (Caridea)

The larval species Atlantocaris gigas Ortmann is shown to be conspecific with Heterocarpus ensifer A. Milne Edwards, while Procletes biangulatus Bate is the larva of Heterocarpus levicarina (Bate). Each species passes through 13–15 zoeal stages and 3–4 megalopal stages. The later zoeal stages are large, have a long toothed rostrum, a carinated carapace and dorsal abdominal spines. The carinae on the carapace are retained in the adult; the rostrum becomes shortened and the abdominal spines modified at metamorphosis. Larval characters support the retention of Heterocarpus in the Pandalidae.
New information on the distribution of both species is included.     

Immunity in Decapod Crustaceans

Immunity in the decapod crustaceans is surveyed. Types of immuneresponses include encapsulation, phagocytosis with or withoutthe aid of serum factors, bactericidins active with or withoutthe aid of hemocyte factors, hemagglutinins, hemolysins, agglutinins,and precipitins. Immunity to gaffkemia in Panulirus interruptusis also discussed.