The calcium dependence of pigment translocation in freshwater shrimp red ovarian chromatophores

The roles of calcium in cell signaling consequent to chromatophorotropin action and as an activator of mechanochemical transport proteins responsible for pigment granule translocation were investigated in the red ovarian chromatosomes of the freshwater shrimp Macrobrachium olfersii. Chromatosomes were perfused with known concentrations of free Ca++ (10(-3) to 10(-9) M) prepared in Mg(++)-EGTA-buffered physiological saline after selectively permeabilizing with 25 microM calcium ionophore A23187 or with 10(-8) M red pigment concentrating hormone (RPCH). The degree of pigment aggregation and the translocation velocity of the leading edges of the pigment mass were recorded in individual chromatosomes during aggregation induced by RPCH or A23187 and dispersion induced by low Ca++. Aggregation is Ca++ dependent, showing a dual extracellular and intracellular requirement. After perfusion with reduced Ca++ (10(-4) to 10(-9) M), RPCH triggers partial aggregation (approximately 65%), although the maximum translocation velocities (approximately 16.5 microns/min) and velocity profiles are unaffected. After aggregation induced at or below 10(-5) M Ca++, spontaneous pigment dispersion ensues, suggesting a Ca++ requirement for RPCH coupling to its receptor, or a concentration-dependent, Ca(++)-induced Ca(++)-release mechanism. The Ca(++)-channel blockers Mn++ (5 mM) and verapamil (50 microM) have no effect on RPCH-triggered aggregation. An intracellular Ca++ requirement for aggregation was demonstrated in chromatosomes in which the Ca++ gradient across the cell membrane was dissipated with A23187. At free [Ca++] above 10(-3) M, aggregation is complete; at 10(-4) M, aggregation is partial, followed by spontaneous dispersion; below 10(-5) M Ca++, pigments do not aggregate but disperse slightly. Aggregation velocities diminish from 11.6 +/- 1.2 microns/min at 5.5 mM Ca++ to 7.4 +/- 1.3 microns/min at 10(-4) M Ca++. Half-maximum aggregation occurs at 3.2 x 10(-5) M Ca++ and half-maximum translocation velocity at 4.8 x 10(-5) M Ca++. Pigment redispersion after 5.5 mM Ca(++)-A23187-induced aggregation is initiated by reducing extracellular Ca++: slight dispersion begins at 10(-7) M, complete dispersion being attained at 10(-9) M Ca++. Dispersion velocities increase from 0.6 +/- 0.2 to 3.1 +/- 0.5 microns/min. Half-maximum dispersion occurs at 7.6 x 10(-9) M Ca++ and half-maximum translocation velocity at 2.9 x 10(-9) M Ca++. These data reveal an extracellular and an intracellular Ca++ requirement for RPCH action, and demonstrate that the centripetal or centrifugal direction of pigment movement, the translocation velocity, and the degree of pigment aggregation or dispersion attained are calcium-dependent properties of the granule translocation apparatus.     

Early embryonic development of the freshwater shrimp Caridina multidentata (Crustacea,Decapoda, Atyidae)

Decapod crustaceans show a great diversity of developmental modes at all levels. In particular, early cleavage varies from total via mixed to superficial modes and from determinate cleavage with a stereotyped pattern to indeterminate cleavage. However, the ground pattern of early decapod development is not clear. To address this problem, we studied the early embryonic development of the caridean shrimp Caridina multidentata with a combination of confocal laser scanning microscopy, scanning electron microscopy, 4D microscopy and 3-D reconstruction software. Despite a yolk-rich egg, the cleavage is holoblastic and shows a distinct pattern of blastomere arrangement, characterized by two interlocking cell bands. This resembles the conditions in dendrobranchiate shrimps, which most likely are the sister group to Pleocyemata to which C. multidentata belongs. Hence, our results offer the possibility to assume total cleavage with blastomeres arranged in two interlocking cell bands as ancestral cleavage mode for Decapoda.     

A spring-matrix model for pigment translocation in the red ovarian chromatophores of the freshwater shrimp Macrobrachium olfersi (Crustacea, Decapoda)

A model for intracellular transport of pigment granules in the red ovarian chromatophores of the freshwater shrimp Macrobrachium olfersi is proposed on the basis of shifts in the equilibrium of resting forces acting on an elastic pigment matrix. The model describes a pigment-transport mechanism in which mechanochemical protein motors like kinesin and myosin alternately stretch and compress a structurally unified, elastic pigment matrix. Quantifiable properties of the spring-matrix obey Hooke's Law during the rapid phases of pigment aggregation and dispersion. The spring-like response of the pigment mass is estimated from previous kinetic experiments on pigment translocation induced by red pigment concentrating hormone, or by the calcium ionophore A23187. Both translocation effectors trigger an initial phase of rapid pigment aggregation, and their removal or washout after complete aggregation produces a phase of rapid pigment dispersion, followed by slow pigment translocation. The rapid-phase kinetics of pigment transport are in reasonable agreement with Hooke's Law, suggesting that such phases represent the release of kinetic energy, probably produced by the mechanochemical protein motors and stored in the form of matrix deformation during the slow phases of translocation. This semiquantitative model should aid in analyzing intracellular transport systems that incorporate an elastic component.     

Nested clade analysis of the freshwater shrimp, Caridina zebra (Decapoda: Atyidae), from north-eastern Australia

The freshwater shrimp, Caridina zebra, is endemic to montane rainforest streams of the Atherton Tableland, north-eastern Australia. As the confluences of many of the headwater streams are in unsuitable habitat, dispersal is expected to be highly restricted. Results from a previous allozyme survey for this species suggested that historical dispersal between separate river drainages had occurred due to rearrangements of the drainage lines at some stage in the recent past. The aim of this study was to use temporal information from the mitochondrial cytochrome oxidase subunit I (CO-I) gene to determine whether the observed genetic structure was a result of historical processes, or alternatively, due to low levels of terrestrial dispersal. The mitochondrial DNA (mtDNA) data were analysed using nested clade analysis, which can differentiate between historical fragmentation and range expansion vs. contemporary restricted gene flow. The results displayed three divergent clades that were likely to have arisen in allopatry. One widespread clade, with individuals in more than one river drainage, reflected a pattern of restricted gene flow. This suggests that this species is capable of terrestrial dispersal.     

The effects of ionic lanthanum and hypertonic physiological salines on the nervous systems of larval and adult stick insects.

The effects of the electron-opaque tracer ionic lanthanum in various concentrations and of hyperosmotic physiological salines on the nervous system of the stick insect, Carausius morosus, have been studied. Examination of the experimentally treated tissues revealed that the diffusion barrier to the exogenous tracer was maintained in all cases in the adult central and peripheral nervous systems, but not in the hatchling. When hatchling nervous tissues were incubated in 50 mM ionic lanthanum in phyerosmotic physiological saline, the tracer readily infiltrated all the extracellular spaces between axons and glia of all components of the nervous system examined. No difference was noted in this regard between fed and unfed hatchlings, Further, in all cases examined of adults and hatchlings, lanthanum readily surrounded those neurosecretory axons which are found in the neutral lamella, or extracellular nerve sheath, of the insect. The possible meanings of these variations in hatchling and adult nervous systems and in the accessibility of different elements of the nervous system to exogenous ionic lanthanum are discussed.     

The toxicity and physiological effects of copper on the freshwater pulmonate snail, Lymnaea stagnalis

Several recent studies have demonstrated that the freshwater pulmonate snail Lymnaea stagnalis is extremely sensitive to metals (Co, Ni, Pb) in chronic exposures. The objective of the current study was to evaluate the acute and chronic sensitivity of L. stagnalis to Cu and investigate the underlying mechanism(s) of toxic action. A 96-h LC50 of 31μg L(-1) Cu was estimated indicating L. stagnalis was moderately acutely sensitive to Cu relative to other aquatic organisms. However, in a 30-day chronic exposure using juvenile snails an EC20 of 1.8μg L(-1) Cu was estimated for snail growth making L. stagnalis the most sensitive organism tested to date for Cu. Hardness-based and BLM-based water quality criteria for Cu at the water quality conditions used in this study were 7.8 and 1.5μg L(-1), respectively, indicating L. stagnalis is significantly under-protected by hardness-based WQC. Investigations into the mechanism(s) of toxic action for Cu were conducted on young adult snails necessitating higher Cu exposures. Exposure to Cu at 12μg L(-1) resulted in no detectable effects on hemolymph osmolality, net Ca(2+) uptake, titratable acid excretion, or ammonia excretion. Exposure to 48μg L(-1) Cu was shown to significantly reduce (91%) net Ca(2+) uptake which is strongly correlated with shell deposition and corresponding snail growth. Snails exposed to 48μg L(-1) Cu also exhibited reduced ammonia excretion, a marked hemolymph acidosis, and a compensatory increase in titratable acid excretion. The reduction in net Ca(2+) uptake was hypothesized to be a secondary effect of Cu-induced inhibition of carbonic anhydrase, but no reduction in carbonic anhydrase activity was detected. Overall, it remains unclear whether inhibition of Ca(2+) uptake is a direct result of Cu exposure or, along with the other observed physiological effects, is secondary to an unidentified primary mode of toxic action. Given the hypersensitivity of L. stagnalis to Cu, further study into the mechanisms of action and effects of varying water chemistry on Cu toxicity is clearly warranted.     

Caridina bruneiana, a new species of freshwater shrimp (Decapoda, Caridea, Atyidae) from Negara Brunei Darussalam, Borneo

A new species of the freshwater atyid shrimp, Caridina bruneiana from Negara Brunei Darussalam, Borneo is described. Caridina bruneiana is characterized by its moderately long and deep rostrum, pereiopod shape, spination and segmental ratios, the shape and spination of its posterior telsonic margin, egg size and the presence of an appendix interna on the endopod of the first male pleopod. The distribution of atyid shrimps in forested streams and their possible use as bioindicators of stream water quality in tropical rainforests are briefly discussed.     

Physiological salines and the mechanical properties of trout red blood cells

Suspensions of rainbow trout erythrocytes in different physiological salines were compared with respect to their haematological and filtration properties.
A method is described for the suspension of erythrocytes in Cortland saline which has proved suitable for studies of their mechanical properties over periods of several hours.
Significant differences were found between whole blood samples taken during cannulation and after several days recovery, particularly mean cell volume, frequency distribution of red cell volumes and the pore passage time through nucleopore filters. These differences were also found using red cell suspensions of the same bloods. The pore passage time of whole blood sampled during cannulation or its suspensions is less than that of recovery blood although its mean cell volume is greater.     

饲料中硒的添加量与中华米虾肌肉中SOD的活性

研究了饲料中添加量为0、0.15、0.30、0.45、0.60、0.75μg/g的硒,对中华米虾(Caridina denticulatasinensis)体内超氧化物歧化酶(SOD)活力的影响。结果表明,硒对中华米虾体内SOD的激活作用显著,并表现出明显的时间效应和剂量效应。随着养殖时间的延长,各实验组虾体内SOD的活性会相应地降低。饲料中添加硒浓度为0.45μg/g时,虾体SOD的活性最高。     

Population dynamics and production of the tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) in the littoral of Lake Sibaya

SUMMARY. Seasonal changes in population structure, standing stock levels and production of Caridina nilotica were studied at three sites in the littoral margins of subtropical Lake Sibaya between January 1975 and March 1976. Average population density at these sites declined from a maximum of c. 1400 to a minimum of c. 350 individuals per m² (3.4–0.4 g m^?2 dry wt) during the study, possibly as a result of emigration into peripheral vegetation inundated by rising lake levels. Shrimps bred perennially and, although egg stocks and instantaneous birth rates (b) were highest during summer, no corresponding increases in populaton density were observed, suggesting that the seasonally higher birth rates were offset by higher mortality rates. Population size structure and size-specific sex ratios did not change seasonally to any marked extent. Relative abundance declined with size and females grew larger than males. Clutch size increased linearly as a function of female carapace length. Estimates of overall mean annual somatic production (g m^?2 year^?1 dry wt) for the three sites between January 1975 and January 1976 ranged between c. 132 (egg-ratio method), 37.5 (summation of growth increments) and 24 (Hynes-Hamilton method) at an annual mean standing stock level of 2.7 g m^?2 dry wt (calorific value, 20.34 kJ g^?1 dry wt). Production at sites 1, 2 and 3 decreased in line with declining annual mean standing stocks (5.32, 3.67 and 0.23 g m^?2, respectively). The growth increment method gave an overall mean annual P/B value of 13.9. Egg production amounted to a further 5.6, 3.6 and 0.1 g m^?2 year^?1 dry wt (calorific value, 28.01 kJ g^?1) at sites 1, 2 and 3, or 2.7 g m^?2 year^?1 on average.     

Geographical distributions of mitochondrial DNA lineages reflect ancient directions of river flow: a case study of the Japanese freshwater shrimp Neocaridina denticulata denticulata (Decapoda: Atyidae)

The mitochondrial DNA phylogeographical structure of the freshwater atyid shrimp Neocaridina denticulata denticulata was investigated near the Yura and Kako Rivers in western Japan. To assess the biological significance of drainage evolution, fragments of 390 base pairs (bp) extending from the NADH dehydrogenase subunit 2 gene to the tryptophan transfer RNA gene were sequenced for 246 specimens from twenty locations. The phylogenetic tree detected two distinct clades corresponding to the region along the Sea of Japan and Seto Inland Sea, respectively. Geographical mapping of the two clades well reflected the river capture, in which the upper reaches of the Yura River draining into the Sea of Japan had been captured from the Kako River into the Seto Inland Sea. The clear pattern of mitochondrial DNA distribution may be accounted for by the ecological characteristics of species that minimize passive downstream drift, local adaptation, and mountain topography.     

The effects of salines and fixatives upon the size of an identified neuron

Because accurate neuronal dimensions are essential for mathematical modeling of neuronal properties, the effects of a number of salines and fixative procedures on neuronal size were compared, including the non-chemical, freeze substitution method. Using an identified neuron we compared diameters and found some of the fixative-saline combinations caused shrinkage by as much as a factor of four from our best estimates of the in vivo size from the quick frozen preparations. A glutaraldehyde based fixation procedure was found which gives results in good agreement with the frozen tissue.     

Impact of organophosphates on the ovarian changes in freshwater caridean prawn Caridina weberi

The toxicity of the pesticides (organophosphates) malathion, dimecron and monochrotophos was tested on the freshwater caridean prawn, Caridina weberi. The lethal concentration was determined in experiments carried out up to 96 hrs. The effect of organophosphates on the reproduction was shown by observing the histological changes in the ovary. The tissues were highly damaged, with loss of ooplasmic material, lack of distinct nucleus, nucleolus and chromatin material.     

Embryonic duration and post-embryonic growth rates of the tropical freshwater shrimp Caridina nilotica (Decapoda:Atyidae) under laboratory and experimental field conditions

SUMMARY. Embryonic durations and post embryonic growth rates of Caridina nilotica were determined under laboratory conditions at constant temperatures near 18, 24 and 30°C. Embryonic durations and intermoult intervals were negative curvilinear functions of temperature. At a given temperature moulting frequency varied inversely with shrimp size and slight sexual differences were apparent. Moulting frequency of berried females was governed by the temperature-specific embryonic durations. Growth rates were determined from changes in carapace length (CL) of individual shrimps (laboratory) or batches of shrimps (field enclosures) over 1 month and these data were used to calculate temperature-specific life-long growth curves for males and females. Growth in body mass was estimated indirectly from the carapace length-mass relationship of C. nilotica. On average, males grew marginally faster than females during the first 2 months of life, but growth of males larger than CL= 4 mm was considerably depressed relative to that of females. Inflexions in growth rate, apparently related to the onset of sexual maturity, were apparent in both sexes. Under laboratory conditions, the growth rate of males increased with temperature, but temperature-related differences were not as marked in females. Notwithstanding the more rapid moulting rate at 30°C the growth rate of females was slightly slower at 30 than at 24°C as a result of marginally but significantly smaller per moult growth increments observed at 30°C in animals up to CL= 5.5 mm. Possible reasons for this depressed growth are discussed. Growth rates of animals in field enclosures in Lake Sibaya over 1 month in winter (20 ± 3°C) were generally comparable to those estimated for the 18°C laboratory experiments. Growth rates in enclosures containing tripled standing stocks were almost identical to those containing the naturally occurring biomass of animals, suggesting a non-limited environment at least during the time of the experiment.