Occurrence and distribution of antioxidant enzymes in the haemolymph of the shore crab Carcinus maenas

The haemocytes and cell-free haemolymph of the shore crab Carcinus maenas were examined for the presence of the antioxidant enzymes, catalase (EC 1.11.1.6), glutathione peroxidase (GPX) (EC 1.11.1.9) and superoxide dismutase (SOD) (EC 1.15.1.1) by biochemical assay and immunocytochemistry. The results show that all three enzymes are present in the haemocytes, but vary in distribution and amount. Catalase was detected principally in the phagocytic hyaline cells, whereas GPX and SOD were found in both the hyaline and granular cells. Catalase and glutathione peroxidase activities were absent from the semi-granular cells, and although SOD was detected in some samples, there was enormous variation in the level of this enzyme between individuals. Cell-free haemolymph, by contrast, was found to be positive for GPX and SOD but lacked catalase activity. Immunocytochemical analyses further showed that only 2 to 16% of the cells stain positively for these enzymes, and where present the enzymes tended to be distributed throughout the cytoplasm. With the granular cells, however, there was some localization of GPX and SOD around the granules. Since the phagocytes of C. maenas are known to produce superoxide anion radicals, hydrogen peroxide, and possible other reactive oxygen species upon stimulation with phorbol myristate acetate, lipopolysaccharide, or concanavalin A in vitro, it is likely that catalase, GPX and SOD are present in the haemolymph to assist in protection of the host tissues against oxyradical damage during host defence in vivo.     

The biology of colonial hydroids. II. The morphology and ultrastructure of the medusa of Eirene viridula (Thecata-Leptomedusa: Campanulinidae)

The free-swimming medusae of Eirene viridula are typical marine hydroids, with distinct subdivisions into body regions, which were studied by comparison of light and electron microscopy. Particular attention is given to the epithelio-muscular and digestive muscle cells. The epidermis — apart from a few nerve cells and cnidocytes-consists of epitheliomuscular cells. At their bases these cells form a musculature and at the apex many secretory vesicles. In the velum, large expansions of the intercellular space are found. The gastrodermis — apart from the mucous and zymogen cells in the manubrium — consists of digestive muscle cells, the structure of which corresponds in principle to that of the epitheliomuscular cells. In its apex, this type of cells contains both normal coated vesicles and discoidal coated vesicles. In the solid tentacles, the digestive muscle cells form a turgescent vesicular tissue. The central nervous system consists of the exumbrellar, subumbrellar, and gastrodermal nerve rings. They are composed of ganglion cells, their processes, and intraepithelial flagella. The static organs are purely ectodermal statocysts which have only one lithocyte and only one sensory cell.     

First evidence of gender-related differences in immune parameters of the clam Ruditapes philippinarum (Mollusca, Bivalvia)

For the first time, gender-related differences in some important functional parameters of haemocytes from the clam Ruditapes philippinarum have been studied. Clams were collected during the pre-spawning phase, when sex can be distinguished by microscopic observation of gonadal smears, in order to ascertain whether the two sexes reach the stressful spawning period with different degrees of immunosurveillance. Total haemocyte count (THC), haemocyte size frequency distribution, capability of haemocytes to assume the vital dye neutral red (NR, indicative of endocytotic activity), lysozyme-like and acid phosphatase activities in both haemocyte lysate (HL) and cell-free haemolymph (CFH), and superoxide dismutase (SOD) and catalase (CAT) activities in HL were all evaluated. No differences in THC values were found between the two sexes, but differing haemocyte size frequency distributions were observed: the fraction of larger haemocytes (7–9 μm diameter, 200 fl volume) was markedly increased in females and that of smaller haemocytes (<5 μm diameter, <200 fl volume) markedly increased in males. Interestingly, when haemocytes were observed under the light microscope, a significantly higher percentage of granulocytes was found in haemolymph from females, compared with that of males. Significantly increased NR uptake was recorded in female haemocytes. No significant variation in lysozyme-like activity was observed in HL, whereas in CFH, enzyme activity was significantly higher in females. HL acid phosphatase activity was significantly higher in males with respect to females; no significant variations in enzyme activity were observed in CFH. HL SOD and CAT activities were significantly higher in females than in males. Overall, on the basis of the cell parameters studied here, gender-related differences in immune parameters were found in R. philippinarum, indicating that females have more active haemocytes than males during the pre-spawning period.     

Mantle-to-shell CaCO<Subscript>3</Subscript> transfer during shell repair at different hydrostatic pressures in the deep-sea vent mussel <Emphasis Type="Italic">Bathymodiolus azoricus</Emphasis> (Bivalvia: Mytilidae)

Calcium carbonate transfer was experimentally examined in hydrothermal mussels Bathymodiolus azoricus, which were collected from 850 m depth at Menez Gwen hydrothermal vent site (31°31′W, 37°50′N) on the Mid Atlantic Ridge in May 2007. In each of four 10-day experiments, groups of mussels were maintained at atmospheric pressure or re-pressurised to depths relevant to their site of occurrence, i.e. 850 m depth at Menez Gwen, 1,750 m at Lucky Strike (31°31′W, 37°18′N) and 2,300 m at Rainbow (31°31′W, 36°13′N). The shells of experimental mussels were perforated and mantle tissue was fixed for light and TEM studies at days 7 and 10 following the injury. Simultaneously, haemocytes from the extrapallial fluid (EPF) at the site of induction were studied. At day 7 the response was most intense in the middle fold of the mantle margin and possibly proportional to hydrostatic pressure. At day 10 the epithelial cells on the mantle surface facing the body cavity produced copious organic secretions that avidly bound calcium. Haemocyte migration was noted within the mantle tissue, and the haemocytes at the mantle surface facing the shell had a Ca-positive granular content. Large haemocytes were detected in the EPF at the injury site, and some showed evidence of an immune reaction while others showed Ca-positive granular content. These results suggest that haemocytes are involved in shell repair in these deep-sea mussels just as in some freshwater and shallow marine molluscs.     

Dark survival strategies in marine phytoplankton assessed by cytometric measurement of metabolic activity with fluorescein diacetate

Cytometric quantification of cellular fluorescence upon cleavage of fluorescein diacetate (FDA) is presented as a sensitive and rapid technique to assess phytoplankton metabolic activity during exposure to prolonged darkness of 10 to 12 d. Two distinct types of metabolic response to darkness are distinguished: Type I cells (Brachiomonas submarina, Pavlova lutheri, Chrysochromulina hirta) adapt to prolonged darkness by reducing their metabolism to a lower level of activity (∼10% of initial in P. lutheri, C. hirta, ∼0.5% in B. submarina) within few days, whereas Type II cells (Prymnesium parvum, Bacteriastrum sp., unidentified pennate diatom) continue with unchanged activity. Type I cells were able to maintain their initial cell abundance and commenced rapid cell growth upon re-illumination after 12 d of darkness. Among Type II cells, diatoms were able to maintain cell abundance and growth capacity as well, whereas P. parvum was not. Type I cells are expected to exhibit competitive advantages in environments with frequent or long dark periods. Bacterivory further supports dark survival in C. hirta. Received: 10 May 1999 / Accepted: 20 September 1999     

Diatom Thalassiosira weissflogii in oligotrophic versus eutrophic culture: models and ultrastructure

Populations of marine diatom Thalassiosira weissflogii were grown in continuous cultures enriched with f/2 medium. One of the two contrasting cultures (‘eutrophic’) received 5.6 times more nutrients than the other (‘oligotrophic’). Two mathematical models are analyzed to estimate eutrophication differences. The second model based on the Michaelis–Menten uptake and Droop growth shows that cells in the eutrophic culture should have about 56% higher content of silica which is the limiting nutrient. Diatom samples were prepared for the transmission electron microscopy after cells have been kept in chemostats for 37 days. The structure of diatom cells was investigated and a comparison is made between cells grown in oligotrophic and eutrophic conditions. In eutrophic culture, dividing cells were encountered more frequently while cell concentration was approximately equal in both chemostats. The central vacuole of cells in eutrophic culture accumulated dispersed and compact material from amorphous to spherical shape. In some cells the large central vacuole had fibrilar and peppered dense materials in addition to translucent granules, vesicules and multivesicular bodies. In the cytoplasm we found increased number of multivesicular bodies, dense and lucent granules some of which enclose membrane particles and lucent vesicules. Dense material depositions observed in the vacuole are also seen in the cytoplasm associated with organelles, mitochondria and plasmalemma. Cells have well-developed, active and slightly increased number of dictyosomes (5–6). Some dictyosomes with dense secretory material in the cistern are apparently engaged in a granule formation process. Functional significance of dense material in the central vacuole, which has not been observed in cells grown in oligotrophic condition, is discussed.     

Cytoenzymatic investigation of intracellular digestion in the symbiont-bearing hydrothermal bivalve <Emphasis Type="Italic">Bathymodiolus azoricus</Emphasis>

Invertebrates harbouring endosymbiotic chemoautotrophic bacteria are widely distributed in a variety of reducing marine habitats, including deep-sea hydrothermal vents. Bathymodiolids are dominants of the biomass at geochemically distinct vent sites of the Mid Atlantic Ridge (MAR) and thus are good candidates to study biological processes in response to site-specific conditions. To satisfy their nutritional requirements, these organisms depend to varying extent on two types of chemoautotrophic symbionts and on filterfeeding. The quantitative relationships of the nutritional modes are poorly understood. Using enzyme cytochemistry, electron microscopy and X-ray microanalysis, the structural and functional aspects of the cellular equipment necessary for lysosomal digestion was studied. We provide evidence for the following: (1) the basis of intracellular digestion of symbionts in Bathymodiolus azoricus from two geochemically distinct vent sites was not mainly in the large lysosomal bodies as previously thought (based on the membranous content resembling bacteria); (2) senescent bacteria are autolysed, possibly by bacterial acid phosphatase, that is more likely a cell cycling of the symbionts rather than an active lysosomal digestion by the host; (3) the consistent absence of hydrolases may indicate the improper use of the name “lysosome” for large vesicles at the base of the gill bacteriocytes (4) nutrient transfer in B. azoricus, therefore, may more likely be accomplished through leaking of metabolites from the symbiont to the host, not excluding lysosomal resorption of dead bacteria as an auxiliary strategy for organic molecule transfer; (5) evidence is provided for microvillar transfer of substances from the seawater that may indicate filter-feeding, in non-symbiotic ciliated gill cells of mussels from Lucky Strike; (6) two types of lysosomal vesicles can be distinguished in digestive cells based on their enzymatic content and their elemental composition.     

Life-history patterns in two forms of Macrophthalmus japonicus (Crustacea: Brachyura)

Two behaviorally distinct forms — courtship signal — (Form L and V) of Macrophthalmus japonicus (De Haan) are known. Monthly samples of each form were collected from two areas in Japan: Form L from Amakusa, western Kyushu, between April 1985 and February 1986; Form V from Fukuoka, northern Kyushu, between November 1982 and December 1983. Life-history traits were compared between two populations and discussed. Individuals from the Amakusa population grew more slowly and matured at a smaller size than those from the Fukuoka population. Maturation period and longevity did not differ significantly. In the first year of reproduction, females in the Fukuoka population produced more, and larger broods than those in the Amakusa population and crab mortality was higher in every age group. Egg size did not differ significantly. The major environmental factors — air-temperature, nitrogen content of the surface mud and period of aerial exposure were similar in both areas, and it is suggested that the differences in life-history exhibited by these crabs are genotypic, and perhaps related to their different form.     

Aspects of iron and nitrogen nutrition in the red tide dinoflagellateGymnodinium sanguineum

Iron-stress-mediated effects on biochemical constituents of the red tide dinoflagellateGymnodinium sanguineum Hirasaka were examined in 1988 by comparing Fe-replete and Fe-deplete batch cultures. The influence of nitrogen source (NO₃ or NH₄) on characteristics of Fe-deplete cells was also studied [i.e., Fe-deplete/NO₃-grown (= — Fe/NO₃) vs Fe-deplete/NH₄-grown (= — Fe/NH₄)]. Common to both N sources were reductions of chlorophylla (chla) and Fe quotas (per cell volume) by 75% and ca. 1.5 orders of magnitude, respectively, under Fe depletion. The Fe requirement ofG. sanguineum exceeded those of certain neritic diatoms by one to two orders of magnitude. — Fe/NH₄ cells exhibited 30 to 50% greater N quotas and free amino acid:protein ratios than did Fe-deplete cells grown on NO₃. In vivo fluorescence:chla increased with Fe deficiency particularly in — Fe/NO₃ cultures, surpassing — Fe/NH₄ values by ca. two-fold. Effects of Fe depletion were consistent with this element's essential role in the biosynthesis of chla and components of the photosynthetic electron transport (PET) system, and also in NO₃ utilization. Fe:N ratios were larger (1.5-fold) for iron-deficient NO₃-grown than NH₄-grown cells, likely reflecting the Fe content of NO₃ assimilatory enzymes [nitrate (NR) and nitrite (NiR) reductase] and of electron transport components needed to provide reductant, coupled with a diminished capacity of — Fe/NO₃ cells to acquire and assimilate nitrogen. Indicators of PET efficiency suggested that under iron stress, supply of Fe for NR and NiR is partly at the expense of iron-containing PET components. Utilization of nitrate by NO₃-grown cells was inhibited sufficiently by Fe depletion to yield symptoms bordering on N deficiency. In an ecological context, the most important effect mediated by nitrogen source may be the determination of critical Q_Fe (i.e., Fe required to just sustain maximal growth), thereby regulating the degree of growth limitation for a given subsaturating iron concentration.     

Deforestation and Development in a Small Open Economy

Our economy faces world prices and starts with a large endowment of land in forest and a small endowment of land in agriculture. Clearing of forested land yields marketable timber and a unit of land for agriculture. Early, the high price of agricultural land drives the clearing process. Later, the profit from marketing timber from the cleared land drives the process. Dates of “phase transitions” are endogenous. We also set out a submodel of perpetual cyclic clearing and reforesting, and show that it when cyclical harvesting—regrowing is optimal, the extent of clearing can be relatively large.     

Female reproductive biology and oocyte development of the red frog crab,Ranina ranina,off Hachijojima,Izu Islands,Japan

Speciments of the red frog crab, Ranina ranina, examined in this study were collected off Hachijojima, Japan from 1987–1988 and 1990–1991. Ovigerous females occurred from May to September, and their carapace length ranged from 61.8 to 102.1 mm. Minimum size at the maturity was estimated to be 50 to 60 mm carapace length. The lobule-type ovary had a longitudinal ovarian cavity at the center. Germinal zones were located along the sides of the cavity. Oogenesis was divided into five main and ten detailed stages: proliferation (oogonium); previtellogenesis (bouquet, early chromatin nucleolus, late chromatin nucleolus); primary vitellogenesis (oil globule and yolk granule); secondary vitellogenesis (primary yolk platelet, secondary yolk platelet and prematuration); and maturation (maturation) stages. Vitellogenesis started at the oil globule stage when weakly positive periodic acid-Schiff granules appear in the cytoplasm. Based on the gonadosomatic index and histological changes in ovary, the reproductive cycle was divided into five stages: multiplication, from December to January; developing, from February to March; ripe in April and early May; spawning, from late May to August; and recovery, from August to November. Each crab spawned more than once during the spawning season.     

Determinants of parental effort: a behavioural study in the Eurasian kestrel,Falco tinnunculus

We recorded behaviour of kestrels (Falco tinnunculus) in western Finland during the courtship (1988–1992), incubation (1989–1991), early nestling (age of young 1–2 weeks, 1989–1992) and late nestling stages (3–4 weeks, 1989–1991) to examine determinants of their parental effort (PE). In males, PE was estimated as the hunting effort (the proportion of budget time spent in flight-hunting) and in females as the food provisioning rate (number of prey items delivered to the nest per hour). The following predictions derived from the parental investment theory were examined. (1) Parents rearing large clutches and broods should invest more in breeding than do parents rearing small clutches and broods. The hunting effort of parents did not increase with clutch or brood size, but males tending large broods had a higher prey delivery rate than males tending small broods (Figs 1–2). (2) PE of parents should increase in the course of the breeding season. In males, this was true only between the incubation and early nestling phases (Fig. 3). (3) The early pairs should invest more in breeding than late ones. This tended to be true during the early (for males) and late nestling phases (for females) (Fig. 4). (4) There should be a negative correlation between PE of mates within pairs, but no evidence for such adjustment was found (Fig. 5). (5) Females mated with bright-coloured attractive males should show higher PE than females mated with dull-coloured males but our results were inconsistent with this prediction. We conclude that PE decisions of kestrels are mainly based on cost-benefit estimates of residual reproductive value, rather than on current investment indicators, like clutch or brood size. This might be beneficial in environments with highly variable survival prospects of offspring caused by pronounced among-year variation in abundance of the main food (microtine rodents). The results also show that hypotheses explaining variation in PE in the short term are not necessarily valid for long-term PE, e.g. tending clutches or broods, which also reflects the demands of female and young.     

A histological and chemical study of the cerata of the opisthobranch molluscTethys fimbria

Tethys fimbria is a poorly studied nudibranch that, recently, has been shown to possess large amounts of unusual prostaglandin (PG) derivatives. The cerata ofT. fimbria collected in the Bay of Naples (Italy) between November 1990 and January 1991 were submitted to histological analysis. This revealed the presence of both longitudinal and transverse smooth muscle fibres together with multicellular defensive glands, responsible for the typical spontaneous contractions of the cerata and for the extrusion of a hyaline secretion, respectively. A role forT. fimbria cerata in mollusc defense behaviour is suggested. Chemical analysis of the cerata led to the isolation of high levels of prostaglandin free acids (PGs) and of PG-1,15-lactones of the E, A and F series, whereas the secretion contained only PG-1,15-lactones of the E and A series. The latter were found to be toxic to mosquito fish at concentrations ranging between 1 and 10 µg ml^–1, whereas PG free acids and PG-1,15-lactones of the F series were not toxic. The possibility that PGE- and PGA-1.15-lactones areT. fimbria defense allomones is discussed.     

Der einfluß der temperatur auf thermostabilität,isoenzym-muster und reaktionskinetik der laktat-dehydrogenase aus fischen

Methodological problems complicate investigations on thermostability of lactate dehydrogenase (LDH). It is difficult to demonstrate a correlation between adaptation-temperature (AT) and LDH thermostability. Heat-inactivation characteristics change completely if diluted or undiluted tissue extracts are heated. In purified LDH (purchased from Boehringer, Mannheim, FRG), additions such as casein, bovine-serum albumin, NADH and pyruvate — even in small concentrations — can alter considerably the degree of heat resistance. It LDH activity is measured as a function of experimental temperature (ET) according to the composition of the actual test mixture (e.g. altered pyruvate concentration), a different temperature optimum is found. If tissue extracts containing unpurified enzymes are used, the accompanying substances act on the enzyme and modify its properties. Thus, possible influence of AT on enzyme properties can be concealed (suppressed, over-emphasized). In Idus idus acclimated to 10° or 20°C, brain, gill, gut and white dorsal muscle reveal identical LDH-isoenzyme patterns. However, liver-LDH shows a pattern dependent on the AT. A total of 11 bands with LDH activity were found. In 10°C fishes, the Isoenzymes 1, 3, 6 and 7 are especially active. However, 20°C fishes show marked activity of Isoenzymes 5 and 8, and a reduced activity of Isoenzyme 7. According to their electrophoretic mobility, the particular isoenzymes of LDH of white dorsal muscle of I. idus or Rhodeus amarus can be clearly distinguished. The ATs 10° or 20°C do not influence the dependence of reaction order on ET: this is not true for the velocity constant.     

Orientation ofRhizophagus grandis (Coleoptera: Rhizophagidae) to oxygenated monoterpenes in a species-specific predator-prey relationship

Summary The predator,Rhizophagus grandis, is linked to its specific prey,Dendroctonus micans, by semiochemical signals regulating oviposition and long range orientation. A mixture of simple oxygenated monoterpenes [(–)—fenchone, (–)—pinocamphone, rac. camphor, terpinene-4-ol, borneol, fenchol and verbenone], identified from the frass ofD. micans has been found to be extremely active in a flight windtunnel as a long—range attractant for the predator. The mixture elicited 84 % of the response to larval frass of the prey. Excluding pinocamphone from the mixture did not influence its activity. Also, changing the absolute configurations of some of the components (fenchol, terpinene-4-ol and borneol) did not influence the predators' response. However, the addition of (–)—-terpineol increased the attractivity of the synthetic blend to almost that of larval frass of the prey. Ecological implications of the identified semiochemicals and their use in pest management are discussed.     

Release of phagocytosis-stimulating factor(s) by morula cells in a colonial ascidian

In vitro yeast phagocytosis by haemocytes of the compound ascidian Botryllus schlosseri was studied, with particular attention to interactions among different immunocyte types. It is demonstrated that the supernatant from haemocyte cultures matched with yeast cells contains factor(s) able to enhance yeast ingestion by Botryllus phagocytes. The increase in phagocytosis is not the consequence of yeast opsonisation, as the phagocytic index does not significantly increase when yeast cells, previously incubated in the culture media, are washed and re-suspended in filtered sea water. When haemocytes were fractionated by density gradient centrifugation and each band was incubated with yeast, the ability to stimulate phagocytosis was found in the supernatants from haemocyte cultures of fractions rich in morula cells (MC). Previous studies have demonstrated that MC express molecules recognised by anti-cytokine antibodies, as a consequence of the recognition of foreign molecules or cells. Our results indicate that molecules immunoreactive with anti-cytokine antibodies are required for modulating phagocyte activity, as the above-reported enhancing effect is completely absent in the presence of anti-IL-1-α and anti-TNF-α, but not of anti-rabbit-IgG antibodies, and they also highlight the presence of ‘cross-talk‘ between MC and phagocytes. A new scenario is therefore sketched, in which MC actively recognise non-self molecular patterns and, upon this recognition, release humoural factor(s) recognised by phagocytes, which modulate phagocytosis.     

Thermal ecology,size effects,and the origins of communal behaviour in Cerceris wasps

Summary Female Cerceris nest in large aggregations in sandy soil, stocking cells with weevils to feed the offspring. Their foraging patterns depend upon weather conditions, and the timing and duration of foraging is predictably variable according to their size. Hence large foragers collect more prey, and can stock more cells, and through a normal season they should stock twice as many cells (thus laying twice as many eggs) as small females. Since they also stock more prey per cell, and provisioning determines offspring size, large females thus produce more and larger children simply through the effects of the weather. Despite their apparent disadvantages, small female wasps never-theless persist, and various factors contribute to this; they do better in hot weather, when large females do not forage due to over-heating risks, they tend to bias their sex ratio more to male production, and they often co-occupy a nest with a larger female. Nest co-occupancy increases in very hot conditions, when a large female benefits by the foraging of a small one while it is nest-bound, a small female benefits by getting a chance to lay in better-stocked cells, and both may benefit from decreased parasitism by satellite flies. Thus two factors which may contribute to joint nesting and a trend towards eusociality along the parasocial route are suggested. Firstly such a trend is more likely in hot dry conditions; and secondly it is more likely in species with a broad range of female sizes. Both these effects can be seen in a survey of wasps of the genus Cerceris so far reported in the literature, and are likely to be more widely applicable in studies where weather effects interacting with foraging patterns have hitherto been ignored.     

The poison gland of the antMyrmicaria eumenoides and its role in recruitment communication

Summary The antMyrmicaria eumenoides is a significant arthropod predator. For rapid attraction of large numbers of nestmates to newly discovered food sources the ants use an efficient recruitment communication system based on the poison gland secretion. Workers exhibit age-based division of labour. Young workers perform brood-care; their poison gland reservoir develops and reaches its final size of 0.5 µl at an age of 6 weeks, when they become foragers. The secretion deposited during combat with enemies or prey is composed of equal amounts of both a high volatile and a low volatile fraction. Within the high volatile fraction (+)—limonene is the main component (97%) and is the only olfactory trigger to alert ants in the vicinity and to recruit them to places of combat, where they assemble. Ants respond to synthetic (+)—limonene in exactly the same way as to the poison gland secretion when applied at the same airborne concentrations. Further components of the high volatile fraction are four additional monoterpene hydrocarbons and hexanoic nitrile. The high volatile and the low volatile fraction of the poison gland secretion each have dual functions: The low volatiles, of which the main component is an alkaloid, serve as a fixative and extend the effective period of the limonene signal by modifying its evaporation kinetics. On the other hand the high volatile recruitment signal (+)—limonene is also the solvent for the alkaloid and enhances its spreading on the surface of the cuticle of arthropod enemies or prey.     

Effect of copper on volume regulation in the marine flagellate Dunaliella marina

The marine flagellate Dunaliella marina responds to hypotonic media in the same way as animal cells: an initial phase of osmotic swelling occurs, followed by a second, more prolonged phase of cell shrinkage — the volume-regulation phase. D. marina also volume-regulates in hypertonic media. This does not usually occur in animal cells exposed to normal concentrations of K⁺. Copper concentrations of 2 ppm and higher inhibit regulation of cell volume in D. marina transferred to hypotonic media. This is probably due to reduced cell-membrane permeability to K⁺ and/or Cl^- and not to an interference with the Na⁺/K⁺ exchange pump. These findings suggest that volume regulation is functionally independent of the Na⁺/K⁺ exchange pump. The method described herein appears to be a suitable biotest for pollutants, providing specific information on their effects on the permeability of cell membrane.     

Study by evolution of nucleic acid content of prepuberal growth in the shrimp Crangon vulgaris

Growth of the shrimp Crangon vulgaris was studied by following the evolution of its nucleic acid concentration and total content. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) analysis were effected on homogenates of whole shrimps. Cell multiplication was estimated from evolution of total DNA content, and cell size increment from evolution of fresh weight: DNA ratio. DNA puric bases ratio and RNA monoribonucleotides percentages were constant throughout the investigation period. A decrease in DNA concentration was observed from 50 to 20 M/g dry defatted weight (DDP), when fresh weight increases from 40 to 570 mg. This decrease was more marked in the first half of the period studied (prepuberal phase). The DNA content in the whole shrimp increases with fresh weight without slowing down at sexual maturity. However, at the beginning of the prepuberal phase the cell-multiplication rate seems to be graduated rather than continuous; this is still to be explained. Cell size, calculated from fresh weight: DNA ratio, increases until the shrimp weighs 300 mg; beyond this weight, cell increment proceeds much more slowly. The weight gain of shrimps throughout the growth period studied is mainly attributable to hyperplasia — which occurs constantly — while hypertrophy insures only 21% weight increment in the largest shrimps. As protein content, RNA content is a linear function of shrimp weight. RNA:DNA ratio evolution is similar to that of cell size and protein content. We suggest that cells have attained a physiological balance when shrimps reach a weight of 300 mg.