Uptake of glycine and release of primary amines by the polychaete Nereis virens (Sars) and the mud snail Hydrobia neglecta muus

Uptake of glycine and release of primary amines by the polychaete Nereis virens (Sars) and the mud snail Hydrobia neglecta Muus was investigated. In a flow system, Nereis virens had a net influx of glycine of 32 to 39 nmol·g^?1 fresh wt·h from a 5-μM solution of glycine. Simultaneously, an efflux of primary amines of 14 nmol·g^?1·h^?1 was measured. The experiments indicated that glycine uptake and release of primary amines are two independent processes. Glycine was absorved by Hydrobia neglecta from 50-μM solutions at an influx of 175 nmol·g^?1 organic wt·h^?1, and simultaneously, there was an independent efflux of 25 nmol primary amine·g^?1·h^?1. In the experiments, released primary amines from both species increased the ambient concentration of primary amines, but after various periods of time these concentrations apparently stabilized. Finally, the significance of micro-organisms in amino-acid uptake experiments is considered.     

The influence of salinity on fertilization and larval development of Nereis virens (Polychaeta, Nereidae) from the White Sea

Effect of salinity on fertilization and early development of the polychaeta Nereis virens (Sars) from the White Sea was examined in laboratory experiments. The comparison of salinity resistance of different developmental stages of N. virens showed gradual increase of euryhalinity during ontogenesis—from fertilized eggs to juveniles.Successful fertilization and effective development (≥70-75%) was possible in narrow salinity range 22-34‰. The salinity range of successful development for trochophore and nectochaete larvae reached 14-45‰. This increase of the limits of salinity tolerance in trochophore and nectochaete larvae probably was due to the formation of protonephridium system.Rate of metamorphosis of N. virens was tested under temperature 5, 10, 17 and 23 °C and salinity 22-14‰. The highest rate of metamorphosis was marked at the temperature of 23 °C in salinities higher than 14‰.Our data confirms that N. virens originates from warm seas with oceanic salinity.     

Experimental study on the influence of bioturbation performed by Nephtys caeca (Fabricius) and Nereis virens (Sars) annelidae on the distribution of dinoflagellate cysts in the sediment

Dinoflagellates include noxious microalgae responsible for the formation of toxic red tides and the poisoning of molluscs and crustaceans, resulting in important economic losses. As a consequence, the life cycle of these algae has been extensively studied, but the dormancy phase (cyst) in the sediment record is little known. In the intertidal zone, bioturbation, an important biological process resulting from the activities of benthic fauna, significantly influences the movement of particles in the sediments. Laboratory experiments have allowed comparing and quantifying the movements of fluorescent microspheres resulting from the activity of two polychaetes annelidae, Nereis virens and Nephtys caeca. The particles, which simulate 45 µm diameter dinoflagellate cysts, are deposited in flat aquaria at the surface or deep in the sediment. Photographs of the aquaria were taken at regular intervals, to observe, in a non-destructive manner, the movement of the particles and to calculate, using adapted software, the optical reworking coefficient (ORC) over time. A difference appears between the movements of the particles generated by both species of polychaetes. Nereis virens create “permanent” galleries that carry the microspheres deeply in the sediment during the digging, bioirrigation and feeding, and Nephtys caeca homogenize the particles in the first centimetres of sediment during its erratic movements. The study shows that the bioturbation generated by these organisms can modify the distribution of the 45 µm diameter dinoflagellate cysts in the sedimentary column, burying them or raising them back to the water-sediment interface.     

Nucleotide pool changes in coelomic cells (eleocytes) of the polychaete Nereis virens during sexual maturation

Eleocytes (a type of coelomic cell) of the polychaete Nereis virens can store large amounts of adenine nucleotides at certain times. Since eleocytes have specific functions related to gametogenesis, we tested whether the presence of these large nucleotide stores in eleocytes is specific to gender or related to specific events during gametogenesis. Nucleotide pools in eleocytes isolated at different stages of sexual maturation from N. virens were analysed using high-performance liquid chromatography. Eleocytes from immature and male animals had extremely high concentrations of both AMP and ADP (each > 10 μmol/ml of packed cell volume). In eleocytes from male animals, the high nucleotide stores were maintained throughout the maturation phase and decreased at a late stage, while in female animals the nucleotides were degraded at an early stage of maturation. In male eleocytes, the decrease in the adenine nucleotide pool may be the result of its conversion to inosine which is then released by the eleocytes and reutilized by male germ cells for nucleic acid biosynthesis, as has been suggested previously. Our study shows that the time of degradation of the adenine nucleotide pool coincides with the period of spermatogonia proliferation which involves intense nucleic acid synthesis. ATP levels (0.4–1.5 μmol/ml packed cell volume) and the guanine nucleotide pool (GTP+GDP+GMP; 0.08–0.18 μmol/ml packed cell volume) were similar in both sexes, did not change during germ cell development and were decreased only in eleocytes from prespawning females. The GTP/GDP ratios were initially higher (up to 14) in eleocytes from females compared to ratios in eleocytes from immature (4–9) and male animals (up to 8), and decreased during the maturation phase of the animals. GTP levels were correlated with those of ATP; this correlation was much closer in eleocytes from females than from males. The results further support the hypothesis that the adenine nucleotide stores in the eleocytes are maintained as a supply of purine precursors for the growing germ cells.     

Oxygen uptake,the circulatory system,and haemoglobin function in the intertidal polychaete Terebella haplochaeta (Ehlers)

The intertidal polychaete Terebella haplochaeta (Ehlers) shows a high degree of oxyregulation in declining pO₂ when confined to its burrow at low tide. This response is achieved by a number of adaptations to the respiratory system. The worm ventilates its burrow in a headward direction by rhythmical conractions of the body. The rate of these pulsations increases at low pO₂ and assists the circulation of the coelomic and vascular fluids. Haemoglobin in the vessels has a high affinity for oxygen and a sigmoidal equilibrium curve. Both the shape and position of the oxygen-binding curve are sensitive to changes in pH, pCO₂, and temperature in a way that suggests augmentation of oxygen delivery at low tide. The concentration of haemoglobin in the vessels is high and is further raised following warm acclimation, presumably to meet an increase in oxygen demand. The ultrastructure of the gills and blood vessels indicates a design for function at low oxygen tensions where diffusion distances must be short and surface areas large in order to enhance the rate of diffusion of oxygen from the near environment.     

The impact of infauna (Nereis diversicolor and Saduria entomon) on the redistribution and biomass of macroalgae on marine soft bottoms

Mass occurrence of macroalgae is a phenomenon attributed to eutrophication, and can lead to drastic changes in the benthic communities on soft bottoms. While the negative effects of macroalgal blooms on the macrozoobenthos have been studied extensively, the effects of the infauna on the macroalgal material have not previously been studied in the northern Baltic Sea. The impact of the infaunal species Nereis diversicolor and Saduria entomon on the burial and biomass of Enteromorpha spp., Cladophora glomerata and Fucus vesiculosus, was assessed through a series of microcosm experiments. Results show that S. entomon did not significantly affect the biomass of the algae, nor actively relocate them. N. diversicolor redistributed the filamentous green algae into the sediment, down to 4 cm at most, and decreased the biomass of the filamentous algae by 140-360%. Furthermore, the loss of biomass promoted in presence of polychaetes proved to be a density dependent process. The effect on the perennial macroalgal species, F. vesiculosus, was less clear, as no redistribution or significant change in macroalgal biomass was observed. Our findings show that infauna can contribute to a loss in macroalgal biomass through feeding and burrowing activities leading to the redistribution and incorporation of the detritus into bioturbated sediment.     

Feeding response of the polychaete Sabellaria alveolata (Sabellariidae) to changes in seston concentration

Sabellaria alveolata is a tube-building gregarious polychaete that constructs large biogenic reefs. In macrotidal shellfish ecosystems, this species competes for food with cultivated suspension-feeders. The suspension-feeding activity and clearance rate of S. alveolata were investigated in response to changes in seston concentration. A flow-through system was designed to study 225 cm² reef blocks with more than 500 individuals. The experimental conditions were characterized by increasing concentrations of suspended particulate matter ranging from 6.5 to 153.8 mg L⁻¹, while the organic content of the diet (microalgae Skeletonema costatum) decreased inversely from 49 to 9%, to mimic the dilution of organic matter by inorganic particles, characteristic of tidal resuspension. We showed that the clearance rate exponentially decreased in relation to an increase in SPM concentration. Clearance rate was estimated at 5.3 10^− 3 L h^− 1 or 0.93 L h^− 1 g^− 1 (dry weight) for the lowest seston concentration (SPM = 6.5 mg L^− 1) and reached the asymptote at CR = 1.97 10^− 3 L h^− 1 or 0.35 L h^− 1 g^− 1 (dry weight) when SPM exceeded 45 mg L^− 1. Using picture analyses of polychaete movements, we showed that, paradoxically, an increase in SPM concentration did not adversely affect the feeding activity of S. alveolata since the number of filtering individuals remained stable from SPM = 6.5 to 55.5 mg L^− 1. These values were applied at the scale of the bay of Mont-Saint-Michel (France) to demonstrate that the filtration pressure of large populations of wild suspension-feeders should not be underestimated when the carrying capacity has to be assessed in the context of increasing bivalve cultures.     

Feeding and growth kinetics of the planktotrophic larvae of the spionid polychaete Polydora ciliata (Johnston)

We studied the effect of food concentration on the feeding and growth rates of different larval developmental stages of the spionid polychaete Polydora ciliata. We estimated larval feeding rates as a function of food abundance by incubation experiments with two different preys, presented separately, the cryptophyte Rhodomonas salina (ESD = 9.7 µm) and the diatom T.weissflogii (ESD = 12.9 µm). Additionally, we determined larval growth rates and gross growth efficiencies (GGE) as a function of R. salina concentration.P.ciliata larvae exhibited a type II functional response. Clearance rates decreased continuously with increasing food concentration, and ingestion rates increased up to a food saturation concentration above which ingestion remained fairly constant. The food concentration at which feeding became saturated varied depending on the food type, from ca. 2 µg C mL^− 1 when feeding on T. weissflogii to ca. 5 µg C mL^− 1 when feeding on R. salina. The maximum carbon specific ingestion rates were very similar for both prey types and decreased with increasing larval size/age, from 0.67 d^− 1 for early larvae to 0.45 d^− 1 for late stage larvae. Growth rates as a function of food concentration (R. salina) followed a saturation curve; the maximum specific growth rate decreased slightly during larval development from 0.22 to 0.17 d^− 1. Maximum growth rates were reached at food concentrations ranging from 2.5 to 1.4 µg C mL^− 1 depending on larval size. The GGE, estimated as the slope of the regression equations relating specific growth rates versus specific ingestion rates, were 0.29 and 0.16 for early and intermediate larvae, respectively. The GGE, calculated specifically for each food level, decreased as the food concentration increased, from 0.53 to 0.33 for early larvae and from 0.27 to 0.20 for intermediate larval stages.From an ecological perspective, we suggest that there is a trade-off between larval feeding/growth kinetics and larval dispersal. Natural selection may favor that some meroplanktonic larvae, such as P.ciliata, present low filtration efficiency and low growth rates despite inhabiting environments with high food availability. This larval performance allows a planktonic development sufficiently long to ensure efficient larval dispersion.     

Social organization and communal breeding in the chestnut-bellied starling (Spreo pulcher)

Chestnut-bellied starlings (Spreo pulcher) live in social groups of 10–30 individuals and during their breeding seasons maintain group ranges which show little overlap with neighbouring groups. A social group may contain two to six breeding pairs, non-breeding adults of both sexes, and immatures. Each breeding female has her own nest and she alone incubates. The parents and up to 12 other starlings feed the nestlings. Individual helpers may successively or simultaneously attend the nests of different breeders. The percentage of nests attended within a group differs for helpers of different sex, age and breeding status: immatures of 1–2 years and non-breeding adult males help most and adult females least. Nests with more helpers have higher fledging success than those with fewer helpers. These results are discussed with reference to the tentative benefits of helping behaviour and kinship relationships within the social group.     

Respiratory system of Gluconacetobacter diazotrophicus PAL5 Evidence for a cyanide-sensitive cytochrome bb and cyanide-resistant cytochrome ba quinol oxidases

In highly aerobic environments, Gluconacetobacter diazotrophicus uses a respiratory protection mechanism to preserve nitrogenase activity from deleterious oxygen. Here, the respiratory system was examined in order to ascertain the nature of the respiratory components, mainly of the cyanide sensitive and resistant pathways. The membranes of G. diazotrophicus contain Q₁₀, Q₉ and PQQ in a 13:1:6.6 molar ratios. UV_360 nm photoinactivation indicated that ubiquinone is the electron acceptor for the dehydrogenases of the outer and inner faces of the membrane. Strong inhibition by rotenone and capsaicin and resistance to flavone indicated that NADH-quinone oxidoreductase is a NDH-1 type enzyme. KCN-titration revealed the presence of at least two terminal oxidases that were highly sensitive and resistant to the inhibitor. Tetrachorohydroquinol was preferentially oxidized by the KCN-sensitive oxidase. Neither the quinoprotein alcohol dehydrogenase nor its associated cytochromes c were instrumental components of the cyanide resistant pathway. CO-difference spectrum and photodissociation of heme-CO compounds suggested the presence of cytochromes b-CO and a₁-CO adducts. Air-oxidation of cytochrome b (432 nm) was arrested by concentrations of KCN lower than 25 μM while cytochrome a₁ (442 nm) was not affected. A KCN-sensitive (I₅₀ = 5 μM) cytochrome bb and a KCN-resistant (I₅₀ = 450 μM) cytochrome ba quinol oxidases were separated by ion exchange chromatography.     

Floral biology of Echinopsis chiloensis ssp. chiloensis (Cactaceae): Evidence for a mixed pollination syndrome

In this study the flower biology of Echinopsis chiloensis ssp. chiloensis, a columnar cactus occurring in Central Chile, is investigated, in particular its pollination syndrome, its visitors, their frequencies and behaviors and their pollination efficiencies. As statements on floral anthesis of this species are contradictory, this study also intended to elucidate both its beginning and duration. A pollinator exclusion study of a total of 162 flowers from 12 plants was conducted at one of the two study sites. Fruit and seed production as well as seed viability were documented to evaluate pollinator efficiencies.     

Variations in flavonoid patterns within the genus Chondropetalum (restionaceae)

HPLC and chemical analyses of the flavonoids in culms of 11 Chondropetalum species divide the genus into two groups: seven, with glycosides of myricetin larycitin and syringetin; and four, with glycosides of kaempferol, quercetin, gossypetin, gossypetin 7-methyl ether and herbacetin 4′-methyl ether. This chemical dichotomy is correlated with anatomical differences and confirms the view that the genus requires taxonomic revision. HPLC measurements on those species with myricetin derivatives show that taxa with a qualitatively similar pattern of glycosides can be readily separated on quantitative grounds. Syringetin 3-arabinoside and a glycoside of herbacetin 4′-methyl ether are reported for the first time from the genus.     

Evidence for a critical period for imprinting in khaki campbell ducklings (Anas platyrhynchos domesticus)

In an attempt to simulate certain aspects of a natural setting, newly hatched and 5-day-old ducklings were exposed to an imprinting stimulus under conditions where flight from the stimulus completely removed them from its presence. The results indicated that while the younger subjects tended to approach the stimulus, the older ducklings rapidly and persistently escaped from it. In a second study, older ducklings were denied the opportunity to escape from the imprinting stimulus. Under these conditions the flight reaction waned and the subjects began to approach the stimulus. The overall pattern of results are consistent with the concept of a critical period for imprinting.     

Evidence for a facultative mutualist nutritional relationship between the green coccoid alga Bracteacoccus sp. (Chlorophyceae) and the zoosporic fungus Rhizidium phycophilum (Chytridiomycota)

Symbiotic interactions between fungi and photosynthetic partners are common among derived fungal lineages. The only fungal-phototroph interactions thus far reported from the early diverging zoosporic fungi are parasitic in nature. Rhizidium phycophilum is a terrestrial, saprotrophic chytrid, which appears to be able to enter a facultative mutualism with a coccoid green alga in the absence of refractory organic material, such as pollen and chitin. Liquid and solid culturing methods were used in a series of differential fitness experiments in conjunction with microscopic analyses to characterize the interaction between R. phycophilum and the alga. The alga in this partnership is identified as a member of the genus Bracteacoccus. Under certain culturing conditions, algal cells grown in coculture with R. phycophilum were shown to grow larger and more prolifically than when cultured axenically under the same conditions. Additionally, dialysis experiments demonstrate that R. phycophilum does not parasitize Bracteacoccus sp., and can be cultured in media infused with unknown algal exudates. Rhizidium phycophilum and Bracteacoccus sp. represent the first facultative positive interaction between a zoosporic fungus and a photoautotroph and may prove a tractable system for modelling interactions between early fungi and plants.     

Feeding responses to particle-bound cues by a deposit-feeding spionid polychaete, Dipolydora quadrilobata (Jacobi 1883)

In marine soft-sediment habitats, chemical sensing by deposit-feeding organisms most likely plays a critical role in feeding behavior, yet, few specifics about this role and its ecological implications are known. We show that several particle-bound chemical cues stimulate feeding activity of a spionid polychaete Dipolydora quadrilobata (Jacobi 1883). Using glass beads as a proxy for sediment, we tested for feeding responses to a selected number of potential cues that might be used to indicate food availability or quality. We presented two sets of beads to individual intact worms: one with and one without covalently bound compounds such as single amino acids, mixtures of amino acids, and single simple sugars. Worms were exposed to the beads under slow flowing seawater so that any dissolved cues were flushed from the test chamber. Each worm was videotaped for 15 min immediately following the addition of beads, and these records were scored for the time the worm spent in a variety of behaviors. Responses to beads with and without cues were compared to identify compounds as stimulatory, inhibitory, or inactive. Five of the seven particle-bound cues tested significantly increased feeding activity, and none of those tested were found to be inhibitory.     

The connectional organization of neural systems in the cat cerebral cortex

BACKGROUND: The mammalian brain consists of the cerebral cortical sheet, which is composed of many distinct areas, the cerebellar cortex, and many non-cortical nuclei. Powerful neuroanatomical techniques have revealed a large number of connections between these structures. The large number of brain structures and the very many connections between them form a strikingly complex network. The complexity of this network has made it difficult to understand how the central nervous system is organized. Recently, however, optimization analysis of an important subset of central nervous connections that occur between the different areas of the cerebral cortex has produced understandable and quantitative representations of the organization of cortical systems of the primate brain. RESULTS: Here we briefly report the extension of this approach to the cortical systems of the cat. There were four connectional clusters of cortical areas in the cat. These clusters of areas corresponded to the visual, auditory, and somato-motor systems, and to the frontal and limbic areas, which we call the fronto-limbic complex. All the major sensory systems were hierarchically organized, and their 'higher' stations were more closely associated with the fronto-limbic complex than were their 'lower' stations. CONCLUSIONS: Features of the organization of the cat brain, together with earlier primate results, suggest that there may be a common cortical plan in mammals. We suggest that this common plan may involve relatively discrete, hierarchically organized, cortical sensory systems and a topologically central fronto-limbic complex. Specific variations on this wiring plan may relate to evolutionary history and selection for particular ecological niches.     

The ultrastructural organization of peripheral nerves in two insect species (Periplaneta americana and Schistocerca gregaria)

The ultrastructural organization of various peripheral nerves, including the crural nerve, has been investigated in the locust and cockroach. In some cases the larger nerves are ensheathed by a fat body layer which is not always complete. However, like many nervous connectives, they do possess a continuous acellular neural lamella and a perineurial cell layer which surround the glial-axonal mass. Adjacent perineurial cells are associated with one another by septate desmosomes, gap junctions and tight junctions. These last may represent the morphological basis of the ‘blood-brain barrier’ observed electrophysiologically in these peripheral nerves in another report. Very small nerves of the cockroach, however, although lying embedded in a neural lamella, do not possess a specialized perineurial layer displaying junctional complexes, unless they contain one or more large axons. If they have only one or more small axons, these small nerves may either appear naked, or display a single glial cell process loosely enveloping them; in either case there is no structural basis for a ‘barrier’ system. Various comparisons have been made between locust crural nerve and the cockroach central nervous connectives in an attempt to correlate some aspects of their ultrastructural organization with relevant electrophysiological information.