Spatial and temporal variations of Penilia avirostris and Evadne tergestina (Crustacea,Branchiopoda) in a Tropical Bay,Brazil

We analysed monthly samples collected in Guanabara Bay, with a conical net of 200 m mesh during 1985. The bay was divided into three areas: an outer region (area A), influenced by oceanic waters; an inner region (area C), influenced by fluvial inflow; and a transition region (area B) with intermediate features. Penilia avirostris and Evadne tergestina were observed in the three areas, with greatest densities, however, in the outermost region, which had the highest salinities and lowest temperatures. Penilia avirostris was more abundant in summer (March), a period with the greatest relative densities of nanoplankton. Evadne tergestina was also abundant in summer, but its peak fell in November, a period with a relative increase in microphytoplankton density in the bay. The two species disappeared in winter: Penilia avirostris was absent from May to August, whereas Evadne tergestina disappeared in August and September.     

Daily variation of marine cladoceran densities in a tropical bay – Brazil

This contribution presents the daily variation of marine cladoceran densities in Guanabara Bay. The samples were obtained by vertical tows with a 200 m mesh-size conical net at different times over a 4-day period in September, 1995. Penilia avirostris was the most common species, followed by Evadne tergestina and E. spinifera. These organisms presented higher densities at nightfall. Physical factors like tide and light are responsible for the highest densities. High tide and nightfall time are requested conditions for the P. avirostris and E. tergestina abundance. Temperature and salinity appear to have no relation with cladoceran densities.     

Distribution and biology of marine cladocerans in the coastal waters of southern China

Geographical and seasonal distributions of marine cladocerans in the coastal waters of southern China were studied. Penilia avirostris was the most common species, followed by Evadne tergestina and Podon schmackeri. P. avirostris and E. tergestina were most common during summer. P. schmackeri, found only in a small bay northeast of Hong Kong, showed no clear seasonal pattern of occurrence. P. avirostris and E. tergestina were found at temperatures ranging from 16–32°C and salinity ranging from 7.3–37.2. P. schmackeri was restricted to a temperature range of 17–29°C and a salinity range of 31.0–37.2. No significant relationships between marine cladoceran abundance and chlorophyll a concentration were found in samples taken from Tolo Harbour. Parthenogenetic brood size of P. avirostris and E. tergestina ranged from 1 to 14, while P. schmackeri was found to carry up to 19 embryos per brood. No geographical trend in fecundity patterns was observed. No correlation was found between body length and brood size. The occurrence of females with resting eggs was rare.     

Study of selective feeding in the marine cladoceran Penilia avirostris by HPLC pigment analysis

Food selection by the marine cladoceran Penilia avirostris was studied in the field by HPLC analysis of phytoplankton marker pigments and in the laboratory by microscopic measurement of cell removal. Comparison between pigment composition in natural phytoplankton and in P. avirostris showed that P. avirostris preferred diatoms, cryptophytes and chlorophytes, and ignored prymnesiophytes and dinoflagellates. Peridinin, the marker pigment for dinoflagellates was found in P. avirostris only when the dinoflagellate populations were dominated by Prorocentrum. Pigment degradation rates ranged from 13.73% for alloxanthin to 36.62% for chlorophyll a. Clearance rates measured in the laboratory provided further evidence of strong preference for diatoms and cryptophytes, and avoidance of dinoflagellates. Microscopic counts suggested that P. avirostris was feeding on prymnesiophytes, although ingestion of prymnesiophytes could not be confirmed by pigment analysis.     

Feeding experiments on Penilia avirostris dana (cladocera: crustacea)

Feeding in the marine cladoceran, Penilia avirostris Dana, was investigated using plastic micronic beads as a controlled particle source. The range of bead size ingested by P. avirostris was largely limited to diameters of 20 μm and below, perhaps a competitive advantage in nature, was found that: (1) as the concentration of beads increased, the number of beads ingested increased: (2) as the number of P. avirostris increased, the number of beads ingested increased: and (3) the number of beads ingested also increased with body size. The size of P. avirostris, however, did not appear to limit the size of bead ingested, while larger sized animals may be better competitors for particles.     

Increasing prevalence of the marine cladoceran Penilia avirostris (Dana, 1852) in the North Sea

Rising sea surface temperatures in the North Sea have had consequential effects on not only indigenous plankton species, but also on the possibility of successful colonisation of the area by invasive plankton species. Previous studies have noted the introduction and integration into the plankton community of various phytoplankton species, but establishment of zooplankton organisms in the North Sea is less well-documented. Examining continuous plankton recorder (CPR) survey data and zooplankton results from the Helgoland Roads study, the autumn of 1999 witnessed the occurrence of the marine cladoceran Penilia avirostris in large numbers in the North Sea. The rapid appearance of the species corresponded with exceptionally warm sea surface temperatures (SSTs). Since 1999, the species has become a regular feature of the autumnal zooplankton community of the North Sea. In 2002 and 2003, the species occurred in greater abundance than recorded before. It is suggested that increased autumn SSTs have proved favourable to P. avirostris, with warmer conditions contributing to the success of the species resting eggs and aiding colonisation.Communicated by H.-D. Franke     

Feeding selectivities and food niche separation of Acartia clausi, Penilia avirostris (Crustacea) and Doliolum denticulatum (Thaliacea) in Blanes Bay (Catalan Sea, NW Mediterranean)

Selectivity-size spectra, clearance and ingestion rates andassimilation efficiencies of Acartia clausi (Copepoda), Peniliaavirostris (Cladocera) and Doliolum denticulatum (Doliolida)from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluatedin grazing experiments over a wide range of food concentrations(0.02–8.8 mm³ L^–1 plankton assemblages from BlanesBay, grown in mesocosms at different nutrient levels). Acartiaclausi reached the highest grazing coefficients for large algae>70 µm (longest linear extension), P. avirostris forintermediate food sizes between 15 and 70 µm, and D. denticulatumfor small sizes from 2.5 to 15 µm. Penilia avirostrisand D. denticulatum acted as passive filter-feeders. Acartiaclausi gave some evidence for a supplementary raptorial feedingmode. Effective food concentration (EFC) decreased linearlywith increasing nutrient enrichment for D. denticulatum andfollowed domed curves for A. clausi and for P. avirostris withmaximum values at intermediate and high enrichment levels, respectively.Clearance rates of crustacean species showed curvilinear responseswith narrow modal ranges to increasing food concentration. Clearancerates of D. denticulatum increased abruptly and levelled intoa plateau at low food concentrations. Mean clearance rates were13.9, 25.5 and 64.1 mL ind.^–1 day^–1, respectively.No clearance could be detected for A. clausi at food concentrations<0.1 mm³ L^–1 and for P. avirostris at food concentrations     

Cladocera of coastal rivers of western Nigeria

Recent studies indicate that there are at least 100 species of Cladocera in the families Bosminidae, Chydoridae, Daphnidae, Macrothricidae, Moinidae and Sididae in the inland waters of Nigeria. Over 50% of these have been found in net plankton samples from the coastal rivers in addition to Evadne tergestina Claus (Family: Podonidae), and Daphnia barbata Weltner, hitherto unreported in the equatorial lowlands of Africa. In effect, the Cladocera of the coastal rivers and creeks consist of the marine/brackish assemblage made up of Penilia avirostris Dana and Evadne tergestina and the freshwater assemblage made up of all other Cladocera found. Unlike in the more inland water bodies, the freshwater assemblage of the coastal rivers is dominated by the Bosminids Bosmina longirostris (O. F. Muller) and Bosminopsis deitersi Richard. The distribution, seasonality and successional patterns of Cladocera in the coastal water bodies of Western Nigeria is presented.     

Salinity and the distribution of Cladocera in Warri River,Nigeria

Hydrobiological investigations of the water quality and plankton of Warri River started in 1981, shortly before the commissioning of the Delta Steel Plant on the banks of the river at Aladja. The 150 km of river gradates from pure freshwater through brackish to marine and so provides a suitable habitat for a study of the limits of migration of any group of zooplankton. The Cladocera of Warri River consists of two bosminids, thirteen chydorids, three daphniids, three macrothricids, one moinid, and two sidids. All except the sididPenilia sp. are well known freshwater forms, which are limited in longitudinal distribution to areas with salinity below 2.5‰. Penilia sp. found in Warri River were restricted to the truely brackish-water areas with salinity values of 7‰ −8‰. In this respect they represent the first reported brackish water Cladocera in Africa. They also differ fromPenilia avirostris Dana found in marine habitats in certain morphological details, and so the Warri RiverPenilia may be a new taxon.     

Limit cycle oscillations of the human eye

The altered feedback technique is very suited to display nonlinearities of the human smooth pursuit system. In fact, when the gain of the retinal feedback path is raised, for the horizontal channel, above its normal unitary negative value, a threshold is met beyond which sustained horizontal self-excited smooth oscillations of the eye can be observed, which point out the existence of a stable limit cycle. Furthermore, the characterizing features of both the transient and steady state show a well defined dependence on the total feedback factor K. In particular, the analytical dependence on K of the amplitude and frequency of limit cycle oscillations can be derived. Implications of the experiment with respect to the mathematical modelling of the system are discussed.     

Vertical zooplankton distribution on the northeastern Florida shelf and its relation to temperature and food abundance

The vertical distribution of abundant zooplankton on the northeastern(NE) Florida shelf was measured and related to depth, temperatureand concentration of particulate matter. High particle concentrationswere observed in low-temperature near-bottom intrusions of upwelledGulf Stream water. Patterns of vertical distribution differedamong the abundant zooplankton taxa. Abundances of the calanoidsEucalanus pileatus and Temora turbinata, late copepodids andadults of the cyclopoid Oncaea sp., the cladcceran Penilia avirostrisand larvae of the cephalochordate Branchiostoma sp. generallyincreased with increasing depth. E. pileatus, T. turbinata,Oncaea sp. and P. avirostris increased with increasing concentrationof paniculate matter. Abundances of young specimens of the tunicateOikopleura, the calanoid Centropages furcatus and during oneperiod, the cyclopoid Oithona sp. were greatest in the uppermixed layer and the thermocline. The abundance of Eucalanus,T. turbinata and the late copepodids/adults of Oncaea showeda significantly positive conelation to the abundance of paniculatematter.     

ENZYME PATTERNS DURING A SYNCHRONOUS GROWTH CYCLE OF CHLORELLA PYRENOIDOSA

There have been no studies in which a significant number of isozymes have been investigated during a synchronous growth cycle of any organism. The present study was designed to obtain information on the fluctuations of a broad spectrum of enzymes during a synchronous growth cycle of Chlorella pyrenoidosa. Of the thirty-two enzymic activities investigated, seventeen could be localized on starch gels from a high temperature strain of Chlorella pyrenoidosa. Nine of these activities were found to possess more than one band of activity by starch gel electrophoresis. Seven of these activities were localized on starch gels throughout a synchronous growth cycle of C. pyrenoidosa grown in continuous light. Assay techniques are described. The fluctuations in enzyme activity are discussed with relation to concurrent metabolic and cytological changes during cell maturation in C. pyrenoidosa.     

Zooplankton annual cycle in a Mediterranean coastal area

The annual cycle of the zooplankton community in the SaronikosGulf (Aegean Sea, Greece) was studied over a period of 2 years.The sampling scheme included monthly hauls at three stationsdifferentiated according to depth and neritic character. Maximumvalues of total zooplankton abundance were found in summer monthsup to early autumn and partially in spring. Copepods dominatedduring most of the year (Clausocalanus furcatus, Paracalanusparvus, Temora stylifera, Ctenocalanus vanus, Oithona similis,Oithona plumifera), while cladocerans (Penilia avirostris) wereabundant in summer months and in September. No important fluctuationswere detected between the 2 years of study, while monthly oneswere more significant in the more neritic station during thewinter–spring period. Correspondence analysis showed thatthe seasonal evolution of zooplankton is related to environmentalparameters: temperature, hydrography expressed in open sea influenceand topography.     

Gene expression and its regulation during the cell cycle of higher plants in synchronous cell culture systems

Summary This review paper describes the importance of synchronous cell cultures as experimental systems for investigations of mechanisms of the cell cycle of higher plants, and various methods of synchronization are discussed. The efficient synchronization methods were double phosphate starvation in Catharanthus roseus cells and aphidicolin treatment in tobacco cells. Using these systems, cell cycle-dependent genes were isolated and characterized. One of them, cyc07, was investigated in detail and the possible function of cyc07 is discussed as an example of genes involved in the progression of the cell cycle of higher plants. Finally, a perspective of investigations of the cell cycle of higher plant cells is discussed.     

Diel cycle in the percentage abundance of parthenogenetic females with embryos of different developmental stages in four species of marine cladocerans

The diel cycle in the percentage abundance of parthenogeneticfemales carrying embryos of different developmental stages inthe marine cladocerans Penilia avirostris, Pseudevadne tergestina,Pleopis polyphymoides and Pleopis schmackeri was studied atthe edge of an artificial rocky shore area in a semi-enclosedbay in Hong Kong. Females carried embryos during both day andnight, but females with fully-developed embryos were found predominantlyat night. The diel cycle in the abundance of females with matureembryos was most pronounced in P. tergestina, and less prominent,but still clearly noticeable in P. avirostris, P. schmackeriand P. polyphymoides. The absence or scarcity of females withmature embryos during daytime could be caused by both selectivepredation by visual predators and nocturnal maturation and releaseof embryos. Juveniles of Acanthopagrus schlegeli (black seabream)were the most abundant planktivorous fish in the study areain spring. Stomach content analyses revealed that these daytimepredators fed intensively on marine cladocerans and exhibiteda strong selection for females with mature embryos. On the otherhand, the gradual decline in the percentage of females withadvanced embryos during the latter part of the night, when feedingby visual predators presumably had not yet begun, suggests thatthere was a tendency for nocturnal release of neonates in marinecladocerans.     

Natural ingestion rates and grazing impact of the marine cladoceran Penilia avirostris Dana in Tolo Harbour, Hong Kong

The gut fluorescence method was used to study algal grazingby Penilia avirostris in a semiestuarine embayment. Grazingimpact estimated from ingestion rate and animal abundance revealedthat only {small tilde}1% of the algal biomass was grazed perday by the cladocerans.     

Cell cycle analysis of tumour-derived cultures ofCrepis capillaris: A kinetic analogy with proliferation of animal tumour cells

Summary Analysis of the cell cycle by three methods has revealed unusual kinetics of proliferation in tumour derived suspensions ofCrepis capillaris. The different methods of analysis yield different estimates of cycle phase durations, and such discrepancies have been explained in terms of low growth fractions with rapid total cycle traverse. Specifically, confidence in the estimation of G₂ duration by the fraction of labelled mitosis analysis, and comparison with shorter G₂ estimates obtained by the two other methods, suggests that cells drop out in G₁. However, cells which do not drop out of the proliferative compartment traverse G₁ extremely rapidly. Extremely short cell cycle durations in which the G₁ phase is virtually non-existent are uncharacteristic of plant cell suspension cultures, in which the G₁ phase has previously been shown to be extended as compared with meristematic root tip cells. A model has been proposed in which a central core of rapidly dividing cells continuously loses cells into a subpopulation of resting or G₀ cells with the G₁ DNA content. Similarities between plant and animal tumours with respect to cell growth and division are discussed.     

Temperature response of the cell cycle of Haplopappus gracilis in suspension culture and its significance to the G1 transition probability model

The effects of temperature on the cell cycle of Haplopappus gracilis suspension cultures were analysed by the fraction of labelled mitoses method. Sphase in these cultures shows a different temperature optimum as compared to optima derived for G₂ and mitosis. G₁ phase has a much lower Q₁₀ than the other cell cycle phases and shows no temperature optimum between 22 and 34° C. These results are discussed in relation to a transition probability model of the cell cycle proposed by Smith and Martin (Proc. Natl. Acad. Sci. USA 70, 1263–1267, 1973), in which each cell has a time independent probability of initiating the transition into another round of DNA replication and division. The implications of such a model for cell cycle analysis are discussed and a tentative model for a probabilistic transition trigger is advanced.Abbreviations FLM Fraction of labelled mitoses - T_B Total B-phase     

THE SEXUAL CYCLE OF NETRIUM DIGITUS

The life cycle of 2 varieties of Netrium digitus, a saccoderm desmid, was studied in pure culture on mineral media. Netrium digitus var. digitus from Indiana is homothallic, and Netrium digitus var. lamellosum from Minnesota is heterothallic. Previous observations by other investigators on the events of the sexual cycle are confirmed and extended. Zygospores of both varieties are formed in the conjugation tube. Fusion of gametic nuclei occurs after the dormant period of zygospores, and meiosis occurs at the time of germination. Conjugation is induced in a reliable manner in both varieties by omitting nitrogen from the medium and by exposing the cultures to the proper conditions of light and temperature. The relationship between photoperiod, nitrogen depletion, and induction of conjugation is discussed.     

Taxonomy of the New Zealand genus Eulimnia,and biology and immature stages of E. philpotti (Diptera: Sciomyzidae)

Abstract

The endemic New Zealand genus Eulimnia and its two species are redescribed. Data are presented on the life cycle of E. philpotti Tonnoir & Malloch, and the habitat, geographical distribution, phenology, and biological features of adults and immature stages are discussed. Adults are found in permanently wet marshes, where the larvae prey on fingernail clams (Bivalvia: Sphaeriidae) while completely submerged. Mature larvae form puparia among vegetation or debris above the water level. The immature stages of E. philpotti are described. The genus is placed in tribe Tetanocerini, and its taxonomic position is discussed.