Cyst production in four species of neritic dinoflagellates

The production of resting cysts in four species of dinoflagellates(Scrippsiella trochoidea, Ensiculifera sp., Alexandrium lusitanicumand Lingulodinium polyedra) was studied in response to severalenvironmental factors of ecological importance (nitrate, phosphate,iron, copper and cyanocobalamin deficiencies, high concentrationsof copper, turbulence, darkness plus concentration. as wellas various media biologically conditioned by dinoflagellates)using unialgal cultures and enrichments of natural populations.Some nutritional deficiencies, mainly phosphorus or nitrogen(in this order), are the most effective inducers of encystment.Among the other deficiencies tested, only iron deficiency wasimportant, affecting only A.lusitanicum. In some cases, biologicalconditioning produced considerable encystment reductions, makingit an important means of competition between species. We suggestthat encystment may be induced in these neritic species by deficienciesin compounds that act as indicators of changes in the hydrographicconditions to which the particular species are adapted.     

Bioluminescence response of four species of dinoflagellates to fully developed pipe flow

Dinoflagellate bioluminescence provides a nearly instantaneousindex of flow sensitivity. This study compared flow sensitivityin four species of morphologically diverse luminescent dinoflagellates(Ceratium fusus, Ceratocorys horrida, Lingulodinium polyedrumand Pyrocystis fusiformis) using fully developed laminar andturbulent pipe flow. Bioluminescence response thresholds alwaysoccurred in laminar flows with wall shear stress levels that,depending on species, ranged from 0.02 to 0.3 N m^–2. Withfew exceptions, such as breaking waves and wave-forced bottomshears in shallow nearshore areas, these threshold shear stresslevels are several orders of magnitude larger than typical oceanicambient flows. For laminar flows above threshold, species alsodiffered in the proportion of organisms responding and the minimumshear stress level where individual flashes reached their highestintensity. Following transition to turbulent flow, there wasnever a dramatic increase in bioluminescence, even when energeticturbulent length scales were similar to the cell size. On thebasis of their bioluminescence response in laminar flow, thesespecies were ranked in order of decreasing sensitivity as C.horrida > P. fusiformis > C. fusus > L. polyedrum.This ranking, though not conclusive, is consistent with increasedflow sensitivity due to increasing size and the presence ofspines. With the exception of a small fraction of the C. horridapopulation that is sensitive enough to flash within the feedingcurrent of a predator, the present study suggests that flashesonly occur with predator contact. Nevertheless, flow sensitivitymay serve as an index of the response to mechanical agitationduring predator contact/handling. Flow sensitivity may be constrainedto maximize the response to predator contact/handling whileminimizing stimulation by background oceanic flows to avoiddepleting luminescent reserves.     

Phenotypic variation in metamorphosis in four species of freshwater copepods

1. Physiological metamorphosis accompanied by an ecological habitat shift is a widespread life-history phenomenon, and both age and size at metamorphosis are highly variable in many organisms. In this study, age and size at metamorphosis (defined as the transition from the last naupliar to the first copepodite stage) were quantified for four species of freshwater copepods to determine the scale on which these two traits vary, if age and size at metamorphosis are equally variable, and if variation at metamorphosis is related to variation in newborn size. 2. Measurements of laboratory-reared and field-caught individuals show that age and size at metamorphosis, together with newborn size, vary among siblings, between families within a population, between populations of one species and between closely related species. 3. In all populations, age at metamorphosis was the most variable trait, a result observed in many other organisms. Most of the variation in age at metamorphosis could be explained by differences between families within a population, while differences among siblings from the same clutch accounted for most of the variation in size at metamorphosis. 4. Although newborn size was variable, differences in this trait could not fully account for variation observed at metamorphosis. Newborn size differed among populations, but most interpopularional differences disappeared by the rime metamorphosis was reached. In particular, size at metamorphosis appears to be tightly constrained in freshwater copepods. 5. Age and size at metamorphosis were not equally variable among species, either. Species-specific metamorphic envelopes (joint distributions of age and size at metamorphosis) result from differences in trait means, variances and covariances, and suggest very different larval growth trajectories among three of the species examined.     

Reproductive potential of four freshwater prawn species in the Amazon region

The bioecology of freshwater prawns can be understood by studying their reproductive biology. Thus, the aim of this paper was to determine and compare the reproductive potential of four freshwater caridean prawns collected in the Amazon region. For two years, we captured females of Macrobrachium brasiliense, Palaemon carteri, Pseudopalaemon chryseus and Euryrhynchus amazoniensis from inland streams in the municipality of Itacoatiara (AM). At the laboratory, we measured the biometric variables total length, carapace length, abdomen length and total weight, and recorded the number of eggs (NE) by direct counting. There was a significant difference for all variables between the species. The females of M. brasiliense were the most abundant and had the largest sizes and NE. However, the fecundity index shows that P. carteri has the highest reproductive potential of the four species. Despite the differences in size and weight, all the species showed low fecundity, which is a characteristic of continental palemonidean K strategist prawns.     

Toxicity of carbaryl and 1-naphthol to four species of freshwater fish

The toxicity of the carbamate insecticide carbaryl (Seven√) and its metabolite, 1-naphthol, to four species of fish was studied. The calculated 96 h LC 60 values of carbaryl forCatla catla (Ham.), Anabas testudineus (Bloch),Mystus cavasius (Ham.) andMystus vittatus (Bloch) are 6.4, 6.6, 4.6 and 2.4 ppm respectively and that of 1-naphthol are 4.3,3, 0.33 and 1.1 ppm respectively. The degradation product of the insecticide was found to be more toxic than the parent compound, to all the four species studied.     

Ichthyotoxicity of four species of gymnodinioid dinoflagellates (Kareniaceae,Dinophyta) and purified karlotoxins to larval sheepshead minnow

Two species of Kareniaceae, Karlodinium veneficum (Swan and Huon River isolates) and Karlodinium conicum, and their respective purified karlotoxins (KmTx), were investigated for ichthyotoxicity on larval sheepshead minnow. Two non-karlotoxin producing species, Karenia mikimotoi and Karlodinium ballantinum were also tested. Algal treatments included live and lysed cells (homogenized and CuSO₄ treated) with fish mortalities observed from lysed Ka. veneficum and Ka. conicum but none observed from K. mikimotoi and Ka. ballantinum. The variance in ichthyotoxicity between live and lysed cells of Ka. veneficum (Swan and Huon River) and Ka. conicum (Southern Ocean) confirm that toxin is cell bound and ichthyotoxicity increases upon lysis. Ichthyotoxic blooms of Ka. veneficum in situ in the Swan River, Western Australia and Chesapeake Bay, Maryland, USA are unrelated to algal cell density as mortality was observed with low densities. In laboratory treatments, no fish mortalities were observed upon exposure to live intact cells of all four species at algal concentrations up to 2.5 × 10⁵ cells/mL in replete nutrient growth conditions. Lysed low density (3 × 10⁴ cells/mL) Ka. veneficum (Swan and Huon River) grown under P-limited nutrients caused quicker fish mortality than those cultured in replete nutrient conditions. Pure toxin isolated from Ka. veneficum (Swan and Huon River) and Ka. conicum (Southern Ocean) were toxic to sheepshead minnow larvae, with the lethal dose lowest for Km^HuonTx 2 (508.2 ng/mL), followed by Km^SwanTx 2-1 (563.2 ng/mL), and Km_conicumTx (762.4 ng/mL).     

Spatial distribution of four freshwater gastropod species in a ditch near Orsay,France

The distribution (both specific and individual) of four pulmonate gastropods was studied in a ditch near Orsay, France, from April 1987 to August 1988. Physa fontinalis L. and Anisus albus (Müller) were restricted to the part of the ditch which never dries up and positively associated with the hydrophytes Ceratophyllum submersum L. and Callitriche hamulata Küntz. On the other hand, Anisus rotundatus (Poiret), which is drought resistant, was abundant in the shallowest part of the ditch and was positively associated with helophytes while Lymnaea palustris (Müller) was ubiquitous and present throughout the ditch. Plant morphology appears to be a major factor determining snail-plant relationships. Within their respective habitats, each species presented an aggregated distribution; their variances were stabilized by logarithmic transformation for L. palustris, Downing's transformation for P. fontinalis and Taylor's transformation for the two remaining species.     

Spatial distribution of four freshwater fish species in different types of artificial European water bodies

Spatial distribution of young-of-the-year (YOY) and older roach, rudd, perch and ruffe was compared in two artificial lakes with macrophytes present and absent, and a valley reservoir, using gillnets. Almost all species of interest and both age categories preferred benthic habitats. The depth distribution in benthic habitats was relatively consistent across water bodies with the highest fish densities found in the shallowest depths. In the macrophyte-rich lake, YOY roach and perch utilize the 3–6 m benthic layer the most, whereas the fish preferred the 0–3 m benthic layer in the macrophyte-poor lake and reservoir. No differences were found in the depth distribution in pelagic habitats sampled by pelagic gillnets for YOY fish between the water bodies. Older fish usually utilized the surface water layer. Macrophytes influenced the depth distribution of YOY fish in benthic habitats, where their density maximum shifted deeper in the macrophyte-rich lake when fewer macrophytes were present in the shallowest benthic depth. In lakes, YOY fish utilized a wider depth spectrum due to the deeper thermocline when compared to the reservoir. Oxygen and temperature stratification are the main factors influencing fish distribution, whereas macrophyte presence particularly influences the depth distribution of YOY fish in benthic habitats.     

Trophic positions of omnivores are not always flexible: Evidence from four species of freshwater crayfish

Omnivores are generally believed to be flexible in their diet and trophic position: seasonal, ontogenetic and site‐based differences in trophic position have been observed. We compared consumed and assimilated diet among four species within a group of omnivorous freshwater crayfish, to determine whether species that occur together at a site occupy different trophic positions. Diets of Geocharax falcata, Gramastacus insolitus, Cherax destructor and Euastacus bispinosus (Decapoda: Parastacidae) were compared using stable isotopes (δ¹³C and δ¹⁵N) and gut content analysis across nine sites that varied in their species composition. Gramastacus insolitus consumed mainly plant material across all sites. Geocharax falcata consumed either plants or animals or both at different sites. Its trophic level was consistently similar to G. insolitus, despite differences in gut contents and source for dietary carbon. Cherax destructor consumed animals and had a relatively stable trophic position among sites. Relative trophic position of these three species was consistent across sites and regardless of food consumed, they were positioned as omnivores at a lower trophic level than predators but higher than primary producers and herbivores. Euastacus bispinosus occupied a higher trophic level than other invertebrate species but δ¹³C levels did not differ among sites. Cherax destructor and G. falcata may show flexibility in food sources and in the assimilation of food that determines their trophic position relative to other crayfish species. In contrast, G. insolitus and E. bispinosus are likely to show both a more fixed diet and less flexible trophic position. Therefore, not all omnivores show the flexible diet and trophic position generally reported in the literature. Some species of omnivorous crayfish may maintain a relatively constant trophic position across sites, seasons or changes in food availability regardless of whether their consumed diet alters or not.     

Preliminary observations on the heavy metal content of four species of freshwater fish in NW England

The concentrations of zinc, lead and cadmium in four species of fish from several lacustrine sites were determined. Cyprinids were found to have significantly higher levels of the three metals studied than perch, Perca fluviatilis . Whilst zinc thresholds may be species specific, levels of lead and cadmium vary both within species and sites. There is some evidence that lead and cadmium levels increase with age in roach, Rutilus rutilus . Additionally both cadmium and lead appear to accumulate in the heart, liver, kidney and brain as well as in the bone. Relatively high levels of lead and cadmium were recorded in the eyes of bream, Abrama bramis .     

Growth response of four freshwater algal species to dissolved organic nitrogen of different concentration and complexity

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Effects of macroalgae Ulva pertusa (Chlorophyta) and Gracilaria lemaneiformis (Rhodophyta) on growth of four species of bloom-forming dinoflagellates

The effects of fresh thalli and culture medium filtrates from two species of marine macroalgae, Ulva pertusa Kjellm (Chlorophyta) and Gracilaria lemaneiformis (Bory) Dawson (Rhodophyta), on growth of marine microalgae were investigated in co-culture under controlled laboratory conditions. A selection of microalgal species were used, all being identified as bloom-forming dinoflagellates: Prorocentrum donghaiense Lu sp., Alexandrium tamarense (Lebour) Balech, Amphidinium carterae Hulburt and Scrippsiella trochoide (Stein) Loeblich III. Results showed that the fresh thalli of either U. pertusa or G. lemaneiformis significantly inhibited the microalgal growth, or caused mortality at the end of the experiment. However, the overall effects of the macroalgal culture filtrates on the growth of the dinoflagellates were species-specific (inhibitory, stimulatory or none) for different microalgal species. Results indicated an allelopathic effect of macroalga on the co-cultured dinoflagellate. We then took P. donghaiense as an example to further assess this hypothesis. The present study was carried out under controlled conditions, thereby excluded the fluctuation in light and temperature. Nutrient assays showed that nitrate and phosphate were almost exhausted in G. lemaneiformis co-culture, but remained at enough high levels in U. pertusa co-culture, which were well above the nutrient limitation for the microalgal growth, when all cells of P. donghaiense were killed in the co-culture. Daily f/2 medium enrichment greatly alleviated the growth inhibition on P. donghaiense in G. lemaneiformis co-culture, but could not eliminate it. Other environmental factors, such as carbonate limitation, bacterial presence and the change of pH were also not necessary for the results. We thus concluded that allelopathy was the most possible reason leading to the negative effect of U. pertusa on P. donghaiense, and the combined roles of allelopathy and nutrient competition were essential for the effect of G. lemaneiformis on P. donghaiense.     

Surface ultrastructure and molecular phylogenetics of four unarmored heterotrophic dinoflagellates, including the type species of the genus Gyrodinium (Dinophyceae)

Small subunit rRNA gene sequences were determined for four unarmored heterotrophic dinoflagellates (Gyrodinium spirals, the type species of the genus Gyrodinium, as well as G. fusiforme, Gymnodinium rubrum and the freshwater species G. helveticum) using a single‐cell polymerase chain reaction (PCR) technique. For identification and record keeping, each cell was carefully observed and photographed using a light microscope under high magnification, prior to single‐cell PCR. G. rubrum and G. helveticum possess an elliptical apical groove and longitudinal striations similar to those of G. spirale and G. fusiforme, and molecular phylogenetic studies reveal that the four species form a single clade. We therefore propose the following new combinations: Gyrodinium rubrum (Kofoid et Swezy) Takano et Horiguchi comb. nov. and Gyrodinium helveticum (Penard) Takano et Horiguchi comb. nov.     

Interactions between allelopathic properties and growth kynetics in four freshwater phytoplankton species studied by model simulations

We chose four species of freshwater phytoplankton: the chlorophyceans Ankistrodesmus falcatus, Chlamydomonas reinhardtii and Selenastrum capricornutum, and the cyanobacteria Oscillatoria sp. in order to study their competitive abilities for nitrate and their allelopathic properties. We parameterized models of nitrate uptake and growth with laboratory experiments. According to them, the species were ranked (from the best to the worst competitors): S. capricornutum, C. reinhardtii, A. falcatus and Oscillatoria sp. C. reinhardtii and Oscillatoria sp. were previously reported as allelopathic. In the present work, Oscillatoria sp. was allelopathic only against A. falcatus. However, none of our species was sensitive to C. reinhardtii. Additionally, we found an unknown allelopathic effect of A. falcatus against Oscillatoria sp. Our findings point out the high specificity of allelopathic interactions. With these data, we constructed a model of interspecific competition for nitrate, including allelopathic interactions. By performing model simulations, we studied how three factors influence the outcome of competition: relative abundance of competing species, resistance to allelopathy, and nitrate concentration. Our simulations showed that the initial ratio of species abundances will significantly determine the outcome of competition. If the worst competitor was the allelopathic species, the more it needs to outnumber the competing species, unless it is very sensitive to allelopathy (not defended). Nitrate has an important influence, showing a non-intuitive outcome of competition experiments at low nitrate concentrations, where the worst competitor (allelopathic species) wins competition in the majority of cases, whereas at intermediate concentrations, the better competitor dominates except for unfavorable ratios of abundances. With the increased amounts of nitrate, conditions again favor the worst competitor (the stronger allelopathic species). Despite the potential for two species coexistence showed by previous theoretical analysis of systems was similar to ours, our simulations did not detect this outcome. We hypothesized that this is due to the strong allelopathic effect of Oscillatoria sp.     

Length‐weight relationships of four freshwater fish species from the coastal drainage system in Peru

The morphometric relationships of three native and one exotic freshwater fish species from the Lower San Juan and Lower Pisco River basins, central Coast of Peru, are presented. Specimens were collected in May and November 2010 using seine nets and electrofishing. Length‐Weight (LWR) relationships for Andinoacara stalsbergi, Trichomycterus punctulatus, Basilichthys archaeus and Poecilia reticulata are provided for the first time, contributing information towards the effort to conserve freshwater fishes.     

Phototactic responses of four marine dinoflagellates with different types of eyespot and chloroplast

Great structural variety is seen in the eyespot of dinoflagellates, a structure involved in phototaxis. Although there are several works on the phototactic responses in some species of dinoflagellates, none of the dinoflagellates used in these studies possessed an eyespot and, therefore, we have no knowledge of the relationship between eyespot type and phototactic response. In this study, we determined wavelength dependency curves for phototaxis in four marine dinoflagellates that possess a different type of either eyespot or chloroplast. These include: (i) a dinoflagellate possessing a peridinin-containing ohioroplast with an eyespot (Scrippsiella hexapraecingula Horiguchi et Chihara); (ii) a dinoflagellate containing a diatom endosymbiont and with the type B eyespot sensu Dodge (1984; (Peridinium foli-aceum (Stein) Biecheler); (iii) a dinoflagellate with peri-dinin-containing chloroplasts, but lacking an eyespot (Atexandrium hiranoi Kita et Fukuyo); and (iv) a dinoflagellate with fucoxanthin, 19′-hexanoyloxyfucoxanthin and 19′-butanoyloxyfucoxanthin, but lacking an eyespot (Gymnodinium mikimotoi Miyabe et Kominami ex Oda), Regardless of the eyespot or the chloroplast type, all four dinoflagellates showed similar wavelength dependency curves for phototaxis, with sensitivity between 380 and 520 nm, the highest peak at approximately 440 or 460 nm and smaller peaks or shoulders at 400–420 nm and 480–500 nm. Substantial peaks have also been noted in the ultraviolet range (260–280 nm). The ultrastructural study of the eye-spot of Scrippsiella hexapraecingula revealed that the eyespot consists of two layers of lipid globules and probably acts as a quarter-wave stack antenna.     

Length–weight relationships of four freshwater ornamental fish species from the Brazilian Negro River basin

The present work reports the length–weight relationships (LWR) for four ornamental fish species from the middle Negro River basin, Amazonas, Brazil. The r² value ranged from 0.810 to 0.941 and values of b varied from 2.346 to 3.442. These results represent the first reference on LWR for all four species, based on FishBase.