Effect of two microalgae concentrations on body size and egg size of the rotifer <Emphasis Type="Italic">Brachionus calyciflorus</Emphasis>

The rotifer, Brachionus calyciflorus, was grown with two algae species (Chlorella sp. and Scenedesmus obliquus) at different concentrations (0.1, 1 and 10 × 10⁶ cells ml⁻¹). The body size (lorica biovolume) of individual rotifer and their egg size were measured when the populations were roughly in the exponential phase of population growth. The body size of the rotifers differed significantly (P < 0.05) among the two algae species used, however this effect was not observed for egg size. The body size of rotifers fed on higher densities of Chlorella sp. (10 × 10⁶ cells ml⁻¹) was significantly larger than for those fed on lower and medium densities (0.1 and 1 × 10⁶ cells ml⁻¹). Body size and egg size of rotifers fed with different amounts of Scenedesmus did not differ significantly. The egg size was significantly larger at higher food level of Chlorella. A significantly positive correlation was observed between the adult rotifer body size and their egg size.     

Effect of Aeolosoma sp. (Aphanoneura: Aeolosomatidae) on the Population Dynamics of Selected Cladoceran Species

Although oligochaete worms naturally coexist with cladocerans in many shallow freshwater ponds and lakes, their influence on the latter is not well established. In this work we studied the effect of Aeolosoma sp. on the population growth of Alona rectangula, Ceriodaphnia dubia, Daphnia pulex, Macrothrix triserialis and Moina macrocopa. Population growth studies were conducted at one algal food density (1 × 10⁶cells ml^–1 of Chlorella vulgaris). The experimental design was similar for all five cladoceran species, where we used 100 ml capacity transparent jars containing 50 ml of EPA medium with the desired algal density and three replicates for each treatment. The test medium was changed daily and fresh algal food was added. The initial density of each of the cladoceran species in the population growth studies was 0.4 ind ml^–1 while that of the worms 1.0 ind ml^–1. Following inoculation, we estimated daily the number of cladocerans and the worms for duration of 21 days. Regardless of the presence of worms, Moina macrocopa and Macrothrix triserialis showed rapid population growth while A. rectangula took more than 2 weeks to reach peak abundances. With the exception of M. triserialis, all the other our cladoceran species declined in the presence of Aeolosoma sp. The lowest peak population density (about 1 ind ml^–1) was observed for M. triserialisin controls. The remaining species had peak densities of about 3–5 ind ml^–1. The rates of population increase per day varied from 0.03 to 0.19 depending on the cladoceran taxa and the treatment. In general we found that pelagic taxa were more adversely affected by the presence of the worms than were the littoral cladocerans.     

Endophytic fungi of teak leaves Tectona grandis L. and rain tree leaves Samanea saman Merr.

Summary In order to study the foliar endophytes from teak (Tectona grandis L.) and rain tree (Samanea saman Merr.) growing in the campus of Chulalongkorn University, healthy leaves were collected at two-monthly intervals during January to December. The number of genera and species, together with their colonization frequency (CF%) in mature teak and rain tree leaves were greater than those in the young leaves. More endophytic isolates in the leaves of both trees were recovered during the rainy season. The fungal genera found in both young and mature teak leaves were Alternaria, Colletotrichum, Nigrospora, Phomopsis and mycelia sterilia. Phomopsis was the dominant genus in both young (newly emerged) and mature leaves. Fusarium, Penicillium, Schizophyllum commune and members of the Xylariaceae were found only in mature leaves. For the rain tree leaves, species of Phomopsis and mycelia sterilia were found in both young newly emerged and mature leaves. Colletotrichum and Penicillium were found only in mature leaves, whereas Nigrospora was found only in young newly emerged leaves. In this study, Phomopsis was the dominant genus in the leaves of both tree species. A total of 37 isolates of endophytic fungi isolated from teak and rain tree leaves were tested for the production of antimicrobial activities. Out of these, 18 isolates could produce inhibitory substances effective against Bacillus subtilis, Staphylococcus aureus and Escherichia coli and 3 isolates inhibited growth of Candida albicans in vitro.     

Production and nutritional quality of the rotifer Brachionus plicatilis fed marine Chlorella sp. at different cell densities

The effect of different cell densities of marine Chlorella sp. on the growth rate, doubling time and production of the rotifer Brachionus plicatilis was investigated. A significant increase in rotifer production was achieved at a density of 50 × 10⁶ Chlorella cells ml^–1. The nutritional quality of rotifers grown at different concentrations of Chlorella is discussed.     

Species-specific ability ofChlorella strains (Chlorophyceae) to form stable symbioses withHydra viridis

46 strains ofChlorella, identified by physiological and biochemical characters, were examined for their ability to form stable symbioses with aposymbioticHydra viridis. It was found to be a species-specific characteristic. Among the 15 taxa studied, onlyC. saccharophila var.ellipsoidea, C. saccharophila var.saccharophila, C. fusca var.vacuolata, C. kessleri, C. luteoviridis, andC. protothecoides formed stable symbioses withHydra viridis. Among the 11 known physiological and biochemical characters of theseChlorella species, only acid tolerance seems to be correlated with symbiosis: All symbiotic species are capable of growing at or below pH 4.0.     

Oligochaeta in Spartina stems: the microdistribution of Enchytraeidae and Tubificidae in a salt marsh,Sapelo Island,USA

The distribution and abundance of Enchytraeidae and Tubificidae in and around Spartina alterniflora plants in a tidal salt marsh on Sapelo Island, Georgia, USA were studied using two different sampling techniques: wet funnel extraction and stem dissection. At least 80% of all worms inhabited leaf sheaths at the bases of S. alterniflora plants, and densities were low in sediment, root and surface debris samples. Oligochaete densities were dependent on the position within the marsh, the height on stems and the stage of sheath decay. Six predominant species were identified and included Marionina appendiculata, Marionina spartinae, Marionina waltersi, Marionina paludis, and Monopylephorus parvus. Individual species were distributed differently on stems and enchytraeids were more common than tubificids on standing-dead and further up S. alterniflora stems. Estimates of oligochaete densities in salt marsh habitats are increased dramatically when the numbers of worms on stems are considered. Possible advantages of the stem microhabitat are discussed in relation to the biology and ecology of oligochaetes.     

New and known taxa ofChlorella (Chlorophyceae): Occurrence as lichen phycobionts and observations on living dictyosomes

The algal partner of the lichenPseudocyphellaria carpoloma is a newChlorella species,Chl. sphaerica. It has a saucer- or band-shaped parietal to subparietal chloroplast with a spherical pyrenoid surrounded by a shell of starch. In some of the fully grown cells two dictyosomes lying parallel to each other and changing their position can be observed in the living state. Reproduction occurs by up to 16 autospores. 8 otherPseudocyphellaria species are also lichenized withChlorella phycobionts, apparently belonging toChl. sphaerica. The phycobiont ofWoessia fusarioides belongs toChlorella saccharophila var.ellipsoidea, and to a strain which is morphologically almost identical to one formerly isolated from the lichenTrapelia coarctata. Its ability to gather granules of india ink on the surface of young cells is one of the remarkable characters differentiating it from the latter. In the lichen thallus its cells are regularly penetrated by fungal haustoria.     

Resource limitation of diving ducks at Myvatn: Food limits production

We monitored numbers and production of diving ducks on Lake Myvatn and its outlet river, the Laxá, over a period of 25 years, 1975–1999. Aquatic insects, a major food source, were monitored for 23 years, 1977–1999, using window traps. In this paper, we focus on the relationship between the demography of five species of diving ducks and the abundance of aquatic insect species, mainly Chironomidae and Simuliidae. Production of ducks was estimated when most young were 2–4 weeks old, either as young per female (Aythya marila and Aythya fuligula) or as total young found (Melanitta nigra, Bucephala islandica, Histrionicus histrionicus). Variation between years in production of young ducks was strongly correlated with variation in the abundance of aquatic insects. Procladius islandicus and Psectrocladius barbimanus, both of which are univoltine with peak emergence in late July (when many young ducks hatch), as well as the bivoltine Orthocladius consobrinus, showed particularly high correlations with duckling numbers. In one year, 1992, catastrophic weather depressed production. Food appeared to determine production, primarily through its availability to the young. Changes in spring density of breeding ducks of all five species were negatively associated with density in the year before. Resources, estimated as food availability or reproductive success in the year before, were positively correlated with change in breeding numbers in A. marila, A. fuligula and B. islandica. Production three years earlier had a weak but significant effect on change in numbers of M. nigra.     

The effects of host plant on the coccinellid functional response: Is the conifer specialist Aphidecta obliterata (L.) (Coleoptera: Coccinellidae) better adapted to spruce than the generalist Adalia bipunctata (L.) (Coleoptera: Coccinellidae)?

Female Aphidecta obliterata consumed an average of 26.6 ± 5.8 Elatobium abietinum and males consumed an average of 19.9 ± 3.2 Elatobium abietinum, but there was no significant difference in the number consumed between the sexes. In Petri dish trials, the larval stages of A. obliterata and all stages of Adalia bipunctata appeared to exhibit a Type II response to prey density, although A. obliterata adults showed a more linear response to prey density. There was no significant difference between the functional responses of the 3rd instars of the two coccinellid species, but there was a significant difference between the responses shown by the 1st instars, with A. obliterata larvae consuming more than those of A. bipunctata, especially at low densities, suggesting that the two species respond differently to an increase in prey density.At low prey densities, adults and 4th instars of both species exhibited a similar response to an increase in prey density but at higher densities the 4th instars and adult stages of A. bipunctata showed higher attack rates when compared with the same stages of A. obliterata.Adult and 4th instar A. obliterata exhibited Type II functional responses on spruce sections. The 4th instar A. obliterata larva appeared to be a more effective predator than the adult of the species, and was more effective when compared with adult A. bipunctata at lower prey densities but A. bipunctata adults appeared to be a more effective predator at higher prey densities.The host plant affected the rate of consumption by adult A. obliterata as adults on Sitka spruce sections consumed significantly higher numbers of aphids than their counterparts on Norway spruce. This was most noticeable at densities above 16 aphids.The distributions of the two coccinellid species in the olfactometer were significantly affected by the presence of host plant material. Aphidecta obliterata adults were found in significantly higher numbers in the Sitka spruce chambers than the control chambers (those without plant material). Adalia bipunctata adults were found in significantly lower numbers in the Norway spruce chamber than the control chamber.Although A. bipunctata has a higher level of voracity than A. obliterata, the latter is more adapted to the spruce environment and the boom and bust population dynamics of E. abietinum.     

Karyology and hyphal characters as taxonomic criteria in Ascomycetous black yeasts and related fungi

Mycelial development of seventy-three strains of black yeasts and related fungi were studied, and numbers of nuclei per hyphal cell were counted. Two main patterns were apparent in expanding hyphae, viz. (1) uninucleate expanding hyphal cells, septum formation strictly following mitosis, and (2) multinucleate, branched, aseptate hyphal tips, septa being formed in a later stage, leading to oligo- or uninucleate mature cells. Characteristic genera in the two groups areExophiala andAureobasidium, respectively. InZasmidium and in someRamichloridium species all mycelial cells are oligonucleate. The character is indicative for relationships at the family level in black yeasts.     

Phylogenetic position of someChlorella species within the chlorococcales based upon complete small-subunit ribosomal RNA sequences

Summary Complete small-subunit rRNA (16S-like rRNA) coding region sequences were determined for eight species of the Chlorococcales (Chlorophyceae). The genera investigated includePrototheca, Ankistrodesmus, Scenedesmus, and fiveChlorella species. Distance matrix methods were used to infer a phylogenetic tree that describes evolutionary relationships between several plant and green algal groups. The tree exhibits a bifurcation within the Chlorococcales consistent with the division into Oocystaceae and Scenedesmaceae, but three of the fiveChlorella species are more similar to other algae than toChlorella vulgaris. All of the sequences contain primary and secondary structural features that are characteristic of 16S-like rRNAs of chlorophytes and higher plants.Anikstrodesmus stipitatus, however, contains a 394-bp group I intervening sequence in its 16S-like rRNA coding region.     

Flocculation of algae using chitosan

Flocculation of three freshwater algae, Spirulina,Oscillatoria and Chlorella, and onebrackish alga, Synechocystis, using chitosan was studiedinthe pH range 4 to 9, and chlorophyll-a concentrations inthe range 80 to 800 mg m^–3, which produces aturbidity of 10 to 100 nephelometric turbidity units (NTU) in water. Chitosanreduced the algal content effectively by flocculation and settling. Theflocculation efficiency is very sensitive to pH, and reached a maximum at pH7.0for the freshwater species, but lower for the marine species. The optimalchitosan concentration that is required to effect maximum flocculation dependedon the concentration of alga. Flocculation and settling were faster whenconcentrations of chitosan higher than optimal are used. The settled algalcellsare intact and live, but will not be redispersed by mechanical agitation. Thede-algated water may be reused to produce fresh cultures of algae.     

Deoxyribonucleic acid reassociation in the taxonomy of the genus Chlorella

DNA hybridization techniques showed Chlorella fusca var. vacuolata and C. kessleri to be homogeneous species with DNA homologies of 90–100% C. fusca var. fusca and var. rubescens, however, have only about 15% DNA homology with C. fusca var. vacuolata and should no longer be regarded as varieties. A good correlation was found so far between biochemical and physiological characters used in the taxonomy of Chlorella and DNA relatedness. Mutant strains of Chlorella were tested for DNA homologies to prove the reliability of the taxonomical interpretation.     

Prey selection by Chaoborus punctipennis under laboratory conditions

Equal numbers of Diaphanosoma leuchtenbergianum, Daphnia parvula, and Diaptomus pallidus were offered to individual, fourth-instar larvae of Chaoborus punctipennis. When the prey species were presented separately to the larvae, 100% of the Diaphanosoma, 67% of the Daphnia, and 57% of the Diaptomus were consumed. However, when the three species were offered to the predator concurrently, 90% of the Diaphanosoma, 10% of the Daphnia and < 1% of the Diaptomus were eaten. This strong selection for Diaphanosoma was consistent at three prey densities.     

Contrasting mechanisms of secondary metabolite accumulation during leaf development in two tropical tree species with different leaf expansion strategies

Young leaves of most species experience remarkably higher herbivore attack rates than mature leaves. Considerable theoretical effort has focused on predicting optimal defense and tradeoffs in defense allocation during leaf expansion. Among others, allocation to secondary chemistry may be dependent on growth constraints. We studied flavanoid production during leaf development in two species of Inga (Fabaceae: Mimosoideae) with different expansion strategies: Inga goldmanii, a species with slowly expanding young leaves, and Inga umbellifera, a species with fast-expanding young leaves. In these two species, the most abundant and toxic class of defensive compounds is flavanoids (which include tannins). We measured their concentration by leaf dry weight, their total content per leaf, their HPLC chemical profile and their toxicity to a generalist herbivore at different expansion levels. Although in both species the flavanoid concentration decreased with increasing leaf expansion, that decrease was twice as pronounced for I. umbellifera as it was for I. goldmanii. I. umbellifera leaves produced flavanoids only during the first half of their development while I. goldmanii leaves continued production throughout. The changes in flavanoid HPLC profiles and toxicity were also more dramatic for I. umbellifera, which had different flavanoids in young than in mature leaves. Relative to I. umbellifera, I. goldmanii showed smaller changes in both flavanoid composition and toxicity in the transition from young to mature leaves. These results indicate that, even though young leaves suffer higher rates of attack and are predicted to have better chemical defenses than mature leaves, growth constraints may modulate defense allocation and thus, evolution of defense strategies.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Dynamics of potentially harmful microalgae in a confined Mediterranean Gulf—Assessing the risk of bloom formation

The population dynamics of potentially harmful microalgae was investigated in the semi-enclosed shallow Gulf of Kalloni, Greece (Aegean Sea, Eastern Mediterranean), during a 2-year period from August 2004 to March 2006. A total of 21 potentially harmful microalgae (bloom-forming and/or toxic) were identified including 3 diatoms and 18 dinoflagellates. The densities of each species were analyzed in time and space and in relation to environmental parameters. Some species such as Alexandrium insuetum, Heterocapsa circularisquama, Karlodinium veneficum, Scrippsiella trochoidea, and Ceratium spp. developed high cell concentrations, particularly during a Pseudo-nitzschia calliantha winter bloom. Other species such as Dinophysis caudata, Ostreopsis ovata, Prorocentrum minimum, and Protoperidinium crassipes were rare or appeared in small numbers. Densities of the most abundant species were closely associated with freshwater nutrient-rich inputs during winter, being negatively correlated with temperature and salinity and positively correlated with nitrogen. The spatial distribution of the abundant species exhibited a marked increase towards the inner part of the gulf, close to the main freshwater inputs, whereas some species were mainly concentrated in the dilute surface layer (1 m depth). Examination of the abundance–occupancy relationship revealed that the species more prone to bloom are those with wide spatial distribution and frequent presence throughout the year such as the diatom P. calliantha. Although blooms of cyst-forming species are rarer, an increased risk can be foreseen under favorable resource supply and environmental conditions during winter.     

Algal bioassays to determine toxicity of metal mixtures

The shortcomings of many established toxicity criteria for metals have resulted from a simplification of bioassays performed with single metals. A more comprehensive approach was needed to diagnose the effects of metal mixtures on aquatic organisms. Using Chlorella, Ankistrodesmus and Scenedesmus as test organisms, we experimented on a number of factors which affected metal toxicity bioassays. These included metal interactions, algal competitions, species sensitivities, the ratio of an excess metal to other metals and nutrient levels. An alternative technique was finally established which involved an evaluation of individual assays of Chlorella and Ankistrodesmus in separate media and a tissue-metal analysis on Chlorella. Chlorella fusca, commonly found in lakes with high metal concentrations, showed high tolerance to mixed-metal solutions, while Ankistrodesmus proved to be very sensitive. By determining the maximum yield ratio between Ankistrodesmus and Chlorella (i.e. the A/Ch ratio) it was possible to compare the toxic strength of harmful metals according to an established standard curve of A/Ch ratio versus mixed-metal concentrations. The levels of tissue-metal analysed in Chlorella also gave some indication as to which metals were responsible for the toxicity.     

Contaminated sediments in the Elbe estuary: Ecological and economic problems for the Port of Hamburg

The effects of food density on competition between Bosmina longirostris and Bosmina fatalis from Lake Kasumigaura were examined in the laboratory. When the animals were reared with a high concentration of Chlorella, B. fatalis, which is slightly larger than B. longirostris in body length, had larger brood sizes and a higher rate of population growth than B. longirostris. When the species were reared together at high food density, B. fatalis overcame B. longirostris. But B. longirostris won the competition at low food density.The effects of Microcystis on the competition were also examined. When the two species of Bosmina were reared in a mixture of Chlorella and Microcystis, the populations of both species hardly increased, although individual B fatalis showed slightly better individual growth and reproduction than B. longirostris. Decomposed Microcystis, however, was utilized well by both species.In Lake Kasumigaura, the decomposition of abundant Microcystis seemed to raise the food level, favouring B. fatalis over B. longirostris.     

Effect of salinity on competition between the rotifers Brachionus rotundiformis Tschugunoff and Hexarthra jenkinae (De Beauchamp) (Rotifera)

We studied the effect of different concentrations (0, 3, 6, 9 and 12 g l^–1) of sodium chloride at one food level of Chlorella (1×10⁶ cells ml^–1) on competition between the rotifers B. rotundiformis and H. jenkinae, both of which were isolated from a saline lake. The population growth experiments were conducted for 3 weeks. Both the rotifer species did not survive beyond one week at a salinity of 0 g l^–1. Regardless of salt concentration and the presence of a competitor, H. jenkinae reached higher densities than B. rotundiformis. When grown alone, both B. rotundiformis and H. jenkinae showed optimal peak population densities at the salinity of 6 and 9 g l^–1. Since biomass wise, B. rotundiformis was larger than H. jenkinae, it showed a lower numerical abundance. Thus, the maximum peak population densities of B. rotundiformis and H. jenkinae recorded in this study were 107±3 and 203±28 ind. ml^–1. The maximal rates of population increase for B. rotundiformis and H, jenkinae when grown alone were 0.264±0.003 and 0.274±0.004, respectively. Our results also indicated that B. rotundiformis and H. jenkinae coexisted better at a salinity of 6 and 9 g l^–1 of sodium chloride while a salinity of 3 g l^–1 favoured Hexarthra over B. rotundiformis. At 12 g l^–1, both the rotifer species grown alone or together showed lower growth rates compared to those at lower salinity levels. Except 0 g l^–1, in all other salinity treatments, H. jenkinae was a superior competitor to B. rotundiformis.     

Nutritional suitability and ecological relevance of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis> as foodplants for the cabbage butterfly, <Emphasis Type="Italic">Pieris rapae</Emphasis>

The thale cress, Arabidopsis thaliana, is considered to be an important model species in studying a suite of evolutionary processes. However, the species has been criticized on the basis of its comparatively small size at maturity (and consequent limitations in the amount of available biomass for herbivores) and on the duration and timing of its life cycle in nature. In the laboratory, we studied interactions between A. thaliana and the cabbage butterfly, Pieris rapae, in order to determine if plants are able to support the complete development of the herbivore. Plants were grown in pots from seedlings in densities of one, two, or four per pot. In each treatment, one, two, or five newly hatched larvae of P. rapae were placed on fully developed rosettes of A. thaliana. In a separate experiment, the same densities of P. rapae larvae were reared from hatching on single mature cabbage (Brassica oleracea) plants. Pupal fresh mass and survival of P. rapae declined with larval density when reared on A. thaliana but not on B. oleracea. However, irrespective of larval density and plant number, some P. rapae were always able to complete development on A. thaliana plants. A comparison of the dry mass of plants in different treatments with controls (= no larvae) revealed that A. thaliana partially compensated for plant damage when larval densities of P. rapae were low. By contrast, single cress plants with 5 larvae generally suffered extensive damage, whereas damage to B. oleracea plants was negligible. Rosettes of plants that were monitored in spring, when A. thaliana naturally grows, were not attacked by any insect herbivores, but there was often extensive damage from pulmonates (slugs and snails). Heavily damaged plants flowered less successfully than lightly damaged plants. Small numbers of generalist plant-parasitic nematodes were also recovered in roots and root soil. By contrast, plants monitored in a sewn summer plot were heavily attacked by insect herbivores, primarily flea beetles (Phyllotreta spp.). These results reveal that, in natural populations of A. thaliana, there is a strong phenological mismatch between the plant and most of its potential specialist insect herbivores (and their natural enemies). However, as the plant is clearly susceptible to attack from non-insect generalist invertebrate herbivores early in the season, these may be much more suitable for studies on direct defense strategies in A. thaliana.