The Influence of Toxic and Filamentous Blue-green Algae on Feeding and Population Growth of the Rotifer Brachionus rubens

The effect of toxic and of filamentous blue-green algae on feeding and population growth of the rotifer Brachionus rubens was investigated in laboratory experiments. A toxic strain of Microcystis aeruginosa was ingested, but rotifers cultured with Microcystis died faster than nonfed controls. The rigid filaments of Cylindrospermopsis raciborskii were not ingested, reduced the ingestion of simultaneously offered algae, and depressed population growth rates. The soft filaments of Anabaena flos-aquae were ingested at a moderate rate, did not reduce ingestion of other algae, and were used as an additional food in population growth experiments.     

On the safety of Aspergillus niger--a review

Aspergillus niger is one of the most important microorganisms used in biotechnology. It has been in use already for many decades to produce extracellular (food) enzymes and citric acid. In fact, citric acid and many A. niger enzymes are considered GRAS by the United States Food and Drug Administration. In addition, A. niger is used for biotransformations and waste treatment. In the last two decades, A. niger has been developed as an important transformation host to over-express food enzymes. Being pre-dated by older names, the name A. niger has been conserved for economical and information retrieval reasons and there is a taxonomical consensus based on molecular data that the only other common species closely related to A. niger in the Aspergillus series Nigri is A. tubingensis. A. niger, like other filamentous fungi, should be treated carefully to avoid the formation of spore dust. However, compared with other filamentous fungi, it does not stand out as a particular problem concerning allergy or mycopathology. A few medical cases, e.g. lung infections, have been reported, but always in severely immunocompromised patients. In tropical areas, ear infections (otomycosis) do occur due to A. niger invasion of the outer ear canal but this may be caused by mechanical damage of the skin barrier. A. niger strains produce a series of secondary metabolites, but it is only ochratoxin A that can be regarded as a mycotoxin in the strict sense of the word. Only 3–10% of the strains examined for ochratoxin A production have tested positive under favourable conditions. New and unknown isolates should be checked for ochratoxin A production before they are developed as production organisms. It is concluded, with these restrictions, that A. niger is a safe production organism. Electronic Publication     

Inorganic nitrogen processing and assimilation in a forested wetland

Feeding selectivity by five epilithic, case-building trichopteran species from a first-order stream was examined using laboratory experiments. Larvae had the choice of three food types: periphyton and detritus from the stream, and nettle broth as an artificial food source. Food type influenced the microdistribution of these species. Larvae were able to distinguish between different food types and showed species-specific responses to the various types of food. Drusus annulatus, Micrasema longulum and Apatania fimbriata favoured periphyton, while Agapetus fuscipes and Silo pallipes showed no preference for periphyton over detritus. Four of the five species examined (Apatania fimbriata was the exception) tended to avoid nettle broth. The complexity of foraging behaviour was illustrated by M. longulum. Given a choice between detritus, periphyton and periphyton with the addition of moss, they clearly preferred the latter food type, scraping mostly on the epiphytic algae. Proportions of a given species selecting periphyton were correlated with percentage areas of algae in the gut contents of that species in the field. D. annulatus, M. longulum and A. fimbriata showed the greatest preference for periphyton, and consumed the highest proportions of algae in the field. A. fuscipes and S. pallipes often selected detritus, and these species had the lowest proportions of algae, and the highest proportions of detritus, in their guts.     

Laboratory study of the grass shrimp feeding preferences

Grass shrimps are very common in various aquatic habitats, and are generally considered omnivorous. But, despite the numerous studies on interspecific trophic interactions, few studies have evaluated their feeding strategy, especially by experimental approaches.In this study, we determined, in the absence of both intra and interspecific competitive interactions, the feeding preferences of the freshwater grass shrimp Palaemonetes antennarius for the most common potential resources in its habitat. Plant and animal items were offered as food to each adult shrimp in multiple-choice laboratory experiments. Resource selection was determined under conditions of low and high food availability and related to the shrimp body size. The role of microbial colonisation in favouring detritivory was also investigated.Results of these experiments showed that P. antennarius consumed only animal items, mostly preferring the isopod Proasellus coxalis. In addition, palatability of the unselected plant remains and non-living prey was not improved by the microbial enrichment. Shrimps also resorted to cannibalism at low ration. By contrast, at high ration they specialised on a narrower range of resources, directing more their feeding efforts towards isopods. The preference ranking of the selected food types was inversely related to the average mass of the prey and varied with the shrimp body size. In particular, the number of live isopods in the diet increased exponentially with the shrimp mass at food high ration, which resulted not to be limiting. In conclusion, food availability influences the food niche of P. antennarius whose feeding strategy in the laboratory is facultative specialisation on dead and live animals rather than omnivory. Ease of handling and/or capture seems to play a role in the food preference ranking.     

Phosphorus acquisition and competitive abilities of two herbivorous zooplankton, <Emphasis Type="Italic">Daphnia pulex</Emphasis> and <Emphasis Type="Italic">Ceriodaphnia quadrangula</Emphasis>

Contrary to an expectation from the size-efficiency hypothesis, small herbivore zooplankton such as Ceriodaphnia often competitively predominate against large species such as Daphnia. However, little is known about critical feeding conditions favoring Ceriodaphnia over Daphnia. To elucidate these conditions, a series of growth experiments was performed with various types of foods in terms of phosphorus (P) contents and composition (algae and bacteria). An experiment with P-rich algae showed that the threshold food level, at which an individual’s growth rate equals zero, was not significantly different between the two species. However, the food P:C ratio, at which the growth rate becomes zero, was lower for Daphnia than for Ceriodaphnia, suggesting that the latter species is rather disfavored by P-poor algae. Ceriodaphnia showed a higher growth rate than Daphnia only when a substantial amount of bacteria was supplied together with a low amount of P-poor algae as food. These results suggest that an abundance of bacteria relative to algae plays a crucial role in favoring Ceriodaphnia over Daphnia because these are an important food resource for the former species but not for the latter.     

Exploring variation in fitness surfaces over time or space

As the number of studies estimating selection on multiple traits has increased in recent years, fitness surfaces have become a fundamental tool for understanding multivariate selection and evolution. However, rigorous statistical comparisons of multivariate selection surfaces over time or space have been limited to parametric analyses of selection coefficients estimated using a quadratic regression model. Although parametric comparisons are useful when selection is approximately linear or quadratic in nature, they are limited when confronting the complex nature of rugged fitness surfaces. Here, I present a novel solution to comparing nonparametric fitness surfaces over time or space. Using a Tucker3 tensor decomposition, which is essentially a higher order principal components analysis, I show how major features of fitness surfaces can be compared statistically. Combined with a bootstrap algorithm, I develop three statistical tests that identify (1) differences in the shape of nonparametric fitness surfaces, (2) differences in the contribution of each surface to variation in fitness across time or space, and (3) specific areas of the surfaces (trait combinations) that vary significantly over time or space. I illustrate the tensor decomposition and statistical analyses using idealized fitness surfaces.     

Possible involvement of microcystins in the unexplained mass mortalities of Lesser Flamingo (<Emphasis Type="Italic">Phoeniconaias minor</Emphasis> Geoffroy) at Lake Manyara in Tanzania

We examined the effects of food and light on the swimming behavior of nauplii of the cyclopoid Apocyclops royi (Lindberg, 1940) (Copepoda: Cyclopoida) and the calanoid Pseudodiaptomus annandalei Sewell, 1919 (Copepoda: Calanoida). Several behavioral parameters such as swimming patterns, speed, and trajectories exhibited distinct ontogenetic differences between the two species. When algae Isochrysis galbana (Haptophyta: Isochrysidales) were offered as food to the nauplii of A. royi, they showed fast circle swimming behavior, while nauplii of P. annandalei never exhibited such behavior, neither with, nor without algae. The different behavioral patterns between the nauplii of both species suggest they both have different foraging strategies in detecting and capturing food.     

Food preferences of tanypodinae larvae (Diptera: Chironomidae)

Analyses of the gut contents of larvae of three species of Tanypodinae, collected from four sites in north-east England and Scotland, invariably showed small particles (1–10 µm²), predominantly of detritus, to be more abundant than large particles (10–100 µm²), mostly algae and diatoms. No animal remains, such as carapaces, head capsules and chaetae, or vascular plant fragments were found in any of the intestines. In contrast, food-choice and growth experiments suggested that animal food (particularly Tubificidae and Chironominae larvae) was important in the tanypod diet. In the food-choice experiments, six different foods offered to small (4–7 mm long) and to large (8–12 mm long) larvae of Procladius choreus Meigen, were chosen in the following order: live Tubificidae spp.; detritus; live Chironominae larvae; a mixture of algae and diatoms; live Ostracoda spp.; and live Cladocera spp. However, when the results of the individual choices were examined, it was clear that the small larvae had consumed greater amounts of the small types of food (i.e. detritus, algae and diatoms) in comparison to the large larvae. In the growth experiment, those larvae of P. choreus reared solely on Tubificidae, detritus or Chironominae larvae thrived, while those fed on algae and diatoms, ostracods or cladocerans grew more slowly and fewer survived the experimental period.It was concluded that although Tanypodinae larvae are primarily predators with definite food preferences in ideal foraging conditions, in adverse conditions they will utilize a range of available stand-by foods, the most important of which appears to be detritus.     

A Survey of Sample Size Formulas for Pairwise and Many‐one Multiple Comparisons in the Parametric,Nonparametric and Binomial Case

We present a survey of sample size formulas derived in other papers for pairwise comparisons of k treatments and for comparisons of k treatments with a control. We consider the calculation of sample sizes with preassigned per‐pair, any‐pair and all‐pairs power for tests that control either the comparisonwise or the experimentwise type I error rate. A comparison exhibits interesting similarities between the parametric, nonparametric and binomial case.     

Isolation and characterization of six polymorphic microsatellite loci in Aspergillus niger

Certain strains of Aspergillus niger produce ochratoxin A in food and in animal feeds. Six polymorphic microsatellite markers suitable for population analysis were developed for A. niger through screening published sequences for microsatellite repeats. Polymorphism was evaluated for 28 isolates of A. niger, including toxigenic strains. Loci displayed six to 13 alleles. Investigation of cross‐species amplifications with Aspergillus carbonarius and Aspergillus japonicus showed limited success.     

Use of dried algae as a food source for zooplankton growth and nutrient release experiments

Zooplankton growth and nutrient recycling are key processes in the operation of pelagic food webs. Most studies investigating these processes rely on complex methods and often require extensive laboratory facilities. Here we introduce a technique for preserving algae by rapid drying for later use in laboratory- or field-based growth and nutrient recycling experiments. Chemostat-grown Scenedesmus acutus was rapidly dried for later experiments evaluating its nutritional composition, suitability for animal growth and potential for use in nutrient release experiments. Reconstituted dried algae had slightly lower nitrogen (N), Phosphorus (P) and protein content (% dry weight) than fresh algae, but lipid content did not differ and elemental ratios were in the range considered to indicate favorable food quality. These elemental and biochemical differences did not appear functionally important, as Daphnia magna grew identically on fresh and dried food. Freeze-dried S.acutus did not work as an alternative to oven drying as it resulted in 100% mortality. NH4 and PO4 concentrations did not change over 24 h when dried algae were resuspended in normal media or boiled lake water. However, concentrations of PO4 decreased over 24 h, suggesting chemical adsorption of PO4 to the dried algae and reinforcing the need for animal-free controls in nutrient release experiments using this approach. N and P release rates for D.magna and natural zooplankton communities were estimated using dried algae, and values were comparable to published ones. Thus, dried algae may be a useful, simple technique for studying food quality and nutrient release in environments where maintaining active algal cultures may not be practical and a constant supply of consistent quality food is needed.      

Food preference of freshwater invertebrates: comparing fresh and decomposed angiosperm and a filamentous alga

1. Fresh and decomposed Mougeotia sp. (a filamentous green alga) and Elodea nuttallii (a vascular plant) were offered as food to three species of aquatic macroinvertebrates (Lymnaea peregra, Asellus meridianus and Endochironomus albipennis) to test: (i) if filamentous algae are preferred to aquatic higher plants (hereafter, called ‘macrophytes’) and (ii), as is known for higher plants, if decomposition also results in greater palatability of filamentous algae. 2. Compared with the alga, the macrophyte in both states was of higher nutritional value. Conditioning improved the nutritional value of both food types, but especially of the macrophyte. 3. Both fresh alga and fresh macrophyte were eaten little by all animals except A. meridianus feeding upon the macrophyte. Consumption was higher for both plants in their decomposed state. However, L. peregra consumed more decomposed macrophyte than the decomposed alga. Both decomposed plants were eaten most by E. albipennis followed by A. meridianus and L. peregra. 4. Digestibility of both plants, but especially of the macrophyte, increased significantly after decomposition. The assimilation efficiencies of all animals on the fresh E. nuttallii were higher than on fresh Mougeotia sp. After decomposition, the efficiency increased significantly only on the alga. Consequently, both decomposed plants were assimilated with similar efficiency by all test animals. 5. Amongst aquatic macrophytes, the increase of their consumption and digestibility upon decomposition has hitherto been known only for vascular plants but not for filamentous algae.     

Effect of algal and animal diets on life history of the freshwater copepod <Emphasis Type="Italic">Eucyclops serrulatus</Emphasis> (Fischer, 1851)

We studied the survivorship and reproduction of the cyclopoid Eucyclops serrulatus using four diet types: algae Chlorella vulgaris and Scenedesmus acutus separately and each together with the rotifer Brachionus havanaensis. We used equal biomass (3.9 mg C l⁻¹) of C. vulgaris and S. acutus while B. havanaensis was offered at a density of 0.5 ind. ml⁻¹. Regardless of the food type, the average lifespan of female E.␣serrulatus varied from 30 to 50 days, and those of males from 22 to 27 days. When Chlorella was offered alone as food, the female lifespan was 40% lower than when fed together with B. havanaensis. The number of nauplii per female (gross reproductive rate, GRR) was higher on Scenedesmus alone than on Chlorella alone or Chlorella and Scenedesmus offered with Brachionus. Thus, GRR was not significantly influenced by the presence of rotifer in mixed diet. Net reproductive rate (R _o) and the rate of population increase (r) were similar at all the four food types. This implies that the diet-related differences of GRR did not ultimately translate to the differences in R _o or r, due to the survivorship patterns of the adult females.     

Memory and chemical communication in the orientation of two mass-recruiting ant species

Summary The relative contribution of visual and chemical components in the orientation ofLasius niger andIridomyrmex humilis (Argentine ant) workers during mass recruitment to newly discovered food sources is analyzed over short time intervals. While both species orient in response to the trail pheromone, a large number ofL. niger foragers rapidly switch to a more individual orientation, based on their memory of environmental cues.I. humilis workers, on the other hand, predominantly use collective chemical cues. The effect of the number of reinforcements on visual learning and its interference with chemical communication show that olfactory cues always prevail in the Argentine ant. InL. niger, the proportion of ants orienting to visual cues is independent of the trail concentration. Detailed observations of the trail-laying behavior of individually marked foragers show that nearly all theI. humilis workers initially lay a trail, whereas only half theL. niger foragers do so. This proportion decreases considerably with the number of trips performed byL. niger workers, while remaining constant for the Argentine ants. These results are interpreted with respect to the species' behavioral ecology.     

Herbivore-Alga Interaction Strength Influences Spatial Heterogeneity in a Kelp-Dominated Intertidal Community

There is a general consensus that marine herbivores can affect algal species composition and abundance, but little empirical work exists on the role of herbivores as modifiers of the spatial structure of resource assemblages. Here, we test the consumption/bulldozing effects of the molluscan grazer Enoplochiton niger and its influence on the spatial structure of a low intertidal community dominated by the bull kelp Durvillaea antarctica and the kelp Lessonia spicata. Through field experiments conducted at a rocky intertidal shore in north-central Chile (~30°-32°S), the edge of the grazer and algae geographic distributions, we estimated the strength and variability of consumptive effects of the grazer on different functional group of algae. We also used data from abundance field surveys to evaluate spatial co-occurrence patterns of the study species. Exclusion-enclosure experiments showed that E. niger maintained primary space available by preventing algal colonization, even of large brown algae species. The grazing activity of E. niger also reduced spatial heterogeneity of the ephemeral algal species, increasing bare space availability and variability through time in similar ways to those observed for the collective effect with other grazers. Overall, our result suggests that E. niger can be considered an important modifier of the spatial structure of the large brown algae-dominated community. Effects of E. niger on resource variability seem to be directly related to its foraging patterns, large body size, and population densities, which are all relevant factors for management and conservation of the large brown algae community. Our study thus highlights the importance of considering functional roles and identity of generalist consumers on spatial structure of the entire landscape.     

Food selection by calanoid copepods in response to between-lake variation in food abundance

1. Food selection experiments were conducted by acclimating calanoid copepods (Eudiaptomus spp.) in suspensions of natural seston and then adding pairs of dual-labelled (¹⁴C/³²P) algae. Each feeding trial measured selectivity between a small, high-quality reference alga, Chlamydomonas reinhardii, and a test alga that differed in size and/or food quality. The influence of food concentration on food selection was tested by using seston from two lakes with contrasting food abundance and by including treatments with filtered lake water ('starved’) and seston diluted with filtered water or enriched with cultured algae. 2. Copepods that had been starved or acclimated to natural seston with low food abundance preferred the larger of two labelled algae, regardless of the nutritional quality of the algae. In agreement with the predictions of an optimal diet model, however, copepods that were acclimated to high food conditions discriminated against low-quality foods, including digestion-resistant algae and dead algae. 3. Selectivity coefficients showed excellent agreement with a previous study involving the same taxa of copepods and labelled algae but in which the copepods had been acclimated to pairs of cultured algae rather than natural seston. Thus, these comparisons emphasize the importance of food availability in modulating copepod selectivity for foods that differ in nutritional quality and suggest that such behaviour occurs in nature.     

Interactions between metazoans,autotrophs, mixotrophs and bacterioplankton in nutrient‐depleted high DOC environments: a long‐term experiment

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The effects of diet mixing on consumer fitness: macroalgae, epiphytes, and animal matter as food for marine amphipods

Herbivores are thought to achieve adequate nutrition by consuming numerous species of plants or by occasionally consuming animal tissue. Although active selection of diverse foods is common in nature, the relationship between diet mixing and consumer fitness is poorly understood, especially in marine environments. We studied the fitness-based consequences of dietary mixing in the sympatric amphipods Ampithoe marcuzzii, A. valida, Cymadusa compta, and Gammarus mucronatus by measuring survivorship, growth, and fecundity of these amphipods when they were offered single species of algae, a single animal food, a mixture of algal species, or a combination of algae and animal matter. For the more sedentary, tube-building amphipods A. marcuzzii, A. valida, and C. compta, fitness on mixed algal diets was matched by fitness on at least one of the monospecific algal diets, suggesting that they could benefit from preferential feeding on those algae in the field. The more mobile amphipod, G. mucronatus, survived and grew similarly on the mixed diets and on the filamentous brown alga Ectocarpus siliculosus. However, its fecundity was significantly higher when feeding on the algal and animal mixture than on Ectocarpus alone. Additionally, for G. mucronatus, fitness on mixed algae, mixed algae plus animal matter, and animal matter alone was equivalent, although female growth (but not gonad production) was slightly lower on animal matter alone than on the mixed algae combined with animal food. Thus the more mobile amphipod, G. mucronatus, was the only species able to perform well on animal food alone. In contrast, A. valida and C. compta experienced large negative effects when limited to consuming animal matter alone. For these two species, combining algae and animal matter did not enhance fitness over combining only algae. Fitness effects of specific algal diets showed some general similarities, but also considerable variance among the amphipods. For example, E. siliculosus was generally better food than other algae for all four amphipods, whereas Sargassum filipendula was generally poor. However, A. marcuzzii did not suffer negative effects of consuming only Sargassum. The red alga Polysiphonia sp. and the green alga Enteromorpha flexuosa decreased fitness in A. marcuzzii, C. compta, and G. mucronatus, but not A. valida, and the negative effects of Polysiphonia were considerably larger for A. marcuzzii than for the other amphipods. Our data show that nutritional requirements, even among related species (e.g., A. marcuzzii and A. valida), can be dramatically different. Diet mixing may benefit more mobile consumers like Gammarus that are better able to search for different foods, and may be less important for more sedentary herbivores like Ampithoe and Cymadusa that consume, and live in close association with, individual host plants. Received: 14 September 1998 / Accepted: 22 October 1999     

Improved Estimation of the Noncentrality Parameter Distribution from a Large Number of t‐Statistics,with Applications to False Discovery Rate Estimation in Microarray Data Analysis

Summary Given a large number of t‐statistics, we consider the problem of approximating the distribution of noncentrality parameters (NCPs) by a continuous density. This problem is closely related to the control of false discovery rates (FDR) in massive hypothesis testing applications, e.g., microarray gene expression analysis. Our methodology is similar to, but improves upon, the existing approach by Ruppert, Nettleton, and Hwang (2007, Biometrics, 63, 483–495). We provide parametric, nonparametric, and semiparametric estimators for the distribution of NCPs, as well as estimates of the FDR and local FDR. In the parametric situation, we assume that the NCPs follow a distribution that leads to an analytically available marginal distribution for the test statistics. In the nonparametric situation, we use convex combinations of basis density functions to estimate the density of the NCPs. A sequential quadratic programming procedure is developed to maximize the penalized likelihood. The smoothing parameter is selected with the approximate network information criterion. A semiparametric estimator is also developed to combine both parametric and nonparametric fits. Simulations show that, under a variety of situations, our density estimates are closer to the underlying truth and our FDR estimates are improved compared with alternative methods. Data‐based simulations and the analyses of two microarray datasets are used to evaluate the performance in realistic situations.