Structure of planktonic microbial food web in a brackish stratified Siberian lake

The distribution of primary components of the microbial community (autotrophic pico- and nanoplankton, phototrophic bacteria, heterotrophic bacteria, microscopic fungi, heterotrophic flagellates, ciliates and heliozoa) in the water column of Lake Shira, a steppe brackish-water, stratified lake in Khakasia, Siberia (Russia), were assessed in midsummer. Bacterioplankton was the main component of the planktonic microbial community, accounting for 65.3 to 75.7% of the total microbial biomass. The maximum concentration of heterotrophic bacteria were recorded in the monimolimnion of the lake. Autotrophic microorganisms contributed more significantly to the total microbial biomass in the pelagic zone (20.2–26.5%) than in the littoral zone of the lake (8.7–14.9%). First of all, it is caused by development of phototrophic sulphur bacteria at the oxic-anoxic boundary. The concentrations of most aerobic phototrophic and heterotrophic microorganisms were maximal in the upper mixolimnion. Heterotrophic flagellates dominated the protozoan populations. Ciliates were minor component of the planktonic microbial community of the lake. Heterotrophic flagellates were the most diverse group of planktonic eucaryotes in the lake, which represented by 36 species. Facultative and obligate anaerobic flagellates were revealed in the monimolimnion. There were four species of Heliozoa and only three of ciliates in the lake.     

Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis

Summary The mean stable-carbon isotope ratios (¹³C) for polar bear (Ursus maritimus) tissues (bone collagen –15.7, muscle –17.7, fat –24.7) were close to those of the same tissues from ringed seals (Phoca hispida) (–16.2, –18.1, and –26.1, respectively), which feed exclusively from the marine food chain. The ¹³C values for 4 species of fruits to which polar bears have access when on land in summer ranged from –27.8 to –26.2, typical of terrestrial plants in the Arctic. An animal's ¹³C signature reflects closely the ¹³C signature of it's food. Accordingly, the amount of food that polar bears consume from terrestrial food webs appears negligible, even though some bears spend 1/3 or more of each year on land during the seasons of greatest primary productivity.     

Evaluation of Microcystis as food for zooplankton in a eutrophic lake

Four experiments were conducted to evaluate Microcystis as food for zooplankton in Lake Kasumigaura, and the following results were obtained. (1) Moina micrura (Cladocera) showed little growth and no reproduction when the animal was reared with Microcystis cultured in the laboratory. The animal did not grow nor reproduce well when Chlorella was mixed with Microcystis as food. (2) Moina micrura assimilated Microcystis much less than Chlorella when the animal fed on single species of Microcystis or a mixture with Chlorella. (3) Microcystis collected from Lake Kasumigaura could not be utilized by Moina micrura even though the colonies were broken up into edible sizes. However, the alga turned into utilizable food when it was decomposed. (4) No inhibitors of Moina micrura population growth could be found in the non-filtered water of Lake Kasumigaura where Microcystis was blooming heavily. Decomposed Microcystis seemed to be utilized by zooplankton as an important food source in Lake Kasumigaura.     

Photoperiod and food regulate termination of diapause in the squash bug, Anasa tristis

The squash bug, Anasa tristis DeGeer (Heteroptera: Coreidae), is a major pest of cultivated cucurbits in much of North America. Its seasonal population dynamics are determined in large part by the early season phenological adaptations of the overwintered adults. Squash bugs were maintained on pumpkin, Cucurbita moschata Duchesne (Cucurbitaceae), seedlings. Factors influencing the termination of diapause in squash bugs were studied. Squash bugs transferred from outdoors to long-day conditions during their prediapause period in October (when the respiratory rate declines to diapause levels) required longer to terminate diapause than squash bugs transferred in the winter after the prediapause period was completed. Females did not oviposit after up to 150 days in short-day conditions. Squash bugs maintained outdoors under natural photoperiods remained in diapause until at least late April. Food was shown to be necessary for the prompt termination of diapause.

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Résumé A. tristis (Hétéropt.: Coreidae) est un ravageur important des cucurbitacées dans une grande partie de l'Amérique du Nord, particulièrement de Cucurbita spp. Les événements phénologiques du début de la saison conditionnent la dynamique de population pour la saison entière. Cette étude concerne l'influence de la photopériode et de l'alimentation dans l'achèvement de la diapause. Les adultes ont été maintenus sur des plantules de Cucurbita moschata Duchesne (var. Libbey's Select). La diapause était établie par la mesure du taux respiratoire et par l'absence de ponte. La diapause était surveillée chez des insectes maintenus à l'extérieur en conditions naturelles, leurs taux respiratoires se maintenaient au taux correspondant à la diapause jusqu'à la fin avril au moins. Placés après novembre en jours longs et à 25°C, la diapause s'interrompait rapidement. Ceux transférés en jours longs plus tôt ont interompu leur diapause mais ont demandé plus de temps pour réagir au changement de photopériode. Transférés à 25°C mais en jours courts, leur diapause n'était pas interrompue jusqu'à la fin de l'expérience 150 jours plus tard. L'alimentation est nécessaire pour une interruption rapide de la diapause en jours longs. L'alimentation associée à des jours longs ou croissants semble nécessaire à l'achèvement de la diapause de A. tristis dans les conditions naturelles.

     

An in situ test of the effects of food quality on Daphnia population growth

The temporal variation of the surface deposit feeders in a mudflat of Chuwei Mangrove Forest showed a significant input of populations from the recruitments in the spring. The chemical analysis of the sediment in the top 8 cm showed that the sedimentary organic content had a subsurface maximum value in the deeper layer in most cases. Most of the temporal variations in the organic carbon and nitrogen contents occurred in the top few centimeters. The high C:N ratio and low organic nitrogen content in the sediment suggests the supply of carbon (or energy) to the benthos was low. The increase of labile protein content in the deep layer might be due to the downcore transport of sediment nutrients by the bioturbation. Laboratory growth experiment suggests that some the chemical characters examined in this study may represent the sediment nutrients to the animals.     

Life history responses of the cladoceran Ceriodaphnia cf. dubia to variation in food concentration

The effect of five different food concentrations on the life history of Ceriodaphnia cf. dubia was examined by following cohorts of 25 individuals from <24 hours until the death of all individuals. The food concentrations used in the study were chosen to reflect densities found in lentic freshwater systems and those commonly used in toxicity testing, and ranged from 1 × 10⁴ cells mL^-1 to 15 × 10⁴ cells mL^-1. Food concentration was found to have a significant effect (p<0.05) on several life history parameters, with a decrease in food concentration leading to a decrease in brood sizes and population growth rate, and an increase in longevity. Population growth rates varied from approximately 0.39 neonates d^-1 to 0.54 neonates d^-1, while mean lifespan ranged from 16.7 days to 42.9 days. A decrease in food concentration also led to an increase in the mean generation time.     

Olfactory discrimination of eight food flavors in the capuchin monkey (Cebus apella): Comparison between fruity and fishy odors

Operant conditioning was used to investigate how primates discriminate between odor qualities. Eight artificial food flavors, selected from either a “Fishy” or “Aroma/Fruity” category, were used. During the presence of one of the two odors S+ or S−, the monkey was reinforced by pushing a response key when S + was presented. The tufted capuchins discriminated most accurately when both odors were Aroma. Discrimination was more accurate when S+ was Fruity odor and S− was Fishy odor. When both odors were Fishy, discrimination could not be acquired in 20 sessions. All of the flavors used, except apple, were novel for the subjects, which suggests that capuchins can innately discriminate among them. The data also suggest that Aroma odors are more salient than Fishy odors. The results also suggested an innate aversion to Fishy odors.     

An invaded wet ecosystem in Central Italy: An arrangement and evidence for an alien food chain

The aim of this work is to provide an account of alien species richness and composition in a remnant Mediterranean coastal wetland of Central Italy. Data were obtained from different taxa-specific methods, in 2001–2005 (terrestrial vertebrates) and in 2005 (fish, arthropoda, mollusca). Among the 353 species sampled, 17 (4.8 %) are aliens (7.1% if we consider only vertebrates).Data on abundance, introduction type and status of alien species are reported. A crustacean, Procambarus clarkii, a fish, Gambusia sp. and three rodents, Myocastor coypus, Rattus norvegicus and Mus domesticus are the naturalized invasive species that locally could constitute a threat on economic and ecological levels. Data on Agapornis nigrigenis and Quelea cardinalis represent the first records for Italy. We also report evidence of a food chain on three levels, among the most invasive species (predation of Gambusia sp. by Procambarus clarkii and of Rattus norvegicus on Procambarus clarkii).      

Phylogenetic in situ/ex situ analysis of a sulfur mat microbial community from a thermal sulfide spring in the north Caucasus

A phylogenetic in situ/ex situ analysis of a sulfur mat formed by colorless filamentous sulfur bacteria in a thermal sulfide spring (northern spur of the main Caucasian ridge) was carried out. Nine phylotypes were revealed in the mat. Thiothrix sp. and Sphaerotilus sp. were the dominant phylotypes (66.3% and 26.3%, respectively). The 16S rRNA gene nucleotide sequence of Sphaerotilus sp. phylotype from the clone library was identical to the sequences of the seven Sphaerotilus strains isolated from the same source. A very high degree of similarity of Sphaerotilus strains revealed by ERIC-PCR fingerprints indicated little or no population diversity of this species in the mat. Thiothrix phylotype from the clone library and two Thiothrix strains isolated from the same mat sample differed in one to three nucleotides of 16S rRNA genes; this is an indication of this organism’s population variability in the mat. 16S rRNA genes of the strains and clones of Thiothrix sp. exhibited the highest similarity (ca. 99%) with Thiothrix unzii; the strains and clones of Sphaerotilus had 99% similarity with the type species Sphaerotilus natans (the only species of this genus) and therefore can be assigned to this species. The minor seven components belong to the phylotypes from the Proteobacteria (3%), as well as the Chlorobia, Cyanobacteria, Clostridia, and Bacteroidetes phylogenetic groups, each of them constituting not more than 1%. Intracellular accumulation of elemental sulfur by Sphaerotilus similar to other filamentous sulfur bacteria was demonstrated for the first time (both in the population of the sulfur spring and in cultures with sulfide). Although mass growth of Sphaerotilus and Thiothrix is typical of bacterial populations of anthropogenic ecosystems (the activated sludge of treatment facilities), stable communities of these bacteria have not been previously found in the sulfur mats or “threads” of natural sulfide springs.     

Food and feeding behaviour of a planktivorous cyprinid, Pelecus cultratus (L.), in a shallow eutrophic lake, Neusiedler See (Austria)

Pelecus cultratus (razor fish), a cyprinid fish, has become a dominant species in Neusiedler See. Gut content analyses of 400 specimens collected in 1989 and 1990 showed that Pelecus fed mainly on large zooplankton (Diaphanosoma, Leptodora and Arctodiaptomus), although their diet also included Insecta (larvae, pupae and adults) and Arachnida (spiders), occasionally small fishes. Comparison of the relative abundance of the zooplankton species in the stomach to the lake indicated that Pelecus strongly selected cladocerans over copepods, and fed mostly on large-sized individuals of Diaphanosoma, Leptodora and Arctodiaptomus. The fish showed a significant positive selectivity only for individuals of Diaphanosoma > 1.0 mm and Leptodora > 4.0 mm. In contrast, selectivity increased continuously in relation to the diameter of the compound eye of both prey species. This suggested that prey visibility was a key factor in determining the prey selectivity by Pelecus. It also seems likely that the persistence of the Leptodora population in Neusiedler See can be attributed to negligible predation pressure on the smaller sized individuals of this species.