Untangling associations between chironomid taxa in Neotropical streams using local and landscape filters

1. Analyses of species association have major implications for selecting indicators for freshwater biomonitoring and conservation, because they allow for the elimination of redundant information and focus on taxa that can be easily handled and identified. These analyses are particularly relevant in the debate about using speciose groups (such as the Chironomidae) as indicators in the tropics, because they require difficult and time‐consuming analysis, and their responses to environmental gradients, including anthropogenic stressors, are poorly known. 2. Our objective was to show whether chironomid assemblages in Neotropical streams include clear associations of taxa and, if so, how well these associations could be explained by a set of models containing information from different spatial scales. For this, we formulated a priori models that allowed for the influence of local, landscape and spatial factors on chironomid taxon associations (CTA). These models represented biological hypotheses capable of explaining associations between chironomid taxa. For instance, CTA could be best explained by local variables (e.g. pH, conductivity and water temperature) or by processes acting at wider landscape scales (e.g. percentage of forest cover). 3. Biological data were taken from 61 streams in Southeastern Brazil, 47 of which were in well‐preserved regions, and 14 of which drained areas severely affected by anthropogenic activities. We adopted a model selection procedure using Akaike’s information criterion to determine the most parsimonious models for explaining CTA. 4. Applying Kendall’s coefficient of concordance, seven genera (Tanytarsus/Caladomyia, Ablabesmyia, Parametriocnemus, Pentaneura, Nanocladius, Polypedilum and Rheotanytarsus) were identified as associated taxa. The best‐supported model explained 42.6% of the total variance in the abundance of associated taxa. This model combined local and landscape environmental filters and spatial variables (which were derived from eigenfunction analysis). However, the model with local filters and spatial variables also had a good chance of being selected as the best model. 5. Standardised partial regression coefficients of local and landscape filters, including spatial variables, derived from model averaging allowed an estimation of which variables were best correlated with the abundance of associated taxa. In general, the abundance of the associated genera tended to be lower in streams characterised by a high percentage of forest cover (landscape scale), lower proportion of muddy substrata and high values of pH and conductivity (local scale). 6. Overall, our main result adds to the increasing number of studies that have indicated the importance of local and landscape variables, as well as the spatial relationships among sampling sites, for explaining aquatic insect community patterns in streams. Furthermore, our findings open new possibilities for the elimination of redundant data in the assessment of anthropogenic impacts on tropical streams.     

The spring development of phytoplankton in Lake Erken

SUMMARY. In Lake Erken there is a regular phytoplankton peak at ice-breakup in the spring. Pechlaner (1970) studied the spring outburst of 1960. We carried out a similar study in 1973, when the climatic factors were completely different, with only 10 cm of ice and almost no snow. Thus, due to light penetration, there was a high phytoplankton biomass under the ice as early as March.
Stephanodiscus astraea (Ehr.) Grun. and Asterionella formosa Hass. dominated the biomass during the spring development in 1973 instead of the normally dominating S. hantzschii v. pusillus Grun.
The nutrient decrease was slower in 1973 than in 1960. A comparison of carbon assimilation and the decrease of nitrate and phosphate indicate sufficient nutrient supply in 1973. In 1960, the population grew logarithmically until the nutrients became limiting. In 1973, the average biomass was greater, but the mean probable primary production was only half that of 1960. From the activity coefficients for the 2 years it is also clear that, in 1960, S. hantzschii v. pusillus was highly productive during its short but intensive growth period. Its minute size and high surface/volume ratio enabled it to take up nutrients rapidly and efficiently. The chlorophyll content of S. astraea in 1973 was only half as much as that of S. hantzschii v. pusillus in 1960. Since the light conditions under the ice in March 1973 were more unfavourable than during the exponential phase of 1960, production was much lower.     

Factors Controlling the Seasonal Variation of Nitrate in Lake Erken

The seasonal variation of the nitrate concentration in the mesotrophic Lake Erken is markedly regular and shows some important differences compared with that of phosphate. Nitrification occurs mainly at the sediment surface. Nitrate accumulates when the nitrification-denitrification sequence is broken at a time when the nitrate assimilation is small. This occurs in Lake Erken during autumn turnover.     

Pelagic growth and colony division of Gloeotrichia echinulata in Lake Erken

Gloeotrichia echinulata colony development was monitored inLake Erken, Sweden and studied in enclosure experiments. Significantcolonial division did not occur in mesh bags, although the abundanceof the pelagic population in the lake increased during the experimentalperiods. On the basis of these findings, it is suggested thatcirculation of G. echinulata to deeper nutrient rich water supportspelagic growth. In support of this, a large part of the buoyantG. echinulata colonies in Lake Erken was found at several metersdepth. In an experiment with nutrient additions, the only treatmentthat favoured G. echinulata development was additions of phosphate,nitrate and iron. Trace element additions had a negative effecton the development of G. echinulata. On the basis of these findings,the nutritional requirements of G. echinulata are discussed.     

Pelagic growth and colony division of Gloeotrichia echinulata in Lake Erken

The Authors     

Growth and phosphorus uptake of summer phytoplankton in Lake Erken (Sweden)

The thermal stratification in Lake Erken was short and relativelyunstable in 1989. Changes in the species composition of thephytoplankton between early May and August followed the generalsuccession pattern outlined for other temperate lakes. Fast-growing,r-strategist cryptophytes, dominant in the early phase of succession,could be separated sufficiently by 12 µm membrane filtersfrom larger K-strategists like Ceratium hirundinella and Gloeotrichiaechinulata which dominated in July. Under more turbulent conditions,the biomass of diatoms increased, and these species were also>12 µm. Growth rates of the phytoplankton and thoseof the two size groups were sensitive to the species composition,but fitted reasonably to the Droop model. Long turnover timesof orthophosphate in the water, the Phosphorus Deficiency Indicatordefined here as the ratio of the light-saturated rate of photosynthesisand the conductivity coefficient of phosphate uptake, and relativegrowth rates generally indicated low P-deficiency. Moderatedeficiency was observed in late July, towards the end of thestratification period. Steady-state net P-uptake rates werecalculated from the Droop model and compared with instantaneousnet P-uptake rates estimated from ³²P uptake kinetics by thelinear force-flow relationship of Falkner et al. (Arch. Microbiol.,152, 353–361, 1989). The two data sets showed surprisinglysimilar seasonal trends. Depletion of epilimnetic soluble reactivephosphorus (SRP) resulted in enhanced utilization of intracellularlystored P. Such periods were, however, interrupted by elevatedSRP inputs to the epilimnion that led to luxury P uptake anda low incidence of P deficiency.     

Fatty acid biosynthesis and dietary regulation in pulmonary adenomas.

Studies of fatty acid metabolism in mouse pulmonary adenomas demonstrate that the alveolar type II cell tumors synthesize fatty acids at a greater rate than either normal or host lungs. This is reflected in elevated levels of both acetyl-CoA (coenzyme A) carboxylase and fatty acid synthase. Carboxylase activity is 4.4-fold, and synthase activity is 7.9-fold higher in the adenomas than normal tissue. Both enzymes from adenomas respond to dietary manipulation in a manner that is qualitatively similar to normal tissue, indicating that the adenomas maintain metabolic control over fatty acid biosynthesis and, therefore, constitute a useful model for normal type II cells. These data suggest that alveolar type II cells have a greater capacity for fatty acid biosynthesis than other cell types of normal lung.     

Fatty acid binding proteins from different tissues show distinct patterns of fatty acid interactions

Fatty acid binding proteins (FABP) form a family of proteins displaying tissue-specific expression. These proteins are involved in fatty acid (FA) transport and metabolism by mechanisms that also appear to be tissue-specific. Cellular retinoid binding proteins are related proteins with unknown roles in FA transport and metabolism. To better understand the origin of these tissue-specific differences we report new measurements, using the acrylodated intestinal fatty acid binding protein (ADIFAB) method, of the binding of fatty acids (FA) to human fatty acid binding proteins (FABP) from brain, heart, intestine, liver, and myelin. We also measured binding of FA to a retinoic acid (CRABP-I) and a retinol (CRBP-II) binding protein and we have extended to 19 different FA our characterization of the FA-ADIFAB and FA-rat intestinal FABP interactions. These studies extend our previous analyses of human FABP from adipocyte and rat FABPs from heart, intestine, and liver. Binding affinities varied according to the order brain approximately myelin approximately heart > liver > intestine > CRABP > CRBP. In contrast to previous studies, no protein revealed a high degree of selectivity for particular FA. The results indicate that FA solubility (hydrophobicity) plays a major role in governing binding affinities; affinities tend to increase with increasing hydrophobicity (decreasing solubility) of the FA. However, our results also reveal that, with the exception of the intestinal protein, FABPs exhibit an additional attractive interaction for unsaturated FA that partially compensates for their trend toward lower affinities due to their higher aqueous solubilities. Thermodynamic potentials were determined for oleate and arachidonate binding to a subset of the FABP and retinoid binding proteins. FA binding to all FABPs was enthalpically driven. The DeltaH degrees values for paralogous FABPs, proteins from the same species but different tissues, reveal an exceptionally wide range of values, from -22 kcal/mol (myelin) to -7 kcal/mol (adipocyte). For orthologous FABPs from the same tissue but different species, DeltaH degrees values were similar. In contrast to the enthalpic dominance of FA binding to FABP, binding of FA to CRABP-I was entropically driven. This is consistent with the notion that FA specificity for FABP is determined by the enthalpy of binding. Proteins from different tissues also revealed considerable heterogeneity in heat capacity changes upon FA binding, DeltaC(p) values ranged between 0 and -1.3 kcal mol(-1) K(-1). The results demonstrate that thermodynamic parameters are quite different for paralogous but are quite similar for orthologous FABP, suggesting tissue-specific differences in FABP function that may be conserved across species.     

Ceratium in Lake Erken: vertical distribution, migration and form variation

External morphological features and growth characteristics of the dinoflagellates Ceratium hirundinella and C. furcoides were investigated in relation to the environmental conditions in Lake Erken. Three distinct population maxima were distinguished, one in June, one in July, and one in September. C. hirundinella dominated the spring and summer populations. C. furcoides was rare in June, but it continuously increased and composed ca. 18% of the Ceratium-cetts in the autumn. The size of a C. hirundinella decreased during the investigation period and a form with a long horn disappeared in June. Ceratium was most numerous during the warmer periods in summer when a distinct thermocline appeared and before the turnover period in September. The alga preferred depths down to 3 m where the blue light dominated and the following parametric magnitudes could be measured: oxygen contents >5 mg 1^-1, pH >7, HCO₃, >1.7 meq. · 1^-1, and a specific conductivity of ca. 250 mS · cm^-1. The algal growth periods displayed doubling times of 2.63 and 4.04 days at surface temperatures of 19°C and 15°C, respectively. The water transparency decreased 3.8 m when Ceratium reached cell densities of 13 individuals · ml^-1 (0–10 m depth). Its vertical migration demonstrated a dial rhythm with accumulation of cells in the surface waters during the day. Complicated patterns of surface avoidance occurred in clear weather and under wind stress.     

Fatty acid composition and content in chironomid species at various life stages dominating in a saline Siberian lake

This paper studies the fatty acid (FA) composition and content of essential polyunsaturated fatty acids (PUFAs) in the biomass of larvae and adults of chironomids from the saline Shira Lake. Species of different genera significantly differ in their larvae FA composition and essential PUFA content, and they also occupy different ecological niches: Chironomus species with a low PUFA content (0.2–0.3 mg g^–1 of wet weight) inhabit a deepwater zone of the lake, while Glyptotendipes barbipes species that were richer in PUFA (2.3 mg g^–1 of wet weight) dwell in the littoral of the lake. The biochemical differences are likely related to different feeding spectra of these taxa and can also be explained by the phylogenetic factor. A comparison does not find differences in the PUFA content in larvae and adults in the samples of the same species G. barbipes; i.e., we do not confirm the data on an increase in the content of these acids during the metamorphosis of chironomids. Thus, the data on the PUFA content in larvae can be used in calculations of PUFA fluxes through chironomid emergence from water bodies; however, the taxonomic affiliation of the emerged chironomids should be taken into consideration due to the high variability in the PUFA content in Chironomidae species.     

The use of fatty acid biomarkers to reflect dietary intake

PURPOSE OF REVIEW: This review compares fatty acid biomarkers to assess compliance in dietary intervention trials with their application in epidemiological studies. RECENT FINDINGS: Although many studies have used fatty acid biomarkers to assess compliance in short-term dietary intervention trials and habitual diets in observational studies, there is little information on the reliability and comparability of these measures. In this review, we summarize the usefulness and limitations of fatty acid biomarkers in clinical and epidemiological studies. As there are very few recent publications in this area, a complete literature review is provided. SUMMARY: Several options are available for the biological assessment of dietary fatty acids. The type of study (short or long-term), the metabolic characteristics and expected variability in the fatty acids of interest are major considerations when determining which tissues reflect a better measure of true intake. Certain fatty acids may not be suitable to assess differences in intake under non-isocaloric conditions and when trying to identify small differences. Serum cholesterol ester is the most suitable serum fraction to assess short-term dietary compliance, but given the multiple factors that affect response, the quantification of compliance should be interpreted with caution. Adipose tissue is the biomarker of choice for long-term intake, but a preferred blood constituent (plasma versus erythrocytes) is difficult to establish given the data available to date. Future studies should explore the use of whole blood as an alternative choice to measure fatty acid intake in epidemiological studies.     

Fatty acid retention under temporally heterogeneous dietary intake in a cladoceran

Omega‐3 (ω3) and ‐6 (ω6) polyunsaturated fatty acids (PUFA) are essential for all aquatic animals, but their dietary availability can be highly heterogeneous in space and time. The way consumers retain PUFA across such heterogeneous feeding conditions remains poorly understood. In a series of feeding experiments, we investigated how retention efficiencies (i.e. amount in consumer biomass/amount ingested) of PUFA and bulk carbon responded to heterogeneous PUFA intake in Daphnia magna. Heterogeneous PUFA intake was achieved by exposing D. magna to algal diets of different PUFA content and composition for specific time periods. The retention efficiency of carbon did not change among dietary treatments. At shorter exposure to PUFA‐rich diet, retention efficiencies of most PUFA were 2–3 times higher than that of bulk carbon, clearly indicating PUFA bioaccumulation in D. magna. Increasing exposure to PUFA‐rich diet caused exponential decrease of retention efficiencies for most PUFA. However, D. magna receiving more PUFA were richer in these compounds despite lower retention efficiency. Eicosapentaenoic (20:5ω3) and arachidonic acid (20:4ω6) and their precursors were always supplied in the same proportions (3.6:1), but the 20:5ω3/20:4ω6 ratio in D. magna (an important measure of nutritional quality for consumers) increased with exposure time to these PUFA from 2.2:1 to 3.8:1, thus eventually matching the diet. Our results suggest that D. magna is an efficient gatherer, accumulator, and repository of PUFA under low/fragmented dietary availability. However, at higher availabilities, PUFA are not always bioaccumulated in D. magna. Hence, the efficiency of PUFA transfer by daphnids in food webs may depend on temporal PUFA availability and its range of variation. Finally, we show that heterogeneity in PUFA intake may also affect higher trophic levels by influencing nutritionally critical PUFA ratios of zooplankton.     

Assessing Phytoplankton and Bacterioplankton Production During Early Spring in Lake Erken, Sweden

The spring development of both phytoplankton and bacterioplankton was investigated between 18 April and 7 May 1983 in mesotrophic Lake Erken, Sweden. By using the lake as a batch culture, our aim was to estimate, via different methods, the production of phytoplankton and bacterioplankton in the lake and to compare these production estimates with the actual increase in phytoplankton and bacterioplankton biomass. The average water temperature was 3.5°C. Of the phytoplankton biomass, >90% was the diatom Stephanodiscus hantzchii var. pusillus, by the peak of the bloom. The ¹⁴C and O₂ methods of estimating primary production gave equivalent results (r = 0.999) with a photosynthetic quotient of 1.63. The theoretical photosynthetic quotient predicted from the C/NO₃ N assimilation ratio was 1.57. The total integrated incorporation of [¹⁴C]bicarbonate into particulate material (>1 μm) was similar to the increase in phytoplankton carbon determined from cell counts. Bacterioplankton increased from 0.5 × 10⁹ to 1.52 × 10⁹ cells liter⁻¹ (~0.5 μg of C liter⁻¹ day⁻¹). Estimates of bacterioplankton production from rates of [³H]thymidine incorporation were ca. 1.2 to 1.7 μg of C liter⁻¹ day⁻¹. Bacterial respiration, measured by a high-precision Winkler technique, was estimated as 4.8 μg of C liter⁻¹ day⁻¹, indicating a bacterial growth yield of 25%. The bulk of the bacterioplankton production was accounted for by algal extracellular products. Gross bacterioplankton production (production plus respiration) was 20% of gross primary production, per square meter of surface area. We found no indication that bacterioplankton production was underestimated by the [³H]thymidine incorporation method.     

Fatty acids in the species of several zygomycete taxa

The composition of fatty acids synthesized de novo by thirty strains of zygomycetes from various taxa was studied. The qualitative fatty acid compositions of the fungal lipids were found to be virtually identical, but there were significant differences in the contents of individual acids. Highly active producers of essential C18 fatty acids, with their content exceeding 30-40% of total fatty acids, were discovered among the fungi of the families Mucoraceae, Pilobolaceae, and Radiomycetaceae. Linoleic acid was found to predominate in the fungi of the genera Radiomyces, Mycotypha, and Circinella, and linolenic acid (identified as its gamma-isomer by gas-liquid chromatography), in the fungi of the genera Absidia, Circinella, Pilaira, and Hesseltinella. The total yield (mg/l) of bioactive acids (C18:3, C18:2, C18:1) varied from 761.4 in Pilaira anomala to 3477.9 in Syncephalastrum racemosum; the total yield of essential acids, from 520.7 in Pilaira anomala to 1154.5 in Hesseltinella vesiculosa; of linoleic acid, from 279.7 in Pilaira anomala to 836.3 in Mycotypha indica; and of linolenic acid, from 120.8 in Mycotypha indica to 708.0 in Hesseltinella vesiculosa. The data on the efficient synthesis of these acids make the actively producing strains promising for biotechnological synthesis of commercially valuable lipids. Linderina pennispora VKM F-1219, a zygomycete of the family Kickxellaceae, which was earlier singled out into the order Kickxellales [12], was shown to differ from zygomycetes of the order Mucorales in having a high content of cis-9-hexadecenoic (palmitoleic) acid, reaching 37.0% of the fatty acid total.     

The Availability of Phosphorus and the Species Composition of the Spring Phytoplankton in Lake Erken

The spring development of phytoplankton and the phosphorus content were monitored intensively in Laken Erken during the springs of 1979 and 1980. The dominant species were dinoflagellates, mainly Woloszynskia ordinata and Peridinium aciculiferum, during the entire spring of 1979. The long period of ice-cover (21 weeks) favoured the motile species, which were able to utilize the available light immediately below the ice. A considerable vertical migration was noticed in March 1979. These large and slow-growing algae were able to store luxury phosphorus, and surplus phosphorus concentrations up to 12 μg P/l were measured, which corresponded to an algal content of 10 μg P/mg C. These values were more than twice as high as those recorded earlier in Lake Erken. Although a spring outburst of diatoms did not occur in 1979 and 1980, the algae were phosphorus-limited in May, as indicated by high alkaline phosphatase activity, low algal surplus phosphorus content and high inorganic N : P ratios.     

The role of Gloeotrichia echinulata in the transfer of phosphorus from sediments to water in Lake Erken

The abundance of Gloeotrichia echinulata colonies in the sediments of Lake Erken and their phosphorus content were investigated to determine the contribution of Gloeotrichia colonies to total sediment phosphorus. Moreover, the potential size of the algal inoculum and the migration to the water during summer were estimated.The surplus phosphorus content of the resting colonies in the sediment was about 45% of total phosphorus, which maximized at 8.5 µg P (mg dw)^–1 or 81 ng P colony^–1. The C:P ratio (by weight) in the early colonies appearing in the lake water was 50:1, while the ratio stabilized at 150 during the major migration period. The internal supply of surplus phosphorus was used during the pelagic growth of the colonies.The internal phosphorus loading to the epilimnion of Lake Erken due to Gloeotrichia migration could, from the measurements of the increase in particulate epilimnetic phosphorus, be estimated at 40 mg P m ^–2 or 2.5 mg P m^–2 d^–1 in late July and early August. Determination of the number of colonies in the sediment before and during the migration verified this value to be a conservative estimate of the internal phosphorus loading due to Gloeotrichia migration to the epilimnion in Lake Erken.The sediment P content calculated from the P concentration in early epilimnion colonies resulted in a value of 35 µg P (g dw)^–1 as a maximum. This corresponds to only 3% of the total phosphorus content in Lake Erken sediment.     

Gender differences in the cardiac response to dietary conjugated linoleic acid isomers

The present study was undertaken to assess the heart function, by the in vivo catheterization technique, of healthy male and female Sprague-Dawley rats fed different conjugated linoleic acid (CLA) isomers, (cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12)) individually and in combination (50:50 mix as triglyceride or fatty acids) from 4 to 20 weeks of age. Whereas the triglyceride form of the CLA isomer mix lowered the heart rate, the rate of contraction (+dP/dt) and rate of relaxation (-dP/dt), systolic and diastolic pressures, mean arterial pressure, and the left ventricular systolic pressure were higher in male rats as compared with all the other dietary groups. In contrast, there were no significant effects in the cardiac function of the female rats in response to the CLA isomer mix in triglyceride form. Whereas the heart rate, +dP/dt, and left ventricular systolic pressure were lower in male rats fed the t10,c12 CLA isomer alone, the heart rate of the female rats was higher, but the systolic pressure, +dP/dt, and mean arterial pressure were lower compared with the control group. Also, the left ventricular end-diastolic pressure was specifically higher in the female rats in response to free fatty acids-containing CLA mix. Furthermore, an additive effect of the free fatty acids-containing CLA mix was seen in the +dP/dt and -dP/dt of female rats compared with the control group. These results indicate that CLA isomers exert differential effects on heart function and suggest the need for a complete evaluation of the benefits, interactions, and potential side effects of each isomer.