Relationships between metal concentrations and organism size in aquatic insects

SUMMARY.

• 1 The influence of organism size on whole-body metal concentrations of eight metals was examined in aquatic insects in field and laboratory studies. Information on the partitioning of metals between adsorbed, absorbed and gut content material was also obtained.
• 2 For Co, Cr, Fe, Sb and Sc, an exponential decrease in concentration with increasing organism size was observed, indicating surface adsorption as an important mode of metal accumulation.
• 3 No, or only a slight, concentration-size relationship was found for K, Mn and Na. This is expected for metals with high absorption efficiencies and a low capacity to be adsorbed.
• 4 Clearing of the gut of the mayfly Stenonema modestum (Ephemeroptera: Heptageniidae) did not significantly after the concentration size relationship for any of the metals studied.
• 5 Studies of Cr uptake with Stenacron interpunctatum (Ephemeroptera: Heptageniidae) indicate that the concentration-size relationship is not affected by variability in the concentration of available Cr.
• 6 About 52% of the whole-body burden of Cr in S. interpunctatum was associated with gut material while at least 33% was adsorbed to the organism's exoskeleton and at most 15% was internally absorbed.

     

Macroinvertebrate functional feeding groups in the middle and lower reaches of the Buffalo River, eastern Cape, South Africa. I. Dietary variability

• 1 The question of whether the diets of twelve abundant macroinvertebrate taxa from the middle and lower reaches of the Buffalo River (eastern Cape, South Africa) were too variable to allow them to be assigned to functional feeding groups (FFGs) was addressed.
• 2 Spatial, temporal and developmental variations in diet were assessed. Foregut content analysis was used as an index to compare diets.
• 3 Foregut contents were compared from early (small) and late (large) instar larvae collected from riffles at thirteen sites in summer, and from riffles, stony backwaters and sediments at four of these sites in spring, summer, autumn and winter, in 1987.
• 4 For all individuals of all taxa, fine amorphous detritus (0.5–250 μm), was the most common dietary item. Differences in diet followed a similar pattern for all taxa. The most frequent differences in dietary content were between large and small larvae. The foreguts of large larvae contained more material, and a wider variety of rare items than small larvae. Neither species nor FFGs could be distinguished on the basis of foregut contents.
• 5 Two dietary types were recognized. The eight mayfly larvae were fine detritivores, having ingested fine detritus almost exclusively. In contrast, the two hydropsychid caddisfly larvae had ingested a mixed diet; their gut contents included chirinous invertebrate remains and other items as well as fine detritus.
• 6 Intra-specific dietary variability was not so great as to prevent these taxa from being assigned to FFGs. On the contrary, inter-specific dietary content was so similar that gut content analysis could not provide a positive basis upon which to identify FFGs.

     

Herbivory in an acid stream

• 1 Spatial and temporal variation in the distribution and feeding of non‐predatory macroinvertebrates was investigated in a first‐order, acid stream in the Ashdown Forest, southern England.
• 2 Stonefly (Nemouridae) and chironomid (Orthocladiinae) larvae were abundant on the upper surfaces of mineral substrata of three sizes (small stones, large stones, bedrock). The density of larvae in each taxonomic group did not vary among substrata of different sizes, although strong seasonal variation existed.
• 3 Nemourids and chironomids (H. marcidus) collected from the upper surfaces of substrata exhibited generalist feeding habits, consuming algae (diatoms, coccoid and filamentous green algae), detritus (biofilm matrix material and fine particulate organic matter (FPOM)) and inorganic debris.
• 4 There was spatial variation in the gut contents of nemourids. The proportion of algae in the guts of larvae often increased with the size of the substratum from which they were collected. Strong temporal variation in the composition of the diet also existed. Nemourids ingested a large quantity of attached algae and biofilm matrix from the biofilm in spring and winter, but consumed loose FPOM and associated microflora in summer and autumn.
• 5 We conclude that, in this acid stream, the trophic linkage between algae and grazers is maintained by ‘detritivorous’ stonefly and chironomid species. The relationship between the feeding habits of these larvae and other life‐history attributes, such as mouthpart morphology and mobility, is discussed.

     

Potential for passive internal dispersal: eggs of an aquatic leaf beetle survive passage through the digestive system of mallards

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Relationship between morphology and diets of six neotropical loricariids

Most loricariids are algivorous and detritivorous and play an important role in both the grazer and detritus food chains of neotropical waters. Relationships between morphological variation and diet were analysed in six syntopic species ( Rhinelepis aspera, Hypostomus regani, H. ternetzi, H. margaritifer, H. microstomus and Megalancistrus aculeatus ) fished commercially in a 10 km² area of the Upper Paraná River upstream from the Itaipu Reservoir. Species feeding on fine grained detritus use suction to obtain food, and possess a well-developed respiratory membrane, long gill rakers, rudimentary labial and pharyngeal teeth, a thin stomach wall, and a long intestine. Species feeding on coarser material (e.g. periphyton), ingest food by scraping the substratum. Their morphological characteristics are large, strong, spatulate teeth, short gill rakers, a well-developed stomach, and a shorter intestine. The first species group is composed by R. aspera while the latter by M. aculeatus and H. microstomus . The others species had an intermediary position.     

The role of lipids as feeding stimulants for shredding aquatic insects

SUMMARY.

• 1 Caddisflies (Trichoptera) that shred leaf detritus preferentially ingested lipid-coated detritus during the last larval in star. This is the interval when these insects accumulate the triglyceride reserves necessary for metamorphosis and reproduction. Early in star larvae, which do not accumulate lipids, showed no preference for any lipids. This behaviour indicates food selection based on changing nutritional needs.
• 2 Pure unsaturated 18- and 20-carbon fatty acids, either as free acids or triglycerides, were most strongly preferred. Crude lipid and the neutral lipid fraction from aquatic hyphomycete fungi, an important component of aquatic leaf detritus, were also preferred.
• 3 Tipula abdominalis (Diptera: Tipulidae) did not prefer any lipids during the last instar.

     

Lipid components and utilization in consumers of a seagrass community: An indication of carbon source

• 1.1. The lipid components of three animals, the rock crab Nectocarcinus integrifons, the rock flathead Platycephalus laevigatus and the southern garfish Hyporhamphus melanochir, feeding in the seagrass beds at Corner Inlet, Victoria, Australia have been examined in detail in order to provide further information on seagrass community structure.
• 2.2. Biological marker compounds detected within animal gut content material were used to recognize dietary sources and then utilized by community members.
• 3.3. Both H. melanochir and N. integrifons have been shown to ingest and to varying degrees incorporate seagrass lipid material, thus further confirming the importance of seagrass carbon in the Corner Inlet environment.
• 4.4. The southern sea garfish H. melanochir is observed to remove C₁₈ PUFAs (polyunsaturated fatty acids) from ingested seagrass material.
• 5.5. Seagrass sterols are altered during incorporation into the lipids of this fish.
• 6.6. Lipid-rich digestive juices play a role in the digestive processes of all three animals.
• 7.7. Components tentatively identified as (NMI) (non-methylene interrupted) fatty acids have been detected in the lipids of the garfish H. melanochir and the crab N. integrifons.
• 8.8. The fecal material of all three animals represent possible sources of these lipids (NMI acids) in Corner Inlet sediments.
• 9.9. Based on lipid compositional data, N. integrifons feeds on Posidonia australis detritus and associated epiphyte material.
• 10.10. The removal of both plant and epibiota cellular lipids along the digestive tract of the crab was observed, although structural components such as long chain mono- and α,ω-dicarboxylic acids, which have been previously recognized as seagrass marker lipids are not directly absorbed.

     

Stable carbon isotope ratios in Fundulus heteroclitus (L.) muscle tissue and gut contents from a North Carolina spartina marsh

Recent food habit and productivity research on the killifish, Fundulus heteroclitus (L.), suggests that this species is important in the movement of organic material within and out of the salt marsh ecosystem. The stable carbon isotope ratios of Fundulus muscle tissue and gut contents were measured seasonally to determine the carbon source of the killifish. For muscle δ¹³C values ranged from -13.9% to -15.8% and -15.8% to -18.4% for gut contents, suggesting differential assimilation of ingested material. Muscle tissue indicate that assimilated carbon probably originated from a mixture of benthic algae and Spartina ingested by major prey species: the filddle: crab, Uca pugnax (Smith): the polychaete, Nereis (Neanthes) succinea Frey and Leuckart; the tanaid, Leptochelia rapax Harger; and other small crustaceans. Small fish (age0–1 yr) showed slightly lower δ¹³C values than larger fish (age 1–3 yr), consistent with differences in their feeding habits. The only seasonal pattern was an enrichment in tissue ¹³C that occurred for both small and large fish in the spring, corresponding to the peak spawning period. The δ¹³C determination is a useful tool in identifying and tracing carbon sources through the salt marsh food web, detecting differences in feeding habits between age classes of organisms, and assessing the relative nutritive value of ingested dietary items if differential assimilation is suspected.     

First feeding diet of young brown trout fry in a temperate area: disentangling constraints and food selection

Trophic interactions are important factors structuring animal communities. We assessed the trophic relations of four fish species that live in sympatry in the River Ladra (NW Spain), and cluster analysis differentiated two feeding strategies: (1) species with omnivorous feeding habits, feeding mainly on detritus and plant material but with aquatic macroinvertebrates as an important complement (Achondrostoma arcasii and Pseudochondrostoma duriense) and (2) species feeding mainly (Salmo trutta) or exclusively (Gasterosteus gymnurus) on aquatic macroinvertebrates. Concerning ingested macroinvertebrates, the trophic overlap was quantified using Schoener’s index and the results obtained revealed a high diet overlap among the species (from 81.3 up to 99.2%). In order to get a deeper insight into mechanisms of fish species coexistence, we used ten biological and ecological traits of macroinvertebrate prey to discriminate feeding preferences. As a result, despite the high similarity among the diets, our analyses suggest that differences in diel activity patterns and drift behaviour of preys, as well as differences in the prey size, are important adaptive features that may reduce the inter-specific competition in the fish community and permit the partitioning of food that allows coexistence.     

Seed dispersal potential by wild mallard duck as estimated from digestive tract analysis

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Amount and time course of ingestion of plant subcellular fractions by two thrips and one reference mite species

Thrips are known as cell-feeding sucking pests, but little information is available on which and how much of each subcellular fraction they ingest. In this study, the ingested amounts of nuclei and plastids in two representative thrips species (the western flower thrips, Frankliniella occidentalis, and the garden thrips, Frankliniella intonsa) along with two reference sucking pests (the two-spotted spider mite, Tetranychus urticae, a cell feeder, and the brown planthopper, Nilaparvata lugens, a sap feeder) were quantified by quantitative PCR using phytoene desaturase and rubisco as respective marker genes following feeding. The ingested amounts of plastids were significantly greater than those of nuclei in the thrips and mite species. In the thrips species, however, the fold differences in ingested amount between the two fractions were substantially lower than their original ratio in intact plant cells, suggesting that thrips ingest nuclei more selectively than plastids. Unlike the thrips species, the ratio between nuclei and plastids increased in T. urticae. In contrast to these cell-feeding insects, no subcellular fraction was detected in N. lugens. These findings suggest that transgenic expression of foreign hairpin RNA in the nucleus would deliver a substantial amount of target molecules to cell-feeding sucking pests, but not sap-feeding pests, when employing ingestion RNA interference-based control strategies.     

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

• 1 The seasonal dynamics of the benthic macroinvertebrate assemblage, and the subset of this assemblage colonising naturally formed detritus accumulations, was investigated in two streams in south‐west Ireland, one draining a conifer plantation (Streamhill West) and the other with deciduous riparian vegetation (Glenfinish). The streams differed in the quantity, quality and diversity of allochthonous detritus and in hydrochemistry, the conifer stream being more acid at high discharge. We expected the macroinvertebrate assemblage colonising detritus to differ in the two streams, due to differences in the diversity and quantity of detrital inputs.
• 2 Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period.
• 3 Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos.
• 4 Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage.
• 5 Within‐stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between‐stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.

     

Behaviour of <Emphasis Type="Italic">Odontomachus chelifer</Emphasis> (Latreille) (Formicidae: Ponerinae) Feeding on Sugary Liquids

Sugary solution intake behavior by Odontomachus chelifer (Latreille), is studied. The feeding mechanism involved is described. Effects of sucrose concentration and solution viscosity on ingested load, feeding time and rate of liquid intake are assessed. Suction was always the feeding mechanism, regardless of concentration or viscosity of the solution. There were no differences in loads ingested for concentrations of up to 30% w/w, but feeding took longer at this concentration. Liquid intake rates were higher at the lowest concentrations. Above 40% w/w, values of all three variables were smaller. O. chelifer’s ability to ingest mildly viscous fluids could be related to its capacity to ingest other viscous fluids present in its diet.     

Diatom–salinity relationships in wetlands: assessing the influence of salinity variability on the development of inference models

We determined in situ feeding rates of three co-occurring coastal mysid species using [methyl-³H]-thymidine-labelled algal detritus (Lessonia corrugata), NaH¹⁴CO₃-labelled phytoplankton (Isochrysis galbana) and zooplankton (Artemia sp. nauplii). All three species showed a wide and overlapping range of feeding rates on the three food types, suggesting they were broadly omnivorous. However, selectivity studies often showed a strong preference for animal prey. Although there was an overlap in the types of food the mysids ingested, some degree of feeding niche partitioning was demonstrated. Paramesopodopsis rufa tended to be more carnivorous, Tenagomysis tasmaniae fed least on zooplankton and phytoplankton, and largely on algal detritus, and Anisomysis mixta australis ingested few zooplankters, and moderate amounts of algal detritus and phytoplankton. Handling editor: P. Viaroli     

Longitudinal zonation and food of larval chironomids (Insecta: Diptera) along the course of a river in temperate Canada

The chironomid larvae of the Rouge River, Ontario, Canada, showed a longitudinal zonation which may have been influenced by water temperature and substrate composition. Species of Orthocladiinae predominated in the cooler headwaters while species of Chironomini dominated the comparatively warmer water near the estuary. In the middle section the chironomid assemblage was of a more mixed nature.
Differences occurred in both food availability and feeding between sites along the river. Within genera, there were differences in the proportions of major food items between the larval guts and the available food material sampled from the same area. In most cases (e.g. Cryptochironomus, Polypedilum and Orthocladius ) larvae selected detritus over diatoms. Some genera (e.g. Microtendipes ) changed the proportions of food items ingested seasonally, while others (e.g. Psectrocladius ) exhibited a more stable diet throughout the year. Second instar larvae appeared to seasonally adjust their diet most often (e.g. Cricotopus. Tanytarsus and Eukiefferiella ), however these changes were not just in the types of food eaten, but also in the proportions of food types consumed. Larvae of all genera continued feeding throughout the cold water conditions (<5°C) of winter. Incidence of predation was very low, for example <10% in the Tanypodinae. In the laboratory, species of Chironomini ingested and assimulated, to varying degress, isolated populations of diatoms, detritus and bacteria.     

Living Apart Together: On the Biology of two Sympatric Leuctra Species (Plecoptera,Leuctridae) in an Apenninic Stream,Italy

Leuctridae is the richest stonefly family on the European continent, with many species of Leuctra often coexisting in sympatry in the same lotic environment. In this work we studied the life cycle and feeding habits of two species, Leuctra fusca and L. hippopus, coexisting in a small Italian Apennine stream. The life cycles of the two species are non‐overlapping, i.e., periods of nymphal growth and adult emergence are separated. Nymphs of both species feed mainly on detritus, but quantities of coarse particulate organic matter (CPOM) and diatoms are also ingested. Larger nymphs of both species ingest more CPOM and fewer diatoms. This suggests a similar trophic behaviour through their development. For example, they act as collector‐gatherers in their earlier instars and as collector‐gatherers or as shredders in their later instars (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Seasonality in Dietary Shifts in Size-Structured Freshwater Fish Assemblages in Three Reservoirs of Sri Lanka

We studied seasonal changes in feeding habits of size-structured fish assemblages in three freshwater reservoirs in Sri Lanka. We obtained fish samples for diet analysis from three reservoirs during the months of rising water level (RIWL) and receding water level (REWL). During RIWL, peripheral areas with terrestrial/semi-terrestrial macrophytes get inundated, which resulted in increased food availability for macrophyte feeding fish. During REWL, detrital food sources increase due to decaying terrestrial plant material, which has inundated. Based on the dietary habits of individual species in the three reservoirs during RIWL and REWL, it is evident that detritivorous and phytoplanktivorous fish species, which belong to low trophic levels do not show significant variation in dietary habits between the two seasons (e.g. Oreochromis mossambicus, Oreochromis niloticus and Amblypharyngodon melettinus). Stenophagous species such as benthic invertebrate predators (Puntius chola and Puntius dorsalis), macrophytophagous species (Etroplus suratensis and Tilapia rendalli) and zooplanktivorous Hemirhamphus limbatus do not exhibit significant variation in dietary habits between seasons. Also their feeding habits do not vary with body size. Euryphagous species such as Puntius filamentosus on the other hand, exhibit variations in dietary habits between seasons as well as with body size. Stenophagous species, which feed on detritus and phytoplankton and euryphagous species, which exhibit temporal dietary plasticity, are therefore abundant in fish assemblages of these reservoirs.     

Feeding of Perla grandis nymphs (Plecoptera: Perlidae) in an Apennine first order stream (Rio Berga,NW Italy)

Feeding habits of Perla grandis (Rambur) nymphs have been investigated in the Rio Berga, an Apenninic stream of Northwestern Italy. In this study, we analysed gut contents of 50 nymphs of this species, with the aim to investigate feeding preferences. Nymphs were collected from a single riffle, of which benthic coenosis was also determined. We detected a change in the diet during ontogenesis, with small instars feeding mainly on detritus and large instars strictly carnivorous. We also detected the existence of an evident trophic selection: diet was almost entirely dominated by Chironomidae, independently from their availability on the substratum. This finding is discussed on the basis of ecological and ethological considerations.     

Heavy metal pollution improves allelopathic effects of Canada goldenrod on lettuce germination

• Large amounts of heavy metals have been released into the environment. Thus, the allelopathic effects of invasive alien species on the germination performance of co-occurring indigenous species may be altered or even heightened with the rapid growth in heavy metal pollution.
• This study evaluated the impacts of Canada goldenrod (Solidago canadensis L.) leaf extracts at concentrations of 0, 10 or 20 gl 1 on the germination of lettuce under different forms of heavy metal pollution (Cu²⁺, Pb²⁺ or a combination of Cu²⁺ and Pb²⁺; 35 mgl 1) during incubation in Petri dishes for 10 days.
• Goldenrod leaf extracts (high concentration) reduced growth of aboveground and belowground parts of lettuce as well as competition for light and soil nutrients. However, low concentrations of goldenrod leaf extracts dramatically improved growth of lettuce roots, competition for light, soil nutrient availability, leaf photosynthetic area and growth competitiveness. The combination of goldenrod leaf extracts and heavy metal pollution was synergistic on most lettuce germination parameters, probably because high concentrations of goldenrod leaf extracts together with heavy metal pollution had a synergistic negative impact on lettuce germination.
• Consequently, increased levels of heavy metal pollution may favour invasion of invasive alien species while largely suppressing germination of indigenous species.

     

Insect–fern interactions: macrolepidopteran utilization and species–area association

Abstract.

• 1 The generalization that ferns are under-utilized by phytophagous insects in comparison to angiosperms may be invalid because of biases involving plant growth form, plant range, and unequal sampling efforts.
• 2 Comparison of nineteen fern species with 652 herb species, the angjosperm growth form most similar to the ferns, indicates no significant difference in the mean number of supported macrolepidopteran species. When the herbs are subdivided into annuals, biennials and perennials, only the annual herbs are significantly different than the ferns.
• 3 Comparisons of the occurrence distributions for ferns and the herb categories also demonstrate that only the annual herbs support more macrolepidopteran species than the ferns. The same results are obtained when random assemblages of herbs are created that are the same size as the fern assemblage.
• 4 Both the occurrence distributions and the species–area relationship for the ferns indicate that host records for insects feeding on ferns may be grossly incomplete.
• 5 The similarity of exploitation of ferns and perennial herbs by the Macro-lepidoptera suggests that other foliage feeding insects may also use ferns at levels equivalent to angiosperms.