Importance of fungi in the diet of Gammarus pulex and Asellus aquaticus

An important component of the interaction between macroinvertebrates and leaf litter in streams in the extent to which consumers can differentiate between undecomposed and decomposing leaves. The detritivores Gammarus pulex and Asellus aquaticus fed preferentially on conditioned rather on unconditioned leaf material. Growth in A. aquaticus was significantly reduced when unconditioned leaves were provided, but in G. pulex no significant effect of conditioning on growth was observed. The capacity of G. pulex to tolerate reductions in food quality seems to be a consequence of a compensatory system in which respiration rates change to compensate for reductions in food quality. In this way a constant growth rate is maintained. Increases in ingestion rates to compensate for low quality food were not observed.     

Importance of fungi in the diet of Gammarus pulex and Asellus aquaticus I: feeding strategies

The importance of fungi in the trophic biology of the freshwater detritivores Gammarus pulex and Asellus aquaticus was investigated. Inspection of leaves used in feeding trials indicated that whereas A. aquaticus scrapes at the leaf surface, G. pulex bites through the leaf material. Both species discriminated between fungal mycelia, fungally colonized and uncolonized leaf material but, although A. aquaticus selectively consumed fungal mycelia, G. pulex fed preferentially on leaf material. Fungi appear to be an important food source for A. aquaticus and selection of food material was positively correlated with fungal biomass. In contrast, for G. pulex, fungi appear to be more important as modifiers of leaf material. However, no significant correlations were found between food preference and any of the leaf modifications measured.     

Decomposition and macroinvertebrate colonization of aquatic and terrestrial leaf material in alkaline and acid still water

• 1 Decomposition of the leaves of Nymphaea alba L. and Betula pubescens Ehrh. was studied in two ponds of contrasting pH, buffering capacity and trophic level. Rates of carbon loss, concentrations of nitrogen, protein and phenolics and colonization of the leaf material by macroinvertebrates were studied.
• 2 Decomposition of B. pubescens leaves was slower than that of N. alba in both ponds. Protein and phenolic concentrations were higher in the decomposing N. alba material, whereas no significant difference was found for nitrogen concentrations.
• 3 Decomposition of both species was slower in the acid water. The effect of acid water on decomposition rate was similar for both species. Both nitrogen and protein concentrations of N. alba remained higher under acid conditions, whereas no effect of study site was observed on the protein and nitrogen concentrations in B. pubescens litter. The concentration of phenolic compounds was higher in N. alba litter from the acid pond; no such difference was observed for B. pubescens litter. The high concentrations of phenolic compounds in N. alba litter from the acid pond probably induced chemical immobilization (tanning reaction), yielding high concentrations of nitrogen and protein in the litter.
• 4 Diversity of the detritivorous macroinvertebrate fauna on the litter of both species was extremely low in the acid pond, while a relatively high diversity occurred in the alkaline water. Exclusion of large macrofauna inhibited decomposition in the alkaline water, while there was no comparable influence in the acid water.
• 5 The effects of low pH on the decomposition of both terrestrial and aquatic macrophyte litter appeared to be caused by interactive effects of low pH on the microbial decomposition, on the detritivorous macroinvertebrates and, in the case of N. alba, on the resource quality of the detritus.

     

The predation on Asellus aquaticus (L.) by perch,Perca fluviatilis (L.), in a small forest lake

Asellus aquaticus (L.) was the most important benthic food item for perch, Perca fluviatilis (L.), in a small, extremely humic forest lake in southern Finland. The proportion of A. aquaticus in the diet of perch varied according to the former's availability, which, in turn, depended on its life cycle. Perch 11.0–12.9 cm (total length) most frequently fed on A. aquaticus; smaller and larger perch fed more frequently on crustacean zooplankton and aquatic insect larvae, respectively. The high density of the perch population, the importance of A. aquaticus in the benthos of the study lake and the general high activity level of the prey resulted in a high predation (0.1–1.8% per day). The population of A. aquaticus was also limited by the scarcity of macrophytic vegetation and the small area of oxygenated littoral in the lake.     

Nitrate Reductase and Glucose-6-phosphate Dehydrogenase Activities as Influenced by Leaf Age and Addition of Protein to Extraction Media

Lea fage influences the level of activity and the decay rate of the enzymes nitrate reductase (NR: E.C. 1.6.6.1) and glucose-6-phosphate dehydrogenase (G6PD; E.C. 1.1.1.49) extracted with and without protein in the extraction media. Such influence was determined in three plant species: corn (Zea mays L.), oats (Arena sativa L.), and tobacco (Nicotiana tabacum L.). Leaves of different ages were obtained from plants of various ages, or by removal of leaf blades from different positions on a single shoot. NR activity (per g fresh weight) declined as leaves of these plant species became older, especially when extraction was effected with conventional media (i.e. without added protein). The instability of NR in these extracts increased as leaves became older. Decay of NR in vitro was exponential with time. Addition of protein [3 %(w/v) casein or bovine serum albumin] to extraction media markedly increased the level of NR activity and its stability, especially in older leaves of all three plant species. Addition of protein did not affect the level of G6PD extracted from corn leaf blades, but slightly enhanced its activity in extracts from the oldest leaf blade of oats. G6PD activity also declined as leaf blades of corn and oats became older.     

Characterization and Localization of a Novel Protein (HFN 40) in Maize Genotypes Without Husk Leaf Blades

Some maize (Zea mays L.) genotypes produced husk leaves without leaf blades. However, the physiological implication of this leaf deformity is unclear. Difference in protein pattern was observed between maize with and without husk leaf blades. A clear band around 38[sim ]40 kDa in seeds of maize genotypes without husk leaf blades appeared, while it was not detected in ones with husk leaf blades. These protein might be involved in leaf blade intiation.     

Palatability of Leaves Conditioned in Streams Affected by Mine Drainage: A Feeding Experiment with Gammarus Pulex (L.)

Both the absence of leaf shredding macroinvertebrates and low microbial activity are of major importance in determining slow and incomplete leaf decay in extremely acidic (pH<3.5) mining streams. These streams are affected by a heavy ochre deposition causing the formation of massive iron plaques on leaf surfaces that hinder microbial exploitation. An investigation was carried out to determine whether iron plaques and leaf conditioning status (acid conditioned with and without iron plaques, neutral conditioned, unconditioned) affect the feeding preference of the shredder Gammarus pulex (L.). Leaf respiration rates and fungal biomass (ergosterol contents) were measured to determine microbial colonization. Neutral conditioned leaves had significantly higher microbial colonization than acid conditioned leaves with iron plaques. Notwithstanding, leaves of both conditioning types were consumed at high rates by G. pulex. The microbial colonization had no influence on feeding preference in the experiment. It is presumed that iron adsorbed organic material caused the high palatability of leaves with iron plaques. The results indicate that the large deposits of leaves coated with iron plaques will be available to the stream food web when water quality will be restored to neutral as planed in scenarios for the future development of mining streams.     

Tannin Dynamics of Propagules and Leaves of Kandelia candel and Bruguiera gymnorrhiza in the Jiulong River Estuary, Fujian, China

Changes in the total phenolics, condensed tannins (CT), protein-precipitable phenolics content and protein precipitation capacity were determined on a series of mangrove leaves from two true viviparous mangrove species (Kandelia candel and Bruguiera gymnorrhiza) at various stages of development and decomposition in the Jiulong River Estuary, Fujian, China. Similar measurements were also done for the propagules at different developmental stages. The results showed that the total phenolics, extractable condensed tannins, total condensed tannins, protein-precipitable phenolics content and protein precipitation capacity in young leaves were higher than those in mature and senescent leaves. Tannin dynamics during leaf decomposition varied with species, and the rapid loss of phenolics observed during decomposition can be ascribed to leaching and degradation. Protein-bound CT and fibre-bound CT tended to increase with leaf decomposition, with CT binding more strongly to protein than to fibre. Protein-bound CT was higher than fibre-bound CT with the exception of mature leaves. Total phenolics, extractable CT and protein-precipitable phenolics contents in flower tissues were relatively lower than those in hypocotyls at different developmental stages. Protein precipitation capacity fluctuated with the development of propagules. Increases in nitrogen in decaying litter, and declines in contents of total phenolics and total condensed tannins of detritus support the general conclusion that decomposing mangrove detritus can be a more palatable heterotrophic substrate than living leaves.     

Comparative ecology of Gammarus pulex (L.) and Asellus aquaticus (L.) II: fungal preferences

This paper continues to explore niche differentiation in Gammarus pulex and Asellus aquaticus by analysis of their food preferences. Individuals from both species discriminated between leaf discs colonized by different fungal species and exhibited strong preferences for Anguillospora longissima and Heliscus lugdunensis. Fungal preferences were not correlated with the relative abundance of fungi in the field and there was considerable intra-population variability in food preferences — both between individuals and for the same individual through time. Niche overlap between animals from all four study populations was high and there was no evidence of differences in the potential trophic niches of animals from sympatric and allopatric populations.     

The diel activity of carabid beetles (Coleoptera) north of the Arctic Circle,with particular reference to Patrobus assimilis Chaud. and Notiophilus aquaticus L.

Summary Diel activity patterns of carabids species caught in pitfall traps in a subalpine birch forest north of the Arctic Circle are described. Patrobus assimilis Chaud. and Notiophilus aquaticus L. were the most common species and were active at all times of the day with peak activity at noon. Seven less common species and the larvae of Notiophilus aquaticus L. showed similar activity patterns. There was a positive correlation between the mean diel variation in temperature and the activity of the different species. Although day to day variations in temperature influenced the level of activity, it had little effect on the daily activity patterns. The adaptive significance of the diurnal activity patterns of carabid beetles in northern areas is discussed in relation to low night temperatures and high predation pressure from birds.     

Enhanced UV-B radiation,artificial wounding and leaf chemical defensive potential in Phlomis fruticosa L.

The combined effects of additional UV-B radiation and artificial wounding on leaf phenolics were studied in a short term field experiment with the drought semi-deciduous Mediterranean shrub Phlomis fruticosa L. The seedlings were grown under ambient or ambient plus supplemental UV-B radiation (biologically equivalent to a 15% ozone depletion over Patras, 38.3° N, 29.1° E) for 7 months before wounding. Unexpectedly, supplemental UV-B radiation decreased leaf phenolics. Subsequently, wounding was effected by removing leaf discs from some of the plants, while the rest remained intact and served as controls. Wounding significantly increased phenolics of the wounded leaves and the increase was more pronounced under supplemental UV-B radiation. In addition, wounding had a significant positive effect on the phenolics of the opposite, intact leaf, but only under additional UV-B radiation. We conclude that UV-B radiation, wounding and their combination may affect the chemical defensive potential of Phlomis fruticosa. In addition, increased levels of phenolics after herbivore attack under field conditions may afford extra protection against enhanced UV-B radiation levels.     

小白菜BcUBCE2基因的克隆及表达分析

采用cDNA-AFLP和RACE技术从小白菜中克隆得到泛素结合酶E2基因(ubiquitin conjugating enzyme E2),命名为BcUBCE2。序列分析表明,BcUBCE2基因cDNA全长830bp,包含1个456bp的开放阅读框,编码152个氨基酸。结构分析发现,该序列包含一个泛素结合酶E2活性位点和一个高度保守的半胱氨酸。进化分析显示,小白菜BcUBCE2蛋白同拟南芥E2蛋白的亲缘关系最近。qRT-PCR分析表明,BcUBCE2基因在小白菜根、茎、叶中均有表达,铜处理10d时BcUBCE2基因的表达量最高。研究认为,BcUBCE2基因可能在铜胁迫响应中发挥重要作用。     

Heartwood extractives and lignin content of different larch species (<Emphasis Type="Italic">Larix </Emphasis>sp.) and relationships to brown-rot decay-resistance

The extractive content of lignin and the brown-rot decay-resistance against Coniophora puteana and Poria placenta were studied in larch heartwood from different species and origin (Larix decidua var. decidua, L. decidua var. sudetica, L. kaempferi , L. × eurolepis). The study material consisted of 106 trees from a 39-year old provenance trial in France. The hot-water-soluble extractives were very variable (from5.66% to 20.50% of dry weight), but there was no significant variation between the investigated species and origins. In contrast, acetone extractives, the total amount of phenolics and lignin showed significant differences. The concentration of phenolics and lignin was significantly higher in L. kaempferi and in L. × eurolepis than in L. decidua. The total phenolics content was strongly correlated with decay-resistance in all investigated larch origins. A higher concentration of phenolics goes hand in hand with higher decay resistance and phenolics might therefore be a promising parameter to rapidly evaluate the level of decay-resistance in larch.     

Biochemical and bioassay analysis of resistance of potato (Solanum tuberosum L.) cultivars to attack by the slug Deroceras reticulatum (Muller)

A method is described for using young field slugs Deroceras reticulatum (Muller) in a bioassay study of biochemical resistance of potato (Solanum tuberosum L.) cultivars to slugs. Tuber parts or an artificial diet were provided as food sources. Comparisons were made of feeding, survival and weight gain between the susceptible cultivar Maris Piper and the resistant cultivar Pentland Dell. Biochemical analyses were made of these two cultivars and the resistant cultivars Stormont Enterprise and Majestic. Comparisons of tuber sections and peelings as food sources indicated factors affecting growth were located in the surface layers of the tubers. Phenolics and glycoalkaloids were concentrated in the surface layers but the amounts were similar in the susceptible and resistant cultivars and the bioassays indicated that neither acting alone could explain resistance. The amounts and distribution of free amino acids also did not correlate with resistance although when supplied in the artificial diet they partly inhibited feeding. Proteinaceous inhibitors of slug gut proteolytic enzymes were present throughout the tubers but were not concentrated in the surface layers and the amounts were similar in the different cultivars thus they too did not explain the difference in susceptibility between the cultivars. Bioassays using acetone extracts (low molecular weight substances) and acetone powders (high molecular weight substances) either alone or in combination indicated that the resistant cultivar Pentland Dell contained a high molecular weight substance which together with a low molecular weight substance from either the same cultivar or the susceptible Maris Piper could confer resistance. Bioassays using protein extracts supplied in the presence or absence of chlorogenic acid indicated that this mechanism could comprise enzymic oxidation of phenolics. Assays of phenolase confirmed this since activity was highest in the outer layers of the tubers and was highest in the three resistant cultivars. Thus the chief resistance factor identified was high phenolase activity acting rapidly on phenolics when the slug first bites the tuber surface. The quantity of phenolics per se did not control the resistance. Thus while phenolics must be available, resistance is compatible with low blackening on cutting the tuber.     

Willow genotype, but not drought treatment, affects foliar phenolic concentrations and leaf-beetle resistance

In a greenhouse experiment we examined the effect of willow genotype and irrigation regime (moderate drought and well‐watered) on plant growth parameters, foliar nitrogen, and phenolic concentrations, as well as on the preference and performance of the blue leaf beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae). The 10 vegetatively propagated willow genotypes in the experiments were F2 full‐sibling hybrids, originated from a cross between Salix viminalis (L.) (Salicaceae) (high in condensed tannins) and Salix dasyclados (L.) (Salicaceae) (rich in phenolic glycosides). Insect bioassays were conducted on detached leaves in Petri dishes as well as with free‐living insects on intact potted plants. The 10‐week long irrigation treatments caused statistically significant phenotypic differences in the potted willow saplings. Total biomass was somewhat higher in the well‐watered treatment. The root to total biomass ratio was higher in the drought‐treatment plants. There was significant genotypic variation in foliar nitrogen concentrations, and they were higher in the drought‐treatment plants. There was also a strong genotypic variation in each of the phenolic substances analyzed. Condensed tannins, which accounted for the greatest proportion of total phenolic mass, were higher in the well‐watered treatment. There was, however, no difference in levels of the other phenolics (salicylates, cinnamic acid, flavonoids, and chlorogenic acid) between irrigation treatments. The sum of these phenolics was higher in the well‐watered treatment. There was a strong variation in P. vulgatissima larval development on different willow genotypes, and larval performance was negatively correlated with levels of salicylates and cinnamic acid. There was, however, no effect of irrigation treatment on larval performance. Phratora vulgatissima preferred to feed on well‐watered plants, and we found a preference for oviposition there, but neither feeding nor oviposition site preference was affected by willow genotype. Adult feeding and oviposition preferences were not correlated with larval performance.     

Strong influence of leaf tie formation and corresponding weak effect of leaf quality on herbivory in eight species of Quercus

1. Leaf shelter construction by herbivorous insects can improve leaf quality, sometimes changing resultant herbivory. In two experiments in a Missouri (USA) deciduous forest we quantified the impact of leaf tie construction and changes to leaf quality on subsequent leaf damage.
2. First, using eight Quercus species, we compared damage to single leaves versus experimental leaf ties that had been stocked with either Pseudotelphusa quercinigracella (Gelechiidae) or Psilocorsis cryptolechiella (Depressariidae) to determine how initial leaf quality (total phenolics) influenced damage caused by shelter inhabitants. Skeletonization by leaf tying caterpillars and leaf edge chewing by free feeding species were 12.2× and 1.3× greater on tied than on non-tied leaves, respectively. July and September leaf phenolic content had a slight positive effect on the probability of skeletonization, none on the probability of edge damage, and a weakly positive or negative effect on the intensity of skeletonization and edge damage, depending on leaf position.
3. Second, we created experimental leaf ties, protected from herbivores, on the same Quercus species to determine whether tie formation changes leaf quality (total phenolics, nitrogen, water, toughness). Tie formation decreased phenolics, but this change was predicted to add only 0.8% leaf area loss.
4. Synthesis. Herbivory increased dramatically when leaves were in ties, with the effect mostly due to the tie itself rather than a change in leaf quality. We predict that the advantages of building and using leaf ties in this system are more likely to be escape from natural enemies and changes in abiotic factors.

     

The ultrastructure of the heart of Oniscus asellus L. and Asellus aquaticus L. (Crustacea,Isopoda)

Summary The endocardium of Oniscus asellus L. and Asellus aquaticus L. consists of lipid cells. The epicardium consists of a layer of cells with a vesiculated cytoplasm covered by a thick extracellular fibrous sheet. The myocardium is a single layer of cells, the sarcolemma invaginates at Z disc level forming transverse tubules, and longitudinal tubules branch off from these. At the A-I level' longitudinal tubules form transverse systems, which form couplings with the sarcoplasmic reticulum. The sarcoplasmic reticulum appears as perforated sheets enveloping the myofibrils. Two types of nerve terminal are found: one is embedded in a myocardial cell process, the other lies in a myocardial cell depression. They contain clear and dense-cored synaptic vesicles.This work was supported by grants from the Norwegian Research Council for Science and the Humanities     

Nutritional quality of specific leaf tissues and selective feeding by a specialist leafminer

Summary Many folivorous insects are selective feeders which consume specific leaf tissues. For specialist herbivores feeding on plants of overall low nutritional quality, selective feeding may allow consumption of a high quality resource. Selective feeding may also allow insects to avoid structural or allelochemical defenses. We examined the structure and chemistry of leaves of American holly, Ilexopaca Aiton, and the feeding site of its principal insect herbivore, the native holly leafminer, Phytomyza ilicicola Loew (Diptera: Agromyzidae), to test the hypothesis that the leafminer consumes tissues which are of greater nutritional quality than the leaf as a whole. Holly leaves have a continuous layer of palisade mesophyll, uninterrupted by fibers or vascular bundles. The leafminer feeds entirely within this layer. The palisade mesophyll contained 196 mg/g dry wt extractable protein, more than twice as much as the leaf as a whole, and 375 mg/g dry wt saponins, more than 9 times that of the leaf as a whole. The water content of the palisade mesophyll was 66% higher than that of the leaf as a whole. The palisade mesophyll is 3–4 cell layers thick in leaves grown in full sun, but only 2 layers thick in shaded leaves. Crystals, probably of calcium oxalate, are abundant in the abaxial cell layer. These may impose mechanical constraints on larval feeding in shade leaves, which are thinner than sun leaves. Selective feeding on the middle palisade mesophyll of sun leaves allows the leafminer to consume a resource which is lacking in mechanical barriers and is rich in protein and water, but which contains large amounts of saponins.The investigation reported in this paper (No. 86-8-7-117) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

High Diversity of Fungi may Mitigate the Impact of Pollution on Plant Litter Decomposition in Streams

We investigated how a community of microbial decomposers adapted to a reference site responds to a sudden decrease in the water quality. For that, we assessed the activity and diversity of fungi and bacteria on decomposing leaves that were transplanted from a reference (E1) to a polluted site (E2), and results were compared to those from decomposing leaves either at E1 or E2. The two sites had contrasting concentrations of organic and inorganic nutrients and heavy metals in the stream water. At E2, leaf decomposition rates, fungal biomass, and sporulation were reduced, while bacterial biomass was stimulated. Fungal diversity was four times lower at the polluted site. The structure of fungal community on leaves decomposing at E2 significantly differed from that decomposing at E1, as indicated by the principal response curves analysis. Articulospora tetracladia, Anguillospora filiformis, and Lunulospora curvula were dominant species on leaves decomposing at E1 and were the most negatively affected by the transfer to the polluted site. The transfer of leaves colonized at the reference site to the polluted site reduced fungal diversity and sporulation but not fungal biomass and leaf decomposition. Overall, results suggest that the high diversity on leaves from the upstream site might have mitigated the impact of anthropogenic stress on microbial decomposition of leaves transplanted to the polluted site.     

Intraspecific variation in growth,defense and herbivory in Dialium guianense (Caesalpiniaceae) mediated by edaphic heterogeneity

Based on resource allocation theory, a negative correlation is predicted between resource availability and plant defense against herbivore attack. Plants growing in resource-limited environments should display lower growth and higher defense against herbivores than plants growing where resources are less limited. Interspecific comparisons generally support these predictions. We evaluated this hypothesis at the intraspecific level, for two sapling populations of the canopy tree Dialium guianense (Caesalpiniaceae) at the Lacandona rain forest in southeast Mexico. The two populations occur in nearby sites, adjacent to the Chajul Field Station, under the same climatic conditions and within the same vegetation type, but with considerable differences in soil quality. The Floodplain site, under the influence of the Lacantún River, has favorable conditions for plant growth, in terms of nutrient and water availability, whereas the Hills site, given its location and soil characteristics, provides more restricted conditions for plant growth. Plants in the Floodplain site had higher growth and lower concentration of phenolic compounds than plants in the Hills (a two-fold difference in leaf area production, 1.3 less total phenolics). These differences were correlated with differences in herbivore attack, as saplings from the Hills, with a higher defensive potential, had lower average levels of herbivory than Floodplain plants (3.86% ± 0.80 vs. 7.75% ± 1.43 of leaf area loss). The relationship between the concentration of phenolic compounds and leaf quality for herbivores was consistent with preference assays carried out under laboratory conditions using two species of generalist herbivores, the army worm Spodoptera fugiperda and the native katydid Orophus sp. In 63.8 and 81.3% of the cases, third-instar larvae of S. fugiperda and adults of Orophus, respectively, preferred leaflets from the Floodplain plants population. Moreover, on average, the adults of Orophus consumed 2.9 times more leaf area from the Floodplain than from the Hills. In addition, a reciprocal transplant experiment indicated that phenotypic plasticity is likely to be the mechanism by which the plants expressed differential growth and traits affecting herbivory levels. In this experiment, growth and herbivory levels were 1.6 and 1.7 times higher, respectively, in plants transplanted into a Floodplain experimental plot than those in a Hills plot. This work contributes to our understanding of how edaphic heterogeneity can determine intraspecific variation in the relationship of plants with their herbivores and evaluates the underlying mechanisms promoting such influence. This revised version was published online in June 2006 with corrections to the Cover Date.