Trophic level assessment of profundal sediments of the artificial Lake Campotosto (Central Italy), using midge larval community (Diptera: Chironomidae)

A study on the profundal chironomids of the artificial Lake Campotosto (Central Italy) was carried out during the summer/early autumn of 1983 and 1984, in order to analyse their composition and community structure in relation to the lake trophic level assessed by water chemical analysis.A total of about 2000 specimens belonging to 15 taxa were collected during the study.Chironomus plumosus group andTanytarsus spp. dominated in 1983 and 1984, respectively, showing a competitive relationship probably due to the larval size. The functional feeding organization was mostly composed of collectors (percentages greater than 90%), revealing the presence of abundant fine organic deposits (FPOM). Diversity and evenness appeared to be negatively affected by the monotony of food, which seems to constitute the key factor in governing both the taxonomic and the trophic structure of chironomid fauna.A clear discrepancy between water chemical data and profundal chironomid analyses was observed in the assessment of the lake trophic level. Sediments exhibited eutrophicated conditions, whereas overlying waters indicated an oligotrophic status. The relevance of profundal macrobenthic investigations in detecting eutrophication is stressed.     

A note on the feeding ofAmphichaeta leydigii (Oligochaeta,Naididae) in lacustrine sandy shores

The analysis of gut contents ofAmphichaeta leydigii, found for the first time in Italy in sandy shores of Lake Vico (Central Italy), proved grazing of the species on diatoms (Centrales and Pennales). Detritus and organic particles, abundant in the substratum, were observed only in small amounts.     

Structure,development and function of the branchial sieve of the common bream,Abramis brama,white bream,Blicca bjoerkna and roach,Rutilus rutilus

Synopsis The filter feeding organ of cyprinid fishes is the branchial sieve, which consists of a mesh formed by gill rakers and tiny channels on the gill arches. In order to establish its possible role during growth we measured the following morphological gill raker parameters over a range of sizes in three cyprinid fishes, bream, white bream and roach: inter raker distance, bony raker length, raker width, cushion length and channel width. At any given standard length common bream has the largest inter raker distance, roach the lowest and white bream is intermediate. In the comb model of filter feeding the inter raker distance is considered to be a direct measure of the mesh size and retention ability (= minimal size of prey that can be retained) of a filter. For the three species under study there is a conflict between the comb model and experimental data on particle retention. Lammens et al. (1987) found that common bream has a large retention ability whereas roach and white bream have a much smaller one. A new model, the channel model (Hoogenboezem et al. 1991) has been developed for common bream; in this model the lateral gill rakers can regulate the mesh size of the medial channels on the other side of the gill slit. The present data indicate that this model is not appropriate for white bream and roach. At any given standard length white bream and roach only reach 70% of the raker length of common bream, which means that in this model the gill slits should to be very narrow during filter feeding. The gill rakers consist of a bony raker and a fleshy cushion. The bony rakers have a rather long needle-like part outside the cushion in bream, but not in white bream and roach which have blunt gill rakers. Blunt gill rakers are not suited to reduce the diameter of the medial channels. The comb model seems more appropriate for white bream and roach, but doubts about the validity of this simple model remain. The sum of the areas of the medial channels is an approximation of the area through which water flows in the filter. This channel area therefore gives an impression of the capacity or flow rate of the filter. With this capacity estimation and an estimation of energy consumption we calculated an energy ratio of filter feeding. The energy ratio decreases with increasing standard length with an exponent close to the expected exponent of -0.40. The energy ratio is highest in bream, intermediate in white bream and lowest in roach.     

Tree killing by herbicide producing ants for the establishment of pureTococa occidentalis populations in the Peruvian Amazon

Populations ofTococa occidentalis (Melastomataceae) and the inhabiting ants (Myrmelachista sp.) were observed for more than eight months in the Peruvian Amazon (Sira mountains). They represent a complex coevolutionary system: the plants offer shelter (leaf domatia, hollow stems) and food (leaf glands), whereas the ants kill all surrounding plants, including large trees up to 10 m, by chemical weapons. Experiments with exposed plants revealed a highly specialized way to attack meristematic tissue and leaf nervature, which leads to a quick decay of the plant individuals. The clearing of the vegetation by the ants allows theTococa population to expand mostly by vegetative shoots to large monocultures (up to 30 m in diameter) free from any other plant species. Artificially introduced plant individuals, from differentT. occidentalis populations, are regarded as a foreign species by the ants.The succession of such aTococa-Myrmelachista system begins with one or a few founder plants on a light place in the midst of the vegetation.Myrmelachista soon inhabits their host plants which otherwise would not survive and begin to clear the place from all foreign plant species.Tococa expands quickly, forming circle shaped populations. Distantly situated canopy trees shade theTococa population after a number of years and cause their decay. The whole place appears contaminated for years and no other plant can establish itself. Some of the consequences of these open places are erosion and a severe influence on the regeneration of the forest.     

Consumption of leaf detritus by a stream shredder: Influence of tree species and nutrient status

Four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen + phosphorus, or no fertilizer (control). The resulting leaf detritus (leached but not microbially colonized) was offered to a stream shredder, Hydatophylax variabilis (Trichoptera: Limnephilidae). In one experiment, shredder consumption of leaf detritus from different nutrient treatments (within tree species) was compared, and in a second experiment, consumption of different tree species (within nutrient treatments) was compared. Larvae preferred leaf detritus from nitrogen + phosphorus treatments (except in poplar where nitrogen treatment was preferred). Alder was preferred over other tree species for all treatments. Chemical and physical analyses of leaf litter showed differences between tree species and nutrient treatments in nutrient content, tannins and leaf toughness. Leaf consumption by larvae was positively associated with nitrogen content and negatively associated with condensed tannin content. Species composition and nutrient status of riparian vegetation may strongly influence detrital food webs in streams.     

Spatial patterns and feeding of meiobenthic harpacticoid copepods in relation to resident microbial flora

Distributional and feeding relationships of harpacticoid copepods and their microbial prey were examined in a tidal channel at Great Sippewissett Marsh. A horizontal zonation of photosynthetic microorganisms was composed of: 1) a diatom area; 2) a purple sulfur bacterial (Thiocapsa sp.) area; and 3) a clear area. Four species of harpacticoid copepods were associated with given areas. Leptocaris brevicornis occurred in very high densities in the diatom area but in relatively low densities in other areas. Mesochra lilljeborgi occurred in significantly higher densities in the purple and clear areas.Feeding experiments, using resident microbial flora labelled with NaH¹⁴CO₃ and ³H-thymidine, were conducted to determine which foods are 1) ingested but simply pass through the gut and 2) ingested, and retained. These experiments indicated that L. brevicornis ingested diatoms and the heterotrophs associated with the diatoms, but only retained the heterotrophic portion. Microscopic examination indicated that diatoms were passed out intact in feces. Oscillatoria sp. (cyanobacterium) was not ingested. Mesochra lilljeborgi ingested Spirulina sp. (cyanobacterium), Thiocapsa sp., and the heterotrophs associated with Thiocapsa but only retained the Thiocapsa label.These data for harpacticoids suggest that spatial distributions of meiofauna may be closely coupled with microbial food organisms which they consume. Also, that while several microbial foods may be ingested, only certain microbes are digested and assimilated as a food resource, further indicating the complexity of feeding relationships among the meiofauna.     

Enhanced formation of mouse hybridomas without hat treatment in a serum-free medium

Summary A newly developed, serum-free medium (NYSF-404) selects for antibody-producing hybridomas after fusion of antigen-sensitized mouse spleen cells with myeloma cell lines P3-X63-Ag8-U1 (P3-U1), P3-X63-Ag8-6.5.3 (Ag8.653), or P3-NSI/1-Ag4-1 (NS-1). Without the need for hypoxanthine-aminopterinthymidine (HAT) selection of hybrid cells, frequency of hybridoma formation in medium NYSF-404 is higher (twice) than that in serum- and HAT-containing medium. Colonies developed upon limiting dilution in the presence of the mortal parent myeloma cells in medium NYSF-404 and pure culture of antibody-secreting cells could be subsequently established. The results suggest that fusions can be done in serum-free medium and that the clonal growth of hybridomas is dependent on factors produced by parent myeloma cells under serum-free culture conditions. Such factors seem deficient in serum- and HAT-containing medium or are masked by serum.     

Nippostrongylus brasiliensis: feeding activity in the mouse

Nippostrongylus brasiliensis incorporated the fluorescent dye, Rhodamine B, while feeding in vivo. Uptake of dye in both sexes of helminth increased linearly from 30 to 120 min after the hosts were given dye per os. Feeding by female N. brasiliensis significantly exceeded that of the male at 4 and 5 days postinfection. Feeding declined in older helminths of both sexes. The density of helminths had no effect on their incorporation of dye in vivo. Feeding in male- and female-only groups of worms was similar to that seen in populations of mixed sexes. Feeding by helminths decreased during the first 36 h of food deprivation in the host, but increased during subsequent fasting of the host. Both sexes of N. brasiliensis resumed feeding within 15 min after the fasted hosts were fed. Growth of N. brasiliensis increased linearly from 4 to 7 days postinfection, based on dry weight. Seven-day-old and older females were significantly heavier than males.     

Effects of Pratylenchus zeae and Quinisulcius acutus Alone and in Combination on Sorghum

Host-parasite relationships of Pratylenchus zeae and Quinisulcius acutus, alone or in combination, were studied on sorghum in the greenhouse and laboratory. Q. acutus at 1,000 or 5,000 nematodes per 15-cm-d pot and P. zeae at 500 nematodes per pot significantly suppressed plant height and fresh and oven dry shoot and root weights. A mixture of 1,000 Q. acutus and 500 P. zeae per pot resulted in greatest suppression of growth. Roots of plants inoculated with Q. acutus alone were reduced in number and size and showed lesions and discoloration. Reproduction of this nematode 42 days after inoculation was much greater in treatments of 100 or 1,000 than 5,000 nematodes. The population density of the two species at 6 weeks after inoculation was significantly less when combined than for each species alone. When the two species were combined, reproduction of P. zeae was greater than that of Q. acutus, but the final populations per gram of root weight were the same. Q. acutus fed ectoparasitically on epidermal cells of sorghum roots in the zone of elongation and differentiation when observed under in vitro conditions.     

On the mimetic association between nymphs of Hyalymenus spp. (Hemiptera: Alydidae) and ants

Nymphs of Hyalymenus , unlike adults, have a highly differentiated ant-like morphology. Both H. tarsatus and H. limbativentris feed mainly on reproductive parts of composites and solanaceous plants, respectively. Mimetic nymphs were observed on plants, together with ants, both day and night; adult Hyalymenus , however, are predominantly nocturnal. Ant-resemblance in nymphs is achieved by several structural adaptations which, when coupled with the mimic's zig-zag locomotion and constantly agitated antennae, produces a striking visual deception. Experiments in captivity showed that mimetic nymphs, but not adult Hyalymenus , are somewhat protected against attacks from the praying mantid Oxyopsis media found on their host plant. Colour and size changes through different nymphal instars of Hyalymenus allow the immature bugs to resemble, during their development, differently sized and coloured ant models. Similar-looking ant species seem to act as Mullerian mimics toward insectivorous vertebrates and invertebrates that avoid ants. It is suggested that nymphs of Hyalymenus gain Batesian protection by resembling available ant models of different Mullerian complexes. Density-dependent selection is thought to be responsible for the observed differences in mimetic morph proportions between populations of mimics, as well as for the mimetic strategy itself employed by nymphs of Hyalymenus.