A comparison of the trophic transfer of fatty acids in freshwater plankton by cladocerans and calanoid copepods

1. Analyses of zooplankton fatty acid (FA) composition in laboratory experiments and samples collected from lakes in New Zealand spanning a wide gradient of productivity were used to assess the extent to which FAs might infer their diet. We used the cladocerans, Daphnia and Ceriodaphnia, and the calanoid copepod, Boeckella, as test organisms, and monocultures of cryptophytes, chlorophytes and cyanobacteria as food. Based on reproductive success, cryptophytes were the highest food quality, chlorophytes were intermediate and cyanobacteria the poorest. 2. Several FA groups were highly correlated between zooplankton and their diets. They were monounsaturated fatty acids (MUFAs), and ω3 and ω6 polyunsaturated fatty acids (PUFAs) for cladocerans, and saturated fatty acids (SAFAs) and ω3 PUFAs for copepods. Several FAs varied significantly less in the zooplankton than in their monoculture diets, e.g. MUFAs in Daphnia, and ω3 and ω6 PUFAs in Ceriodaphnia, despite clear dietary dependency for these FAs. 3. Zooplankton collected from lakes in New Zealand had more eicosapentaenoic acid (EPA) (Daphnia), more highly unsaturated ω3 and ω6 FAs (C₂₀, C₂₂; Daphnia, Ceriodaphnia, Boeckella) and less ω3 C₁₈ PUFAs (Daphnia, Ceriodaphnia, Boeckella) and ω6 C₁₈ PUFAs (Daphnia, Ceriodaphnia) than measured in the same species reared on phytoplankton in the laboratory. 4. Analyses of FA composition of seston and freshwater zooplankton globally showed that, in general, zooplankton had a significantly higher proportion of arachidonic acid and EPA than seston, and copepods also had a higher percentage of docosahexaenoic acid than seston. 5. These results suggest that zooplankton selectively incorporate the most physiologically important FAs. This could be a consequence of preferential assimilation, selective feeding on more nutritious cells or locating and feeding within higher food quality food patches.     

Photoprotective compounds in weakly and strongly pigmented copepods and co-occurring cladocerans

1. The prevalence of mycosporine‐like amino acids (MAAs) – a group of potential ultraviolet (UV)‐photoprotective compounds – was surveyed across 11 species of freshwater copepods from 20 lakes of varying ultraviolet radiation (UVR) transparency in North America, New Zealand and Argentina. Co‐occurring cladocerans were also analysed (seven species from 12 lakes). Many of the calanoid copepod populations were red with carotenoid pigmentation, allowing comparison of MAA and carotenoid accumulation as photoprotective strategies. 2. In two Pennsylvania (U.S.A.) lakes, MAA and carotenoid contents were followed during the early spring to mid‐summer period of lake warming. A pronounced seasonal pattern of higher carotenoid/low MAA content in spring, shifting to low carotenoid/higher MAA content in summer, was observed in calanoids from the more UV transparent lake. 3. All copepod samples contained MAAs. Visibly red calanoids, especially southern Hemisphere Boeckella, often had moderate to high concentrations (2.5–11 μg MAA mg^?1 dw), but low concentrations (0.04–1 μg MAA mg^?1 dw) in some N. American red calanoids show that high carotenoid pigmentation (e.g. 5–10 μg carotenoid mg^?1 dw) does not necessarily imply high MAA content. 4. No cladoceran sample had more than trace amounts of MAAs (<0.05 μg mg^?1 dw). Therefore, MAA accumulation does not seem to be a photoprotective strategy utilized by Daphnia (five species from nine lakes) or other cladocerans. 5. Seven identifiable MAAs were widely distributed among both calanoids and cyclopoids. Shinorine was ubiquitous and was usually the most abundant MAA in N. American samples. In contrast, porphyra‐334 was the predominant MAA in the southern Hemisphere Boeckella. 6. Copepods from higher UVR lakes tended to have a higher MAA content, but this relationship was statistically weak overall and taxon‐specific when found.     

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.

     

Thermal and Ionic Factors in the Ultraviolet Photolysis of Plant Cell Membranes

The exposure of red beet root tissue to ultraviolet (254 nm) at 2 × 10⁶ erg × cm^?2× min^?1 (0.2 J × cm^?2× min^?1) causes release of betacyanin after a 20 minute induction period. Ultraviolet-photolysis is temperature-sensitive having a thermal threshold at about 10°C. Reduction in pigment release was effected by chlorides of Mg, Ca and Sr, but not by Li, Na or K. This effect was marked but not complete, even at 40 mM concentration. It is concluded that photolysis is indirect, and involves a lytic factor, possibly an oxidant, derived from an original photochemical product.     

Lightmicroscopic Observations on Structure and Division of Histomonas meleagridis (Smith)*

SYNOPSIS. Culture forms and lumen-dwelling phases of the ameboflagellate Histomonas meleagridis, which are structurally indistinguishable from each other, have a single flagellum. Their well-developed pelta is connected to the anterior segment of the broad, spatulate axostylar capitulum, applied to the left-ventral surface of the nearly spheroid or somewhat ellipsoid or ovoid nucleus. The capitulum narrows into a very slender axostylar trunk that tapers to a fine point and does not project beyond the body surface. The parabasal apparatus consists of a V-shaped parabasal body and a large parabasal filament. A new flagellum appears early during division and soon approaches its full length. The 2 flagella persist thruout division and each becomes the locomotory organelle of a daughter histomonad. The arms of the parental parabasal body appear to separate, each going to 1 of the daughter mastigont systems; some parabasal material is lost early in division. The 2nd arm is regenerated in each daughter parabasal body. The large parabasal filament seems not to be retained in the parental mastigont system, and new filaments are seen at both poles before 2 daughter nuclei are formed. The old axostyle degenerates from the anterior toward the posterior end; at the same time lamellar primordia of the daughter pelta-axostyle complexes appear in the separating mastigont systems that are connected by an extranuclear spindle during the entire division process. The structure and taxonomic status of H. meleagridis are discussed in the light of this and previous studies.     

Specific Cell-Induced Transformation of Paramecium Surface Antigens

Paramecia may induce in other paramecia specific changes in the expression of genes determining surface protein synthesis, probably via cell-to-cell contact. Transformation from one antigenic type to a newly induced one is stimulated by the pretreatment of a cell with 5-fluorouracil. These observations are considered in terms of the regulation of the activity of genes in stable cells and in unstable cells which tend to transform spontaneously.     

Fourteen polymorphic microsatellite loci characterized in the house sparrow Passer domesticus (Passeridae,Aves)

We characterized 14 polymorphic microsatellite loci in the house sparrow Passer domesticus. Four loci were isolated from house sparrow genomic libraries and 10 loci were identified by testing 100 loci that had been originally isolated in other passerine species. Loci were characterized in 37–54 unrelated sparrows from British and Norwegian populations. Each locus displayed between two and 31 alleles, with the observed heterozygosity ranging between 0.30 and 0.91.     

Regulation of Prestalk-specific Acid Phosphatase in Dictyostelium discoideum

Acid phosphatase–2, as characterized by gel electrophoresis under non-denaturing conditions, is a convenient marker for prestalk cells in Dictyostelium discoideum . We have purified this prestalk-specific enzyme and have examined its regulation during development. Under denaturing conditions, the enzyme has a molecular weight of 50,000 and an isoelectric point of 4.0. On the other hand, acid phosphatase-I have a Mr-55,000 polypeptide (AP1–55) and a minor Mr-50,000 polypeptide (AP1–50) and both have diffuse isoelectric point from 3.4 to 4.1. Using monoclonal antibodies directed against acid phosphatase-2 as probes, we showed that some acid phosphatase-2 are newly synthesized at slug stage and some are converted from AP1–50 which was synthesized during ealy development.