Floral Ontogeny in Scirpus, Eriophorum and Dulichium (Cyperaceae), with Special Reference to the Perianth

Annals of Botany 95: 1199–1209, 2005 Unfortunately, Figure 7 of this article was printed as a negative.The correct figure appears overleaf. The publisher apologizes     

Ultrastructure of Spironucleus barkhanus N. Sp. (Diplomonadida: Hexamitidae) from Grayling Thymallus thymallus (L.) (Salmonidae) and Atlantic Salmon Salmo salar L. (Salmonidae)

ABSTRACT. A hexamitid flagellate Spironucleus barkhanus n. sp., from the lumen of the gut and gall bladder of wild grayling Thymallus thymallus , and from muscle abscesses of farmed Atlantic salmon Salmo salar from Norway, is described by light, scanning and transmission electron microscopy. The flagellate was axenically cultured in trypticase, yeast extract, iron serum medium. Live trophozoites from axenic cultures incubated at 5° C, measure 11–20 x 6–14 μm. The flagellates show a typical bi-radial symmetry. Each recurrent flagellum is almost completely surrounded by a striated lamina. In the posterior end the lamina widens, appearing heart shaped in transverse section. Accompanying each recurrent flagellum are three narrow bands of microtubules, following the longitudinal groove created by the incomplete closure of the striated lamina. The recurrent flagella emerge posterio-medially through cytostome openings halfway surrounded by crescent-shaped ridges, oriented in opposite directions in the two openings. The position and adornment of the cytostome openings, and the arrangement and number of the microtubules accompanying the recurrent flagella, distinguish Spironucleus barkhanus n. sp. from previously described species of Spironucleus .     

Growth of macrophytes and ecosystem consequences in a lowland Danish stream

SUMMARY. 1. The River Suså is a small, nutrient-rich stream situated in an open landscape with clayish subsoil under intensive cultivation. Discharge was variable daily and seasonally due to low groundwater input. Above-ground development of submerged macrophytes was restricted to late May to November, when water velocity and depth were low. Dominant macrophytes were rooted Potamogeton pectinatus and Sparganium emersum and unrooted Cladophora . Biomass development was closet) related to light availability.
2. Growth rates of macrophytes were linearly related to light availability when self-shading was accounted for. Potamogeton pectinatus grew rapidly m May-June, concentrated the biomass at the water-surface during July-August, and then declined exponentially when the shoots became basally senescent. Sparganium emersum had linear, flexible leaves that were continuously replaced from a basal meristem. Sparganium emersum was less susceptible to high water velocities than Potamogeton pectinatus and the biomass declined later and at lower rates during autumn. Sparganium emersum also regrew after culling that left its meristem intact in the sediment. Unrooted Cladophora developed a high biomass during sunny periods and subsequently disappeared at high discharges. The summer biomass of rooted macrophytes was greater in years with high summer discharge, whereas the biomass of Cladophora and of the epiphytic microbial community was lower due to scouring.
3. Submerged macrophytes played a key role in structure and functioning of the ecosystem. They reduced water velocities two to four fold during summer and promoted extensive organic sedimentation. The biomass of benthic diatoms declined parallel to increased macrophyte shading and sedimentation. In addition, submerged macrophytes formed a large substratum for macroinvertebrates and for a microbial community.     

Automatic Cell Counting in Continuous Flow Cultures of Tetrahymena pyriformis*

This report describes an electronic cell counter constructed for determining cell number in cultures of the ciliate, Tetrahymena pyriformis. The culture chamber has been equipped with a device which determines the number of cells per unit volume and records the number automatically. As cell multiplication is unaffected by the counting procedure the cells are returned to the culture. Furthermore, keeping the culture volume constant we have arranged a continuous flow of fresh nutrient medium through the culture chamber and thus established conditions under which cell multiplication has continued for months while determinations of cell concentrations have been recorded every 10 min. Since the culture volume has been small, ～25 ml, growth studies utilizing this method require less than one liter of fresh medium per week in spite of the fast multiplication (9 generations per 24 hr) occurring in cultures of Tetrahymena pyriformis under optimal conditions.     

Studies of Messenger RNA during the Cell Cycle in Synchronized Mass Cultures of Tetrahymena pyriformis GL by Hybridization

SYNOPSIS RNA isolated from free ribosomes, from cell structures and from soluble cell phase after indole lysis of synchronized Tetrahymena cells showed different abilities to hybridize with DNA. The supraoptimal temperature (34 C) caused a decrease in the ability to hybridize in all 3 RNA fractions. The same effect was noted at the time of cell division. Synthesized messenger RNA as a proportion of the total quantity of RNA was roughly constant during the whole cell cycle. However, in contrast to synchronized mammalian cells the messenger RNA synthesis did not proceed at a constant rate thruout the cell cycle.     

Induction of Isocitrate Lyase in Synchronous Cultures of Chlorella fusca

Isocitrate lyase (ICL) of Chlorella was induced with acetate, and induction kinetics followed in autospores and 6 h old cells of a synchronous culture. The enzyme could not be induced in illuminated cells. With both cell types 1.2 mM acetate was the optimal inducer concentration. Freeze-thawed cells and acetone powders were used for measurement of activity. With the former the time course of increase in activity was different at the two cell ages. With 6 h old cells the activity fluctuated: There was first a period of increase, then one with decrease and again one of increase. No such variation was found with freee-thawed autospores or with acetone powders of both cell stages. Darkening 6 h old cells for different periods of time before induction reduced the peak of activity, leaving the rate of the third phase unchanged. Illumination of darkened cells before induction increased the peak. Increasing the duration of both treatments increased their respective effects. Acetone extracts taken at different times after start of induction inhibited the ICL activity of a test preparation. The inhibition decreased concurrently with the variation in the ICL activity-found-when freee-thawed cells were used in the enzyme assay. The inducibility, taken as the rate of the third phase, was measured at different times during the 24 h synchronous cycle. Using three different acetate concentrations and both methods of cell preparation, we found that the inducibility was constant for 17 h whereafter it increased rapidly to a final level.     

Nitrogen deposition induced changes in DOC : NO3‐N ratios determine the efficiency of nitrate removal from freshwaters

With a unique data set comprising 1041 boreal forested and low human impacted lakes included in three Swedish lake inventories for 1995, 2000 and 2005 and with time series for 12 of the lakes from 1988 to 2008 we show that nitrate‐nitrogen (NO₃‐N) is accumulated in freshwaters along with increasing atmospheric nitrogen deposition (N_dep). At the same time we observe decreasing DOC : NO₃‐N ratios in the water column. We suggest that NO₃‐N is accumulated in freshwaters when denitrifying bacteria are limited by their energy source rather than the availability of NO₃‐N, i.e. at low DOC : NO₃‐N ratios. We obtained further support for a close relationship between N_dep driven DOC : NO₃‐N ratios and the efficiency of nitrate removal by using a published global data set on measured nitrate removal rates in unproductive reference streams. Owing to the currently decreasing N_dep in large regions of, for instance, Northern Europe, this process is now reversed, resulting in increasing DOC : NO₃‐N ratios and more efficient nitrate removal from freshwaters. Depending on NO_x emissions, nitrogen limited regions may expand with an immediate effect on nitrate concentrations in freshwaters.     

Taxonomy of the African giant pouched rats (Nesomyidae: Cricetomys): molecular and craniometric evidence support an unexpected high species diversity

Our study combined a mitochondrial cytochrome b phylogeny with cranial measurements from giant pouched rats collected across sub‐Saharan Africa. The mitochondrial phylogeny resolves two West African clades and a clade with east and central Africa representatives. This last clade can be further divided into four subclades. Altogether they represent six species (Cricetomys gambianus, Cricetomys ansorgei, Cricetomys emini, and three undescribed taxa) that can be distinguished on the basis of their mitochondrial DNA sequences and craniometry. In the absence of adequate craniometric data the existence of Cricetomys kivuensis cannot be confirmed by our data. Our combined molecular and craniometric data allowed us to broadly delineate the distribution ranges of the detected species. Cricetomys gambianus occurs in the savannah and forest clearings of West Africa. Cricetomys ansorgei is distributed in the savannah of East and southern Africa. Cricetomys emini, as currently recognized across the Guineo‐Congolian forest of Africa, is shown to be diphyletic. Cricetomys sp. 1, a separate operational taxonomic unit closely resembling C. emini, occurs in the forest zone of West Africa. An undescribed sister‐species of C. ansorgei, Cricetomys sp. 2, occurs in the forest of Central Africa along the left bank of the Congo River. Cricetomys sp. 3 occurs on the right bank of the Congo River from Cameroon to the Republic of Congo, whereas the true C. emini also occurs on the right bank of the Congo River but appears to be restricted to the Democratic Republic of Congo. Cranial phenotype within the genus tends to conform to ecological zonation (either forest or savannah) rather than to phylogenetic affiliation of the species concerned, suggesting that diversifying selection across environmental gradients could be responsible for biological diversification within the genus.     

The influence of introduced trout on the benthic communities of paired headwater streams in the Sierra Nevada of California

1. Non‐native trout have been stocked in streams and lakes worldwide largely without knowledge of the consequences for native ecosystems. Although trout have been introduced widely throughout the Sierra Nevada of California, U.S.A., fishless streams and their communities of native invertebrates persist in some high elevation areas, providing an opportunity to study the effects of trout introductions on natural fishless stream communities. 2. We compared algal biomass and cover, organic matter levels and invertebrate assemblages in 21 natural fishless headwater streams with 21 paired nearby streams containing stocked trout in Yosemite National Park. 3. Although environmental conditions and particulate organic matter levels did not differ between the fishless and trout streams, algal biomass (as chlorophyll a concentration) and macroalgal cover were, on average, approximately two times and five times higher, respectively, in streams containing trout. 4. There were no differences in the overall densities of invertebrates in fishless versus paired trout streams; however, invertebrate richness (after rarefaction), evenness, and Simpson and Shannon diversities were 10–20% higher in fishless than in trout streams. 5. The densities of invertebrates belonging to the scraper‐algivore and predator functional feeding guilds were higher, and those for the collector‐gatherer guild lower, in fishless than trout streams, but there was considerable variation in the effects of trout on specific taxa within functional feeding groups. 6. We found that the densities of 10 of 50 common native invertebrate taxa (found in more than half of the stream pairs) were reduced in trout compared to fishless streams. A similar number of rarer taxa also were absent or less abundant in the presence of trout. Many of the taxa that declined with trout were conspicuous forms (by size and behaviour) whose native habitats are primarily high elevation montane streams above the original range of trout. 7. Only a few taxa increased in the presence of trout, possibly benefiting from reductions in their competitors and predators by trout predation. 8. These field studies provide catchment‐scale evidence showing the selective influence of introduced trout on stream invertebrate and algal communities. Removal of trout from targeted headwater streams may promote the recovery of native taxa, community structure and trophic organisation.