Some aspects of the seasonal distribution of flagellates in mountain lakes

In a larger regional survey in Tyrol, phytoplankton species composition and biovolume of mid-altitude and high-mountain lakes was studied. Results from eight lakes showed that flagellates (mainly Chrysophyceae, Dinophyceae, and Cryptophyceae) are important components of the phytoplankton.In the mid-altitude lakes a spring and an autumn maximum of Chrysophyceae as well as a summer maximum of large dinoflagellates are observed, whereas Cryptophyceae and Dinophyceae show irregular distributions. In the high-mountain lakes the seasonal variations of phytoplankton, including flagellates, are limited by the long duration of the winter situation. However similar sequences of phytoplankton assemblages as in the midaltitude lakes can be observed. Flagellates in high-mountain lakes are important to sustain phytoplankton standing crop under the winter snow and ice cover.In order to show similarities and differences of high-mountain and mid-altitude lakes, vertical profiles of phytoplankton from three lakes and seasonal patterns of Gymnodinium uberrimum from two lakes are compared. In addition the patterns of cryptomonads differing in their ecological requirements (Cryptomonas spp. and Rhodomonas minuta) are shown for a meromictic mid-altitude lake.     

Reduced Growth of Blastocrithidia culicis and Crithidia oncopelti Freed of Intracellular Symbiotes by Chloramphenicol*

The intracellular symbiotes of Blastocrithidia culicis and Crithidia oncopelti can be eliminated from cultures of the flagellates by a single chloramphenicol (CAP) treatment. Effective dosages were determined to be 0.01–0.08% (w/v) CAP after a treatment for 2 weeks or more for B. culicis and 0.08% (w/v) after 1 month for C. oncopelti in most cases. Ineffective dosages only lowered the numbers of symbiote-bearing flagellates. Growth of both species of flagellates in the presence of CAP was reduced in proportion to the drug concentration. Repeated subcultures at effective dosages yielded symbiote-free flagellates, which maintained a low level of growth rate. After repeated subcultures at ineffective dosages, the growth rate rose and the symbiote-bearing cells, initially very few, increased in number. The lowest effective dosages proved to be marginal, often producing symbiote-free cultures, but occasionally cultures with a few symbiote-bearing cells. After repeated subcultures at these drug concentrations, symbiote-containing cultures grew faster than the symbiote-free cultures. Hence, the symbiotic bacteria benefit the growth of their hosts, perhaps by supplying essential factors that are inadequate even in a rich blood medium.     

异养鞭毛虫原位生长研究进展

近年来,异养鞭毛虫随水体生态内浮游动物小型化进程的加剧,所占比重越来越,已成为当前生态学研究的重要对象,其研究方法也伴随着发生了革命性变化,通过简单介绍异养鞭毛虫的原位研究方法,并就近来研究成果进行了系统综述。     

The significance of inter- and intraspecific variation in bacterivorous and herbivorous protists

This paper reviews the emerging evidence on the significance of inter- and intraspecific variation in the feeding behaviour of aquatic protists. Small heterotrophic nanoflagellates (HNF) have been identified as the primary bacterial consumers in most aquatic environments. Recent research using novel techniques such as flow cytometry and high resolution video microscopy revealed that their feeding strategies and grazing rates are diverse. There is an important conceptual difference between uptake rates measured in short-term (min to h) experiments and grazing rates averaged over a longer-term (d). This is because the latter are strongly affected by digestion rates which are species-specific, i.e. the same bacterial prey may be digested differently by various grazers, and the same predator may selectively digest variable prey. Planktonic ciliates are the most important algal consumers in many lakes and marine systems. Large species-specific differences in their feeding behaviour and growth rates have been documented for closely related species. Intraspecific variation, which is, most likely, caused by varying clonal composition may be as important as interspecific variation. Finally, there is some evidence that the individual variability within a given population is generally large, both among bacterivorous HNF and among herbivorous ciliates. The consequences of this diversity becoming apparent at the levels of the species, population, clone and individual need to be considered by aquatic ecologists in their conceptual models. This revised version was published online in August 2006 with corrections to the Cover Date.     

THE OCCURRENCE AND STRUCTURE OF FLAGELLAR SCALES IN SOME FRESHWATER CRYPTOPHYTES1

Flagellar scales were found in seven out of eleven fresh-water cryptophytes investigated by shadowing whole cells. All scales examined were 140 to 170 nm in diameter and had a basic seven-sided rosette pattern with delicate interlacing. The results of this study indicate that flagellar scales are common in cryptophytes .     

Different growth responses of C3 and C4 grasses to seasonal water and nitrogen regimes and competition in a pot experiment

Understanding temporal niche separation between C₃ and C₄ species(e.g. C₃ species flourishing in a cool spring and autumn whileC₄ species being more active in a hot summer) is essential forexploring the mechanism for their co-existence. Two parallelpot experiments were conducted, with one focusing on water andthe other on nitrogen (N), to examine growth responses to wateror nitrogen (N) seasonality and competition of two co-existingspecies Leymus chinensis (C₃ grass) and Chloris virgata (C₄grass) in a grassland. The two species were planted in eithermonoculture (two individuals of one species per pot) or a mixture(two individuals including one L. chinensis and one C. virgataper pot) under three different water or N seasonality regimes,i.e. the average model (AM) with water or N evenly distributedover the growing season, the one-peak model (OPM) with morewater or N in the summer than in the spring and autumn, andthe two-peak model (TPM) with more water or N in the springand autumn than in the summer. Seasonal water regimes significantlyaffected biomass in L. chinensis but not in C. virgata, whileN seasonality impacted biomass and relative growth rate of bothspecies over the growing season. L. chinensis accumulated morebiomass under the AM and TPM than OPM water or N treatments.Final biomass of C. virgata was less impacted by water and Nseasonality than that of L. chinensis. Interspecific competitionsignificantly decreased final biomass in L. chinensis but notin C. virgata, suggesting an asymmetric competition betweenthe two species. The magnitude of interspecific competitionvaried with water and N seasonality. Changes in productivityand competition balance of L. chinensis and C. virgata undershifting seasonal water and N availabilities suggest a contributionof seasonal variability in precipitation and N to the temporalniche separation between C₃ and C₄ species. Key words: Chloris virgata, competition, growth, Leymus chinensis, nitrogen seasonality, water seasonality Received 19 November 2007; Revised 29 January 2008 Accepted 4 February 2008     

Micronomads of the Mediterranean sea

Abstract

The Structural Heterogeneity of Plants with a Thallus. Plants that evolved in aquatic environments developed a thallus, that is a multicellular body without structures deputed to the mass transportation of water along great distances. The structural organisations of thalli shows a number of different solution to reach the coordination necessary to the expression of differentiation in the multicellular thalli. Some of these structures are comparatively esamined, pointing out their peculiarities. The diversity observed among plants evolved in aquatic environments is expressed not only by the taxa that can be recognized, but also by a great number of solutions developed to express the differentiation of parts in a complex multicellular body.     

Trypanosomatids, Other Than Phytomonas spp., Isolated and Cultured from Fruit

Trypanosomatids were isolated from edible fruit. One of the isolates (from tangerine) presented a set of enzymes for the metabolism of arginine-ornithine similar to that of Leptomonas spp., and failed to be recognized by monoclonal antibodies specific for Phytomonas spp. The possibility that trypanosomatids other than Phytomonas spp. could infect fruit was further examined by inoculating tomatoes with species of Crithidia, Leptomonas and Herpetomonas. Some of these flagellates multiplied in tomatoes. Besides, house flies became infected with Crithidia sp. when fed on tomatoes experimentally inoculated with this flagellate. Therefore, isolation of a trypanosomatid from a plant should not constitute an absolute criterion for placing it in the genus Phytomonas.     

An application of a bioenergetics model to Eurasian perch (Perca fluviatilis L.)

A bioenergetics model was developed for Eurasian perch ( Perca fluviatilis L.) by revising an existing model for yellow perch and walleye. Data were gathered from field studies and the literature. Besides adjusting the original parameters of the model, effects of season on consumption and metabolic rates were added. The predictive capability of the revised model was high both concerning the levels of growth and its seasonal development in the Baltic coastal waters to which the model was applied. Perch young-of-the-year attained almost maximum consumption and growth except in the highest temperatures experienced. In larger fish, the model estimated consumption to be about 50 per cent of the maximum possible rate.     

Identification of (24S)-24-methylcholesta-5,22-dien-3β-ol as the major sterol of a marine cryptophyte and a marine prymnesiophyte

The major sterol in the two unicellular marine algae Cryptomonas sp. and Isochrysis galbana has been identified as (24S)-24-methylcholesta-5,22-dien-3β-ol (epibrassicasterol). The production of a sterol with the 24α-configuration by cryptophycean and prymnesiophycean algae and by diatoms contrasts with the situation in many other algae which produce sterols with the 24β-configuration.     

STRUCTURE OF EXTRACELLULAR POLYSACCHARIDES PRODUCED BY A SOIL CRYPTOMONAS SP. (CRYPTOPHYCEAE)1

The Hindak strain of a Cryptomonas species (Cryptophyceae) produces extracellular polysaccharides. Because there is no information on the structure of these compounds in the Cryptophyceae we conducted structural studies. Gas–liquid chromatographic analyses showed that the polysaccharide is composed of fucose, rhamnose, xylose, mannose, glucose, galactose, galacturonic acid, glucuronic acid, and traces of 3-O-methyl galactose. The polysaccharide was separated into two subtractions by ion-exchange chromatography. Fraction A consisted mainly of 1,3-linked galactose units and 1,4-linked galacturonic acid. Unlike fraction B, fraction A did not have xylose, 3-O-methyl galactose, or glucuronic acid. Also, its degree of branching was low compared to that of fraction B. Only traces of sulfate were present infraction A, but fraction B was 10–15% sulfated. Protein was approximately 1% in both fractions. These polysaccharides appear to be a novel type of polymer in algae.     

The development of seasonal variation in gonadal hormones and body weight in the maturing squirrel monkey

Captive-born squirrel monkeys of three different subtypes (Colombian, Bolivian, Peruvian), ranging in age from 1 to 4.5 years for males and 1 to 3.5 years for females, were examined at 3-month intervals throughout the year for seasonal changes in levels of plasma testosterone and progesterone and in body weight. Cyclical activity of testosterone in males began between 2 and 3 years of age but became more defined by the time the animals were 3–4 years old. Peak values occurred in February and May and corresponded to the the time of year in which adults normally mate. Elevations of progesterone occurred initially at approximately 2.5 years of age in February and May, and mainly infernales of the Colombian subtype. However,unlike levels of testosterone in males of this age, which declined in August and November (following the typical breeding season), levels of progesterone in females continued to increase during these months. Seasonal changes in body weight were also found in males but these changes were less evident than, and did not correlate with, hormonal changes.     

Growth retardation in weight and catch-up growth following infection by measles and whooping cough among babies of rural Zaire (Lake Tumba)

This study has shown that measles and whooping cough affect growth in weight among babies of rural Zaire (Lake Tumba). The average loss in weight due to measles, is more than twice the amount due to whooping cough. However, the time needed to regain the original growth channel after infection by measles, is about half the time needed to fully catch up after whooping cough. The amount of weight loss is proportional to the child's weight at the onset of the disease. There is no difference in the susceptibility to lose weight after measles or whooping cough, between boys and girls, nor between Oto and Twa. This study has also shown that the effect of measles and whooping cough on the growth in weight, is independent of the season of the hear, although the incidence of these diseases showed a significant seasonal pattern. Finally, this study gives evidence for the fact that the incidence of weight loss one month after the onset of measles or whooping cough is age-related.