Oxygen concentration profiles and exchange in sediment cores with circulated overlying water

SUMMARY. 1. The overlying water of intact sediment cores was constantly stirred with an impeller at a rate sufficient to mix turbulently the water column and maintain the diffusive boundary layer at a determined thickness. The system allowed standardization of water circulation in laboratory sediment core experiments.
2. Both oxygen concentration and oxygen penetration depth in the sediments decreased, the former by 70% and the latter from 4.2 mm to 2.0 mm, when the overlying water was not stirred for 24 h, as measured with oxygen microelectrodes in a lake sediment core.
3. Oxygen profiles measured in sediment cores in the laboratory were similar to those measured in situ when the overlying water was stirred with an impeller at such a rate that a similar thickness of the diffusive boundary layer at the sediment-water interface developed in the laboratory as that in situ.
4. Sediment oxygen consumption was calculated from: (1) measured oxygen profiles in the diffusive boundary layer and the molecular diffusion coefficient for oxygen in water; (2) the measured oxygen decrease in the top of the sediments and the estimated diffusion coefficient in the sediment; and (3) by oxygen differences in the overlying water after incubation of sediment cores.     

Ecological aspects of a silicified bivalve fauna from the Silurian of Gotland

The silicified Wenlockian (Silurian) bivalve fauna from MÖllbos, Gotland, is part of a life assemblage. The vast number of shells show unusual phenomena, e.g. shell repair, pearl and tumour formation, etc. A number of shells contain epibionts and bored, round holes. Presumptive predators of the bivalve community are discussed. Size-frequency distribution of the two most abundant species possibly reflects age classes. The fauna, comprising eleven species, is dominated by deposit-feeders (90 %). They exhibit niche diversification, including at least three different feeding levels within the sediment.     

Breeding biology during establishment of a reintroduced Griffon Vulture Gyps fulvus population

We studied the breeding parameters of a reintroduced population of individually marked Griffon Vultures Gyps fulvus in the Grand Causses region of southern France from the time of first reintroduction in 1982 to 1992. Among nesters, 65% of the birds released as immatures or born in the wild recruited into the breeding population when 4 years old, i.e. 1 year earlier than previously described. The proportion of birds nesting each year was relatively high and increased with time, suggesting that conspecific attraction favoured recruitment. We detected a permanent adverse effect of long-term captivity on the nesting success of birds released when more than 2 years old: compared to the natural population, birds which had been kept in captivity showed a reduced breeding success during the whole study period. The breeding success of released immatures and wild-born birds was similar to the highest values observed in a natural population in the Spanish and French Pyrenees. Breeding failures did not usually result in mate change but affected nest-site fidelity. Birds not born in the wild were more likely to recruit to the largest subcolonies available, which highlights the role of social attraction. The observed philopatry of wild-born birds probably resulted from such a social attraction since most of them were born in the largest subcolony. Conspecific attraction maintained the spatial aggregation of nests, whereas nest changes after a breeding failure favoured the spatial expansion of the colony.     

Vegetative anatomy and systematics of subtribe Dendrobiinae (Orchidaceae)

Anatomy of leaf, stem, and root of more than 100 species in subtribe Dendrobiinae (Orchidaceae) was studied with the light microscope to provide a comparative anatomical treatment of these organs, to serve as an independent source of evidence that might be taxonomically important, and to recommend such reinterpretations of existing classifications as are suggested by a phylogenetic assessment of data. We based our classification on that of Rudolf Schlechter as the most complete and widely accepted today. We found that the anatomy of plants in subtribe Dendrobiinae reflects a high degree of morphological diversity, and many of the anatomical characters appear to be homoplasous. When these anatomical data are used to interpret the systematic relationships among the genera, they indicate that Dendrobium is not monophyletic and that Cadetia and Pseuderia are apparently nested within the structure of Dendrobium when section Grastidium is chosen as a functional outgroup. Lack of resolution in the strict consensus tree illustrates the difficulty of determining the phylogenetic relationships of many of Schlechter's sections using anatomical characters. Nevertheless, we recommend that his sectional classification, with appropriate modifications based on available data, be retained for the present, pending a more detailed understanding of the phylogeny of Dendrobiinae based on morphology, micromorphology, anatomy, and DNA studies.     

YI-S, a Casein-free Medium for Axenic Cultivation of Entamoeba histolytica, Related Entamoeba, Giardia intestinalis and Trichomonas vaginalis

ABSTRACT. Pancreatic digests of casein are major ingredients of media used in the axenic cultivation of lumen-dwelling parasitic protozoa, especially Entamoeba, Giardia , and trichomonads. The digest used almost exclusively in the development of these media, Medo-Peptone (Trypticase® BBL), has not been available since 1981. Moreover, none of dozens of similar type digests tested since then in our laboratory has proved equal to Medo-Peptone, and in the last two years it has become increasingly difficult to obtain new batches which will support even modest growth of Entamoeba histolytica . In response to this problem we have developed a casein-free medium, YI-S, consisting of a nutrient broth, vitamin mixture and serum. We recommend it as a replacement for the casein-dependent medium TYI-S-33, currently the most widely used for axenic culture of Entamoeba histolytica and other lumen-dwellers.     

Comparative anatomy and systematics of woody Saxifragaceae. Aphanopetalum Endl.

The floral and vegetative anatomy of the small Australian genus Aphanopetalum were studied. Wood is described for the first time and is characterized by predominantly solitary pores, scalariform vessel element perforation plates with low bar numbers, imperforate tracheary elements with distinctly bordered pits, sparse axial parenchyma, and a combination of homocellular and heterocellular rayS. Starch occurs in both axial and ray parenchyma of the wood. Stems possess unilacunar, one-trace nodes and the uncommon feature of an endodermis with well-defined Casparian stripS. Leaves have anomocytic stomata, a bifacial mesophyll and semicraspedodromous venation or a combination of semicraspedodromous and brochidodromous venation. The tetramerous flowers are apetalous or have minute petals. The compound, half-inferior gynoecium consists of essentially totally united carpels. The pattern of floral vascularization resembles different Saxifragaceae sensu lalo in that the compound sepal-plane and petal-plane traces give rise to staman bundles as well as sepal, petal, and carpel wall venation in their respective planes. The ventral ovarian bundles are fused into a single ventral complex that subdivides at the top of the ovary to form ventral bundles and to supply the one ovule in each locule. Vegetative and floral features provide compelling evidence to suggest that Aphanopetalum has its nearest relatives among the Saxifragaceae sensu lato rather than Cunoniaceae. The genus is probably best treated as forming its own subfamily (or family) among the saxifragaean alliance.     

Incubation in Mice Provides a Signal for the Differentiation of Trypanosoma cruzi Epimastigotes to Trypomastigotes1

The differentiation of Trypanosoma cruzi epimastigotes into trypomastigotes was studied in diffusion chambers sub-cutaneously implanted in mice. Using epimastigotes of the Tulahuén strain, transformation was first evident at 16 h after implantation and reached its maximum (92% trypomastigotes) by 24 h. Shortly before their differentiation into trypomastigotes, epimastigotes were found to develop resistance to lysis by the alternative pathway of complement. Furthermore, implantation of stationary-phase (as opposed to log-phase) parasites resulted in the accumulation of large numbers of complement-resistant epimastigotes in the chambers. These observations suggest that epimastigotes pass through a complement-resistant transitional stage before differentiating into trypomastigotes and that transformation may require cell division. In a further series of experiments, epimastigotes recovered 7 h after implantation in mice were found to differentiate into trypomastigotes when cultured in vitro for an additional 17 h at 37°C. This observation indicates that the events which trigger the morphologic transformation of epimastigotes into trypomastigotes can be dissociated operationally from the differentiation process itself.