Field experiments on the mobility of benthic invertebrates in a southern English stream

1. In each of twenty-six week-long experiments, the colonization by macroinvertebrates of boxes of natural sediment in a stony stream was measured. The experiments took place between February and November 1992 and environmental conditions prevailing during the weeks (particularly discharge and temperature) differed widely.
2. Colonization rate also varied widely between the weekly experiments and was sensitive to discharge, temperature and background benthic density, depending on the taxa considered.
3. A 'mobility index' measured colonization rate independently of background benthic density. This index was most strongly and positively correlated with discharge for the abundant stonefly Leuctra nigra, the net-spinning caddis Plectrocnemia conspersa and the Chironomidae, perhaps indicating that their mobility is physically driven by the influence of flow on drift.
4. Mobility in a second stonefly ( Nemurella pictetii ) was greatest in summer, when flows were low but temperature was high. Peak mobility in this species occurred during an ochreous bloom on the stream bed. It is likely the mobility of N. pictetii is more active than the other taxa.
5. There were thus differences among taxa in their mobility at baseflow and in their susceptibility to flow fluctuations. The population consequences of differences in mobility among taxa are discussed.     

A NEW GENUS OF ARCHIPOLYPODAN MILLIPEDE FROM THE COSELEY LAGERSTÄTTE, UPPER CARBONIFEROUS, UK

Abstract:  A new archipolypodan millipede, Anaxeodesmus diambonotus gen. et sp. nov., is described from the Upper Carboniferous (Westphalian B) Coseley Lagerstätte, West Midlands, UK. This taxon is unique amongst Archipolypoda in having tergites unornamented by spines or tubercles. It appears to have archidesmidan affinities as it shares similarities in sternal morphology with the Early Devonian archipolypodan Palaeodesmus tuberculata (Brade-Birks) from the Midland Valley of Scotland. Anaxeodesmus diambonotus significantly increases the ordinal diversity of Archipolypoda in the Late Carboniferous as all other Archipolypoda from this time period belong to the spiny Euphoberiida.     

Microbial growth and detritus transformations during decomposition of leaf litter in a stream

SUMMARY. 1. Despite the widely accepted importance of bacteria and fungi in degrading detritus in aquatic ecosystems there is still very little quantitative information on the abundance and dynamics of these microorganisms. Using epifluorescent microscopy, we measured the biomass of bacteria and fungi during decomposition of three types of leaf detritus. Bacterial production was determined from the rate of incorporation of ³H-thymidine into DNA.
2. The transformation of leaf carbon into dissolved organic carbon and fine particulate organic carbon was followed in order to compare the amounts of leaf material that were converted into these 'end-products' of decomposition versus the amount converted into microbial biomass.
3. The amount of microbial carbon in the leaf-detritus complex never exceeded 5.2% of the total carbon, and fungal biomass was always much greater than bacterial biomass. Despite the greater standing stock of fungi, the rapid turnover of bacteria (doubling about once per day) implies that their role in degrading leaf litter or as a food source for detritivores might be as great as for fungi.
4. Removal of microbial biomass from leaf litter may occur as release of fungal spores and consumption or shedding of bacterial biomass. Fungal spores can be a significant part of the fine particulate organic carbon released from leaf detritus and potentially represent an important food resource for filter-feeding organisms.     

Population Dynamics of Soil and Vegetation Protozoa

Many fresh-water protozoa can be found in litters and soils,but the ubiquitous species are those which are able to copewith fluctuating moisture conditions. Terrestrial protozoa aremore characteristic of bryophyte-soil habitats than aquaticecosystems. Nutritionally, two groups have evolved in responseto the plant community: naked, predominantly bacterial feeders,whose abundance is determined by the decomposability of thelitter in which they live; and the slow growing, humusassociatedtestacea, which are more abundant in the litters of slow decomposability.Ubiquitous species comprise about 90% of the protozoa in soils.More continuous moisture conditions enhance the appearance ofadditional species. Hence species diversity indicates highermoisture content of a soil. Protozoa may contribute to the functioningof the soil ecosystem by inducing fiocculation of bacterialpopulations and recycling of minerals through ingestion of bacteriaand excretion of soluble products. The surface of vegetationappears to represent the most terrestrial habitat a protozoancan exploit, because in contrast to the litter-soil ecosystem,only one species, Colpoda cucullus, dominates the population.     

Membrane Polypeptides associated with Photochemical Systems

WE wish to report a specific relationship between certain chloroplast membrane polypeptides and functional properties of the chloroplast usually associated with one or the other of the two photochemical systems (designated PSI and PSII). We have known this by the analysis of the chloroplast membrane polypeptides of the wild type strain of the unicellular green alga Chlamydomonas reinhardi and of mutant strains derived from it which have lost the capacity to carry out normal photosynthesis. These mutants have been characterized by the loss of particular membrane-bound components of the photosynthetic electron transport chain^1,2. This relationship is supported by analysis of the membrane polypeptides obtained from chloroplast fractions of wild type C. reinhardi and spinach enriched for reactions characteristic of either PSI or PSII by fractionation of the membranes either with digitonin^3,4 or ‘Triton X-100’⁵.     

MAMMALIAN EXTINCTIONS IN THE LATE PLEISTOCENE OF NORTHERN EURASIA AND NORTH AMERICA

The 'mass extinctions' at the end of the Pleistocene were unique, both in the Pleistocene and earlier in the geological record, in that the species lost were nearly all large terrestrial mammals. Although a global phenomenon, late Pleistocene extinctions were most severe in North America, South America and Australia, and moderate in northern Eurasia (Europe plus Soviet Asia). In Africa, where nearly all of the late Pleistocene 'megafauna' survives to the present day, losses were slight. Ruling out epidemic disease or cosmic catastrophe, the contending hypotheses to explain late Pleistocene extinctions are: (a) failure to adapt to climatic/environmental change; and (b) extermination by human hunters ('prehistoric overkill'). This review focuses on extinctions in northern Eurasia (mainly Europe) in comparison with North America. In addition to reviewing the faunal evidence, the highly relevant environmental and archaeological backgrounds are summarized. The latest survival dates of extinct species are estimated from stratigraphic occurrences of fossil remains, radiocarbon dates, or association with archaeological industries. The Middle and Upper Pleistocene (ca. 700,000-10,000 BP) in northern Eurasia and North America was a time of constantly changing climate, ranging from phases of extensive glaciation in cold stages, to temperate periods (interglacials). In the Lateglacial (ca. 15,000-10,000 BP), during which most extinctions occurred, there was a major reorganization of vegetation, mainly involving the replacement of open vegetation by forests. These changes were more profound than earlier in the Last Cold Stage, but similar in nature to vegetational changes that took place at previous cold stage/interglacial transitions. The archaeological record shows that humans have been present in Europe since the early Middle Pleistocene. The arrival in Europe ca. 35,000 BP of 'anatomically modern humans', with their technologically more advanced upper palaeolithic industries, was a 'quantum leap' in human history. Extinctions occurred throughout the European Pleistocene, but until the late Pleistocene most losses were replaced by the evolution or immigration of new species, and most of those lost without replacement were small mammals. In marked contrast, extinctions without replacement in the late Pleistocene were almost entirely confined to the largest mammals (greater than 1000 kg) and some medium-large species (100-1000 kg).(ABSTRACT TRUNCATED AT 400 WORDS)     

Extracellular Killing of Trypanosoma cruzi Amastigotes by Human Eosinophils1

Granules released from human eosinophils upon interaction with Trypanosoma cruzi amastigotes in vitro were seen attached to the surface of non-internalized parasites by electron microscopy. Amastigote damage was preceded by the binding of eosinophil granule material to its membrane, and eosinophil granule major basic protein (MBP) bound to the parasite surface was readily detectable. Additional evidence of eosinophil cytotoxicity for extracellular amastigotes was the observation that amastigotes trapped between two eosinophils, without being ingested by either one, were destroyed at the interface. Amastigotes isolated from the spleens of infected mice or grown in culture were similarly sensitive to the lytic effects of purified MBP. These results demonstrate the ability of human eosinophils to lyse T. cruzi amastigotes extracellularly in the absence of antibody and suggest that MBP may be involved in the effect. Thus, eosinophils, known to be capable of destroying phagocytosed amastigotes, could also contribute to the clearance of these parasites through extracellular killing.     

Dynamics of tuberculosis in a naturally infected Badger population

The dynamics of bovine tuberculosis infection in a wild Badger population have been studied since 1981. Faeces are sampled regularly to determine the distribution of infection in the study area. Badgers in known infected social groups, plus the neighbouring groups, are periodically caught and subjected to full clinical and bacteriological examination to monitor the progression of infection within and between groups of Badgers. The interim results of this study are presented and discussed. During 5 years (1981–1985), the temporal spread of infection between social groups in the study area was slow and restricted. Some clinically affected Badgers have survived for long periods. Evidence of infection in individual Badgers indicates that pseudo-vertical (mother to cub) transmission may be important in the maintenance of infection in the Badger population. There is also evidence of horizontal transmission by bite wounding and aerosol infection. Badger mortality due to Mycobacterium bovis infection was low, and the prevalence of infection in male Badgers is greater than in females. The data accumulated so far show no apparent relationship between Badger population density and the prevalence of M. bovis infection, nor is there any evidence to support the hypothesis that M. bovis infection acts to depress Badger population density significantly below disease-free levels. Cattle and infected Badgers can co-exist for long periods without the disease necessarily being transmitted to cattle.     

Further Studies on Substrates Inducing Metacyclogenesis in Trypanosoma cruzi

Epimastigotes of Trypanosoma cruzi, Peru strain, incubated in Contreras' artificial triatomine urine transformed into metacyclic trypomastigotes when 10 mM L-glutamine, L-asparagine or D-fructose was added to the medium. Metacyclogenesis with these substrates was comparable to the percent metacyclic morphotype formation induced by L-proline and significantly greater than that stimulated by 10 mM D-glucose. Sodium acetate (10 mM) increased transformation induced by L-proline, and L-hydroxyproline (10 mM) increased transformation induced by D-fructose. Phosphoenolpyruvate (10 mM) inhibited L-proline-induced metacyclic trypomastigote stage formation. Three antimetabolites, azetidine 2-carboxylate (5 mM), malonic acid (1 mM), and desthiobiotin (5 mM), completely inhibited D-fructose-induced but not L-proline-induced transformation. The Costa Rica, Y, and CL strains of T. cruzi showed different patterns of percent metacyclogenesis with substrates that induce transformation in the Peru strain.