Spatial and temporal response of stream bacteria to sources of dissolved organic carbon in a blackwater stream system

1. We hypothesized that changes in bacterial colony growth would be correlated to shifts in riparian vegetation (via leachate quality) along a river continuum of a south-eastern, blackwater stream (U.S.A.). Spatially, we expected bacterial assemblages from downstream reaches to utilize more sources of leachate and at higher concentrations than bacteria collected from headwater reaches. Temporally, we predicted higher colony growth on leachate from autumn-shed (senescent) leaves compared with leachate from fresh, green leaves.
2. We examined spatial differences in assemblage growth by culturing bacteria sampled along the stream continuum on gradient plates using leachates from four common riparian species ( Taxodium distichum , Carya spp., Acer rubrum and Decumaria barbara ). Bacteria from the lowest site were able to use all sources provided and at all concentrations, whereas bacteria from upper reaches could not. Colony density was correlated to relative leachate concentration at all sites along the continuum.
3. Leachates from fresh and senescent A. rubrum leaves were used to determine temporal differences. Winter assemblages of bacteria could not grow on fresh leaf leachate at any concentration but grew well on autumn leaf leachate at higher concentrations. Differential response of bacterial assemblages indicated local adaptation to potential sources of dissolved organic matter.
4. Growth response of stream bacterial colonies appeared to be dependent on the timing and source of leachate as well as on sources of dissolved organic carbon from further upstream. Growth of bacterial assemblages exhibited 'generalist' characteristics in headwater reaches and 'specialist' characteristics at the mouth of our study stream drainage. Thus, our findings lend support to the argument that variable resource habitats favour a small, generalist assemblage, while environments with stable resource supplies allow for highly diverse assemblages dominated by specialists.     

Polyamine Synthesis and Interconversion by the Microsporidian Encephalitozoon cuniculi

Polyamines are small cationic molecules necessary for growth and differentiation in all cells. Although mammalian cells have been studied extensively, particularly as targets of polyamine antagonists, i.e. antitumor agents, polyamine metabolism has also been studied as a potential drug target in microorganisms. Since little is known concerning polyamine metabolism in the microsporidia, we investigated it in Encephalitozoon cuniculi, a microspordian associated with disseminated infections in humans. Organisms were grown in RK-13 cells and harvested using Percoll gradients. Electron microscopy indicated that the fractions banding at 1.051-1.059/g/ml in a microgradient procedure, and 1.102-1.119/g/ml in a scaled-up procedure were nearly homogenous, consisting of pre-emergent (immature) spores which showed large arrays of ribosomes near polar filament coils. Intact purified pre-emergent spores incubated with [1H] ornithine and methionine synthesized putrescine, spermidine, and spermine, while [14C]spermine was converted to spermidine and putrescine. Polyamine production from ornithine was inhibitable by DL-alpha-difluoromethylornithine (DFMO) but not by DL-alpha-difluoromethylarginine (DFMA). Cell-free extracts from mature spores released into the growth media had ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (AdoMetdc), and spermidine/spermine N1-acetyltransferase (SSAT) activities. ODC activity was inhibited by DFMO, but not by DFMA. AdoMetdc was putrescine-stimulated and inhibited by methylglyoxal-bis(guanylhydrazone); arginine decarboxylase activity could not be detected. It is apparent from these studies that Encephalitozoon cuniculi pre-emergent spores have a eukaryotic-type polyamine biosynthetic pathway and can interconvert exogenous polyamines. Pre-emergent spores were metabolically active with respect to polyamine synthesis and interconversion, while intact mature spores harvested from culture supernatants had little metabolic activity.     

Evaluating the population‐level impact of an invasive species,Ring‐necked Parakeet Psittacula krameri,on native avifauna

The introduction of exotic species to ecosystems can have severe consequences for populations of native organisms, but logistical limitations and shortage of historical data often hinder attempts to quantify the ecological implications of such relationships. The establishment and rapid expansion of Ring‐necked Parakeets Psittacula krameri in England therefore presents a rare opportunity to apply novel analytical methods to existing extensive national bird monitoring data from the UK Breeding Bird Survey for an invasive species. A previous study from Belgium suggests that Ring‐necked Parakeets have the potential to reduce the abundance of Eurasian Nuthatch Sitta europaea through competition for nesting cavities. Our analysis provides no evidence for a significant impact through competition on Nuthatch populations or those of any other cavity‐nesting species within the Parakeet’s current range in the UK. However, we cannot exclude the possibility that competitive exclusion could be occurring at a minority of sites at which availability of nest cavities is limiting. This may yet have significant implications for future conflict if Parakeets continue to increase in numbers and range.     

Hypomania: a transcultural perspective

This study examined the transcultural robustness of a screening instrument for hypomania, the Hypomania Checklist-32, first revised version (HCL-32 R1). It was carried out in 2606 patients from twelve countries in five geographic regions (Northern, Southern and Eastern Europe, South America and East Asia). In addition, GAMIAN Europe contributed data from its members. Exploratory and confirmatory factor analyses were used to examine the transregional stability of the measurement properties of the HCL-32 R1, including the influence of sex and age as covariates. Across cultures, a two-factor structure was confirmed: the first factor (F1) reflected the more positive aspects of hypomania (being more active, elated, self-confident, and cogni-tively enhanced); the second factor (F2) reflected the more negative aspects (being irritable, impulsive, careless, more substance use). The measurement properties of the HCL-32 R1 were largely invariant across cultures. Only few items showed transcultural differences in their relation to hypomania as measured by the test. F2 was higher among men and in more severe manic syndromes; F1 was highest in North and East Europe and lowest in South America. The scores decreased slightly with age. The frequency of the 32 items showed remarkable similarities across geographic areas, with two excep-tions: South Europeans had lower symptom frequencies in general and East Europeans higher rates of substance use. These findings support the interna-tional applicability of the HCL-32 R1 as a screening instrument for hypomania.     

The Onset of Germination Ability in Developing Wheat

The ability of primary wheat grains (cv. Sappo) to germinatewas determined at different times from anthesis. Fresh, prematurelyharvested grains germinated best at low temperatures (<10°C). The temperature range over which appreciable germinationtook place broadened and the maximum percentage germinationachieved increased with lengthening time between anthesis andharvest. Chilling and exogenous applications of GA₃ each affectedthe rate of germination and the maximum percentage germinationof grains in their own ways. The results are discussed in relationto the identification of ‘dormancy’ in wheat grains.     

Influence of an ecosystem engineer,the emergent macrophyte Sparganium erectum,on seed trapping in lowland rivers and consequences for landform colonisation

1. Plant physical ecosystem engineers can influence vegetation population and community dynamics by modifying, maintaining or creating habitats. They may also have the potential to act upon biotic processes, such as seed dispersal. 2. Examples exist of reduction in seed dispersal distances in vegetated compared to unvegetated terrestrial environments, and concentration of seed deposits associated with plant patches. Such effects in aquatic environments have been little studied, but the engineering effect of plant patches on patterns of flow velocity and sediment deposition in streams suggests that they may play a similar role. 3. In this study, we assess the potential of an emergent aquatic species, Sparganium erectum, to play a role in physically modifying river habitats and trapping seeds by examining patterns of seed deposition and substrate type in 47 river reaches across England and southern Scotland, U.K. 4. Areas of the river channel within or adjacent to S. erectum patches harboured more plant seeds and more species than unvegetated areas and had finer, sandier substrates with higher organic matter, total nitrogen and total phosphorus content. Most seed species were competitive, indicating that they were well suited to colonise the competitive environment of an S. erectum patch, and could potentially further stabilise accumulated sediments and contribute to landform development. 5. We demonstrate that S. erectum patches influence both the physical environment and the retention of seeds, in consistent patterns across the channel bed, for a range of lowland rivers that vary in stream power and geology and which can be expected to vary in levels of supply of fine sediment and seeds. 6. Our findings support the hypothesis that the fundamental influence of a riverine ecosystem‐engineering species on slowing fluid flow links the habitat creation process of sediment sorting and retention to seed trapping. We suggest the process is applicable to a wide range of aquatic and riparian vegetation. We also suggest that the mono‐specific and competitive growth, which is typical of these engineering species, will strongly influence the recruitment of trapped seeds.     

The Physiological Mechanisms of Acclimatization in Tropical Reef Corals

SYNOPSIS. The ability of scleractinian corals to survive changesthat are predicted in the global environment over the next centurywill lie in their physiological mechanisms of acclimatization.Corals display rapid modifications in behavior, morphology andphysiology enabling them to photoacclimate to changing lightconditions, a scenario that demonstrates considerable biologicalflexibility. Here we argue that the acclimatization mechanismsin corals are fundamentally similar to those exhibited by otherinvertebrate taxa. We discuss protein metabolism as a mechanismunderlying acclimatization responses in reef corals, and explorethe relationship between protein turnover, metabolic rate, growthrate, and acclimatization capacity. Our preliminary analysessuggest that corals with low growth rates (µCa/mgN/h)and high metabolic rates (µO₂/cm²/hr), such as the massivespecies, acclimatize more effectively than those with high growthrates and low metabolic rates, a feature that is characteristicof branching species. We conclude that studies of protein turnover,combined with temporally relevant investigations into the dynamicaspects of coral dinoflagellate symbioses will provide considerableinsight into why corals exhibit such a high level of variationin response to the same environmental challenge. Furthermore,a more detailed understanding of acclimatization mechanismsis essential if we are to predict how a coral assemblage willrespond to present and future environmental challenges.