Structural and Functional Characterization of Paramecium Dynein: Initial Studies

ABSTRACT Dynein arms and isolated dynein from Paramecium tetraurelia ciliary axonemes are comparable in structure, direction of force generation, and microtubule translocation ability to other dyneins. In situ arms have dimensions and substructure similar to those of Tetrahymena. Based on spoke arrangement in intact axonemes, arms translocate axonemal microtubules in sliding such that active dynein arms are (-) end directed motors and the doublet to which the body and cape of the arms binds (N) translocates the adjacent doublet (N+1) upward. After salt extraction, based on ATPase activity, paramecium dynein is found as a 22S and a 14S species. the 22S dynein is a three-headed molecule that has unfolded from the in situ dimensions; the 14S dynein is single headed. Both dyneins can be photocleaved by UV light (350 nm) in the presence of Mg^2-, ATP and vanadate; the photocleavage pattern of 22S dynein differs from that seen with Tetrahymena. Both isolated dyneins translocate taxol-stabilized, bovine brain microtubules in vitro. Under standard conditions, 22S dynein, like comparable dyneins from other organisms, translocates at velocities that are about three times faster than 14S dynein.     

The influence of channelisation on riparian plant assemblages

1. A comparative study of species diversity and assemblage patterns of herbaceous ground‐flora communities in riparian areas was performed along natural mid‐sized lowland streams and their channelised counterparts. The areas had open vegetation and were positioned along 18 similar‐sized third to fourth order stream reaches. 2. Alpha diversity was significantly higher along natural streams both at the sample plot and reach scale. Sample plot diversity peaked at intermediate distance from the natural stream reaches, whereas it increased with increasing distance from the channelised reaches. Both gamma diversity, measured and estimated from species‐area curves, and beta diversity, which is a measure of the change in diversity between areas, was similar along the two types of streams. 3. Alpha diversity correlated with several of the measured and calibrated environmental variables. The positive correlation between bank slope and alpha diversity indicates that flooding plays a key role in maintaining high levels of diversity along natural streams. 4. Species composition varied significantly between the two stream types. A cluster analysis identified four clusters of which two clusters (one and three) primarily included species associated with sample plots in areas along natural streams. Most cluster one and three species were also identified as indicator species for this stream type. 5. Canonical correspondence analysis revealed that cluster one species were less productive species associated with high total soil carbon and nitrogen contents, whereas cluster three species were highly productive species associated with high soil moisture levels, probably partly resulting from flooding. Our results suggest that distance from the stream channel imposes a probabilistic gradient that sustains co‐occurrence of these two communities in riparian areas along natural mid‐sized lowland streams.     

Movement of Amyloplasts in the Statocytes of Geotropically Stimulated Roots. The Pre-Inversion Effect

Previously inverted Lepidium roots were placed in a horizontal position and the amyloplasts in the statocytes of the root cap allowed to fall through their entire range of movement across the cell. Under these conditions the amyloplasts first follow a mainly downward course for 6 to 8 min at a speed between 0.5 and 0.8 μm per min. For the next 10 min they move slightly more slowly in a direction away from the apical end of the cell, still sinking somewhat, but without reaching the plasmalemma along the lower wall. Previous experiments have shown that conditions assumed to allow the amyloplasts to slide parallel to the longitudinal cell walls are those that give rise to the largest geotropic curvatures. Such conditions are for instance (1) stimulation at 135° (root tips pointing obliquely upward) and (2) inversion of roots for 16 min followed by stimulation at 45°. Treatments assumed not to permit extensive sliding of the amyloplasts produce smaller geotropic curvatures, namely (3) stimulation at 45° without pre-inversion and (4) inversion followed by stimulation at 135°. The location of the amyloplasts after these four kinds of treatment has now been determined on photomicrographs and the assumptions concerning the paths and extent of sliding of the amyloplasts confirmed. Observations on electron micrographs showed that under all conditions the amyloplasts are separated from the plasmalemma by other organelles, such as ER, nucleus or vacuoles. In roots rotated for 15 min parallel to the horizontal axis of the klinostat at 2 rpm, the amyloplasts are not clumped together as densely as in normal, inverted or stimulated roots, but they are not scattered over the entire cell volume. The statolith function of the amyloplasts is discussed in view of these and other observations.     

Indian migrant butterflies displaced to Arabia by monsoon storm 'Aurora' in August 1983

Although many insect species are now thought to travel hundreds and even thousands of kilometres on the wind (Pedgley, 1982) only a few are butterflies. Three species for which there is reasonably convincing but circumstantial evidence are Danaus plexippus L. from the U.S.A. to the British Isles (Hurst, 1969), Hypolimnas bolina nerina (F.) from Australia to New Zealand (Tomlinson, 1973) and Nymphalis antiopa L. from northern Europe to the British Isles (Chalmers-Hunt, 1977). In this paper we describe the sudden appearance of Indian butterflies in Arabia and provide evidence that they were windborne across the Arabian Sea.     

Chukar Seasonal Survival and Probable Causes of Mortality

ABSTRACT Chukars (Alectoris chukar) have been introduced throughout the world. Despite this widespread distribution, limited information regarding seasonal survival, probable causes of mortality, and other basic life history characteristics is available to manage this harvested species. We estimated the probable cause of mortality for chukars with radiotransmitters by examining evidence at kill sites. We used model selection to evaluate influences of seasonal effects (fall raptor migration, peak migration, and reproductive period), demographic effects (age and sex), radio weight, and year on survival of chukars in western Utah, USA, by using a known-fate model in Program MARK and 2 years of telemetry data. We captured and randomly fitted 125 individual chukars with 2 different-sized radiotransmitters (97 F, 20 M, 8 sex undetermined). Model selection results showed our top 3 models accounted for 99% of Akaike's Information Criterion weight, and each one had seasonal and year effects. Two-week survival estimates were lower during peak raptor migration in both years and significantly (P < 0.05) so in year 2 (2-week S = 0.87, 95% CI = 0.77–0.94) compared with other year 2 intervals (2-week S > 0.91). Annual survival was lower in 2005 (S = 0.03, 95% CI = 0.01–0.09) compared with 2006 (S = 0.19, 95% CI = 0.12–0.31). We documented 95 deaths and classified 56% unknown, 33% avian predation, 8% hunter harvest, and 3% mammalian predation. Our research suggests that predation on chukars is substantial during the peak fall raptor migratory period and that the hunting take under current regulations is relatively small and likely compensatory.     

Climate change predicted to cause severe increase of organic carbon in lakes

Riverine transport of organic carbon (OC) to the ocean is a significant component in the global carbon (C) cycle and the concentration of total organic carbon (TOC) in rivers and lakes is vital for ecosystem properties and water quality for human use. By use of a large dataset comprising chemical variables and detailed catchment information in ～1000 Norwegian pristine lakes covering a wide climatic range, we were able to predict TOC concentrations with high accuracy. We further predict, using a ‘space‐for‐time’ approach and a downscaled, moderate, climate change scenario, that northern, boreal regions likely will experience strong increases in OC export from catchments to surface waters. Median concentrations of OC in these lakes will increase by 65%, from the current median of 2.0–3.3 mg C L^?1. This is a long‐term effect, primarily mediated by increased terrestrial vegetation cover in response to climate change. This increase OC will have severe impacts on food‐webs, productivity and human use. Given the robustness of the estimates and the general applicability of the parameters, we suggest that these findings would be relevant to boreal areas in general.     

Low‐level effects of inert sediments on temperate stream invertebrates

1. The delivery, entrainment and deposition of inert fine sediments are among the most significant contributors to stream and river impairment worldwide. Associated ecological effects have been observed frequently, but specific experiments to identify sensitivity and avoidance behaviour in stream organisms are few, particularly in headwaters. 2. In a field‐experiment, we added fine sand at low levels (c. 4–5 kg m^?2) to 10 m reaches of two replicate headwater streams in the Usk catchment (Wales, U.K.) over two periods (autumn and summer). Upstream reaches were used as control in a classic before‐after‐control‐impact design. Invertebrate drift and benthic composition were measured for 2 days before and 1 day after sediment impact. 3. Sediment addition significantly increased overall drift density (by 45%) and propensity (by 200%), with effects largest on the night following addition rather than immediately (i.e. within 9 h). The mayflies Baetis rhodani, B. muticus and Ecdyonurus spp., simuliid and chironomid dipterans, and helodid beetles were the strongest contributors. 4. There were no marked effects on benthic composition, but density declined in treated reaches by 30–60%, particularly in B. rhodani, Ecdyonurus spp. and Leuctra hippopus + L. moselyi. 5. All effects were consistent between both seasons and streams. 6. These data show how even low‐level, short‐term, increases in fine sediment loading to upland, stony streams can reduce overall benthic density through increased drift. We suggest that the likely cause of the delayed drift response was a change in habitat quality which prompted avoidance behaviour. Longer‐term experiments are required to assess whether these effects reduce fitness or explain the losses of some types of organisms observed recently in sediment‐impaired reaches of this and other catchments.     

The evolutionary significance of dry and wet season forms in some tropical butterflies

An explanation is developed for the adaptive significance of the forms characteristic of the dry season and wet season adult generations of some tropical butterflies. The divergent phenotypes are accounted for as adaptive responses to a shift in the optimum balance between dependence on the alternative (but interdependent) strategies of active anti-predator devices and of crypsis. The seasonal polyphenisms exhibited by the satyrines Melanitis leda (Fabricius) and Orsotrioena medus (Fabricius) and the nymphalid Junonia almana (Linné) are examined in detail. The wet season forms show prominent marginal eyespot patterns which are displayed at rest and function principally in the deflection of attacks by vertebrate predators. In contrast, the dry season forms show very small or no spots and are wholly cryptic. Wet season butterflies are more active in general than those in the dry season when aestivation behaviour is often observed. The alternative phenotypes represent responses to the differences in behaviour, environment and nature of predation. Reproductive success is optimized in each season by an interaction of phenotype and behaviour. The hypothesis must be tested in detail by an investigation of the behavioural ecology and population biology of particular species. It is argued that these seasonal polyphenisms provide examples of adaptations to a repeating pattern of changing environments where the mode of selection is, in broad terms, understood.