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.     

Resilience Theory in Archaeology

The past can be characterized by periods of changing and stable relationships between human groups and their environment. In this article, I argue that use of "resilience theory" as a conceptual framework will assist archaeologists in interpreting the past in ways that are interesting and potentially relevant to contemporary issues. Many of the authors in this "In Focus" section primarily concentrate on the relationships associated with patterns of human extraction of resources and the impacts of those human activities on the continuing condition of the ecosystem. These processes are, of course, embedded in a complex web of relationships that are based on multiple interactions of underlying patterns and processes of both the ecological and social domains. In this article, I introduce a resilience theory perspective to argue that these transformations were characterized by very different reorganizations of the socioecological landscape and were the product of a variety of factors that operated at different scales of geography, time, and social organization.     

Acoustic adaptations of periodical cicadas (Hemiptera: Magicicada)

We studied the trade-off between traits that function in mate attraction and those that function in enemy avoidance by contrasting features of acoustic communication in cicadas differentially at risk to predators in the same environment. Two genera of North American cicadas were studied: Magicicada and Tibicen. Magicicada species of periodical cicadas, with 17-year life cycles, seek mates in dense aggregations of calling males that are made possible by the relative ineffectiveness of predators to control their numbers. During the breeding season, Magicicada are so abundant that they satiate their predators. From their relative freedom from predation, it is to be expected that traits for attracting mates are emphasized in Magicicada compared with the more solitary genus Tibicen , which reproduce at much lower densities. Males of solitary species are expected to sing more loudly and at low pitch because both features enhance long-distance transmission. These two features were confirmed by measurement. Magicicada septendecim appears to be the most divergent species, evolutionarily, in terms of an unusually sharply tuned sound resonating system, low resonant frequency, and quietness of its song that cannot be entirely explained by body size. These characteristics represent adaptations to the problem of communicating unambiguously to females at close range in a loud and heterogeneous sound environment. Sensitivity to predators, parasitoids, and congeneric species may also have shaped the evolution of their communication systems.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 15–24.     

Allozyme variation in sympatric populations of British grasshoppers,—evidence of natural selection

Seven species of British grasshopper were analysed for variation at 15 enzyme loci. Where possible, sympatric populations were collected so that direct comparisons could be made. Allozyme frequencies in Chorthippus brunneus and C. albomarginatus were compared using correlation analysis. A positive correlation was noted for a phosphoglucomutase allozyme and a negative correlation for an isocitrate dehydrogenase allozyme. It was suggested that natural selection may affect allozyme frequencies in the wild.
Using cluster analysis and principal component analysis, evolutionary relationships of grasshoppers have been examined and compared with interpretations based on morphology.     

Potential effects of the invasive ‘killer shrimp’ (Dikerogammarus villosus) on macroinvertebrate assemblages and biomonitoring indices

1. Water quality monitoring data from 10 watercourses and laboratory mesocosm studies were used to assess the potential impacts of the crustacean amphipod invader Dikerogammarus villosus on resident macroinvertebrate assemblage structure in Central European fresh waters. 2. The presence of D. villosus was associated with a decline in the prevalence of many native species, pollution sensitive as well as pollution tolerant, and changes in biotic indices, despite the trends of improved water quality coinciding with the invasion period. A general increase in the prevalence of other invaders was also noted. The potential impacts of D. villosus were substratum dependent, differing between stone, concrete and sand‐dominated sites. 3. Mean Multimetric Macroinvertebrate Index Flanders (MMIF) values were marginally lower when D. villosus was present (P < 0.06), as opposed to when other amphipod species or no amphipods were present, despite the improved water quality. Mesocosm studies showed that several macroinvertebrate taxa were completely eliminated in treatments with D. villosus, oligochaete worms, Caenidae mayfly, chironomids and tipulids being particularly vulnerable to D. villosus predation. Biological Monitoring Working Party (BMWP) scores were lower in mesocosms with D. villosus as opposed to the native Gammarus pulex or no amphipods at all. 4. We predict that resident macroinvertebrate assemblages in both Central Europe and Britain will come under increasing pressure as D. villosus invasions progress. Consequently, macroinvertebrate biotic indices, such as the MMIF or BMWP, may need to be revised to account for changes in taxa sensitivities to water quality as well as increased predation and competition.     

Small and impoverished regional species pools constrain colonisation of restored river reaches by fishes

1. Using an extensive data set from 18 river restoration projects in the lower mountain ranges of Germany and 5462 river reaches in their surroundings, we estimated the spatial extent of the regional fish species pool from which restored river reaches are colonised. 2. Restoration resulted in a marginally significant increase in fish species richness; however, restored reaches still deviated markedly from natural reference conditions. Nearly all (96.6%) species occurring in restored reaches were present in reaches within a distance of 5 km up‐ or downstream of the restored reach. 3. Species richness in restored reaches was correlated with species richness within a 5‐km species pool. This relationship was more pronounced for common than for rare fishes and applied to both the total number of fish species at the restored reach and the number of additional fish species that were not present at unrestored conditions. 4. The richness of the regional species pools was greatly impoverished. On average, only 50% of all species considered to represent natural reference assemblages were present. The limited success in establishing natural fish assemblages in restored reaches was attributed to spatial limitation (e.g. due to fragmentation) and an impoverished regional species pools from which restored reaches recruit. 5. We recommend that integrated river restoration management should consider not only the abiotic prerequisites of successful restorations, but also the structure and quality of the regional species pool.     

Deciduous sapling responses to season and large herbivores in a semi‐arid African savanna

Impacts of large herbivores (>5 kg) on woody plants in African savannas are potentially most severe among plants shorter than 1.6 m. It is well established that severe browsing leads to longer shoots, yet prevents saplings from recruiting into adult size‐classes in African savannas. Increased shoot length, indicating faster shoot growth, is often associated with reduced concentrations of tannins and increased nutrient concentrations, suggesting carbon limitation. We hypothesized that, on average, large herbivores suppress stem height or circumference, but increase shoot length. We also hypothesized that if there were concomitant positive effects on nutrients, or negative effects on tannin concentrations, they would be greatest early in the wet season. We sampled saplings of four deciduous woody species (Acacia grandicornuta, Dichrostachys cinerea, Combretum apiculatum and Grewia flavescens) at different stages of the wet season in a large‐scale, long‐term herbivore exclusion experiment in Kruger National Park, South Africa. Plant height, shoot length and stem circumference were generally not adversely affected by large herbivores, suggesting C limitation is rarely present among deciduous saplings in semi‐arid African savannas, allowing them to tolerate browsing. Time since first rainfall emerged as a predominant factor consistently affecting nutrient and tannin concentrations, rather than large herbivores. Nitrogen and phosphorus generally decreased (by 20–50%), while condensed tannin concentration increased (150–350%) during the wet season, except for one species. We postulate that A. grandicornuta is less prone than other species to accumulating tannins during the wet season because of high investment of C in spines. Although nutrient and tannin concentrations were generally not affected by large herbivores, species‐specific responses were evident very early in the wet season, which is when herbivore populations are most likely to be affected by differential forage quality among plants.     

Bioelectronome. Integrated Approach to Receptor Chemistry,Radicals, Electrochemistry,Cell Signaling,and Physiological Effects Based on Electron Transfer

Bioelectronome refers to the host of electron transfer (ET) reactions that occur in living systems. This review presents an integrated approach to receptor chemistry based on electron transfer, radicals, electrochemistry, cell signaling, and end result. First, receptor activity is addressed from the unifying standpoint of redox transformations in which various receptors are discussed. After a listing of receptor-binding modes, receptor chemistry is treated with focus on generation of reactive oxygen species (ROS), activation by ROS, and subsequent cell signaling involving ROS. A general electrostatic mechanism is proposed for receptor-ligand action with supporting evidence. Cell-signaling processes appear to entail electron transfer, ROS, redox chains, and relays. The widespread involvement of phosphate from phosphorylation may be rationalized electrostatically by analogy with DNA phosphate. Extensive evidence supports important participation of ET functionalities in the mechanism of drugs and toxins. The integrated approach is applied to the main ET classes, namely, quinones, metal complexes, iminium species, and aromatic nitro compounds.     

Territorial dynamics of Mexican Ant‐thrushes Formicarius moniliger revealed by individual recognition of their songs

The ability to monitor interactions between individuals over time can provide us with information on life histories, mating systems, behavioural interactions between individuals and ecological interactions with the environment. Tracking individuals over time has traditionally been a time‐ and often a cost‐intensive exercise, and certain types of animals are particularly hard to monitor. Here we use canonical discriminant analysis (CDA) to identify individual Mexican Ant‐thrushes using data extracted with a semi‐automated procedure from song recordings. We test the ability of CDA to identify individuals over time, using recordings obtained over a 4‐year period. CDA correctly identified songs of 12 individual birds 93.3% of the time from recordings in one year (2009), while including songs of 18 individuals as training data. Predicting singers in one year using recordings from other years indicated some instances of variation, with correct classification in the range of 67–88%; one individual was responsible for the great majority (66%) of classification errors. We produce temporal maps of the study plot showing that considerably more information was provided by identifying individuals from their songs than by ringing and re‐sighting colour‐ringed individuals. The spatial data show site fidelity in males, but medium‐term pair bonds and an apparently large number of female floaters. Recordings can be used to monitor intra‐ and intersexual interactions of animals, their movements over time, their interactions with the environment and their population dynamics.