Regulation of the K channels by cytoplasmic domains

Regulation of intracellular potassium levels is one of the basic functions of all cells, controlling cellular osmolarity and transmitting information. In higher organisms, elaborate control of transmembrane potassium flux has evolved to endow nervous systems with the remarkable ability to transmit electrical signals between cells. Multiple genes, gene splicing, mRNA editing, and selective tetrameric assembly of K channel genes provide the basis for creating distinct electrophysiological properties at varying developmental and cellular stages. This assembly mechanism, primarily governed by the T1 domain, is under the control of intracellular signals. Atomic structures of the isolated T1 domains of Shaker and Shaw subfamilies provided us with valuable structural insights into understanding both channel assembly and functional regulation of the entire channel molecule through conformational changes.     

Macrozoobenthos of Lake Peipsi-Pihkva: taxonomical composition, abundance, biomass, and their relations to some ecological parameters

The large but shallow (3,558 km², up to 15.3 m deep) lake is eutrophic, with Chironomus plumosus and Potamothrix hammoniensis as dominating macroinvertebrates in the profundal. The extensive well-aerated sublittoral with sandy bottom sediments has a mesotrophic appearance and supports a diverse fauna with several oxyphilous species, including a very abundant population of Dreissena polymorpha. The phytophilous fauna is limited to small sheltered areas only. The average abundance of the small animals of macrozoobenthos (without big molluscs) was 2,617 ind. m^–2, their biomass 12.34 g m^–2 (corresponding to 52.2 kJ m^–2) in 1964–1994. The same figures for big molluscs (mostly Dreissena) were 304 ind. m^–2 and 238 g m^–2 in 1964–1994, and even 864 ind. m^–2 and 687 g m^–2 in 1985–1988, at the time of their special mapping. The sublittoral zone revealed the lowest biomass of small animals but the highest biomass of big molluscs. The southern, shallower lake regions, more enriched with nutrients and better protected from wind, revealed a significantly higher biomass of small macrozoobenthos in the near-shore zone than the cleaner and open northern part, while no positive effect of enrichment was observed neither in the biomass of profundal zoobenthos nor in that of big molluscs. The production of the small macrozoobenthos was calculated as 111 and 53 kJ m^–2 during two annual cycles in Lake Peipsi s. s., the most productive period being the autumn overturn. Lake Peipsi-Pihkva has the highest abundance and biomass of macrozoobenthos among the large lakes of North Europe.     

Transport pathways shape the biogeography of alien freshwater fishes in Australia

Aim

Changing preferences regarding which species humans have transported to new regions can have major consequences for the potential distribution of alien taxa, but the mechanisms shaping these patterns are poorly understood. We assessed the extent to which changes in human preferences for transporting and introducing alien freshwater fishes have altered their biogeography.

Location

Australia.

Methods

We compiled an up‐to‐date database of alien freshwater fishes established in drainages in Australia before and after the number of established alien fish species doubled (pre‐1970 and post‐1970, respectively). Using metacommunity models, we analysed the influence of species traits and drainage features on the distribution of alien fishes that established pre‐ and post‐1970.

Results

Alien fishes in Australia were introduced via four main transport pathways: acclimatization, aquaculture, biocontrol and ornamental trade. The relative importance of each pathway changed substantially between the two periods, accompanied by changes in the distribution of alien fishes and the variables predicting their distribution. Pre‐1970, most species (64%) were introduced by acclimatization societies for purposes such as angling and biocontrol, and these fish have established in inland drainages more heavily impacted by human activities. In contrast, most of the post‐1970 introductions (69%) were ornamental fishes, with most species established in small, north‐eastern, tropical and subtropical coastal drainages.

Main conclusions

Substantial changes in introduction preferences and transport pathways over time have altered both the patterns and underlying processes shaping the biogeography of alien fishes in Australia. Our findings highlight the need for caution when using historical data to infer potential future distributions of alien species. The continuing spread of alien species means traditional biogeographical units may no longer be identifiable in the foreseeable future.

     

Temperature‐dependent mutational robustness can explain faster molecular evolution at warm temperatures,affecting speciation rate and global patterns of species diversity

Distribution of species across the Earth shows strong latitudinal and altitudinal gradients with the number of species decreasing with declining temperatures. While these patterns have been recognized for well over a century, the mechanisms generating and maintaining them have remained elusive. Here, we propose a mechanistic explanation for temperature‐dependent rates of molecular evolution that can influence speciation rates and global biodiversity gradients. Our hypothesis is based on the effects of temperature and temperature‐adaptation on stability of proteins and other catalytic biomolecules. First, due to the nature of physical forces between biomolecules and water, stability of biomolecules is maximal around + 20°C and decreases as temperature either decreases or increases. Second, organisms that have adapted to cold temperatures have evolved especially flexible (but unstable) proteins to facilitate catalytic reactions in cold, where molecular movements slow down. Both these effects should result in mutations being on average more detrimental at cold temperatures (i.e. lower mutational robustness in cold). At high temperatures, destabilizing water–biomolecule interactions, and the need to maintain structures that withstand heat denaturation, should decrease mutational robustness similarly. Decreased mutational robustness at extreme temperatures will slow down molecular evolution, as a larger fraction of new mutations will be removed by selection. Lower mutational robustness may also select for reduced mutation rates, further slowing down the rate of molecular evolution. As speciation requires the evolution of epistatic incompatibilities that prevent gene flow among incipient species, slow rate of molecular evolution at extreme temperatures will directly slow down the rate at which new species arise. The proposed mechanism can thus explain why molecular evolution is faster at warm temperatures, contributing to higher speciation rate and elevated species richness in environments characterized by stable and warm temperatures.     

Distribution and dispersal capacity of the Ponto-Caspian tubificid oligochaete Potamothrix moldaviensis Vejdovský et Mrázek, 1903 in the Baltic Sea Region

Over the last few centuries, several Ponto-Caspian tubificid oligochaetes have gradually dispersed from the Black Sea – Caspian Sea region to the north-west and west over Europe. The present world distribution comprising also the Great Lakes of North America clearly demonstrates that anthropochorous vectors of dispersal are involved. Passive transportation in the ballast water of ships has radically changed the possibilities of dispersal for many invertebrate species and has even made dispersal between continents possible. The construction of navigable canals has furthermore facilitated the crossing of watersheds and continents. Other likely vectors of longway dispersal for oligochaetes, as well as for other small-size aquatic invertebrates, are birds and mammals. The dispersal of the Potamothrixspecies is likely to have taken place in successive waves (three) with front-lines still on the move from the east to the west over the Baltic States and Scandinavia. The rheophilous species Potamothrix moldaviensishas presently reached – apart from the large rivers of Russia and many Central-European water bodies – also the Baltic States and south-eastern Sweden. Trajectories of dispersal demonstrate routes across the Baltic Sea – via the ballast water of ships. In the largest rivers of the Eastern Baltic Region (Neva, Daugava, Nemunas), downstream dispersal is the most likely way of transportation. P. moldaviensis together with P. heuscheri(second wave) and P. vejdovskyi(third wave) are presently forming front-lines running obliquely from the north-east to the south-west over south Sweden. In mesotrophic-eutrophic basins of eastern Lake Mälaren, the abundance as well as the species diversity of oligochaetes is particularly high wherever Ponto-Caspian Potamothrixspecies – often several species together – are involved.     

Evaluation of methods for detection of fluorescence labeled subcellular objects in microscope images

Background  

Several algorithms have been proposed for detecting fluorescently labeled subcellular objects in microscope images. Many of these algorithms have been designed for specific tasks and validated with limited image data. But despite the potential of using extensive comparisons between algorithms to provide useful information to guide method selection and thus more accurate results, relatively few studies have been performed.     

Evolution of bacterial life‐history traits is sensitive to community structure

Very few studies have experimentally assessed the evolutionary effects of species interactions within the same trophic level. Here we show that when Serratia marcescens evolve in multispecies communities, their growth rate exceeds the growth rate of the bacteria that evolved alone, whereas the biomass yield gets lower. In addition to the community effects per se, we found that few species in the communities caused strong effects on S. marcescens evolution. The results indicate that evolutionary responses (of a focal species) are different in communities, compared to species evolving alone. Moreover, selection can lead to very different outcomes depending on the community structure. Such context dependencies cast doubt on our ability to predict the course of evolution in the wild, where species often inhabit very different kinds of communities.     

Cytoplasmic gatekeepers of K+-channel flux: a structural perspective

Recently, rapid progress in our structural knowledge of K(+)-selective channels has started to provide a basis for comprehending the biophysical machinery underlying their electrophysiological properties. These studies have begun to reveal how a diverse array of distinct, cytoplasmically positioned domains affect the activity of associated channels. Some of these establish functional diversity by selectively mediating channel assembly. More importantly, these cytoplasmic domains couple intracellular signals to the gating of their associated pore. New structural insights are providing a clearer understanding of the fundamental molecular mechanisms of these K(+) channels that, in turn, partly underlie complex neurological phenomena.