Ion channels in icosahedral virus: a comparative analysis of the structures and binding sites at their fivefold axes.

An analysis of the crystallographically determined structures of the icosahedral protein coats of Tomato Bushy Stunt Virus, Southern Bean Mosaic Virus, Satellite Tobacco Necrosis Virus, Human Rhinovirus 14 and Mengovirus around their fivefold axes is presented. Accessibilities surfaces, electrostatic energy profile calculations, ion-protein interaction energy calculations, free energy perturbation methods and comparisons with structures of chelating agents are used in this study. It is concluded that the structures built around the viral fivefold axes would be adequate for ion binding and transport. Relative ion preferences are derived for the binding sites, using free energy perturbation methods, which are consistent with the experimental data when available. In the cases where crystallographic studies determined the existence of ions on the fivefold axes, our results indicate that they would correspond to ions in crystallization or purification buffers. The environment of the fivefold axes are rich in polar residues in all icosahedral viral structures whose atomic coordinates are available, including some that are not being analyzed in detail in this work. The fivefold channel-like structures have most of the basic properties expected for real ion channels including a funnel at the entrance, a polar internal environment with frequent alternation of acidic and basic residues, ion binding sites, the capability to induce ion dehydration and ion transit from the external viral surface to the binding sites.     

Echolocation calls in Central American emballonurid bats: signal design and call frequency alternation

In southern Central America, 10 species of emballonurid bats occur, which are all aerial insectivores: some hunt flying insects preferably away from vegetation in open space, others hunt in edge space near vegetation and one species forages mainly over water. We present a search call design of each species and link signal structure to foraging habitat. All emballonurid bats use a similar type of echolocation call that consists of a central, narrowband component and one or two short, frequency-modulated sweeps. All calls are multi-harmonic, generally with most energy concentrated in the second harmonic. The design of search calls is closely related to habitat type, in particular to distance of clutter. Emballonurid bats foraging in edge space near vegetation and over water used higher frequencies, shorter call durations and shorter pulse intervals compared with species mostly hunting in open, uncluttered habitats. Peak frequency correlated negatively with body size. Regular frequency alternation between subsequent calls was typical in the search sequences of four out of 10 species. We discuss several hypotheses regarding the possible role of this frequency alternation, including species identification and partitioning of acoustic channels. Furthermore, we propose a model of how frequency alternation could increase the maximum detection distance of obstacles by marking search calls with different frequencies.     

Organising multi-dimensional biological image information: the BioImage Database.

Nowadays it is possible to unravel complex information at all levels of cellular organization by obtaining multi-dimensional image information. At the macromolecular level, three-dimensional (3D) electron microscopy, together with other techniques, is able to reach resolutions at the nanometer or subnanometer level. The information is delivered in the form of 3D volumes containing samples of a given function, for example, the electron density distribution within a given macromolecule. The same situation happens at the cellular level with the new forms of light microscopy, particularly confocal microscopy, all of which produce biological 3D volume information. Furthermore, it is possible to record sequences of images over time (videos), as well as sequences of volumes, bringing key information on the dynamics of living biological systems. It is in this context that work on BioImage started two years ago, and that its first version is now presented here. In essence, BioImage is a database specifically designed to contain multi-dimensional images, perform queries and interactively work with the resulting multi-dimensional information on the World Wide Web, as well as accomplish the required cross-database links. Two sister home pages of BioImage can be accessed at http://www. bioimage.org and http://www-embl.bioimage.org     

Biome transitions as centres of diversity: habitat heterogeneity and diversity patterns of West African bat assemblages across spatial scales

It is widely accepted that species diversity is contingent upon the spatial scale used to analyze patterns and processes. Recent studies using coarse sampling grains over large extents have contributed much to our understanding of factors driving global diversity patterns. This advance is largely unmatched on the level of local to landscape scales despite being critical for our understanding of functional relationships across spatial scales. In our study on West African bat assemblages we employed a spatially explicit and nested design covering local to regional scales. Specifically, we analyzed diversity patterns in two contrasting, largely undisturbed landscapes, comprising a rainforest area and a forest‐savanna mosaic in Ivory Coast, West Africa. We employed additive partitioning, rarefaction, and species richness estimation to show that bat diversity increased significantly with habitat heterogeneity on the landscape scale through the effects of beta diversity. Within the extent of our study areas, habitat type rather than geographic distance explained assemblage composition across spatial scales. Null models showed structure of functional groups to be partly filtered on local scales through the effects of vegetation density while on the landscape scale both assemblages represented random draws from regional species pools. We present a mixture model that combines the effects of habitat heterogeneity and complexity on species richness along a biome transect, predicting a unimodal rather than a monotonic relationship with environmental variables related to water. The bat assemblages of our study by far exceed previous figures of species richness in Africa, and refute the notion of low species richness of Afrotropical bat assemblages, which appears to be based largely on sampling biases. Biome transitions should receive increased attention in conservation strategies aiming at the maintenance of ecological and evolutionary processes.     

Energetics and life-history of bats in comparison to small mammals

Mammals can be aligned along a slow-fast life-history continuum and a low–high metabolic rate continuum based on their traits. Small non-volant mammals occupy the fast/high end in both continua with high reproductive rates and short life spans linked with high mass-specific metabolic rates. Bats occupy the high end of the metabolic continuum, but the slow end of the life-history continuum with low reproductive rates and long life spans. Typically, both continua are linked, and similar life-history traits of species are reflected in more similar metabolic rates. We therefore hypothesized that metabolic rates are similar in species with similar life-history traits. Resting metabolic rates (RMR) were measured for three ecologically and morphologically similar sympatric bat species (Myotis nattereri, M. bechsteinii, and Plecotus auritus; Vespertilionidae) and compared to data from other similar-sized, temperate insectivorous mammals with other life-history strategies. The bat species share similar life-histories and RMRs, both of which differ from the remaining mammals and therefore supporting our hypothesis. To verify that bats are similar in RMR, two energetically contrasting periods were compared. RMRs in post-lactating females did not differ between bat species. It was, however, positively correlated with parasite load in both Myotis species. However, RMRs differed during energy-demanding pregnancy where M. nattereri had the significantly lowest RMR, suggesting metabolic compensation as an energy-saving strategy. We conclude that the energy requirements of bat species with similar life-history traits resemble each other during periods of low energetic demands and are more similar to each other than to other small temperate mammals.     

Ectoparasite Infestations of Hedgehogs (Erinaceus europaeus) are Associated with Small-Scale Landscape Structures in an Urban–Suburban Environment

Animals that exploit heterogeneous and patchy environments encounter different local habitat conditions that influence their interaction with the environment, such as the acquisition of parasites. How and at which scales interaction processes between parasites, hosts, and the environment are realized remains largely unknown. We examined the infestation patterns of 56 hedgehogs (Erinaceus europaeus) with fleas and ticks at a small spatial scale within a 12 km² area along a suburban–urban gradient in southwestern Germany. The structure and type of habitats surrounding hedgehog capture locations were estimated from digital land cover data within radii of 20, 50, and 100 m. These were assumed to match the ranging area and underlying heterogeneous landscape matrix in which host–parasite interactions take place. Landscape-based models suggested that flea burdens significantly decreased with the diversity and heterogeneity of land cover, as well as with the areal coverage of roads within radii of 50 and 100 m. Overall tick infestation levels were mostly explained by the number of arable patches and the areal coverage of roads within radii of 50 and 100 m, as well as date of capture. Examination of the semivariance in model residuals revealed no evident spatial structure in any of the models with flea or tick infestation patterns as response variables. Our results, which are based on a sampling scheme within a relatively small spatio-temporal window, suggest that heterogeneous landscape matrices affect parasitization rates of animals in urban environments, with clear differences at the individual level.     

Movement trajectories and habitat partitioning of small mammals in logged and unlogged rain forests on Borneo

1. Non-volant animals in tropical rain forests differ in their ability to exploit the habitat above the forest floor and also in their response to habitat variability. It is predicted that specific movement trajectories are determined both by intrinsic factors such as ecological specialization, morphology and body size and by structural features of the surrounding habitat such as undergrowth and availability of supportive structures. 2. We applied spool-and-line tracking in order to describe movement trajectories and habitat segregation of eight species of small mammals from an assemblage of Muridae, Tupaiidae and Sciuridae in the rain forest of Borneo where we followed a total of 13,525 m path. We also analysed specific changes in the movement patterns of the small mammals in relation to habitat stratification between logged and unlogged forests. Variables related to climbing activity of the tracked species as well as the supportive structures of the vegetation and undergrowth density were measured along their tracks. 3. Movement patterns of the small mammals differed significantly between species. Most similarities were found in congeneric species that converged strongly in body size and morphology. All species were affected in their movement patterns by the altered forest structure in logged forests with most differences found in Leopoldamys sabanus. However, the large proportions of short step lengths found in all species for both forest types and similar path tortuosity suggest that the main movement strategies of the small mammals were not influenced by logging but comprised generally a response to the heterogeneous habitat as opposed to random movement strategies predicted for homogeneous environments. 4. Overall shifts in microhabitat use showed no coherent trend among species. Multivariate (principal component) analysis revealed contrasting trends for convergent species, in particular for Maxomys rajah and M. surifer as well as for Tupaia longipes and T. tana, suggesting that each species was uniquely affected in its movement trajectories by a multiple set of environmental and intrinsic features.     

Seasonal changes in daily torpor patterns of free-ranging female and male Daubenton’s bats (Myotis daubentonii)

Daily torpor can provide significant energy and water savings in bats during cold ambient temperatures and food scarcity. However, it may reduce rates of foetal and juvenile development. Therefore, reproductive females should optimize development by minimizing times in torpor. To test this hypothesis, the use of torpor by female and male free-ranging Daubenton’s bats (Myotis daubentonii) during reproduction (gestation, lactation, and post-lactation period) was investigated in 1998 and 1999. Temperature-sensitive radio transmitters were attached to the bats to measure skin temperature. Simultaneously, ambient temperature was recorded. While both sexes became torpid during daytime, male bats used daily torpor (>6°C below individual active temperature) significantly more often during reproductive period (mean: 78.4 % of day time in May and 43 % in June) than females. Female bats went into daily torpor, particularly in late summer when juveniles were weaned (mean: 66.6 % of daytime). Lowest skin temperatures occurred in a female bat with 21.0°C during post-lactation. Skin temperatures of male bats fluctuated from 16.8°C in torpor to 37.2°C during times of activity. There was a significant effect of reproductive period on skin temperature in females whereas mean ambient temperature had no significant effect. However, mean ambient temperature affected mean skin temperatures in males. Our findings indicate that female Daubenton’s bats adopt their thermoregulatory behaviour in particular to optimize the juvenile development.     

Differential mobility in two small phyllostomid bats,<Emphasis Type="Italic">Artibeus watsoni</Emphasis> and<Emphasis Type="Italic">Micronycteris microtis</Emphasis>, in a fragmented neotropical landscape

To assess the influence of habitat fragmentation on small bats, we determined home range size and mobility of the frugivorousArtibeus watsoni Thomas, 1901 and the gleaning insectivorousMicronycteris microtis Miller, 1898 by radiotracking on different-sized islands (2.7–17 ha) in Lake Gatún, Panamá. The two species differed in their response to fragmentation. Home range size was highly variable in the five trackedA. watsoni, ranging from 1.8 to 17.9 ha with a mean of about 9 ha. Some individuals flew regularly between islands and/or the mainland, thereby traversing up to 180 m of open water. In comparison, home ranges of threeM. microtis were with about 3.8 ha only half as large. All ofM. microtis exhibited sedentary foraging behaviour and did not cross open water, suggesting that they might persist at least on some of the islands as resident populations. Our findings are consistent with radiotracking data from a previous study and indicate that small habitat patches are still used by small bats, provided the degree of isolation is low and that sufficient resources and larger habitat patches exist in close vicinity, potentially acting as additional feeding grounds and source populations.