Environmental Factors Influencing Local Fish Species Richness and Differences between Hydroregions in South‐Western France

The aim of this study was to investigate the influence of 5 typological variables on the spatial distribution patterns of fish species richness in south‐western France, and, subsequently, to analyse differences in the number of species occurring in 6 major hydroregions located within the overall study area. The data were collected at 329 sampling sites. General Linear Modelling was used to assess the influence of each typological variable on local fish species richness, and to determine the differences in local fish species richness between the 6 hydroregions. Local species richness was significantly influenced by altitude, slope and catchment area, whereas distance from the source and stream width showed no significant relations with local richness. The Côteaux de Gascogne hydroregion had a significantly lower species richness, whereas no significant differences occurred among other neighbouring hydroregions. These results were congruent with the spatial distribution patterns of freshwater invertebrate species richness in the area, which were analysed in previous studies. At such a regional scale, we suggest that congruent patterns between fish and invertebrate species richness are almost certainly a result of similar responses by different taxa to environmental conditions, rather than to biotic interactions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microscopic elements of electrical excitation in Chara: Transient activity of Cl− channels in the plasma membrane

The plasma membrane of Chara corallina was made accessible for patch pipettes by cutting a small window through the cell wall of plasmolyzed internodal cells. With pipettes containing Cl^– as Ca²⁺ or Ba²⁺ (50 or 100 mm), but not as Mg²⁺ or K⁺ salt, it was possible to record in the cell-attached mode for long periods with little channel activity, randomly interspersed with intervals of transient activation of two Cl^– channel types (cord conductance at +50 mV: 52 and 16 pS, respectively). During these periods of transient channel activity, variable numbers (up to some 10) of the two Cl^– channel types activated and again inactivated over several 100 msec in a coordinated fashion. Transient Cl channel activity was favored by voltages positive of the free running membrane voltage (> –45 mV); but positive voltage alone was neither a sufficient nor a necessary condition for activtion of these channels. Neither type of Cl^– channel was markedly voltage dependent. A third, nonselective 4 pS channel is a candidate for Ca²⁺ translocation. The activity of this channel does not correlate in time with the transient activity of the Cl^– channels. The entire set of results is consistent with the following microscopic mechanism of action potentials in Chara, concerning the role of Ca²⁺ and Cl^– for triggering and time course: Ca²⁺ uptake does not activate Cl^– channels directly but first supplies a membrane-associated population of Ca²⁺ storage sites. Depolarization enhances discharge of Ca²⁺ from these elements (none or few under the patch pipette) resulting in a local and transient increase of free Ca²⁺ concentration ([Ca²⁺]_cyt) at the inner side of the membrane before being scavenged by the cytoplasmic Ca²⁺ buffer system. In turn, the transient rise in [Ca²⁺]_cyt causes the transient activity of those Cl^– channels, which are more likely to open at an elevated Ca²⁺ concentration.The financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged.     

Rapidly declining fine-scale spatial genetic structure in female red deer

A growing literature now documents the presence of fine-scale genetic structure in wild vertebrate populations. Breeding population size, levels of dispersal and polygyny--all hypothesized to affect population genetic structure--are known to be influenced by ecological conditions experienced by populations. However the possibility of temporal or spatial variation in fine-scale genetic structure as a result of ecological change is rarely considered or explored. Here we investigate temporal variation in fine-scale genetic structure in a red deer population on the Isle or Rum, Scotland. We document extremely fine-scale spatial genetic structure (< 100 m) amongst females but not males across a 24-year study period during which resource competition has intensified and the population has reached habitat carrying capacity. Based on census data, adult deer were allocated to one of three subpopulations in each year of the study. Global F(ST) estimates for females generated using these subpopulations decreased over the study period, indicating a rapid decline in fine-scale genetic structure of the population. Global F(ST) estimates for males were not different from zero across the study period. Using census and genetic data, we illustrate that, as a consequence of a release from culling early in the study period, the number of breeding females has increased while levels of polygyny have decreased in this population. We found little evidence for increasing dispersal between subpopulations over time in either sex. We argue that both increasing female population size and decreasing polygyny could explain the decline in female population genetic structure.     

The signaling pathway in histidine kinase and the response regulator complex revealed by X-ray crystallography and solution scattering

The structure of a histidine kinase (ThkA) complexed with a response regulator (TrrA) in the two-component regulatory system from hyperthermophile Thermotoga maritima was determined by a combination of X-ray crystallography at a resolution of 4.2 A and small-angle X-ray scattering (SAXS). The boundary of the three component domains (PAS-sensor, dimerization and catalytic domains) of ThkA and the bound TrrA molecule were unambiguously assigned in the electron density map at 4.2 A resolution. ThkA forms a dimer with crystallographic 2-fold symmetry and two monomeric TrrAs bind to the ThkA dimer. SAXS experiments also confirmed this association state in solution and specific binding between ThkA and TrrA (Kd=8.2x10(-11) M(-2)). The association interface between ThkA and TrrA contains the phosphotransfer His residue in the ThkA, indicative of an efficient receipt of the phosphoryl group. One Per-Arnt-Sim (PAS) domain does not interact with the other PAS domain, but with the catalytic domain of the same polypeptide chain and with one TrrA molecule. Observed inter-domain and inter-molecular interactions reveal a definite pathway of signal transduction in the kinase/regulator complex. In addition, we propose a responsible role of TrrA for the feedback regulation of sensing and/or kinase activities of ThkA.     

Recent advances in applications of liquid chromatography-tandem mass spectrometry to the analysis of reactive drug metabolites

Biotransformation of chemically stable compounds to reactive metabolites which can bind covalently to macromolecules, such as proteins and DNA, is considered as an undesirable feature of drug candidates. As part of an overall assessment of absorption, distribution, metabolism and excretion (ADME) properties, many pharmaceutical companies have put methods in place to screen drug candidates for their tendency to generate reactive metabolites and as well characterize the nature of the reactive metabolites through in vitro and in vivo studies. After identification of the problematic compounds, steps can be taken to minimize the potential of bioactivation through appropriate structural modifications. For these reasons, detection, structural characterization and quantification of reactive metabolites by mass spectrometry have become an important task in the drug discovery process. Triple quadrupole mass spectrometry is traditionally employed for the analysis of reactive metabolites. In the past 3 years, a number of new mass spectrometry methodologies have been developed to improve the sensitivity, selectivity and throughput of the analysis. This review focuses on the recent advances in the detection and characterization of reactive metabolites by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in drug discovery and development, especially through the use of linear ion trap (LTQ), hybrid triple quadrupole-linear ion trap (Q-trap) and the high resolution LTQ-Orbitrap instruments.     

Stable germination behavior but partly changing seed–seed interactions along a steep rainfall gradient

Germination marks a critical transition in plant life that is prone to high mortality. Strong selection pressure is therefore expected to finely tune it to environmental conditions. Our study on the common Mediterranean grass Brachypodium hybridum assessed whether germination behavior changes systematically along a steep natural rainfall gradient ranging from harsh desert to rather mild mesic-Mediterranean conditions. We specifically tested hypotheses that germination behavior confers greater risk-spreading in populations from drier, unpredictable environments, and that seeds from wetter populations are better competitors.In 14 populations (spanning 114–954 mm annual rainfall) we assessed three alternative key parameters of germination in a greenhouse experiment: between-year dormancy, days to emergence within a season, and temporal spread. Addition of neighbor seeds accounted for competition as another crucial environmental factor. In six of the 14 populations, we also compared seeds originating from corresponding north (more mesic) and south (more arid) exposed hill slopes to test whether germination patterns along the large-scale rainfall gradient are paralleled at this smaller scale.B. hybridum exhibited generally high germination fractions and rapid emergence with very little temporal spread, indicating overall little risk-spreading germination. Surprisingly, none of the three parameters changed systematically with increasing aridity, neither at large scale along the rainfall gradient nor at small scale between north and south exposures. Neighbor seeds, however, mildly suppressed germination. Germination of neighbor seeds, in turn, was more strongly suppressed by B. hybridum seeds from drier populations, and this effect was stronger for forb than for grass neighbor species.Our results provide strong evidence that increased risk-spreading germination is not a universal, essential strategy to persist in increasingly dry, unpredictable environments. They also highlight that competition with neighbors occurs even at the earliest plant life stage. Since neighbor effects were species-specific, competition among seeds can affect community composition at later plant stages.     

A test of ecologically dependent postmating isolation between sympatric sticklebacks

Ecological speciation occurs when reproductive isolation evolves ultimately as a result of divergent natural selection between populations inhabiting different environments or exploiting alternative resources. I tested a prediction of the ecological model concerning the fitness of hybrids between two young, sympatric species of threespine sticklebacks (Benthics and Limnetics). The two species are ecologically and morphologically divergent: the Benthic is adapted to feeding on invertebrates in the littoral zone of the lake whereas the Limnetic is adapted to feeding on zooplankton in the open water. The growth rate of two types of hybrids, the Benthic backcross and the Limnetic backcross, as well as both parent species, was evaluated in enclosures in both parental habitats in the lake. The use of backcrosses is ideal because a comparison of their growth rates in the two habitats estimates an ecologically dependent component of their fitness while controlling for any intrinsic genetic incompatibilities that may exist between the Benthic and Limnetic genomes. The backcross results revealed a striking pattern of ecological dependence: in the littoral zone, Benthic backcrosses grew at approximately twice the rate of Limnetic backcrosses, while in the open water, Limnetic backcrosses grew at approximately twice the rate of Benthic backcrosses. Such a reversal of relative fitness of the two cross-types in the two environments provides strong evidence that divergent natural selection has played a central role in the evolution of postmating isolation between Benthics and Limnetics. Although the rank order of growth rates of all cross-types in the littoral zone was Benthic > Benthic backcross > Limnetic backcross > Limnetic, neither backcross differed significantly from the parent from which it was mainly derived. Implications of this result are discussed in terms of ecological speciation and possible introgressive hybridization between the species. Results in the open water were less clear and were not fully consistent with the ecological model of speciation, mainly as a result of the low growth rate of Limnetics. However, analysis of the diet of the fish in the open water suggests that these enclosures may not have been fully successful at replicating the food regimes characteristic of this habitat.     

巴氯芬对慢性吗啡依赖后条件化位置偏好和戒断症状的抑制

小鼠连续7天腹腔注射吗啡(40mg/kg)建立条件化位置偏好模型,连续皮下递增注射吗啡(25、50、75、100、125、150mg/kg),成瘾后腹腔注射纳络酮(6mg/kg)诱导戒断症状(跳跃行为)建立戒断模型。腹腔注射GABAB受体激动剂巴氯芬(2mg/kg)可以有效地抑制吗啡诱导的条件化位置偏好和减轻纳络酮诱导的戒断症状,结果表明GABA系统参与动物成瘾后渴求和戒断过程,激动GABAB受体可以在一定程度上抑制成瘾的心理和生理戒断症状。