Concurrent habitat and life history influences on effective/census population size ratios in stream-dwelling trout

Lower effective sizes (N(e)) than census sizes (N) are routinely documented in natural populations, but knowledge of how multiple factors interact to lower N(e)/N ratios is often limited. We show how combined habitat and life-history influences drive a 2.4- to 6.1-fold difference in N(e)/N ratios between two pristine brook trout (Salvelinus fontinalis) populations occupying streams separated by only 750 m. Local habitat features, particularly drainage area and stream depth, govern trout biomass produced in each stream. They also generate higher trout densities in the shallower stream by favoring smaller body size and earlier age-at-maturity. The combination of higher densities and reduced breeding site availability in the shallower stream likely leads to more competition among breeding trout, which results in greater variance in individual reproductive success and a greater reduction in N(e) relative to N. A similar disparity between juvenile or adult densities and breeding habitat availability is reported for other species and hence may also result in divergent N(e)/N ratios elsewhere. These divergent N(e)/N ratios between adjacent populations are also an instructive reminder for species conservation programs that genetic and demographic parameters may differ dramatically within species.     

Performance of a clonal species in patchy environments: effects of environmental context on yield at local and whole-plant scales

Yield of the clonal plant Glechoma hederacea was compared at different spatial scales, in heterogeneous and homogeneous environments providing the same amount of nutrients. For the heterogeneous treatments, environments were created with different patch sizes and different degrees of contrast in nutrient concentration between patches of different quality. Total clone yield differed by almost 2.5-fold across treatments, being highest in environments with large patches and high contrast, lowest in environments with small patches and high contrast, and intermediate under homogeneous conditions. Compared with plants in homogeneous conditions, there were significant increases or decreases in yield at all scales of measurement in many of the heterogeneous treatments. These effects on yield reflected a combination of local responses to growing conditions and modification of these responses due to physiological integration with other parts of the plant growing in contrasting conditions, supporting the proposal of de Kroon et al. (2005 New Phytol 166:73–82). The results show that plant yield at all scales is strongly dependent on environmental context, and that maximum yield can only be realized under a limited range of heterogeneous conditions.     

Synthesis and antibacterial activity of the C-7 side chain of 3-aminoquinazolinediones

A novel series of bacterial topoisomerase (3-aminoquinazolinediones) inhibitors are described. The side-chain SAR against Gram-positive and Gram-negative organisms as well as DNA gyrase activity is reported.     

Dispersal in a stream dwelling salmonid: Inferences from tagging and microsatellite studies

We used both direct (mark-recapture) andindirect (microsatellite analysis)methodologies to investigate dispersal betweentwo putative populations of brook charr (Salvelinus fontinalis) in Freshwater River,Cape Race, Newfoundland, Canada. Over a 5-yearstudy period, mark-recapture data revealed somemovement by fish, but the proportion ofrecaptured fish migrating from one populationarea to another was low (0–4.1%).Additionally, during sampling periods in thespawning seasons, no fish was found in thealternate population area to that of its firstcapture. Despite this pattern of limitedmovement, microsatellite analysis based onsixteen polymorphic loci provided no evidenceof genetic differentiation. Indirect estimatesof dispersal parameters varied greatly betweendifferent methods of analysis. While use of acoalescent-based model yielded estimatedmigration rates congruent with the results ofthe mark-recapture study, other methodsresulted in much higher estimates of migrationbetween the populations. In particular, thelack of genetic differentiation coupled withlikely violations of the assumed island modelprevented generation of meaningful estimates ofdispersal using F_st. The disparitiesbetween migration rates estimated from themark-recapture work and from the differentindirect methods highlight the difficulties ofusing indirect methods to estimate dispersal onan ecological timescale. However,mark-recapture methods can fail to detecthistorical or episodic movement that isimportant in an evolutionary context, and wetherefore argue that a combination of directand indirect methods can provide a morecomplete picture of dispersal than eitherapproach alone.     

Starvation tolerance, development time and egg production of Calanoides carinatus in the Southern Benguela Current

The intermittent nature of phytoplankton blooms in the extremesouth of the Benguela Current may be an important factor limitingthe zooplankton population. Calanoides carinatus, a dominantzooplankton species, was studied in the laboratory to measureits tolerance to starvation, development time and rate of eggproduction. The species was found to have a large food reservein the form of a lipid sac which gives it a high tolerance tostarvation. Starvation tolerance depends on age, temperatureand feeding during development but once mature, feeding doesnot increase the tolerance. Development time depends on temperatureand feeding and is of the order of 25 days at average temperaturesin the area (13–15C). Egg production is rapid (–70eggs per female per day) when food is abundant and ceases immediatelyfood is removed. Overall the species shows considerable toleranceof a patchy food regime but nevertheless is probably controlledto some degree by the intermittent food supply, especially duringthe juvenile stages.     

Dynamic Localization of Tat Protein Transport Machinery Components in Streptomyces coelicolor

The Tat pathway transports folded proteins across the bacterial cytoplasmic membrane and is a major route of protein export in the Streptomyces genus of bacteria. In this study, we have examined the localization of Tat components in the model organism Streptomyces coelicolor by constructing enhanced green fluorescent protein (eGFP) and mCherry fusions with the TatA, TatB, and TatC proteins. All three components colocalized dynamically in the vegetative hyphae, with foci of each tagged protein being prominent at the tips of emerging germ tubes and of the vegetative hyphae, suggesting that this may be a primary site of Tat secretion. Time-lapse imaging revealed that localization of the Tat components was highly dynamic during tip growth and again demonstrated a strong preference for apical sites in growing hyphae. During aerial hypha formation, TatA-eGFP and TatB-eGFP fusions relocalized to prespore compartments, indicating repositioning of Tat components during the Streptomyces life cycle.     

Synthesis and evaluation of alkoxy-phenylamides and alkoxy-phenylimidazoles as potent sphingosine-1-phosphate receptor subtype-1 agonists

In the design of potent and selective sphingosine-1-phosphate receptor agonists, we were able to identify two series of molecules based on phenylamide and phenylimidazole analogs of FTY-720. Several designed molecules in these scaffolds have demonstrated selectivity for S1P receptor subtype 1 versus 3 and excellent in vivo activity in mouse. Two molecules PPI-4621 (4b) and PPI-4691 (10a), demonstrated dose responsive lymphopenia, when administered orally.