Do intraspecific life history patterns follow interspecific predictions? A test using latitudinal variation in ringed seals

Mammals adapted to unpredictable and low-energy environments often evolve a “bet-hedging” life history strategy characterized by less costly reproductive outputs over a longer and slower-growing life. In contrast, species adapted to more predictable (i.e., low variation) and higher energy environments may evolve greater fecundity over a shorter and faster-growing life. We tested whether this known interspecific pattern also occurs within a species. We compared life history traits of the ringed seal (Pusa hispida) in the Canadian High Arctic to those closer to the southern limit of the species' circumpolar distribution. We found that northern seals grew slower than southern seals (Brody growth coefficient), achieved a greater asymptotic body weight (82 and 69 kg vs. 74 and 54 kg female and male, respectively), reached sexual maturity later (6.1 years vs. 4.5 years), had lower fecundity (1.8 years vs. 1.3 years interbirth interval), longer average lifespan (5 years vs. 3 years median age), and greater movements (1,269 vs. 681 km). Mating systems also likely differed with northern seals showing morphological evidence of a promiscuous mating system with potential sperm competition as indicated by greater relative testes size. The northern region was also characterized by more unpredictable environmental timing of seasonal events, such as spring sea ice breakup. Life history variation between the intraspecific groups of seals appears to agree with interspecific patterns and provides a better understanding of how species' life history parameters shift in concert with environmental conditions.     

Stochastic exits from dormancy give rise to heavy‐tailed distributions of descendants in bacterial populations

Variance in reproductive success is a major determinant of the degree of genetic drift in a population. While many plants and animals exhibit high variance in their number of progeny, far less is known about these distributions for microorganisms. Here, we used a strain barcoding approach to quantify variability in offspring number among replicate bacterial populations and developed a Bayesian method to infer the distribution of descendants from this variability. We applied our approach to measure the offspring distributions for five strains of bacteria from the genus Streptomyces after germination and growth in a homogenous laboratory environment. The distributions of descendants were heavy‐tailed, with a few cells effectively ‘winning the jackpot’ to become a disproportionately large fraction of the population. This extreme variability in reproductive success largely traced back to initial populations of spores stochastically exiting dormancy, which provided early‐germinating spores with an exponential advantage. In simulations with multiple dormancy cycles, heavy‐tailed distributions of descendants decreased the effective population size by many orders of magnitude and led to allele dynamics differing substantially from classical population genetics models with matching effective population size. Collectively, these results demonstrate that extreme variability in reproductive success can occur even in growth conditions that are far more homogeneous than the natural environment. Thus, extreme variability in reproductive success might be an important factor shaping microbial population dynamics with implications for predicting the fate of beneficial mutations, interpreting sequence variability within populations and explaining variability in infection outcomes across patients.     

Characteristics of microwave evoked body movements in mice

Microwave evoked body movements were studied in mice. A resonant cavity was used to provide head and neck exposure of the mouse to pulsed and gated continuous wave (CW) 1.25 GHz microwaves. No difference in response to pulsed and gated CW stimuli of equal average power was found. The incidence of the microwave evoked body movements increased proportionally with specific absorption (dose) when the whole-body average specific absorption rate was at a constant level (7300 W/kg). Under a constant average specific absorption rate, the response incidence reached a plateau at 0.9 kJ/kg. For doses higher than 0.9 kJ/kg, response incidence was proportional to the specific absorption rate and reached a plateau at 900 W/kg. Body movements could be evoked by a single microwave pulse. The lowest whole-body specific absorption (SA) tested was 0.18 kJ/kg, and the corresponding brain SA was 0.29 kJ/kg. Bulk heating potentials of these SAs were less than 0.1 °C. For doses higher than 0.9 kJ/kg, the response incidence was also proportional to subcutaneous temperature increment and subcutaneous heating rate. The extrapolated absolute thresholds (0% incidence) were 1.21 °C temperature increment and 0.24 °C/s heating rate. Due to high subcutaneous heating rates, these microwaves must be perceived by the mouse as an intense thermal sensation but not a pain sensation because the temperature increment was well below the threshold for thermal pain. Results of the present study should be considered in promulgation of personnel protection guideline against high peak power but low average power microwaves. © 1994 Wiley-Liss, Inc.     

Probing the structure of the Ff bacteriophage major coat protein transmembrane helix dimer by solution NMR

The transmembrane (TM) segment of the major coat protein from Ff bacteriophage has been extensively studied as an example of dimerization in detergent and lipid bilayer systems. However, almost all the information regarding this interaction has been gained through mutagenesis studies, with little direct structural information being available. To this end solution NMR has the potential to provide new insights into structure of the dimer. In order to evaluate the utility of this approach we have studied a selectively ¹⁵N-labeled peptide containing the TM segment of MCP (MCP_TM) by solution NMR. This peptide was found to give rise to detergent concentration-dependent spectra that were assigned to monomeric and dimeric forms. The standard free energy of this interaction in SDS was estimated from these spectra and found to be consistent with weak but specific dimerization. In addition, similar spectra could be obtained in β-octyl glucoside with intermolecular paramagnetic relaxation experiments demonstrating a parallel arrangement of TM helices in the dimer. In both detergents backbone chemical shift differences between monomeric and dimeric forms of MCP_TM showed that the largest changes occur around its GXXXG motif. The resulting structural model is consistent with observations made for MCP mutants previously characterized in biological membranes, opening the door to detailed structural characterization of this form of MCP. These results also have general implications for the study of weakly interacting TM segments by solution NMR since the use of similar sample conditions should allow structural data to be accessed for oligomeric states from a wide range systems that undergo biologically relevant but weak associations in the membrane.     

Automated in situ measurement of cell-specific antibody secretion and laser-mediated purification for rapid cloning of highly-secreting producers

Cloning of highly-secreting recombinant cells is critical for biopharmaceutical manufacturing, but faces numerous challenges including the fact that secreted protein does not remain associated with the producing cell. A fundamentally new approach was developed combining in situ capture and measurement of individual cell protein secretion followed by laser-mediated elimination of all non- and poorly-secreting cells, leaving only the highest-secreting cell in a well. Recombinant cells producing humanized antibody were cultured serum-free on a capture matrix, followed by staining with fluorescently-labeled anti-human antibody fragment. A novel, automated, high-throughput instrument (called LEAP) was used to image and locate every cell, quantify the cell-associated and secreted antibody (surrounding each cell), eliminate all undesired cells from a well via targeted laser irradiation, and then track clone outgrowth and stability. Temporarily sparing an island of helper cells around the clone of interest improved cloning efficiency (particularly when using serum-free medium), and helper cells were easily eliminated with the laser after several days. The in situ nature of this process allowed several serial sub-cloning steps to be performed within days of one another, resulting in rapid generation of clonal populations with significantly increased and more stable, homogeneous antibody secretion. Cell lines with specific antibody secretion rates of > 50 pg/cell per day (in static batch culture) were routinely obtained as a result of this cloning approach, often times representing up to 20% of the clones screened.     

Nitrogen use efficiency by a slow-growing species as affected by CO2 levels, root temperature, N source and availability

This study examines the importance of N source and concentration on plant response to distinct CO₂ concentrations and root temperatures. The experimental design of this work was a factorial combination of: CO₂ concentration, nitrogen concentration, nitrogen source and root temperature. Carob (Ceratonia siliqua L.) was assessed as a potential model of a slow growing Mediterranean species.

The results showed that: 1) biomass increment under high CO₂ varied between 13 and 100 percnt; in relation to plants grown under the same conditions but at ambient CO₂ concentrations, depending on the root temperature and nitrogen source; 2) nitrate-fed plants attained a larger increase in biomass production compared to ammonium-fed ones. This performance seems to be linked to the co-ordinated regulation of the activities of glutamine synthetase and sucrose phosphate synthase. The variations in the magnitude and nature of growth responses to elevated CO₂ observed resulted in substantial changes in the chemical composition of the plant material and consequently in plant nitrogen use efficiency.

Although performed with seedlings and under controlled conditions, this work emphasizes the importance of the nitrogen source used by the plants, a factor rarely taken into consideration when forecasting plant responses to global changes. Particularly, the results presented here, highlight the potential for uncoupling biomass accumulation from increment of air CO₂ concentration and show that more than nitrogen availability N source may offset positive plant growth responses under elevated CO₂ and root temperature.     

High‐Temperature Shock Enabled Nanomanufacturing for Energy‐Related Applications

Functional nanomaterials are playing a crucial role in the emerging field of energy‐related devices. Recently, as a novel synthesis method, high‐temperature shock (HTS), which is rapid, low cost, eco‐friendly, universal, scalable, and controllable, has provided a promising option for the rational design and synthesis of various high‐quality nanomaterials. In this report, the HTS technique, including the equipment setup and operating principle, is systematically introduced, and recent progress in the synthesis of nanomaterials for energy storage and conversion applications using this HTS method is summarized. The growth mechanisms of nanoparticles and carbonaceous nanomaterials are thoroughly discussed, followed by the summary of the characteristic advantages of the HTS strategy. A series of nanomaterials prepared by the HTS method, including carbon‐based films, metal nanoparticles and compound nanoparticles, show high performance in the diverse applications of storage energy batteries, highly active catalysts, and smart energy devices. Finally, the future perspectives and directions of HTS in nanomanufacturing for broader applications are presented.     

An apoA-I mimetic peptibody generates HDL-like particles and increases alpha-1 HDL subfraction in mice

The aim of this study is to investigate the capability of an apoA-I mimetic with multiple amphipathic helices to form HDL-like particles in vitro and in vivo. To generate multivalent helices and to track the peptide mimetic, we have constructed a peptibody by fusing two tandem repeats of 4F peptide to the C terminus of a murine IgG Fc fragment. The resultant peptidbody, mFc-2X4F, dose-dependently promoted cholesterol efflux in vitro, and the efflux potency was superior to monomeric 4F peptide. Like apoA-I, mFc-2X4F stabilized ABCA1 in J774A.1 and THP1 cells. The peptibody formed larger HDL particles when incubated with cultured cells compared with those by apoA-I. Interestingly, when administered to mice, mFc-2X4F increased both pre-β and α-1 HDL subfractions. The lipid-bound mFc-2X4F was mostly in the α-1 migrating subfraction. Most importantly, mFc-2X4F and apoA-I were found to coexist in the same HDL particles formed in vivo. These data suggest that the apoA-I mimetic peptibody is capable of mimicking apoA-I to generate HDL particles. The peptibody and apoA-I may work cooperatively to generate larger HDL particles in vivo, either at the cholesterol efflux stage and/or via fusion of HDL particles that were generated by the peptibody and apoA-I individually.