The placement, recovery, and loss of scatter hoards by eastern chipmunks,Tamias striatus

Although eastern chipmunks typically larder hoard food in theirburrows, some scatter hoarding occurs, especially by newly emergedjuveniles and by females with young. To examine patterns ofscatter hoard placement and their adaptive significance, weused standard food provisioning tests followed by continuousmonitoring to determine the longevity and fate of scatter hoards.Longevity of scatter hoards was low (median 74 min) and pilferagewas high (46%). Chipmunks placed scatter hoards away from thepatch, closer to their burrow and within the defended area ofprimary use. Scatter hoard placement was affected by the numberof competitors at the patch. However, juveniles and femaleswith young differed slightly in their responses. competitorsthat approached scatteihoards were sometimes chased away bythe scatter hoard's owner, and the scatter hoard was moved toanother location by the owner. Females with young recoveredtheir largest scatter hoards first, but there was little additionalpattern in scatter hoard recovery. An experiment using simulatedscatter hoards showed that scatter hoards farther from a patchof food lasted longer and that disturbing and marking scatterhoards reduced their longevity. These observations indicate:(1) that scatter hoard placement is more related to avoidingpilferage of completed caches than to rapidly sequestering fooditems from an ephemeral patch and (2) that optimal cache distributionmay be affected by the cache-defense ability of individuals,by the relationship between competitor density and cache securitynear the patch, and by the territorial behavior of neighboringconspecifics.     

Effective population size,genetic diversity,and coalescence time in subdivided populations

A formula for the effective population size for the finite island model of subdivided populations is derived. The formula indicates that the effective size can be substantially greater than the actual number of individuals in the entire population when the migration rate among subpopulations is small. It is shown that the mean nucleotide diversity, coalescence time, and heterozygosity for genes sampled from the entire population can be predicted fairly well from the theory for randomly mating populations if the effective population size for the finite island model is used.     

Overexpression of cloned genes using recombinant Escherichia coli regulated by a T7 promoter: II. Two-stage continuous cultures and model simulations

A two-stage culture strategy was studied for continuous high-level production of a foreign protein in the chemically inducible T7 expression system. The first stage is dedicated to the maintenance of plasmid-bearing cells and the second stage to the target protein synthesis by induction of cells coming from the first stage. On entering the second stage, recombinant cells undergo a gradual induction of the target gene expression. These plasmid-bearing cells experience dynamic changes in intracellular compositions and specific growth rates with their individual residence times. Therefore, the overall cultural characteristics in the production stage are really averages of the contributions from the various cells with different residence times. The behavior of the two-stage culture is described by a model, which accounts for dynamic variations of cell growth and protein synthesis rates with cell residence times. Model simulations were compared with experimental results at a variety of operating conditions such as inducer concentration and dilution rate. This model is useful for understanding the behavior of two-stage continuous cultures. (c) 1993 John Wiley & Sons, Inc.     

Molecular integrity of monoclonal antibodies produced by hybridoma cells in batch culture and in continuous-flow culture with integrated product recovery

The molecular integrity of monoclonal antibodies (MCAB) produced by murine hybridoma cell line TB/C3 was studied in batch and continuous-flow cultures. In batch culture, one band of MCAB was detected initially by Western blotting of sodium dodecyl sulfate (SDS)-polyacrylamide gels run under unreduced conditions, but heterogenous MCAB bands appeared as the culture aged. The latter were due to the degradation of MCAB by proteases active at the neutral pH of the culture. The deleterious effect of proteases was minimized in the continuous-flow cultures which were integrated for product recovery. The MCAB of high quality was purified over 26 days from a culture grown at a dilution rate of 0.025 h(-1) (experiment 1). However, at a lower dilution rate of 0.015 h(-1) (experiment 2), the integrity of MCAB was compromised after the initial 13 days of culture. This was shown to be due to the variation in the carbohydrate content of MCAB produced, as judged by the increased sialylation of heavy chains and the varied reactivity of MCAB with lectins (Maackia amurensis agglutinin, Galanthus nivalis agglutinin, and Datura stramonium agglutinin) as the age of the culture increased. The concentration of the purified MCAB samples by enzyme-linked immunosorbent assay (ELISA) (used normally) was usually higher than that estimated by absorbance at 280 nm. Best correlation between the two methods (ELISA-280 nm ratio of 1.02-1.25) was obtained with experiment 1 samples. This ratio increased in experiment 2 and batch culture samples as the heterogeneity of MCAB produced increased, being 1.03-2.94 and 2.53-4.62, respectively. Therefore, ELISA overestimated MCAB concentration when the molecular integrity of the latter was compromised. The ELISA-A(280) nm ratio might hence provide a useful indicator for assessing the quality of MCAB produced. Comparison of SDS-polyacrylamide gels stained with Coomassie Brilliant Blue R and silver showed that the former correlated better with the MCAB activity stain, whereas the silver stained both the protein- and carbohydrate-rich components. Comparison of the patterns produced with these two stains might therefore offer another parameter to monitor the overall integrity of MCAB produced. Finally, the data presented have important implications on the validity of using long-term and intensive cultures for generating MCAB because such cultures would be subjected to the additive effects reported for batch and continuous modes of growth. (c) 1993 John Wiley & Sons, Inc.     

Emulsion liquid membrane extraction of lactic acid from aqueous solutions and fermentation broth

Studies on the batch extraction of lactic acid using an emulsion liquid membrane system are reported. The membrane phase consists of the tertiary amine carrier Alamine 336 and the surfactant Span 80 dissolved in n-heptane/paraffin and aqueous solutions of sodium carbonate in the internal phase. The effects of internal phase reagent, extraction temperature, and initial external phase pH on the extraction efficiency and the emulsion swelling are examined. A statistical factorial experiment on extraction from clarified lactic acid fermentation broth was carried out to obtain knowledge of the performance of the extraction system from a broth. The extraction efficiency from the fermentation broth is found to be lower as compared to aqueous solutions of pure lactic acid. The effect of pH and the presence of other ionic species on selectivity are discussed. (c) 1993 John Wiley & Sons, Inc.     

Development of a recovery and recycle process for a pseudomonas lipase used for large-scale enzymatic synthesis

Enzymes are potential catalysts for a wide range of large-scale chemical synthesis steps, particularly when the creation of a specific chiral center is desired. The efficient recycling of the enzyme catalyst and the removal of carryover impurities were crucial factors in the improvement of a stereoselective ester hydrolysis step used in the synthesis of a selective leukotriene antagonist. In this enzymatic reaction step, the substrate and product were both largely insoluble, while the enzyme was soluble in the aqueous reaction mixture. Microfiltration and ultrafiltration of the slurry reaction mother liquor indicated near 100% enzyme protein recovery, while activity recovery was about 70% to 80%. These activity losses might be accounted for by enzyme degradation (1 to 2 mg/L . h) during the 40-hour reaction period. Dissolved impurities, principally a diacid byproduct, in the enzyme recycling stream were reduced 60% to 70% by either lowering the solution pH to 4.0 or raising the solution ionic strength to 1 M. (c) 1993 John Wiley & Sons, Inc.     

Variable generation times and Darwinian fitness measures

Summary Reproductive value (RV) and net reproductive output (R _o) are frequently used fitness measures. We argue that they are only appropriate when intervals between reproductive events are fixed, as they are dimensionless generation-to-generation scalings with units offspring per parent. A fitness measure should account for two different effects of a decrease in generation time: (1) increased survival due to shorter exposure to mortality agents and (2) increased frequency of reproduction.R _o andRV deal with the first of these two effects, while a measure with a physical dimensionper time [T^–1] is needed to account for the second. The Malthusian growth parameter,r, meets this requirement and in situations where time to reproduction is variable, we propose, the instantaneous rate of spread of descendants (from an individual) be used instead ofR _o. As an alternative toRV, we suggest using the instantaneous difference = –r, wherer is the population rate of increase. WhileRV andR _o are dimensionless ratios, , and areper time rates which are appropriate in accounting for alterations in generation time.     

Seagrass ecosystem multifunctionality under the rise of a flagship marine megaherbivore

Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality.     

Heat tolerance of marine ectotherms in a warming Antarctica

Global warming is affecting the Antarctic continent in complex ways. Because Antarctic organisms are specialized to living in the cold, they are vulnerable to increasing temperatures, although quantitative analyses of this issue are currently lacking. Here we compiled a total of 184 estimates of heat tolerance belonging to 39 marine species and quantified how survival is affected concomitantly by the intensity and duration of thermal stress. Species exhibit thermal limits displaced toward colder temperatures, with contrasting strategies between arthropods and fish that exhibit low tolerance to acute heat challenges, and brachiopods, echinoderms, and molluscs that tend to be more sensitive to chronic exposure. These differences might be associated with mobility. A dynamic mortality model suggests that Antarctic organisms already encounter temperatures that might be physiologically stressful and indicate that these ecological communities are indeed vulnerable to ongoing rising temperatures.     

Fire affects wood formation dynamics and ecophysiology of Pinus pinaster Aiton growing in a dry Mediterranean area

The increase in frequency and intensity of wildfires is seriously affecting forest ecosystems, especially in drought-prone areas. Trees’ recovery after fire is related to direct tree damage and is influenced by climate conditions, such as warm temperature and water shortage. In this study, we evaluate the post-fire effects on a Pinus pinaster Aiton forest growing in a hot and dry area of the Mediterranean region by comparing burned trees with severe crown reduction against unburned and not-defoliated trees. Inter-annual analyses of dendrochronology and stable isotopes in tree rings were combined with xylogenesis monitoring to investigate the effects of fire on tree growth, ecophysiological processes and wood formation. Tree-ring and isotope data showed a growth reduction and a decrease in photosynthetic activity in the burned trees, compared to control individuals, in the three years after fire. Further, the monitoring of cambial activity demonstrated a negative influence of warm and dry periods on wood formation, low xylem production, a delay in phenology and a reduction in xylem plasticity in burned trees. Our findings suggest that substantial photosynthetic limitations caused by crown defoliation and recurrent drought events could lead to severe growth decrease and reduction of trees ability to regain the pre-disturbance productivity rates.